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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.Test.Utilities;
using Microsoft.CodeAnalysis.Threading;
using Roslyn.Test.Utilities;
using Roslyn.Utilities;
using Xunit;
namespace Microsoft.CodeAnalysis.UnitTests;
[Trait(Traits.Feature, Traits.Features.AsyncLazy)]
public sealed partial class AsyncLazyTests
{
[Fact]
public void GetValueAsyncReturnsCompletedTaskIfAsyncComputationCompletesImmediately()
{
// Note, this test may pass even if GetValueAsync posted a task to the threadpool, since the
// current thread may context switch out and allow the threadpool to complete the task before
// we check the state. However, a failure here definitely indicates a bug in AsyncLazy.
var lazy = AsyncLazy.Create(static c => Task.FromResult(5));
var t = lazy.GetValueAsync(CancellationToken.None);
Assert.Equal(TaskStatus.RanToCompletion, t.Status);
Assert.Equal(5, t.Result);
}
[Theory]
[InlineData(TaskStatus.RanToCompletion)]
[InlineData(TaskStatus.Canceled)]
[InlineData(TaskStatus.Faulted)]
public void SynchronousContinuationsDoNotRunWithinGetValueCall(TaskStatus expectedTaskStatus)
{
var synchronousComputationStartedEvent = new ManualResetEvent(initialState: false);
var synchronousComputationShouldCompleteEvent = new ManualResetEvent(initialState: false);
var requestCancellationTokenSource = new CancellationTokenSource();
// First, create an async lazy that will only ever do synchronous computations.
var lazy = AsyncLazy.Create(
asynchronousComputeFunction: static (arg, c) => { throw new Exception("We should not get an asynchronous computation."); },
synchronousComputeFunction: static (arg, c) =>
{
// Notify that the synchronous computation started
arg.synchronousComputationStartedEvent.Set();
// And now wait when we should finish
arg.synchronousComputationShouldCompleteEvent.WaitOne();
c.ThrowIfCancellationRequested();
if (arg.expectedTaskStatus == TaskStatus.Faulted)
{
// We want to see what happens if this underlying task faults, so let's fault!
throw new Exception("Task blew up!");
}
return 42;
},
arg: (synchronousComputationStartedEvent, synchronousComputationShouldCompleteEvent, expectedTaskStatus));
// Second, start a synchronous request. While we are in the GetValue, we will record which thread is being occupied by the request
Thread? synchronousRequestThread = null;
Task.Factory.StartNew(() =>
{
try
{
synchronousRequestThread = Thread.CurrentThread;
lazy.GetValue(requestCancellationTokenSource.Token);
}
finally // we do test GetValue in exceptional scenarios, so we should deal with this
{
synchronousRequestThread = null;
}
}, CancellationToken.None, TaskCreationOptions.None, TaskScheduler.Current);
// Wait until this request has actually started
synchronousComputationStartedEvent.WaitOne();
// Good, we now have a synchronous request running. An async request should simply create a task that would
// be completed when the synchronous request completes. We want to assert that if we were to run a continuation
// from this task that's marked ExecuteSynchronously, we do not run it inline atop the synchronous request.
bool? asyncContinuationRanSynchronously = null;
TaskStatus? observedAntecedentTaskStatus = null;
var asyncContinuation = lazy.GetValueAsync(requestCancellationTokenSource.Token).ContinueWith(antecedent =>
{
var currentSynchronousRequestThread = synchronousRequestThread;
asyncContinuationRanSynchronously = currentSynchronousRequestThread != null && currentSynchronousRequestThread == Thread.CurrentThread;
observedAntecedentTaskStatus = antecedent.Status;
},
CancellationToken.None,
TaskContinuationOptions.ExecuteSynchronously,
TaskScheduler.Default);
// Excellent, the async continuation is scheduled. Let's complete the underlying computation.
