save progress
This commit is contained in:
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// <copyright file="HlcClockSkewException.cs" company="StellaOps">
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// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
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// </copyright>
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namespace StellaOps.HybridLogicalClock;
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/// <summary>
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/// Exception thrown when clock skew exceeds the configured tolerance.
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/// </summary>
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/// <remarks>
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/// <para>
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/// This exception indicates that a remote timestamp differs from the local
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/// physical clock by more than the configured maximum skew tolerance.
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/// This typically indicates:
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/// </para>
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/// <list type="bullet">
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/// <item><description>NTP synchronization failure on one or more nodes</description></item>
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/// <item><description>Malicious/corrupted remote timestamp</description></item>
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/// <item><description>Overly aggressive skew tolerance configuration</description></item>
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/// </list>
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/// </remarks>
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public sealed class HlcClockSkewException : Exception
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{
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/// <summary>
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/// Initializes a new instance of the <see cref="HlcClockSkewException"/> class.
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/// </summary>
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/// <param name="observedSkew">The observed clock skew.</param>
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/// <param name="maxAllowedSkew">The maximum allowed skew.</param>
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public HlcClockSkewException(TimeSpan observedSkew, TimeSpan maxAllowedSkew)
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: base($"Clock skew of {observedSkew.TotalMilliseconds:F0}ms exceeds maximum allowed {maxAllowedSkew.TotalMilliseconds:F0}ms")
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{
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ObservedSkew = observedSkew;
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MaxAllowedSkew = maxAllowedSkew;
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}
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/// <summary>
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/// Initializes a new instance of the <see cref="HlcClockSkewException"/> class.
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/// </summary>
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/// <param name="message">The error message.</param>
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public HlcClockSkewException(string message)
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: base(message)
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{
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}
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/// <summary>
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/// Initializes a new instance of the <see cref="HlcClockSkewException"/> class.
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/// </summary>
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/// <param name="message">The error message.</param>
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/// <param name="innerException">The inner exception.</param>
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public HlcClockSkewException(string message, Exception innerException)
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: base(message, innerException)
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{
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}
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/// <summary>
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/// Initializes a new instance of the <see cref="HlcClockSkewException"/> class.
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/// </summary>
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public HlcClockSkewException()
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{
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}
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/// <summary>
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/// Gets the observed clock skew.
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/// </summary>
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public TimeSpan ObservedSkew { get; }
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/// <summary>
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/// Gets the maximum allowed clock skew.
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/// </summary>
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public TimeSpan MaxAllowedSkew { get; }
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}
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77
src/__Libraries/StellaOps.HybridLogicalClock/HlcOptions.cs
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77
src/__Libraries/StellaOps.HybridLogicalClock/HlcOptions.cs
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// <copyright file="HlcOptions.cs" company="StellaOps">
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// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
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// </copyright>
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using System.ComponentModel.DataAnnotations;
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namespace StellaOps.HybridLogicalClock;
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/// <summary>
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/// Configuration options for the Hybrid Logical Clock.
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/// </summary>
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public sealed class HlcOptions
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{
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/// <summary>
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/// Configuration section name.
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/// </summary>
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public const string SectionName = "HybridLogicalClock";
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/// <summary>
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/// Gets or sets the unique node identifier.
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/// </summary>
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/// <remarks>
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/// Should be stable across restarts (e.g., "scheduler-east-1").
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/// If not set, will be auto-generated from machine name and process ID.
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/// </remarks>
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public string? NodeId { get; set; }
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/// <summary>
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/// Gets or sets the maximum allowed clock skew.
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/// </summary>
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/// <remarks>
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/// Remote timestamps differing by more than this from local physical clock
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/// will be rejected with <see cref="HlcClockSkewException"/>.
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/// Default: 1 minute.
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/// </remarks>
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[Range(typeof(TimeSpan), "00:00:01", "01:00:00")]
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public TimeSpan MaxClockSkew { get; set; } = TimeSpan.FromMinutes(1);
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/// <summary>
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/// Gets or sets the PostgreSQL connection string for state persistence.
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/// </summary>
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/// <remarks>
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/// If null, uses in-memory state store (state lost on restart).
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/// </remarks>
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public string? PostgresConnectionString { get; set; }
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/// <summary>
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/// Gets or sets the PostgreSQL schema for HLC tables.
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/// </summary>
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public string PostgresSchema { get; set; } = "scheduler";
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/// <summary>
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/// Gets or sets whether to use in-memory state store.
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/// </summary>
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/// <remarks>
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/// If true, state is not persisted. Useful for testing.
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/// If false and PostgresConnectionString is set, uses PostgreSQL.
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/// </remarks>
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public bool UseInMemoryStore { get; set; }
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/// <summary>
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/// Gets the effective node ID, generating one if not configured.
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/// </summary>
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/// <returns>The node ID to use.</returns>
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public string GetEffectiveNodeId()
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{
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if (!string.IsNullOrWhiteSpace(NodeId))
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{
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return NodeId;
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}
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// Generate deterministic node ID from machine name and some unique identifier
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var machineName = Environment.MachineName.ToLowerInvariant();
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var processId = Environment.ProcessId;
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return $"{machineName}-{processId}";
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}
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}
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@@ -0,0 +1,127 @@
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// <copyright file="HlcServiceCollectionExtensions.cs" company="StellaOps">
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// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
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// </copyright>
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using Microsoft.Extensions.DependencyInjection;
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using Microsoft.Extensions.DependencyInjection.Extensions;
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using Microsoft.Extensions.Logging;
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using Microsoft.Extensions.Options;
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namespace StellaOps.HybridLogicalClock;
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/// <summary>
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/// Extension methods for registering HLC services with dependency injection.
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/// </summary>
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public static class HlcServiceCollectionExtensions
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{
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/// <summary>
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/// Adds Hybrid Logical Clock services to the service collection.
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/// </summary>
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/// <param name="services">The service collection.</param>
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/// <param name="configureOptions">Optional action to configure HLC options.</param>
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/// <returns>The service collection for chaining.</returns>
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public static IServiceCollection AddHybridLogicalClock(
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this IServiceCollection services,
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Action<HlcOptions>? configureOptions = null)
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{
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ArgumentNullException.ThrowIfNull(services);
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// Register options
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if (configureOptions is not null)
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{
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services.Configure(configureOptions);
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}
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services.AddOptions<HlcOptions>()
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.ValidateDataAnnotations()
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.ValidateOnStart();
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// Register Dapper type handler
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HlcTimestampTypeHandler.Register();
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// Register TimeProvider if not already registered
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services.TryAddSingleton(TimeProvider.System);
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// Register state store based on configuration
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services.AddSingleton<IHlcStateStore>(sp =>
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{
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var options = sp.GetRequiredService<IOptions<HlcOptions>>().Value;
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if (options.UseInMemoryStore)
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{
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return new InMemoryHlcStateStore();
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}
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if (!string.IsNullOrEmpty(options.PostgresConnectionString))
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{
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var logger = sp.GetService<ILogger<PostgresHlcStateStore>>();
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return new PostgresHlcStateStore(
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options.PostgresConnectionString,
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options.PostgresSchema,
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logger);
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}
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// Default to in-memory if no connection string
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return new InMemoryHlcStateStore();
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});
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// Register the clock
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services.AddSingleton<IHybridLogicalClock>(sp =>
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{
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var options = sp.GetRequiredService<IOptions<HlcOptions>>().Value;
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var timeProvider = sp.GetRequiredService<TimeProvider>();
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var stateStore = sp.GetRequiredService<IHlcStateStore>();
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var logger = sp.GetService<ILogger<HybridLogicalClock>>();
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var clock = new HybridLogicalClock(
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timeProvider,
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options.GetEffectiveNodeId(),
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stateStore,
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options.MaxClockSkew,
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logger);
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return clock;
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});
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return services;
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}
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/// <summary>
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/// Adds Hybrid Logical Clock services with a specific node ID.
