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Make MemoryCache thread-safety tests deterministic #129897

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21a7a96
Make MemoryCache thread-safety tests deterministic
sami-daniel Jun 26, 2026
b1fada5
Merge branch 'dotnet:main' into sami-daniel-issue-72890
sami-daniel Jun 26, 2026
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164 changes: 56 additions & 108 deletions src/libraries/Microsoft.Extensions.Caching.Memory/tests/MemoryCacheSetAndRemoveTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -570,61 +570,53 @@ public void SetGetAndRemoveWorksWithObjectKeysWhenDifferentReferences()

[Fact]
[ActiveIssue("https://github.com/dotnet/runtime/issues/72879")] // issue in cache
[ActiveIssue("https://github.com/dotnet/runtime/issues/72890")] // issue in test
public void GetAndSet_AreThreadSafe_AndUpdatesNeverLeavesNullValues()
{
var cache = CreateCache();
string key = "myKey";
var cts = new CancellationTokenSource();
var readValueIsNull = false;
bool readValueIsNull = false;

cache.Set(key, new Guid());

var task0 = Task.Run(() =>
{
while (!cts.IsCancellationRequested)
{
cache.Set(key, Guid.NewGuid());
}
});
const int WriterCount = 2;
const int Iterations = 100_000;
var barrier = new Barrier(WriterCount + 1);

var task1 = Task.Run(() =>
var writers = new Task[WriterCount];
for (int i = 0; i < WriterCount; i++)
{
while (!cts.IsCancellationRequested)
writers[i] = Task.Run(() =>
{
cache.Set(key, Guid.NewGuid());
}
});
barrier.SignalAndWait();
for (int j = 0; j < Iterations; j++)
{
cache.Set(key, Guid.NewGuid());
}
});
}

var task2 = Task.Run(() =>
var reader = Task.Run(() =>
{
while (!cts.IsCancellationRequested)
barrier.SignalAndWait();
for (int j = 0; j < Iterations; j++)
{
if (cache.Get(key) == null)
{
// Stop this task and update flag for assertion
readValueIsNull = true;
break;
}
}
});

var task3 = Task.Delay(TimeSpan.FromSeconds(7));

Task.WaitAny(task0, task1, task2, task3);
var all = new Task[WriterCount + 1];
Array.Copy(writers, all, WriterCount);
all[WriterCount] = reader;
Task.WaitAll(all);

Assert.False(readValueIsNull);
Assert.Equal(TaskStatus.Running, task0.Status);
Assert.Equal(TaskStatus.Running, task1.Status);
Assert.Equal(TaskStatus.Running, task2.Status);
Assert.Equal(TaskStatus.RanToCompletion, task3.Status);

cts.Cancel();
Task.WaitAll(task0, task1, task2, task3);
}

[Fact]
[ActiveIssue("https://github.com/dotnet/runtime/issues/72890")]
public void OvercapacityPurge_AreThreadSafe()
{
var cache = new MemoryCache(new MemoryCacheOptions
Expand All @@ -633,64 +625,38 @@ public void OvercapacityPurge_AreThreadSafe()
SizeLimit = 10,
CompactionPercentage = 0.5
});
var cts = new CancellationTokenSource();
var limitExceeded = false;

var task0 = Task.Run(() =>
{
while (!cts.IsCancellationRequested)
{
if (cache.Size > 10)
{
limitExceeded = true;
break;
}
cache.Set(Guid.NewGuid(), Guid.NewGuid(), new MemoryCacheEntryOptions { Size = 1 });
}
}, cts.Token);

var task1 = Task.Run(() =>
{
while (!cts.IsCancellationRequested)
{
if (cache.Size > 10)
{
limitExceeded = true;
break;
}
cache.Set(Guid.NewGuid(), Guid.NewGuid(), new MemoryCacheEntryOptions { Size = 1 });
}
}, cts.Token);
const int NumberOfThreads = 3;
const int IterationsPerThread = 50_000;
var barrier = new Barrier(NumberOfThreads);
bool limitExceeded = false;

