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ExecutionStrategy.cs
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ExecutionStrategy.cs
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// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using System.Transactions;
using JetBrains.Annotations;
using Microsoft.EntityFrameworkCore.Diagnostics;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Utilities;
namespace Microsoft.EntityFrameworkCore.Storage
{
/// <summary>
/// The base class for <see cref="IExecutionStrategy" /> implementations.
/// </summary>
public abstract class ExecutionStrategy : IExecutionStrategy
{
/// <summary>
/// The default number of retry attempts.
/// </summary>
protected static readonly int DefaultMaxRetryCount = 6;
/// <summary>
/// The default maximum time delay between retries, must be nonnegative.
/// </summary>
protected static readonly TimeSpan DefaultMaxDelay = TimeSpan.FromSeconds(30);
/// <summary>
/// The default maximum random factor, must not be lesser than 1.
/// </summary>
private const double DefaultRandomFactor = 1.1;
/// <summary>
/// The default base for the exponential function used to compute the delay between retries, must be positive.
/// </summary>
private const double DefaultExponentialBase = 2;
/// <summary>
/// The default coefficient for the exponential function used to compute the delay between retries, must be nonnegative.
/// </summary>
private static readonly TimeSpan _defaultCoefficient = TimeSpan.FromSeconds(1);
/// <summary>
/// Creates a new instance of <see cref="ExecutionStrategy" />.
/// </summary>
/// <param name="context"> The context on which the operations will be invoked. </param>
/// <param name="maxRetryCount"> The maximum number of retry attempts. </param>
/// <param name="maxRetryDelay"> The maximum delay between retries. </param>
protected ExecutionStrategy(
[NotNull] DbContext context,
int maxRetryCount,
TimeSpan maxRetryDelay)
: this(
context.GetService<ExecutionStrategyDependencies>(),
maxRetryCount,
maxRetryDelay)
{
}
/// <summary>
/// Creates a new instance of <see cref="ExecutionStrategy" />.
/// </summary>
/// <param name="dependencies"> Parameter object containing service dependencies. </param>
/// <param name="maxRetryCount"> The maximum number of retry attempts. </param>
/// <param name="maxRetryDelay"> The maximum delay between retries. </param>
protected ExecutionStrategy(
[NotNull] ExecutionStrategyDependencies dependencies,
int maxRetryCount,
TimeSpan maxRetryDelay)
{
if (maxRetryCount < 0)
{
throw new ArgumentOutOfRangeException(nameof(maxRetryCount));
}
if (maxRetryDelay.TotalMilliseconds < 0.0)
{
throw new ArgumentOutOfRangeException(nameof(maxRetryDelay));
}
Dependencies = dependencies;
MaxRetryCount = maxRetryCount;
MaxRetryDelay = maxRetryDelay;
}
/// <summary>
/// The list of exceptions that caused the operation to be retried so far.
/// </summary>
protected virtual List<Exception> ExceptionsEncountered { get; } = new List<Exception>();
/// <summary>
/// A pseudo-random number generator that can be used to vary the delay between retries.
/// </summary>
protected virtual Random Random { get; } = new Random();
/// <summary>
/// The maximum number of retry attempts.
/// </summary>
protected virtual int MaxRetryCount { get; }
/// <summary>
/// The maximum delay between retries.
/// </summary>
protected virtual TimeSpan MaxRetryDelay { get; }
/// <summary>
/// Parameter object containing service dependencies.
/// </summary>
protected virtual ExecutionStrategyDependencies Dependencies { get; }
private static readonly AsyncLocal<bool?> _suspended = new AsyncLocal<bool?>();
/// <summary>
/// Indicates whether the strategy is suspended. The strategy is typically suspending while executing to avoid
/// recursive execution from nested operations.
/// </summary>
protected static bool Suspended
{
get => _suspended.Value ?? false;
set => _suspended.Value = value;
}
/// <summary>
/// Indicates whether this <see cref="IExecutionStrategy" /> might retry the execution after a failure.
/// </summary>
public virtual bool RetriesOnFailure => !Suspended;
/// <summary>
/// Executes the specified operation and returns the result.
/// </summary>
/// <param name="state"> The state that will be passed to the operation. </param>
/// <param name="operation">
/// A delegate representing an executable operation that returns the result of type <typeparamref name="TResult" />.
