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PollingResolver.cs
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PollingResolver.cs
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#region Copyright notice and license
// Copyright 2019 The gRPC Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#endregion
#if SUPPORT_LOAD_BALANCING
using Grpc.Core;
using Grpc.Net.Client.Balancer.Internal;
using Grpc.Net.Client.Internal;
using Grpc.Shared;
using Microsoft.Extensions.Logging;
namespace Grpc.Net.Client.Balancer;
/// <summary>
/// An abstract base type for <see cref="Resolver"/> implementations that use asynchronous polling logic to resolve the <see cref="Uri"/>.
/// <para>
/// <see cref="PollingResolver"/> adds a virtual <see cref="ResolveAsync"/> method. The resolver runs one asynchronous
/// resolve task at a time. Calling <see cref="Refresh()"/> on the resolver when a resolve task is already running has
/// no effect.
/// </para>
/// <para>
/// Note: Experimental API that can change or be removed without any prior notice.
/// </para>
/// </summary>
public abstract class PollingResolver : Resolver
{
// Internal for testing
internal Task _resolveTask = Task.CompletedTask;
private Action<ResolverResult>? _listener;
private bool _disposed;
private bool _resolveSuccessful;
private readonly object _lock = new object();
private readonly CancellationTokenSource _cts = new CancellationTokenSource();
private readonly ILogger _logger;
private readonly IBackoffPolicyFactory? _backoffPolicyFactory;
/// <summary>
/// Gets the listener.
/// </summary>
protected Action<ResolverResult> Listener => _listener!;
/// <summary>
/// Initializes a new instance of the <see cref="PollingResolver"/>.
/// </summary>
/// <param name="loggerFactory">The logger factory.</param>
protected PollingResolver(ILoggerFactory loggerFactory)
: this(loggerFactory, null)
{
}
/// <summary>
/// Initializes a new instance of the <see cref="PollingResolver"/>.
/// </summary>
/// <param name="loggerFactory">The logger factory.</param>
/// <param name="backoffPolicyFactory">The backoff policy factory.</param>
protected PollingResolver(ILoggerFactory loggerFactory, IBackoffPolicyFactory? backoffPolicyFactory)
{
ArgumentNullThrowHelper.ThrowIfNull(loggerFactory);
_logger = loggerFactory.CreateLogger(typeof(PollingResolver));
_backoffPolicyFactory = backoffPolicyFactory;
}
/// <summary>
/// Starts listening to resolver for results with the specified callback. Can only be called once.
/// <para>
/// The <see cref="ResolverResult"/> passed to the callback has addresses when successful,
/// otherwise a <see cref="Status"/> details the resolution error.
/// </para>
/// </summary>
/// <param name="listener">The callback used to receive updates on the target.</param>
public sealed override void Start(Action<ResolverResult> listener)
{
ArgumentNullThrowHelper.ThrowIfNull(listener);
if (_listener != null)
{
throw new InvalidOperationException("Resolver has already been started.");
}
_listener = (result) =>
{
if (result.Status.StatusCode == StatusCode.OK)
{
_resolveSuccessful = true;
}
Log.ResolveResult(_logger, GetType(), result.Status.StatusCode, result.Addresses?.Count ?? 0);
listener(result);
};
OnStarted();
}
/// <summary>
/// Executes after the resolver starts.
/// </summary>
protected virtual void OnStarted()
{
}
/// <summary>
/// Refresh resolution. Can only be called after <see cref="Start(Action{ResolverResult})"/>.
/// <para>
/// The resolver runs one asynchronous resolve task at a time. Calling <see cref="Refresh()"/> on the resolver when a
/// resolve task is already running has no effect.
/// </para>
/// </summary>
public sealed override void Refresh()
{
ObjectDisposedThrowHelper.ThrowIf(_disposed, GetType());
if (_listener == null)
{
throw new InvalidOperationException("Resolver hasn't been started.");
}
lock (_lock)
{
Log.ResolverRefreshRequested(_logger, GetType());
if (_resolveTask.IsCompleted)
{
_resolveTask = ResolveNowAsync(_cts.Token);
_resolveTask.ContinueWith(static (t, state) =>
{
var pollingResolver = (PollingResolver)state!;
Log.ResolveTaskCompleted(pollingResolver._logger, pollingResolver.GetType());
}, this);
}
else
{
Log.ResolverRefreshIgnored(_logger, GetType());
}
}
}
private async Task ResolveNowAsync(CancellationToken cancellationToken)
{
// Reset resolve success to false. Will be set to true when an OK result is sent to listener.