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/// </summary>
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/// <param name="services">The service collection.</param>
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/// <param name="nodeId">The node identifier.</param>
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/// <returns>The service collection for chaining.</returns>
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public static IServiceCollection AddHybridLogicalClock(
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this IServiceCollection services,
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string nodeId)
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{
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ArgumentException.ThrowIfNullOrWhiteSpace(nodeId);
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return services.AddHybridLogicalClock(options =>
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{
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options.NodeId = nodeId;
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});
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}
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/// <summary>
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/// Initializes the HLC clock from persistent state.
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/// Should be called during application startup.
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/// </summary>
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/// <param name="serviceProvider">The service provider.</param>
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/// <param name="ct">Cancellation token.</param>
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/// <returns>A task representing the async operation.</returns>
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public static async Task InitializeHlcAsync(
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this IServiceProvider serviceProvider,
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CancellationToken ct = default)
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{
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ArgumentNullException.ThrowIfNull(serviceProvider);
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var clock = serviceProvider.GetRequiredService<IHybridLogicalClock>();
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if (clock is HybridLogicalClock hlc)
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{
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await hlc.InitializeAsync(ct).ConfigureAwait(false);
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}
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}
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}
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222
src/__Libraries/StellaOps.HybridLogicalClock/HlcTimestamp.cs
Normal file
222
src/__Libraries/StellaOps.HybridLogicalClock/HlcTimestamp.cs
Normal file
@@ -0,0 +1,222 @@
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// <copyright file="HlcTimestamp.cs" company="StellaOps">
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// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
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// </copyright>
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using System.Diagnostics.CodeAnalysis;
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using System.Globalization;
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using System.Text.Json.Serialization;
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namespace StellaOps.HybridLogicalClock;
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/// <summary>
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/// Hybrid Logical Clock timestamp providing monotonic, causally-ordered time
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/// across distributed nodes even under clock skew.
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/// </summary>
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/// <remarks>
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/// <para>
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/// HLC combines the benefits of physical time (human-readable, bounded drift)
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/// with logical clocks (guaranteed causality, no rollback). The timestamp
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/// consists of three components:
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/// </para>
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/// <list type="bullet">
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/// <item><description>PhysicalTime: Unix milliseconds UTC, advances with wall clock</description></item>
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/// <item><description>NodeId: Unique identifier for the generating node</description></item>
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/// <item><description>LogicalCounter: Increments when events occur at same physical time</description></item>
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/// </list>
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/// <para>
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/// Total ordering is defined as: (PhysicalTime, LogicalCounter, NodeId)
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/// </para>
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/// </remarks>
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[JsonConverter(typeof(HlcTimestampJsonConverter))]
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public readonly record struct HlcTimestamp : IComparable<HlcTimestamp>, IComparable
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{
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/// <summary>
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/// Physical time component (Unix milliseconds UTC).
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/// </summary>
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||||
public required long PhysicalTime { get; init; }
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||||
/// <summary>
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/// Unique node identifier (e.g., "scheduler-east-1").
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||||
/// </summary>
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||||
public required string NodeId { get; init; }
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||||
/// <summary>
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/// Logical counter for events at same physical time.
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/// </summary>
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||||
public required int LogicalCounter { get; init; }
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/// <summary>
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/// Gets the physical time as a <see cref="DateTimeOffset"/>.
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||||
/// </summary>
|
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[JsonIgnore]
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public DateTimeOffset PhysicalDateTime =>
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DateTimeOffset.FromUnixTimeMilliseconds(PhysicalTime);
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||||
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/// <summary>
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/// Gets a zero/uninitialized timestamp.
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||||
/// </summary>
|
||||
public static HlcTimestamp Zero => new()
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||||
{
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||||
PhysicalTime = 0,
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||||
NodeId = string.Empty,
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||||
LogicalCounter = 0
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||||
};
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||||
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||||
/// <summary>
|
||||
/// String representation for storage: "0001704067200000-scheduler-east-1-000042".
|
||||
/// Format: {PhysicalTime:D13}-{NodeId}-{LogicalCounter:D6}
|
||||
/// </summary>
|
||||
/// <returns>A sortable string representation.</returns>
|
||||
public string ToSortableString()
|
||||
{
|
||||
return string.Create(
|
||||
CultureInfo.InvariantCulture,
|
||||
$"{PhysicalTime:D13}-{NodeId}-{LogicalCounter:D6}");
|
||||
}
|
||||
|
||||
/// <summary>
|
||||
/// Parse from sortable string format.
|
||||
/// </summary>
|
||||
/// <param name="value">The sortable string to parse.</param>
|
||||
/// <returns>The parsed <see cref="HlcTimestamp"/>.</returns>
|
||||
/// <exception cref="ArgumentNullException">Thrown when value is null.</exception>
|
||||
/// <exception cref="FormatException">Thrown when value is not in valid format.</exception>
|
||||
public static HlcTimestamp Parse(string value)
|
||||
{
|
||||
ArgumentNullException.ThrowIfNull(value);
|
||||
|
||||
if (!TryParse(value, out var result))
|
||||
{
|
||||
throw new FormatException($"Invalid HLC timestamp format: '{value}'");
|
||||
}
|
||||
|
||||
return result;
|
||||
}
|
||||
|
||||
/// <summary>
|
||||
/// Try to parse from sortable string format.
|
||||
/// </summary>
|
||||
/// <param name="value">The sortable string to parse.</param>
|
||||
/// <param name="result">The parsed timestamp if successful.</param>
|
||||
/// <returns>True if parsing succeeded; otherwise false.</returns>
|
||||
public static bool TryParse(
|
||||
[NotNullWhen(true)] string? value,
|
||||
out HlcTimestamp result)
|
||||
{
|
||||
result = default;
|
||||
|
||||
if (string.IsNullOrEmpty(value))
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
// Format: {PhysicalTime:D13}-{NodeId}-{LogicalCounter:D6}
|
||||
// Example: 0001704067200000-scheduler-east-1-000042
|
||||
// The NodeId can contain hyphens, so we parse from both ends
|
||||
|
||||
var firstDash = value.IndexOf('-', StringComparison.Ordinal);
|
||||
if (firstDash < 1)
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
var lastDash = value.LastIndexOf('-');
|
||||
if (lastDash <= firstDash || lastDash >= value.Length - 1)
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
var physicalTimeStr = value[..firstDash];
|
||||
var nodeId = value[(firstDash + 1)..lastDash];
|
||||
var counterStr = value[(lastDash + 1)..];
|
||||
|
||||
if (!long.TryParse(physicalTimeStr, NumberStyles.None, CultureInfo.InvariantCulture, out var physicalTime))
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
if (string.IsNullOrEmpty(nodeId))
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
if (!int.TryParse(counterStr, NumberStyles.None, CultureInfo.InvariantCulture, out var counter))
|
||||
{
|
||||
return false;
|
||||
}
|
||||
|
||||
result = new HlcTimestamp
|
||||
{
|
||||
PhysicalTime = physicalTime,
|
||||
NodeId = nodeId,
|
||||
LogicalCounter = counter
|
||||
};
|
||||
|
||||
return true;
|
||||
}
|
||||
|
||||
/// <summary>
|
||||
/// Compare for total ordering.
|
||||
/// Order: (PhysicalTime, LogicalCounter, NodeId).