/// </param>
/// <param name="verifySucceeded"> A delegate that tests whether the operation succeeded even though an exception was thrown. </param>
/// <typeparam name="TState"> The type of the state. </typeparam>
/// <typeparam name="TResult"> The return type of <paramref name="operation" />. </typeparam>
/// <returns> The result from the operation. </returns>
/// <exception cref="RetryLimitExceededException">
/// The operation has not succeeded after the configured number of retries.
/// </exception>
public virtual TResult Execute<TState, TResult>(
TState state,
Func<DbContext, TState, TResult> operation,
Func<DbContext, TState, ExecutionResult<TResult>> verifySucceeded)
{
Check.NotNull(operation, nameof(operation));
if (Suspended)
{
return operation(Dependencies.CurrentContext.Context, state);
}
OnFirstExecution();
return ExecuteImplementation(operation, verifySucceeded, state);
}
private TResult ExecuteImplementation<TState, TResult>(
Func<DbContext, TState, TResult> operation,
Func<DbContext, TState, ExecutionResult<TResult>> verifySucceeded,
TState state)
{
while (true)
{
TimeSpan? delay;
try
{
Suspended = true;
var result = operation(Dependencies.CurrentContext.Context, state);
Suspended = false;
return result;
}
catch (Exception ex)
{
Suspended = false;
if (verifySucceeded != null
&& CallOnWrappedException(ex, ShouldVerifySuccessOn))
{
var result = ExecuteImplementation(verifySucceeded, null, state);
if (result.IsSuccessful)
{
return result.Result;
}
}
if (!CallOnWrappedException(ex, ShouldRetryOn))
{
throw;
}
ExceptionsEncountered.Add(ex);
delay = GetNextDelay(ex);
if (delay == null)
{
throw new RetryLimitExceededException(CoreStrings.RetryLimitExceeded(MaxRetryCount, GetType().Name), ex);
}
Dependencies.Logger.ExecutionStrategyRetrying(ExceptionsEncountered, delay.Value, async: true);
OnRetry();
}
using (var waitEvent = new ManualResetEventSlim(false))
{
waitEvent.WaitHandle.WaitOne(delay.Value);
}
}
}
/// <summary>
/// Executes the specified asynchronous operation and returns the result.
/// </summary>
/// <param name="state"> The state that will be passed to the operation. </param>
/// <param name="operation">
/// A function that returns a started task of type <typeparamref name="TResult" />.
/// </param>
/// <param name="verifySucceeded"> A delegate that tests whether the operation succeeded even though an exception was thrown. </param>
/// <param name="cancellationToken">
/// A cancellation token used to cancel the retry operation, but not operations that are already in flight
/// or that already completed successfully.
/// </param>
/// <typeparam name="TState"> The type of the state. </typeparam>
/// <typeparam name="TResult"> The result type of the <see cref="Task{T}" /> returned by <paramref name="operation" />. </typeparam>
/// <returns>
/// A task that will run to completion if the original task completes successfully (either the
/// first time or after retrying transient failures). If the task fails with a non-transient error or
/// the retry limit is reached, the returned task will become faulted and the exception must be observed.
/// </returns>
/// <exception cref="RetryLimitExceededException">
/// The operation has not succeeded after the configured number of retries.