_resolveSuccessful = false;
try
{
var backoffPolicy = _backoffPolicyFactory?.Create();
for (var attempt = 0; ; attempt++)
{
try
{
await ResolveAsync(cancellationToken).ConfigureAwait(false);
// ResolveAsync may report a failure but not throw. Check to see whether an OK result
// has been reported. If not then start retry loop.
if (_resolveSuccessful)
{
return;
}
}
catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
{
// Ignore cancellation.
break;
}
catch (Exception ex)
{
Log.ResolveError(_logger, GetType(), ex);
var status = GrpcProtocolHelpers.CreateStatusFromException("Error refreshing resolver.", ex);
Listener(ResolverResult.ForFailure(status));
}
// No backoff policy specified. Exit immediately.
if (backoffPolicy == null)
{
break;
}
var backoffTicks = backoffPolicy.NextBackoff().Ticks;
// Task.Delay supports up to Int32.MaxValue milliseconds.
// Note that even if the maximum backoff is configured to this maximum, the jitter could push it over the limit.
// Force an upper bound here to ensure an unsupported backoff is never used.
backoffTicks = Math.Min(backoffTicks, TimeSpan.TicksPerMillisecond * int.MaxValue);
var backkoff = TimeSpan.FromTicks(backoffTicks);
Log.StartingResolveBackoff(_logger, GetType(), backkoff);
await Task.Delay(backkoff, cancellationToken).ConfigureAwait(false);
}
}
catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
{
// Ignore cancellation.
}
catch (Exception ex)
{
Log.ErrorRetryingResolve(_logger, GetType(), ex);
}
}
/// <summary>
/// Resolve the target <see cref="Uri"/>. Updated results are passed to the callback
/// registered by <see cref="Start(Action{ResolverResult})"/>. Can only be called
/// after the resolver has started.
/// </summary>
/// <param name="cancellationToken">A cancellation token.</param>
/// <returns>A task.</returns>
protected abstract Task ResolveAsync(CancellationToken cancellationToken);
/// <summary>
/// Releases the unmanaged resources used by the <see cref="LoadBalancer"/> and optionally releases
/// the managed resources.
/// </summary>
/// <param name="disposing">
/// <c>true</c> to release both managed and unmanaged resources; <c>false</c> to release only unmanaged resources.
/// </param>
protected override void Dispose(bool disposing)
{
_cts.Cancel();
_disposed = true;
}
internal static class Log
{
private static readonly Action<ILogger, string, Exception?> _resolverRefreshRequested =
LoggerMessage.Define<string>(LogLevel.Trace, new EventId(1, "ResolverRefreshRequested"), "{ResolveType} refresh requested.");
private static readonly Action<ILogger, string, Exception?> _resolverRefreshIgnored =
LoggerMessage.Define<string>(LogLevel.Trace, new EventId(2, "ResolverRefreshIgnored"), "{ResolveType} refresh ignored because resolve is already in progress.");
private static readonly Action<ILogger, string, Exception> _resolveError =
LoggerMessage.Define<string>(LogLevel.Error, new EventId(3, "ResolveError"), "Error resolving {ResolveType}.");
private static readonly Action<ILogger, string, StatusCode, int, Exception?> _resolveResult =
LoggerMessage.Define<string, StatusCode, int>(LogLevel.Trace, new EventId(4, "ResolveResult"), "{ResolveType} result with status code '{StatusCode}' and {AddressCount} addresses.");
private static readonly Action<ILogger, string, TimeSpan, Exception?> _startingResolveBackoff =
LoggerMessage.Define<string, TimeSpan>(LogLevel.Trace, new EventId(5, "StartingResolveBackoff"), "{ResolveType} starting resolve backoff of {BackoffDuration}.");
private static readonly Action<ILogger, string, Exception> _errorRetryingResolve =
LoggerMessage.Define<string>(LogLevel.Error, new EventId(6, "ErrorRetryingResolve"), "{ResolveType} error retrying resolve.");
private static readonly Action<ILogger, string,Exception?> _resolveTaskCompleted =
LoggerMessage.Define<string>(LogLevel.Trace, new EventId(7, "ResolveTaskCompleted"), "{ResolveType} resolve task completed.");
public static void ResolverRefreshRequested(ILogger logger, Type resolverType)
{
_resolverRefreshRequested(logger, resolverType.Name, null);
}
public static void ResolverRefreshIgnored(ILogger logger, Type resolverType)
{
_resolverRefreshIgnored(logger, resolverType.Name, null);
}
public static void ResolveError(ILogger logger, Type resolverType, Exception ex)
{
_resolveError(logger, resolverType.Name, ex);
}
public static void ResolveResult(ILogger logger, Type resolverType, StatusCode statusCode, int addressCount)
{
_resolveResult(logger, resolverType.Name, statusCode, addressCount, null);
}
public static void StartingResolveBackoff(ILogger logger, Type resolverType, TimeSpan delay)
{
_startingResolveBackoff(logger, resolverType.Name, delay, null);
}
public static void ErrorRetryingResolve(ILogger logger, Type resolverType, Exception ex)
{
_errorRetryingResolve(logger, resolverType.Name, ex);
}
public static void ResolveTaskCompleted(ILogger logger, Type resolverType)
{
_resolveTaskCompleted(logger, resolverType.Name, null);
}
}
}
#endif