|
||||
/// </summary>
|
||||
/// <param name="other">The other timestamp to compare.</param>
|
||||
/// <returns>Comparison result.</returns>
|
||||
public int CompareTo(HlcTimestamp other)
|
||||
{
|
||||
// Primary: physical time
|
||||
var physicalCompare = PhysicalTime.CompareTo(other.PhysicalTime);
|
||||
if (physicalCompare != 0)
|
||||
{
|
||||
return physicalCompare;
|
||||
}
|
||||
|
||||
// Secondary: logical counter
|
||||
var counterCompare = LogicalCounter.CompareTo(other.LogicalCounter);
|
||||
if (counterCompare != 0)
|
||||
{
|
||||
return counterCompare;
|
||||
}
|
||||
|
||||
// Tertiary: node ID (for stable tie-breaking)
|
||||
return string.Compare(NodeId, other.NodeId, StringComparison.Ordinal);
|
||||
}
|
||||
|
||||
/// <inheritdoc/>
|
||||
public int CompareTo(object? obj)
|
||||
{
|
||||
if (obj is null)
|
||||
{
|
||||
return 1;
|
||||
}
|
||||
|
||||
if (obj is HlcTimestamp other)
|
||||
{
|
||||
return CompareTo(other);
|
||||
}
|
||||
|
||||
throw new ArgumentException($"Object must be of type {nameof(HlcTimestamp)}", nameof(obj));
|
||||
}
|
||||
|
||||
/// <summary>
|
||||
/// Less than operator.
|
||||
/// </summary>
|
||||
public static bool operator <(HlcTimestamp left, HlcTimestamp right) => left.CompareTo(right) < 0;
|
||||
|
||||
/// <summary>
|
||||
/// Less than or equal operator.
|
||||
/// </summary>
|
||||
public static bool operator <=(HlcTimestamp left, HlcTimestamp right) => left.CompareTo(right) <= 0;
|
||||
|
||||
/// <summary>
|
||||
/// Greater than operator.
|
||||
/// </summary>
|
||||
public static bool operator >(HlcTimestamp left, HlcTimestamp right) => left.CompareTo(right) > 0;
|
||||
|
||||
/// <summary>
|
||||
/// Greater than or equal operator.
|
||||
/// </summary>
|
||||
public static bool operator >=(HlcTimestamp left, HlcTimestamp right) => left.CompareTo(right) >= 0;
|
||||
|
||||
/// <inheritdoc/>
|
||||
public override string ToString() => ToSortableString();
|
||||
}
|
||||
@@ -0,0 +1,60 @@
|
||||
// <copyright file="HlcTimestampJsonConverter.cs" company="StellaOps">
|
||||
// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
|
||||
// </copyright>
|
||||
|
||||
using System.Text.Json;
|
||||
using System.Text.Json.Serialization;
|
||||
|
||||
namespace StellaOps.HybridLogicalClock;
|
||||
|
||||
/// <summary>
|
||||
/// JSON converter for <see cref="HlcTimestamp"/> using sortable string format.
|
||||
/// </summary>
|
||||
/// <remarks>
|
||||
/// <para>
|
||||
/// Serializes to and deserializes from the sortable string format:
|
||||
/// "{PhysicalTime:D13}-{NodeId}-{LogicalCounter:D6}"
|
||||
/// </para>
|
||||
/// <para>
|
||||
/// Example: "0001704067200000-scheduler-east-1-000042"
|
||||
/// </para>
|
||||
/// </remarks>
|
||||
public sealed class HlcTimestampJsonConverter : JsonConverter<HlcTimestamp>
|
||||
{
|
||||
/// <inheritdoc/>
|
||||
public override HlcTimestamp Read(
|
||||
ref Utf8JsonReader reader,
|
||||
Type typeToConvert,
|
||||
JsonSerializerOptions options)
|
||||
{
|
||||
if (reader.TokenType == JsonTokenType.Null)
|
||||
{
|
||||
return HlcTimestamp.Zero;
|
||||
}
|
||||
|
||||
if (reader.TokenType != JsonTokenType.String)
|
||||
{
|
||||
throw new JsonException($"Expected string token for HlcTimestamp, got {reader.TokenType}");
|
||||
}
|
||||
|
||||
var value = reader.GetString();
|
||||
|
||||
if (!HlcTimestamp.TryParse(value, out var result))
|
||||
{
|
||||
throw new JsonException($"Invalid HlcTimestamp format: '{value}'");
|
||||
}
|
||||
|
||||
return result;
|
||||
}
|
||||
|
||||
/// <inheritdoc/>
|
||||
public override void Write(
|
||||
Utf8JsonWriter writer,
|
||||
HlcTimestamp value,
|
||||
JsonSerializerOptions options)
|
||||
{
|
||||
ArgumentNullException.ThrowIfNull(writer);
|
||||
|
||||
writer.WriteStringValue(value.ToSortableString());
|
||||
}
|
||||
}
|
||||
@@ -0,0 +1,59 @@
|
||||
// <copyright file="HlcTimestampTypeHandler.cs" company="StellaOps">
|
||||
// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
|
||||
// </copyright>
|
||||
|
||||
using System.Data;
|
||||
using Dapper;
|
||||
|
||||
namespace StellaOps.HybridLogicalClock;
|
||||
|
||||
/// <summary>
|
||||
/// Dapper type handler for <see cref="HlcTimestamp"/>.
|
||||
/// </summary>
|
||||
/// <remarks>
|
||||
/// <para>
|
||||
/// Maps HlcTimestamp to/from TEXT column using sortable string format.
|
||||
/// Register with: <c>SqlMapper.AddTypeHandler(new HlcTimestampTypeHandler());</c>
|
||||
/// </para>
|
||||
/// </remarks>
|
||||
public sealed class HlcTimestampTypeHandler : SqlMapper.TypeHandler<HlcTimestamp>
|
||||
{
|
||||
/// <summary>
|
||||
/// Gets the singleton instance of the type handler.
|
||||
/// </summary>
|
||||
public static HlcTimestampTypeHandler Instance { get; } = new();
|
||||
|
||||
/// <summary>
|
||||
/// Registers this type handler with Dapper.
|
||||
/// Should be called once at application startup.
|
||||
/// </summary>
|
||||
public static void Register()
|
||||
{
|
||||
SqlMapper.AddTypeHandler(Instance);
|
||||
}
|
||||
|
||||
/// <inheritdoc/>
|
||||
public override HlcTimestamp Parse(object value)
|
||||
{
|
||||
if (value is null or DBNull)
|
||||
{
|
||||
return HlcTimestamp.Zero;
|
||||
}
|
||||
|
||||
if (value is string strValue)
|
||||
{
|
||||
return HlcTimestamp.Parse(strValue);
|
||||
}
|
||||
|
||||
throw new DataException($"Cannot convert {value.GetType().Name} to HlcTimestamp");
|
||||
}
|
||||
|
||||
/// <inheritdoc/>
|
||||
public override void SetValue(IDbDataParameter parameter, HlcTimestamp value)
|
||||
{
|
||||
ArgumentNullException.ThrowIfNull(parameter);
|
||||
|
||||
parameter.DbType = DbType.String;
|
||||
parameter.Value = value.ToSortableString();
|
||||
}
|
||||
}
|
||||
@@ -0,0 +1,272 @@
|
||||
// <copyright file="HybridLogicalClock.cs" company="StellaOps">
|
||||
// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
|
||||
// </copyright>
|
||||
|
||||
using Microsoft.Extensions.Logging;
|
||||
using Microsoft.Extensions.Logging.Abstractions;
|
||||
|
||||
namespace StellaOps.HybridLogicalClock;
|
||||
|
||||
/// <summary>
|
||||
/// Default implementation of <see cref="IHybridLogicalClock"/>.
|
||||
/// </summary>
|
||||
/// <remarks>
|
||||
/// <para>
|
||||
/// Implements the Hybrid Logical Clock algorithm which combines physical time
|
||||
/// with logical counters to provide:
|
||||
/// </para>
|
||||
/// <list type="bullet">
|
||||
/// <item><description>Monotonicity: timestamps always increase</description></item>
|
||||
/// <item><description>Causality: if A happens-before B, then HLC(A) < HLC(B)</description></item>
|
||||
/// <item><description>Bounded drift: physical component stays close to wall clock</description></item>
|
||||
/// </list>
|
||||
/// <para>
|
||||
/// Thread-safety is guaranteed via internal locking.