if (expectedTaskStatus == TaskStatus.Canceled)
{
requestCancellationTokenSource.Cancel();
}
synchronousComputationShouldCompleteEvent.Set();
// And wait for our continuation to run
asyncContinuation.Wait();
AssertEx.NotNull(asyncContinuationRanSynchronously, "The continuation never ran.");
Assert.False(asyncContinuationRanSynchronously.Value, "The continuation did not run asynchronously.");
Assert.Equal(expectedTaskStatus, observedAntecedentTaskStatus!.Value);
}
[Fact]
public void GetValueThrowsCorrectExceptionDuringCancellation()
=> GetValueOrGetValueAsyncThrowsCorrectExceptionDuringCancellation((lazy, ct) => lazy.GetValue(ct), includeSynchronousComputation: false);
[Fact]
public void GetValueThrowsCorrectExceptionDuringCancellationWithSynchronousComputation()
=> GetValueOrGetValueAsyncThrowsCorrectExceptionDuringCancellation((lazy, ct) => lazy.GetValue(ct), includeSynchronousComputation: true);
[Fact]
public void GetValueAsyncThrowsCorrectExceptionDuringCancellation()
{
// NOTE: since GetValueAsync inlines the call to the async computation, the GetValueAsync call will throw
// immediately instead of returning a task that transitions to the cancelled state
GetValueOrGetValueAsyncThrowsCorrectExceptionDuringCancellation((lazy, ct) => lazy.GetValueAsync(ct), includeSynchronousComputation: false);
}
[Fact]
public void GetValueAsyncThrowsCorrectExceptionDuringCancellationWithSynchronousComputation()
{
// In theory the synchronous computation isn't used during GetValueAsync, but just in case...
GetValueOrGetValueAsyncThrowsCorrectExceptionDuringCancellation((lazy, ct) => lazy.GetValueAsync(ct), includeSynchronousComputation: true);
}
private static void GetValueOrGetValueAsyncThrowsCorrectExceptionDuringCancellation(Action<AsyncLazy<object>, CancellationToken> doGetValue, bool includeSynchronousComputation)
{
// A call to GetValue/GetValueAsync with a token that is cancelled should throw an OperationCancelledException, but it's
// important to make sure the correct token is cancelled. It should be cancelled with the token passed
// to GetValue, not the cancellation that was thrown by the computation function
var computeFunctionRunning = new ManualResetEvent(initialState: false);
AsyncLazy<object> lazy;
Func<ManualResetEvent?, CancellationToken, object>? synchronousComputation = null;
if (includeSynchronousComputation)
{
synchronousComputation = (arg, c) =>
{
computeFunctionRunning.Set();
while (true)
{
c.ThrowIfCancellationRequested();
}
};
}
lazy = AsyncLazy.Create(
static (computeFunctionRunning, c) =>
{
computeFunctionRunning.Set();
while (true)
{
c.ThrowIfCancellationRequested();
}
},
synchronousComputeFunction: synchronousComputation!,
arg: computeFunctionRunning);
var cancellationTokenSource = new CancellationTokenSource();
// Create a task that will cancel the request once it's started
Task.Run(() =>
{
computeFunctionRunning.WaitOne();
cancellationTokenSource.Cancel();
});
try
{
doGetValue(lazy, cancellationTokenSource.Token);
AssertEx.Fail(nameof(AsyncLazy<object>.GetValue) + " did not throw an exception.");
}
catch (OperationCanceledException oce)
{
Assert.Equal(cancellationTokenSource.Token, oce.CancellationToken);
}
}
[Fact]
public void GetValueAsyncThatIsCancelledReturnsTaskCancelledWithCorrectToken()
{
var cancellationTokenSource = new CancellationTokenSource();
var lazy = AsyncLazy.Create(static (cancellationTokenSource, c) => Task.Run((Func<object>)(() =>
{
cancellationTokenSource.Cancel();
while (true)
{
c.ThrowIfCancellationRequested();
}
}), c), arg: cancellationTokenSource);
var task = lazy.GetValueAsync(cancellationTokenSource.Token);
// Now wait until the task completes
try
{
task.Wait();
AssertEx.Fail(nameof(AsyncLazy<object>.GetValueAsync) + " did not throw an exception.");
}
catch (AggregateException ex)
{
var operationCancelledException = (OperationCanceledException)ex.Flatten().InnerException!;
Assert.Equal(cancellationTokenSource.Token, operationCancelledException.CancellationToken);
}
}
[Theory, CombinatorialData]
private static void CancellationDuringInlinedComputationFromGetValueOrGetValueAsyncStillCachesResult(bool includeSynchronousComputation)
{
var computations = 0;
var requestCancellationTokenSource = new CancellationTokenSource();
object? createdObject = null;
Func<CancellationToken, object> synchronousComputation = c =>
{
Interlocked.Increment(ref computations);
// We do not want to ever use the cancellation token that we are passed to this
// computation. Rather, we will ignore it but cancel any request that is
// outstanding.