/// </exception>
public virtual Task<TResult> ExecuteAsync<TState, TResult>(
TState state,
Func<DbContext, TState, CancellationToken, Task<TResult>> operation,
Func<DbContext, TState, CancellationToken, Task<ExecutionResult<TResult>>> verifySucceeded,
CancellationToken cancellationToken = default)
{
Check.NotNull(operation, nameof(operation));
if (Suspended)
{
return operation(Dependencies.CurrentContext.Context, state, cancellationToken);
}
OnFirstExecution();
return ExecuteImplementationAsync(operation, verifySucceeded, state, cancellationToken);
}
private async Task<TResult> ExecuteImplementationAsync<TState, TResult>(
Func<DbContext, TState, CancellationToken, Task<TResult>> operation,
Func<DbContext, TState, CancellationToken, Task<ExecutionResult<TResult>>> verifySucceeded,
TState state,
CancellationToken cancellationToken)
{
while (true)
{
cancellationToken.ThrowIfCancellationRequested();
TimeSpan? delay;
try
{
Suspended = true;
var result = await operation(Dependencies.CurrentContext.Context, state, cancellationToken);
Suspended = false;
return result;
}
catch (Exception ex)
{
Suspended = false;
if (verifySucceeded != null
&& CallOnWrappedException(ex, ShouldVerifySuccessOn))
{
var result = await ExecuteImplementationAsync(verifySucceeded, null, state, cancellationToken);
if (result.IsSuccessful)
{
return result.Result;
}
}
if (!CallOnWrappedException(ex, ShouldRetryOn))
{
throw;
}
ExceptionsEncountered.Add(ex);
delay = GetNextDelay(ex);
if (delay == null)
{
throw new RetryLimitExceededException(CoreStrings.RetryLimitExceeded(MaxRetryCount, GetType().Name), ex);
}
Dependencies.Logger.ExecutionStrategyRetrying(ExceptionsEncountered, delay.Value, async: true);
OnRetry();
}
await Task.Delay(delay.Value, cancellationToken);
}
}
/// <summary>
/// Method called before the first operation execution
/// </summary>
protected virtual void OnFirstExecution()
{
if (Dependencies.CurrentContext.Context.Database.CurrentTransaction != null
|| Dependencies.CurrentContext.Context.Database.GetEnlistedTransaction() != null
|| Transaction.Current != null)
{
throw new InvalidOperationException(
CoreStrings.ExecutionStrategyExistingTransaction(
GetType().Name,
nameof(DbContext)
+ "."
+ nameof(DbContext.Database)
+ "."
+ nameof(DatabaseFacade.CreateExecutionStrategy)
+ "()"));
}
ExceptionsEncountered.Clear();
}
/// <summary>
/// Method called before retrying the operation execution
/// </summary>
protected virtual void OnRetry()
{
}
/// <summary>
/// Determines whether the operation should be retried and the delay before the next attempt.
/// </summary>
/// <param name="lastException"> The exception thrown during the last execution attempt. </param>
/// <returns>
/// Returns the delay indicating how long to wait for before the next execution attempt if the operation should be retried;
/// <c>null</c> otherwise
/// </returns>
protected virtual TimeSpan? GetNextDelay([NotNull] Exception lastException)
{
var currentRetryCount = ExceptionsEncountered.Count - 1;
if (currentRetryCount < MaxRetryCount)
{
var delta = (Math.Pow(DefaultExponentialBase, currentRetryCount) - 1.0)
* (1.0 + Random.NextDouble() * (DefaultRandomFactor - 1.0));
var delay = Math.Min(
_defaultCoefficient.TotalMilliseconds * delta,
MaxRetryDelay.TotalMilliseconds);
return TimeSpan.FromMilliseconds(delay);
}
return null;
}
/// <summary>
/// Determines whether the specified exception could be thrown after a successful execution.
/// </summary>
/// <param name="exception"> The exception object to be verified. </param>
/// <returns>
/// <c>true</c> if the specified exception could be thrown after a successful execution, otherwise <c>false</c>.
/// </returns>
protected internal virtual bool ShouldVerifySuccessOn([NotNull] Exception exception)
=> ShouldRetryOn(exception);
/// <summary>
/// Determines whether the specified exception represents a transient failure that can be compensated by a retry.
/// </summary>
/// <param name="exception"> The exception object to be verified. </param>
/// <returns>
/// <c>true</c> if the specified exception is considered as transient, otherwise <c>false</c>.
/// </returns>
protected internal abstract bool ShouldRetryOn([NotNull] Exception exception);
/// <summary>
/// Recursively gets InnerException from <paramref name="exception" /> as long as it is an
/// exception created by Entity Framework and calls <paramref name="exceptionHandler" /> on the innermost one.
/// </summary>
/// <param name="exception"> The exception to be unwrapped. </param>
/// <param name="exceptionHandler"> A delegate that will be called with the unwrapped exception. </param>
/// <typeparam name="TResult"> The return type of <paramref name="exceptionHandler" />. </typeparam>
/// <returns>
/// The result from <paramref name="exceptionHandler" />.
/// </returns>
public static TResult CallOnWrappedException<TResult>(
[NotNull] Exception exception, [NotNull] Func<Exception, TResult> exceptionHandler)
=> exception is DbUpdateException dbUpdateException
? CallOnWrappedException(dbUpdateException.InnerException, exceptionHandler)
: exceptionHandler(exception);
}
}