|
||||
/// </para>
|
||||
/// </remarks>
|
||||
public sealed class HybridLogicalClock : IHybridLogicalClock
|
||||
{
|
||||
private readonly TimeProvider _timeProvider;
|
||||
private readonly IHlcStateStore _stateStore;
|
||||
private readonly TimeSpan _maxClockSkew;
|
||||
private readonly ILogger<HybridLogicalClock> _logger;
|
||||
private readonly object _lock = new();
|
||||
|
||||
private long _lastPhysicalTime;
|
||||
private int _logicalCounter;
|
||||
|
||||
/// <summary>
|
||||
/// Initializes a new instance of the <see cref="HybridLogicalClock"/> class.
|
||||
/// </summary>
|
||||
/// <param name="timeProvider">Time provider for physical clock.</param>
|
||||
/// <param name="nodeId">Unique identifier for this node.</param>
|
||||
/// <param name="stateStore">Persistent state store.</param>
|
||||
/// <param name="maxClockSkew">Maximum allowed clock skew (default: 1 minute).</param>
|
||||
/// <param name="logger">Optional logger.</param>
|
||||
public HybridLogicalClock(
|
||||
TimeProvider timeProvider,
|
||||
string nodeId,
|
||||
IHlcStateStore stateStore,
|
||||
TimeSpan? maxClockSkew = null,
|
||||
ILogger<HybridLogicalClock>? logger = null)
|
||||
{
|
||||
ArgumentNullException.ThrowIfNull(timeProvider);
|
||||
ArgumentException.ThrowIfNullOrWhiteSpace(nodeId);
|
||||
ArgumentNullException.ThrowIfNull(stateStore);
|
||||
|
||||
_timeProvider = timeProvider;
|
||||
NodeId = nodeId;
|
||||
_stateStore = stateStore;
|
||||
_maxClockSkew = maxClockSkew ?? TimeSpan.FromMinutes(1);
|
||||
_logger = logger ?? NullLogger<HybridLogicalClock>.Instance;
|
||||
}
|
||||
|
||||
/// <inheritdoc/>
|
||||
public string NodeId { get; }
|
||||
|
||||
/// <inheritdoc/>
|
||||
public HlcTimestamp Current
|
||||
{
|
||||
get
|
||||
{
|
||||
lock (_lock)
|
||||
{
|
||||
return new HlcTimestamp
|
||||
{
|
||||
PhysicalTime = _lastPhysicalTime,
|
||||
NodeId = NodeId,
|
||||
LogicalCounter = _logicalCounter
|
||||
};
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
/// <inheritdoc/>
|
||||
public HlcTimestamp Tick()
|
||||
{
|
||||
HlcTimestamp timestamp;
|
||||
|
||||
lock (_lock)
|
||||
{
|
||||
var physicalNow = _timeProvider.GetUtcNow().ToUnixTimeMilliseconds();
|
||||
|
||||
if (physicalNow > _lastPhysicalTime)
|
||||
{
|
||||
// Physical clock advanced - reset counter
|
||||
_lastPhysicalTime = physicalNow;
|
||||
_logicalCounter = 0;
|
||||
}
|
||||
else
|
||||
{
|
||||
// Same or earlier physical time - increment counter
|
||||
// This handles clock regression gracefully
|
||||
_logicalCounter++;
|
||||
|
||||
// Check for counter overflow (unlikely but handle it)
|
||||
if (_logicalCounter < 0)
|
||||
{
|
||||
_logger.LogWarning(
|
||||
"HLC logical counter overflow detected, advancing physical time. NodeId={NodeId}",
|
||||
NodeId);
|
||||
_lastPhysicalTime++;
|
||||
_logicalCounter = 0;
|
||||
}
|
||||
}
|
||||
|
||||
timestamp = new HlcTimestamp
|
||||
{
|
||||
PhysicalTime = _lastPhysicalTime,
|
||||
NodeId = NodeId,
|
||||
LogicalCounter = _logicalCounter
|
||||
};
|
||||
}
|
||||
|
||||
// Persist state asynchronously (fire-and-forget with error logging)
|
||||
_ = PersistStateAsync(timestamp);
|
||||
|
||||
return timestamp;
|
||||
}
|
||||
|
||||
/// <inheritdoc/>
|
||||
public HlcTimestamp Receive(HlcTimestamp remote)
|
||||
{
|
||||
HlcTimestamp timestamp;
|
||||
|
||||
lock (_lock)
|
||||
{
|
||||
var physicalNow = _timeProvider.GetUtcNow().ToUnixTimeMilliseconds();
|
||||
|
||||
// Validate clock skew
|
||||
var skew = TimeSpan.FromMilliseconds(Math.Abs(remote.PhysicalTime - physicalNow));
|
||||
if (skew > _maxClockSkew)
|
||||
{
|
||||
_logger.LogError(
|
||||
"Clock skew exceeded: observed={ObservedMs}ms, max={MaxMs}ms, remote={RemoteNodeId}",
|
||||
skew.TotalMilliseconds,
|
||||
_maxClockSkew.TotalMilliseconds,
|
||||
remote.NodeId);
|
||||
|
||||
throw new HlcClockSkewException(skew, _maxClockSkew);
|
||||
}
|
||||
|
||||
var prevPhysicalTime = _lastPhysicalTime;
|
||||
var maxPhysical = Math.Max(Math.Max(prevPhysicalTime, remote.PhysicalTime), physicalNow);
|
||||
|
||||
if (maxPhysical == prevPhysicalTime && maxPhysical == remote.PhysicalTime)
|
||||
{
|
||||
// All three equal - take max counter and increment
|
||||
_logicalCounter = Math.Max(_logicalCounter, remote.LogicalCounter) + 1;
|
||||
}
|
||||
else if (maxPhysical == prevPhysicalTime)
|
||||
{
|
||||
// Local was max - increment local counter
|
||||
_logicalCounter++;
|
||||
}
|
||||
else if (maxPhysical == remote.PhysicalTime)
|
||||
{
|
||||
// Remote was max - take remote counter and increment
|
||||
_logicalCounter = remote.LogicalCounter + 1;
|
||||
}
|
||||
else
|
||||
{
|
||||
// Physical clock advanced - reset counter
|
||||
_logicalCounter = 0;
|
||||
}
|
||||
|
||||
_lastPhysicalTime = maxPhysical;
|
||||
|
||||
// Check for counter overflow
|
||||
if (_logicalCounter < 0)
|
||||
{
|
||||
_logger.LogWarning(
|
||||
"HLC logical counter overflow on receive, advancing physical time. NodeId={NodeId}",
|
||||
NodeId);
|
||||
_lastPhysicalTime++;
|
||||
_logicalCounter = 0;
|
||||
}
|
||||
|
||||
timestamp = new HlcTimestamp
|
||||
{
|
||||
PhysicalTime = _lastPhysicalTime,
|
||||
NodeId = NodeId,
|
||||
LogicalCounter = _logicalCounter
|
||||
};
|
||||
}
|
||||
|
||||
// Persist state asynchronously
|
||||
_ = PersistStateAsync(timestamp);
|
||||
|
||||
return timestamp;
|
||||
}
|
||||
|
||||
/// <summary>
|
||||
/// Initialize clock state from persistent store.
|
||||
/// Should be called once during startup.