var task2 = Task.Run(() =>
var tasks = new Task[NumberOfThreads];
for (int i = 0; i < NumberOfThreads; i++)
{
while (!cts.IsCancellationRequested)
tasks[i] = Task.Run(() =>
{
if (cache.Size > 10)
barrier.SignalAndWait();
for (int j = 0; j < IterationsPerThread; j++)
{
limitExceeded = true;
break;
if (cache.Size > 10)
{
limitExceeded = true;
break;
}
cache.Set(Guid.NewGuid(), Guid.NewGuid(), new MemoryCacheEntryOptions { Size = 1 });
}
cache.Set(Guid.NewGuid(), Guid.NewGuid(), new MemoryCacheEntryOptions { Size = 1 });
}
}, cts.Token);

cts.CancelAfter(TimeSpan.FromSeconds(5));
var task3 = Task.Delay(TimeSpan.FromSeconds(7));
});
}

Task.WaitAll(task0, task1, task2, task3);
Task.WaitAll(tasks);

Assert.Equal(TaskStatus.RanToCompletion, task0.Status);
Assert.Equal(TaskStatus.RanToCompletion, task1.Status);
Assert.Equal(TaskStatus.RanToCompletion, task2.Status);
Assert.Equal(TaskStatus.RanToCompletion, task3.Status);
CapacityTests.AssertCacheSize(cache.Count, cache);
Assert.InRange(cache.Count, 0, 10);
Assert.False(limitExceeded);
}

[Fact]
[ActiveIssue("https://github.com/dotnet/runtime/issues/72890")]
public void AddAndReplaceEntries_AreThreadSafe()
{
var cache = new MemoryCache(new MemoryCacheOptions
Expand All @@ -699,46 +665,28 @@ public void AddAndReplaceEntries_AreThreadSafe()
SizeLimit = 20,
CompactionPercentage = 0.5
});
var cts = new CancellationTokenSource();

var random = new Random();

var task0 = Task.Run(() =>
{
while (!cts.IsCancellationRequested)
{
var entrySize = random.Next(0, 5);
cache.Set(random.Next(0, 10), entrySize, new MemoryCacheEntryOptions { Size = entrySize });
}
});

var task1 = Task.Run(() =>
{
while (!cts.IsCancellationRequested)
{
var entrySize = random.Next(0, 5);
cache.Set(random.Next(0, 10), entrySize, new MemoryCacheEntryOptions { Size = entrySize });
}
});
const int NumberOfThreads = 3;
const int IterationsPerThread = 50_000;
var barrier = new Barrier(NumberOfThreads);

var task2 = Task.Run(() =>
var tasks = new Task[NumberOfThreads];
for (int i = 0; i < NumberOfThreads; i++)
{
while (!cts.IsCancellationRequested)
// Each thread gets its own Random; Random is not thread-safe.
var random = new Random(i);
tasks[i] = Task.Run(() =>
{
var entrySize = random.Next(0, 5);
cache.Set(random.Next(0, 10), entrySize, new MemoryCacheEntryOptions { Size = entrySize });
}
});

cts.CancelAfter(TimeSpan.FromSeconds(5));
var task3 = Task.Delay(TimeSpan.FromSeconds(7));

Task.WaitAll(task0, task1, task2, task3);
barrier.SignalAndWait();
for (int j = 0; j < IterationsPerThread; j++)
{
var entrySize = random.Next(0, 5);
cache.Set(random.Next(0, 10), entrySize, new MemoryCacheEntryOptions { Size = entrySize });
}
});
}

Assert.Equal(TaskStatus.RanToCompletion, task0.Status);
Assert.Equal(TaskStatus.RanToCompletion, task1.Status);
Assert.Equal(TaskStatus.RanToCompletion, task2.Status);
Assert.Equal(TaskStatus.RanToCompletion, task3.Status);
Task.WaitAll(tasks);

var cacheSize = 0;
for (var i = 0; i < 10; i++)
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