requestCancellationTokenSource.Cancel();
createdObject = new object();
return createdObject;
};
var lazy = AsyncLazy.Create(
static (synchronousComputation, c) => Task.FromResult(synchronousComputation(c)),
includeSynchronousComputation ? static (synchronousComputation, c) => synchronousComputation(c) : null!,
arg: synchronousComputation);
var thrownException = Assert.Throws<OperationCanceledException>(() =>
{
// Do a first request. Even though we will get a cancellation during the evaluation,
// since we handed a result back, that result must be cached.
lazy.GetValue(requestCancellationTokenSource.Token);
});
// And a second request. We'll let this one complete normally.
var secondRequestResult = lazy.GetValue(CancellationToken.None);
// We should have gotten the same cached result, and we should have only computed once.
Assert.Same(createdObject, secondRequestResult);
Assert.Equal(1, computations);
}
[Fact]
public void SynchronousRequestShouldCacheValueWithAsynchronousComputeFunction()
{
var lazy = AsyncLazy.Create(static c => Task.FromResult(new object()));
var firstRequestResult = lazy.GetValue(CancellationToken.None);
var secondRequestResult = lazy.GetValue(CancellationToken.None);
Assert.Same(secondRequestResult, firstRequestResult);
}
[Theory, CombinatorialData]
public async Task AwaitingProducesCorrectException(bool producerAsync, bool consumerAsync)
{
var exception = new ArgumentException();
Func<CancellationToken, Task<object>> asynchronousComputeFunction =
async cancellationToken =>
{
await Task.Yield();
throw exception;
};
Func<CancellationToken, object> synchronousComputeFunction =
cancellationToken =>
{
throw exception;
};
var lazy = producerAsync
? AsyncLazy.Create(asynchronousComputeFunction)
: AsyncLazy.Create(asynchronousComputeFunction, synchronousComputeFunction);
var actual = consumerAsync
? await Assert.ThrowsAsync<ArgumentException>(async () => await lazy.GetValueAsync(CancellationToken.None))
: Assert.Throws<ArgumentException>(() => lazy.GetValue(CancellationToken.None));
Assert.Same(exception, actual);
}
[Fact]
public async Task CancelledAndReranAsynchronousComputationDoesNotBreakSynchronousRequest()
{
// We're going to create an AsyncLazy where we will call GetValue synchronously, and while that operation is
// running we're going to call GetValueAsync() more than once; the first time we will let cancel, the second time will
// run to completion.
var synchronousComputationStartedEvent = new ManualResetEvent(initialState: false);
var synchronousComputationShouldCompleteEvent = new ManualResetEvent(initialState: false);
// We don't want the async path to run sooner than we expect, so we'll set it once ready
Func<CancellationToken, Task<string>>? asynchronousComputation = null;
var lazy = AsyncLazy.Create(
asynchronousComputeFunction: static (arg, ct) =>
{
AssertEx.NotNull(arg.asynchronousComputation, $"The asynchronous computation was not expected to be running.");
return arg.asynchronousComputation(ct);
},
synchronousComputeFunction: static (arg, ct) =>
{
// Let the test know we've started, and we'll continue once asked
arg.synchronousComputationStartedEvent.Set();
arg.synchronousComputationShouldCompleteEvent.WaitOne();
return "Returned from synchronous computation: " + Guid.NewGuid();
},
arg: (asynchronousComputation, synchronousComputationStartedEvent, synchronousComputationShouldCompleteEvent));
// Step 1: start the synchronous operation and wait for it to be running
var synchronousRequest = Task.Run(() => lazy.GetValue(CancellationToken.None));
synchronousComputationStartedEvent.WaitOne();
// Step 2: it's running, so let's let a async operation get started and then cancel. We're ensuring that if this cancels, we might forget we have
// the synchronous operation running if we weren't careful.