|
||||
/// </summary>
|
||||
/// <param name="ct">Cancellation token.</param>
|
||||
/// <returns>True if state was recovered; false if starting fresh.</returns>
|
||||
public async Task<bool> InitializeAsync(CancellationToken ct = default)
|
||||
{
|
||||
var persisted = await _stateStore.LoadAsync(NodeId, ct).ConfigureAwait(false);
|
||||
|
||||
if (persisted is { } state)
|
||||
{
|
||||
lock (_lock)
|
||||
{
|
||||
// Ensure we never go backward
|
||||
var physicalNow = _timeProvider.GetUtcNow().ToUnixTimeMilliseconds();
|
||||
_lastPhysicalTime = Math.Max(state.PhysicalTime, physicalNow);
|
||||
|
||||
if (_lastPhysicalTime == state.PhysicalTime)
|
||||
{
|
||||
// Same physical time - continue from persisted counter + 1
|
||||
_logicalCounter = state.LogicalCounter + 1;
|
||||
}
|
||||
else
|
||||
{
|
||||
// Physical time advanced - reset counter
|
||||
_logicalCounter = 0;
|
||||
}
|
||||
}
|
||||
|
||||
_logger.LogInformation(
|
||||
"HLC state recovered: PhysicalTime={PhysicalTime}, Counter={Counter}, NodeId={NodeId}",
|
||||
_lastPhysicalTime,
|
||||
_logicalCounter,
|
||||
NodeId);
|
||||
|
||||
return true;
|
||||
}
|
||||
|
||||
lock (_lock)
|
||||
{
|
||||
_lastPhysicalTime = _timeProvider.GetUtcNow().ToUnixTimeMilliseconds();
|
||||
_logicalCounter = 0;
|
||||
}
|
||||
|
||||
_logger.LogInformation(
|
||||
"HLC initialized fresh: PhysicalTime={PhysicalTime}, NodeId={NodeId}",
|
||||
_lastPhysicalTime,
|
||||
NodeId);
|
||||
|
||||
return false;
|
||||
}
|
||||
|
||||
private async Task PersistStateAsync(HlcTimestamp timestamp)
|
||||
{
|
||||
try
|
||||
{
|
||||
await _stateStore.SaveAsync(timestamp).ConfigureAwait(false);
|
||||
}
|
||||
catch (Exception ex)
|
||||
{
|
||||
// Fire-and-forget with error logging
|
||||
// Clock continues operating; state will be recovered on next successful save
|
||||
_logger.LogWarning(
|
||||
ex,
|
||||
"Failed to persist HLC state: NodeId={NodeId}, PhysicalTime={PhysicalTime}",
|
||||
NodeId,
|
||||
timestamp.PhysicalTime);
|
||||
}
|
||||
}
|
||||
}
|
||||
@@ -0,0 +1,44 @@
|
||||
// <copyright file="IHlcStateStore.cs" company="StellaOps">
|
||||
// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
|
||||
// </copyright>
|
||||
|
||||
namespace StellaOps.HybridLogicalClock;
|
||||
|
||||
/// <summary>
|
||||
/// Persistent storage for HLC state (survives restarts).
|
||||
/// </summary>
|
||||
/// <remarks>
|
||||
/// <para>
|
||||
/// Implementations should provide atomic update semantics to prevent
|
||||
/// state corruption during concurrent operations. The store is used to:
|
||||
/// </para>
|
||||
/// <list type="bullet">
|
||||
/// <item><description>Persist HLC state after each tick (fire-and-forget)</description></item>
|
||||
/// <item><description>Recover state on node restart</description></item>
|
||||
/// <item><description>Ensure clock monotonicity across restarts</description></item>
|
||||
/// </list>
|
||||
/// </remarks>
|
||||
public interface IHlcStateStore
|
||||
{
|
||||
/// <summary>
|
||||
/// Load last persisted HLC state for node.
|
||||
/// </summary>
|
||||
/// <param name="nodeId">The node identifier to load state for.</param>
|
||||
/// <param name="ct">Cancellation token.</param>
|
||||
/// <returns>The last persisted timestamp, or null if no state exists.</returns>
|
||||
Task<HlcTimestamp?> LoadAsync(string nodeId, CancellationToken ct = default);
|
||||
|
||||
/// <summary>
|
||||
/// Persist HLC state (called after each tick).
|
||||
/// </summary>
|
||||
/// <remarks>
|
||||
/// <para>
|
||||
/// This operation should be atomic and idempotent. Implementations may use
|
||||
/// fire-and-forget semantics with error logging for performance.
|
||||
/// </para>
|
||||
/// </remarks>
|
||||
/// <param name="timestamp">The timestamp state to persist.</param>
|
||||
/// <param name="ct">Cancellation token.</param>
|
||||
/// <returns>A task representing the async operation.</returns>
|
||||
Task SaveAsync(HlcTimestamp timestamp, CancellationToken ct = default);
|
||||
}
|
||||
@@ -0,0 +1,65 @@
|
||||
// <copyright file="IHybridLogicalClock.cs" company="StellaOps">
|
||||
// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
|
||||
// </copyright>
|
||||
|
||||
namespace StellaOps.HybridLogicalClock;
|
||||
|
||||
/// <summary>
|
||||
/// Hybrid Logical Clock for monotonic timestamp generation.
|
||||
/// </summary>
|
||||
/// <remarks>
|
||||
/// <para>
|
||||
/// Implementations must guarantee:
|
||||
/// </para>
|
||||
/// <list type="number">
|
||||
/// <item><description>Successive Tick() calls return strictly increasing timestamps</description></item>
|
||||
/// <item><description>Receive() merges remote timestamp maintaining causality</description></item>
|
||||
/// <item><description>Clock state survives restarts via persistence</description></item>
|
||||
/// </list>
|
||||
/// </remarks>
|
||||
public interface IHybridLogicalClock
|
||||
{
|
||||
/// <summary>
|
||||
/// Generate next timestamp for local event.
|
||||
/// </summary>
|
||||
/// <remarks>
|
||||
/// <para>Algorithm:</para>
|
||||
/// <list type="number">
|
||||
/// <item><description>l' = l (save previous logical time)</description></item>
|
||||
/// <item><description>l = max(l, physical_clock())</description></item>
|
||||
/// <item><description>if l == l': c = c + 1 else: c = 0</description></item>
|
||||
/// <item><description>return (l, node_id, c)</description></item>
|
||||
/// </list>
|
||||
/// </remarks>
|
||||
/// <returns>A new monotonically increasing timestamp.</returns>
|
||||
HlcTimestamp Tick();
|
||||
|
||||
/// <summary>
|
||||
/// Update clock on receiving remote timestamp, return merged result.
|
||||
/// </summary>
|
||||
/// <remarks>
|
||||
/// <para>Algorithm:</para>
|
||||
/// <list type="number">
|
||||
/// <item><description>l' = l (save previous)</description></item>
|
||||
/// <item><description>l = max(l', m_l, physical_clock())</description></item>
|
||||
/// <item><description>Update c based on which max was chosen</description></item>
|
||||
/// <item><description>return (l, node_id, c)</description></item>
|
||||
/// </list>
|
||||
/// </remarks>
|
||||
/// <param name="remote">The remote timestamp to merge.</param>
|
||||
/// <returns>A new timestamp incorporating the remote causality.</returns>
|
||||
/// <exception cref="HlcClockSkewException">
|
||||
/// Thrown when the remote timestamp differs from physical clock by more than max skew tolerance.
|
||||
/// </exception>
|
||||
HlcTimestamp Receive(HlcTimestamp remote);
|
||||
|
||||
/// <summary>
|
||||
/// Gets the current clock state (for persistence/recovery).
|
||||
/// </summary>
|
||||
HlcTimestamp Current { get; }
|
||||
|
||||
/// <summary>
|
||||
/// Gets the node identifier for this clock instance.
|
||||
/// </summary>
|
||||
string NodeId { get; }
|
||||
}
|
||||
@@ -0,0 +1,54 @@
|
||||
// <copyright file="InMemoryHlcStateStore.cs" company="StellaOps">
|
||||
// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
|
||||
// </copyright>
|
||||
|
||||
using System.Collections.Concurrent;
|
||||
|
||||
namespace StellaOps.HybridLogicalClock;
|
||||
|
||||
/// <summary>
|
||||
/// In-memory implementation of <see cref="IHlcStateStore"/> for testing and development.
|
||||
/// </summary>
|
||||
/// <remarks>
|
||||
/// <para>
|
||||
/// State is lost on process restart. Use <see cref="PostgresHlcStateStore"/> for production.
|
||||
/// </para>
|
||||
/// </remarks>
|
||||
public sealed class InMemoryHlcStateStore : IHlcStateStore
|
||||
{
|
||||
private readonly ConcurrentDictionary<string, HlcTimestamp> _store = new(StringComparer.Ordinal);
|
||||
|
||||
/// <inheritdoc/>
|
||||
public Task<HlcTimestamp?> LoadAsync(string nodeId, CancellationToken ct = default)
|
||||
{
|
||||
ArgumentNullException.ThrowIfNull(nodeId);
|
||||
|
||||
return Task.FromResult<HlcTimestamp?>(
|
||||
_store.TryGetValue(nodeId, out var timestamp) ? timestamp : null);
|
||||
}
|
||||
|
||||
/// <inheritdoc/>
|
||||
public Task SaveAsync(HlcTimestamp timestamp, CancellationToken ct = default)
|
||||
{
|
||||
_store.AddOrUpdate(
|
||||
timestamp.NodeId,
|
||||
timestamp,
|
||||
(_, existing) =>
|
||||
{
|
||||
// Only update if new timestamp is greater (prevents regression on concurrent saves)
|
||||
return timestamp > existing ? timestamp : existing;
|
||||
});
|
||||
|
||||
return Task.CompletedTask;
|
||||
}
|
||||
|
||||
/// <summary>
|
||||
/// Clear all stored state (for testing).
|
||||
/// </summary>
|
||||
public void Clear() => _store.Clear();
|
||||
|
||||
/// <summary>
|
||||
/// Gets the count of stored entries (for testing).
|
||||
/// </summary>
|
||||
public int Count => _store.Count;
|
||||
}
|
||||
@@ -0,0 +1,171 @@
|
||||
// <copyright file="PostgresHlcStateStore.cs" company="StellaOps">
|
||||
// Copyright (c) StellaOps. Licensed under AGPL-3.0-or-later.
|
||||
// </copyright>
|
||||
|
||||
using System.Globalization;
|
||||
using Dapper;
|
||||
using Microsoft.Extensions.Logging;
|
||||
using Microsoft.Extensions.Logging.Abstractions;
|
||||
using Npgsql;
|
||||
|
||||
namespace StellaOps.HybridLogicalClock;
|
||||
|
||||
/// <summary>
|
||||
/// PostgreSQL implementation of <see cref="IHlcStateStore"/> with atomic update semantics.
|
||||
/// </summary>
|
||||
/// <remarks>
|
||||
/// <para>
|
||||
/// Requires the following table (created via migration or manually):
|
||||
/// </para>
|
||||
/// <code>
|
||||
/// CREATE TABLE scheduler.hlc_state (
|
||||
/// node_id TEXT PRIMARY KEY,
|
||||
/// physical_time BIGINT NOT NULL,
|
||||
/// logical_counter INT NOT NULL,
|
||||
/// updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
|
||||
/// );
|
||||
/// </code>
|
||||
/// </remarks>
|
||||
public sealed class PostgresHlcStateStore : IHlcStateStore
|
||||
{
|
||||
private readonly string _connectionString;
|
||||
private readonly string _schema;
|
||||
private readonly ILogger<PostgresHlcStateStore> _logger;
|
||||
|
||||
/// <summary>
|
||||
/// Initializes a new instance of the <see cref="PostgresHlcStateStore"/> class.
|
||||
/// </summary>
|
||||
/// <param name="connectionString">PostgreSQL connection string.</param>
|
||||
/// <param name="schema">Schema name (default: "scheduler").</param>
|
||||
/// <param name="logger">Optional logger.</param>
|
||||
public PostgresHlcStateStore(
|
||||
string connectionString,
|
||||
string schema = "scheduler",
|
||||
ILogger<PostgresHlcStateStore>? logger = null)
|
||||
{
|
||||
ArgumentException.ThrowIfNullOrWhiteSpace(connectionString);
|
||||
ArgumentException.ThrowIfNullOrWhiteSpace(schema);
|
||||
|
||||
_connectionString = connectionString;
|
||||
_schema = schema;
|
||||
_logger = logger ?? NullLogger<PostgresHlcStateStore>.Instance;
|
||||
}
|
||||
|
||||
/// <inheritdoc/>
|
||||
public async Task<HlcTimestamp?> LoadAsync(string nodeId, CancellationToken ct = default)
|
||||
{
|
||||
ArgumentNullException.ThrowIfNull(nodeId);
|
||||
|
||||
var sql = string.Create(
|
||||
CultureInfo.InvariantCulture,
|
||||
$"""
|
||||
SELECT physical_time, logical_counter
|
||||
FROM {_schema}.hlc_state
|
||||
WHERE node_id = @NodeId
|
||||
""");
|
||||
|
||||
await using var connection = new NpgsqlConnection(_connectionString);
|
||||
await connection.OpenAsync(ct).ConfigureAwait(false);
|
||||
|
||||
var result = await connection.QuerySingleOrDefaultAsync<HlcStateRow>(
|
||||
new CommandDefinition(
|
||||
sql,
|
||||
new { NodeId = nodeId },
|
||||
cancellationToken: ct)).ConfigureAwait(false);
|
||||
|
||||
if (result is null)
|
||||
{
|
||||
return null;
|
||||
}
|
||||
|
||||
return new HlcTimestamp
|
||||
{
|
||||
PhysicalTime = result.physical_time,
|
||||
NodeId = nodeId,
|
||||
LogicalCounter = result.logical_counter
|
||||
};
|
||||
}
|
||||
|
||||
/// <inheritdoc/>
|
||||
public async Task SaveAsync(HlcTimestamp timestamp, CancellationToken ct = default)
|
||||
{
|
||||
// Atomic upsert with monotonicity guarantee:
|
||||
// Only update if new values are greater than existing
|
||||
var sql = string.Create(
|
||||
CultureInfo.InvariantCulture,
|
||||
$"""
|
||||
INSERT INTO {_schema}.hlc_state (node_id, physical_time, logical_counter, updated_at)
|
||||
VALUES (@NodeId, @PhysicalTime, @LogicalCounter, NOW())
|
||||
ON CONFLICT (node_id) DO UPDATE
|
||||
SET physical_time = GREATEST({_schema}.hlc_state.physical_time, EXCLUDED.physical_time),
|
||||
logical_counter = CASE
|
||||
WHEN EXCLUDED.physical_time > {_schema}.hlc_state.physical_time THEN EXCLUDED.logical_counter
|
||||
WHEN EXCLUDED.physical_time = {_schema}.hlc_state.physical_time
|
||||
AND EXCLUDED.logical_counter > {_schema}.hlc_state.logical_counter THEN EXCLUDED.logical_counter
|
||||
ELSE {_schema}.hlc_state.logical_counter
|
||||
END,
|
||||
updated_at = NOW()
|
||||
""");
|
||||
|
||||
await using var connection = new NpgsqlConnection(_connectionString);
|
||||
await connection.OpenAsync(ct).ConfigureAwait(false);
|
||||
|
||||
try
|
||||
{
|
||||
await connection.ExecuteAsync(
|
||||
new CommandDefinition(
|
||||
sql,
|
||||
new
|
||||
{
|
||||
timestamp.NodeId,
|
||||
timestamp.PhysicalTime,
|
||||
timestamp.LogicalCounter
|
||||
},
|
||||
cancellationToken: ct)).ConfigureAwait(false);
|
||||
}
|
||||
catch (NpgsqlException ex)
|
||||
{
|
||||
_logger.LogWarning(
|
||||
ex,
|
||||
"Failed to save HLC state to PostgreSQL: NodeId={NodeId}, PhysicalTime={PhysicalTime}",
|
||||
timestamp.NodeId,
|
||||
timestamp.PhysicalTime);
|
||||
throw;
|
||||
}
|
||||
}
|
||||
|
||||
/// <summary>
|
||||
/// Ensure the HLC state table exists (for development/testing).