var cancellationTokenSource = new CancellationTokenSource();
var asynchronousRequestToBeCancelled = lazy.GetValueAsync(cancellationTokenSource.Token);
cancellationTokenSource.Cancel();
await asynchronousRequestToBeCancelled.NoThrowAwaitableInternal();
Assert.Equal(TaskStatus.Canceled, asynchronousRequestToBeCancelled.Status);
// Step 3: let's now let an async request run normally, producing a value
asynchronousComputation = _ => Task.FromResult("Returned from asynchronous computation: " + Guid.NewGuid());
var asynchronousRequest = lazy.GetValueAsync(CancellationToken.None);
// Now let's finally complete our synchronous request that's been waiting for awhile
synchronousComputationShouldCompleteEvent.Set();
var valueReturnedFromSynchronousRequest = await synchronousRequest;
// We expect that in this case, we should still get the same value back
Assert.Equal(await asynchronousRequest, valueReturnedFromSynchronousRequest);
}
[Fact]
public async Task AsynchronousResultThatWasCancelledDoesNotBreakSynchronousRequest()
{
// We're going to do the following sequence of operations:
//
// 1. Start an asynchronous request
// 2. Cancel the asynchronous request (but it's still consuming CPU because it hasn't observed the cancellation yet)
// 3. Start a synchronous request
// 4. Let the asynchronous request complete, as if the cancellation was never observed
// 5. Complete the synchronous request
var synchronousComputationStartedEvent = new ManualResetEvent(initialState: false);
var synchronousComputationShouldCompleteEvent = new ManualResetEvent(initialState: false);
var asynchronousComputationReadyToComplete = new ManualResetEvent(initialState: false);
var asynchronousComputationShouldCompleteEvent = new ManualResetEvent(initialState: false);
var asynchronousRequestCancellationToken = new CancellationTokenSource();
var lazy = AsyncLazy.Create(
asynchronousComputeFunction: static (arg, ct) =>
{
arg.asynchronousRequestCancellationToken.Cancel();
// Now wait until the cancellation is sent to this underlying computation
while (!ct.IsCancellationRequested)
Thread.Yield();
// Now we're ready to complete, so this is when we want to pause
arg.asynchronousComputationReadyToComplete.Set();
arg.asynchronousComputationShouldCompleteEvent.WaitOne();
return Task.FromResult("Returned from asynchronous computation: " + Guid.NewGuid());
},
synchronousComputeFunction: static (arg, _) =>
{
// Let the test know we've started, and we'll continue once asked
arg.synchronousComputationStartedEvent.Set();
arg.synchronousComputationShouldCompleteEvent.WaitOne();
return "Returned from synchronous computation: " + Guid.NewGuid();
},
arg: (asynchronousRequestCancellationToken, asynchronousComputationReadyToComplete, asynchronousComputationShouldCompleteEvent, synchronousComputationStartedEvent, synchronousComputationShouldCompleteEvent));
// Steps 1 and 2: start asynchronous computation and wait until it's running; this will cancel itself once it's started
var asynchronousRequest = Task.Run(() => lazy.GetValueAsync(asynchronousRequestCancellationToken.Token));
asynchronousComputationReadyToComplete.WaitOne();
// Step 3: while the async request is cancelled but still "thinking", let's start the synchronous request
var synchronousRequest = Task.Run(() => lazy.GetValue(CancellationToken.None));
synchronousComputationStartedEvent.WaitOne();
// Step 4: let the asynchronous compute function now complete
asynchronousComputationShouldCompleteEvent.Set();
// At some point the asynchronous computation value is now going to be cached
string? asyncResult;
while (!lazy.TryGetValue(out asyncResult))
Thread.Yield();
// Step 5: let the synchronous request complete
synchronousComputationShouldCompleteEvent.Set();
var synchronousResult = await synchronousRequest;
// We expect that in this case, the synchronous result should have been thrown away since the async result was computed first
Assert.Equal(asyncResult, synchronousResult);
}
}
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