|
||||
/// In production, use migrations.
|
||||
/// </summary>
|
||||
/// <param name="ct">Cancellation token.</param>
|
||||
/// <returns>A task representing the async operation.</returns>
|
||||
public async Task EnsureTableExistsAsync(CancellationToken ct = default)
|
||||
{
|
||||
var sql = string.Create(
|
||||
CultureInfo.InvariantCulture,
|
||||
$"""
|
||||
CREATE SCHEMA IF NOT EXISTS {_schema};
|
||||
|
||||
CREATE TABLE IF NOT EXISTS {_schema}.hlc_state (
|
||||
node_id TEXT PRIMARY KEY,
|
||||
physical_time BIGINT NOT NULL,
|
||||
logical_counter INT NOT NULL,
|
||||
updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
|
||||
);
|
||||
|
||||
CREATE INDEX IF NOT EXISTS idx_hlc_state_updated
|
||||
ON {_schema}.hlc_state(updated_at DESC);
|
||||
""");
|
||||
|
||||
await using var connection = new NpgsqlConnection(_connectionString);
|
||||
await connection.OpenAsync(ct).ConfigureAwait(false);
|
||||
await connection.ExecuteAsync(new CommandDefinition(sql, cancellationToken: ct)).ConfigureAwait(false);
|
||||
|
||||
_logger.LogInformation("HLC state table ensured in schema {Schema}", _schema);
|
||||
}
|
||||
|
||||
#pragma warning disable IDE1006 // Naming Styles - matches DB column names
|
||||
private sealed record HlcStateRow(long physical_time, int logical_counter);
|
||||
#pragma warning restore IDE1006
|
||||
}
|
||||
320
src/__Libraries/StellaOps.HybridLogicalClock/README.md
Normal file
320
src/__Libraries/StellaOps.HybridLogicalClock/README.md
Normal file
@@ -0,0 +1,320 @@
|
||||
# StellaOps.HybridLogicalClock
|
||||
|
||||
A Hybrid Logical Clock (HLC) implementation for deterministic, monotonic job ordering across distributed nodes. HLC combines physical time with logical counters to provide causally-ordered timestamps even under clock skew.
|
||||
|
||||
## Overview
|
||||
|
||||
Traditional wall-clock timestamps are susceptible to clock skew across distributed nodes. HLC addresses this by combining:
|
||||
|
||||
- **Physical time**: Unix milliseconds UTC, advances with wall clock
|
||||
- **Node ID**: Unique identifier for the generating node
|
||||
- **Logical counter**: Increments when events occur at the same physical time
|
||||
|
||||
This provides:
|
||||
- **Monotonicity**: Successive timestamps always increase
|
||||
- **Causality**: If event A happens-before event B, then HLC(A) < HLC(B)
|
||||
- **Bounded drift**: Physical component stays close to wall clock
|
||||
|
||||
## Installation
|
||||
|
||||
```csharp
|
||||
// In your Startup.cs or Program.cs
|
||||
services.AddHybridLogicalClock(options =>
|
||||
{
|
||||
options.NodeId = "scheduler-east-1";
|
||||
options.MaxClockSkew = TimeSpan.FromMinutes(1);
|
||||
options.PostgresConnectionString = configuration.GetConnectionString("Default");
|
||||
});
|
||||
```
|
||||
|
||||
## Quick Start
|
||||
|
||||
### Basic Usage
|
||||
|
||||
```csharp
|
||||
public class JobScheduler
|
||||
{
|
||||
private readonly IHybridLogicalClock _clock;
|
||||
|
||||
public JobScheduler(IHybridLogicalClock clock)
|
||||
{
|
||||
_clock = clock;
|
||||
}
|
||||
|
||||
public Job EnqueueJob(JobPayload payload)
|
||||
{
|
||||
// Generate monotonic timestamp for the job
|
||||
var timestamp = _clock.Tick();
|
||||
|
||||
return new Job
|
||||
{
|
||||
Id = Guid.NewGuid(),
|
||||
Timestamp = timestamp,
|
||||
Payload = payload
|
||||
};
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### Receiving Remote Timestamps
|
||||
|
||||
When processing messages from other nodes:
|
||||
|
||||
```csharp
|
||||
public void ProcessRemoteMessage(Message message)
|
||||
{
|
||||
// Merge remote timestamp to maintain causality
|
||||
var localTimestamp = _clock.Receive(message.Timestamp);
|
||||
|
||||
// Now localTimestamp > message.Timestamp is guaranteed
|
||||
ProcessPayload(message.Payload, localTimestamp);
|
||||
}
|
||||
```
|
||||
|
||||
### Initialization from Persistent State
|
||||
|
||||
During application startup, initialize the clock from persisted state:
|
||||
|
||||
```csharp
|
||||
var host = builder.Build();
|
||||
|
||||
// Initialize HLC from persistent state before starting
|
||||
await host.Services.InitializeHlcAsync();
|
||||
|
||||
await host.RunAsync();
|
||||
```
|
||||
|
||||
## API Reference
|
||||
|
||||
### HlcTimestamp
|
||||
|
||||
A readonly record struct representing an HLC timestamp.
|
||||
|
||||
```csharp
|
||||
public readonly record struct HlcTimestamp : IComparable<HlcTimestamp>
|
||||
{
|
||||
// Unix milliseconds UTC
|
||||
public required long PhysicalTime { get; init; }
|
||||
|
||||
// Unique node identifier
|
||||
public required string NodeId { get; init; }
|
||||
|
||||
// Logical counter for same-time events
|
||||
public required int LogicalCounter { get; init; }
|
||||
|
||||
// Convert to sortable string: "0001704067200000-node-id-000042"
|
||||
public string ToSortableString();
|
||||
|
||||
// Parse from sortable string
|
||||
public static HlcTimestamp Parse(string value);
|
||||
public static bool TryParse(string? value, out HlcTimestamp result);
|
||||
|
||||
// Get physical time as DateTimeOffset
|
||||
public DateTimeOffset PhysicalDateTime { get; }
|
||||
}
|
||||
```
|
||||
|
||||
### IHybridLogicalClock
|
||||
|
||||
The main interface for HLC operations.
|
||||
|
||||
```csharp
|
||||
public interface IHybridLogicalClock
|
||||
{
|
||||
// Generate next timestamp for local event
|
||||
HlcTimestamp Tick();
|
||||
|
||||
// Merge with remote timestamp, return new local timestamp
|
||||
HlcTimestamp Receive(HlcTimestamp remote);
|
||||
|
||||
// Current clock state
|
||||
HlcTimestamp Current { get; }
|
||||
|
||||
// Node identifier
|
||||
string NodeId { get; }
|
||||
}
|
||||
```
|
||||
|
||||
### IHlcStateStore
|
||||
|
||||
Interface for persisting clock state across restarts.
|
||||
|
||||
```csharp
|
||||
public interface IHlcStateStore
|
||||
{
|
||||
Task<HlcTimestamp?> LoadAsync(string nodeId, CancellationToken ct = default);
|
||||
Task SaveAsync(HlcTimestamp timestamp, CancellationToken ct = default);
|
||||
}
|
||||
```
|
||||
|
||||
Built-in implementations:
|
||||
- `InMemoryHlcStateStore`: For testing (state lost on restart)
|
||||
- `PostgresHlcStateStore`: Persists to PostgreSQL
|
||||
|
||||
## Configuration
|
||||
|
||||
### HlcOptions
|
||||
|
||||
| Property | Type | Default | Description |
|
||||
|----------|------|---------|-------------|
|
||||
| `NodeId` | string? | auto | Unique node identifier (e.g., "scheduler-east-1") |
|
||||
| `MaxClockSkew` | TimeSpan | 1 minute | Maximum allowed difference from remote timestamps |
|
||||
| `PostgresConnectionString` | string? | null | Connection string for PostgreSQL persistence |
|
||||
| `PostgresSchema` | string | "scheduler" | PostgreSQL schema for HLC tables |
|
||||
| `UseInMemoryStore` | bool | false | Force in-memory store (for testing) |
|
||||
|
||||
### Configuration via appsettings.json
|
||||
|
||||
```json
|
||||
{
|
||||
"HybridLogicalClock": {
|
||||
"NodeId": "scheduler-east-1",
|
||||
"MaxClockSkew": "00:01:00",
|
||||
"PostgresConnectionString": "Host=localhost;Database=stellaops;Username=app",
|
||||
"PostgresSchema": "scheduler"
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
## PostgreSQL Schema
|
||||
|
||||
Create the required table:
|
||||
|
||||
```sql
|
||||
CREATE SCHEMA IF NOT EXISTS scheduler;
|
||||
|
||||
CREATE TABLE scheduler.hlc_state (
|
||||
node_id TEXT PRIMARY KEY,
|
||||
physical_time BIGINT NOT NULL,
|
||||
logical_counter INT NOT NULL,
|
||||
updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
|
||||
);
|
||||
|
||||
CREATE INDEX idx_hlc_state_updated ON scheduler.hlc_state(updated_at DESC);
|
||||
```
|
||||
|
||||
## Serialization
|
||||
|
||||
### JSON (System.Text.Json)
|
||||
|
||||
HlcTimestamp includes a built-in JSON converter that serializes to the sortable string format:
|
||||
|
||||
```csharp
|
||||
var timestamp = clock.Tick();
|
||||
var json = JsonSerializer.Serialize(timestamp);
|
||||
// Output: "0001704067200000-scheduler-east-1-000042"
|
||||
|
||||
var parsed = JsonSerializer.Deserialize<HlcTimestamp>(json);
|
||||
```
|
||||
|
||||
### Dapper
|
||||
|
||||
Register the type handler for Dapper:
|
||||
|
||||
```csharp
|
||||
HlcTimestampTypeHandler.Register();
|
||||
|
||||
// Now you can use HlcTimestamp in Dapper queries
|
||||
var job = connection.QuerySingle<Job>(
|
||||
"SELECT * FROM jobs WHERE timestamp > @Timestamp",
|
||||
new { Timestamp = minTimestamp });
|
||||
```
|
||||
|
||||
## Error Handling
|
||||
|
||||
### HlcClockSkewException
|
||||
|
||||
Thrown when a remote timestamp differs from local physical clock by more than `MaxClockSkew`:
|
||||
|
||||
```csharp
|
||||
try
|
||||
{
|
||||
var localTs = clock.Receive(remoteTimestamp);
|
||||
}
|
||||
catch (HlcClockSkewException ex)
|
||||
{
|
||||
logger.LogError(
|
||||
"Clock skew exceeded: observed {ObservedMs}ms, max {MaxMs}ms",
|
||||
ex.ObservedSkew.TotalMilliseconds,
|
||||
ex.MaxSkew.TotalMilliseconds);
|
||||
|
||||
// Reject the message or alert operations
|
||||
}
|
||||
```
|
||||
|
||||
## Testing
|
||||
|
||||
For unit tests, use FakeTimeProvider and InMemoryHlcStateStore:
|
||||
|
||||
```csharp
|
||||
[Fact]
|
||||
public void Tick_ReturnsMonotonicallyIncreasingTimestamps()
|
||||
{
|
||||
var timeProvider = new FakeTimeProvider(DateTimeOffset.UtcNow);
|
||||
var stateStore = new InMemoryHlcStateStore();
|
||||
var clock = new HybridLogicalClock(timeProvider, "test-node", stateStore);
|
||||
|
||||
var t1 = clock.Tick();
|
||||
var t2 = clock.Tick();
|
||||
var t3 = clock.Tick();
|
||||
|
||||
Assert.True(t1 < t2);
|
||||
Assert.True(t2 < t3);
|
||||
}
|
||||
```
|
||||
|
||||
## Performance
|
||||
|
||||
Benchmarks on typical hardware:
|
||||
|
||||
| Operation | Throughput | Allocation |
|
||||
|-----------|------------|------------|
|
||||
| Tick | ~5M ops/sec | 0 bytes |
|
||||
| Receive | ~3M ops/sec | 0 bytes |
|
||||
| ToSortableString | ~10M ops/sec | 80 bytes |
|
||||
| Parse | ~5M ops/sec | 48 bytes |
|
||||
|
||||
Run benchmarks:
|
||||
```bash
|
||||
cd src/__Libraries/StellaOps.HybridLogicalClock.Benchmarks
|
||||
dotnet run -c Release
|
||||
```
|
||||
|
||||
## Algorithm
|
||||
|
||||
The HLC algorithm (Lamport + Physical Clock Hybrid):
|
||||
|
||||
**On local event or send (Tick):**
|
||||
```
|
||||
l' = l # save previous logical time
|
||||
l = max(l, physical_clock()) # advance to at least physical time
|
||||
if l == l':
|
||||
c = c + 1 # same physical time, increment counter
|
||||
else:
|
||||
c = 0 # new physical time, reset counter
|
||||
return (l, node_id, c)
|
||||
```
|
||||
|
||||
**On receive (Receive):**
|
||||
```
|
||||
l' = l
|
||||
l = max(l', m_l, physical_clock())
|
||||
if l == l' == m_l:
|
||||
c = max(c, m_c) + 1 # all equal, take max counter + 1
|
||||
elif l == l':
|
||||
c = c + 1 # local was max, increment local counter
|
||||
elif l == m_l:
|
||||
c = m_c + 1 # remote was max, take remote counter + 1
|
||||
else:
|
||||
c = 0 # physical clock advanced, reset
|
||||
return (l, node_id, c)
|
||||
```
|
||||
|
||||
## References
|
||||
|
||||
- [Logical Physical Clocks and Consistent Snapshots](https://cse.buffalo.edu/tech-reports/2014-04.pdf) - Original HLC paper
|
||||
- [Time, Clocks, and the Ordering of Events](https://lamport.azurewebsites.net/pubs/time-clocks.pdf) - Lamport clocks
|
||||
|
||||
## License
|
||||
|
||||
AGPL-3.0-or-later
|
||||
@@ -0,0 +1,21 @@
|
||||
<Project Sdk="Microsoft.NET.Sdk">
|
||||
|
||||
<PropertyGroup>
|
||||
<TargetFramework>net10.0</TargetFramework>
|
||||
<ImplicitUsings>enable</ImplicitUsings>
|
||||
<Nullable>enable</Nullable>
|
||||
<LangVersion>preview</LangVersion>
|
||||
<TreatWarningsAsErrors>true</TreatWarningsAsErrors>
|
||||
<Description>Hybrid Logical Clock (HLC) implementation for deterministic, monotonic job ordering across distributed nodes.</Description>
|
||||
</PropertyGroup>
|
||||
|
||||
<ItemGroup>
|
||||
<PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
|
||||
<PackageReference Include="Microsoft.Extensions.Logging.Abstractions" />
|
||||
<PackageReference Include="Microsoft.Extensions.Options" />
|
||||
<PackageReference Include="Microsoft.Extensions.Options.DataAnnotations" />
|
||||
<PackageReference Include="Npgsql" />
|
||||
<PackageReference Include="Dapper" />
|
||||
</ItemGroup>
|
||||
|
||||
</Project>
|
||||
Reference in New Issue
Block a user