protected void ExecuteOnDispatcher(Func <Task> action)
{
if (!SingleThreadedTestSynchronizationContext.IsSingleThreadedSyncContext(SynchronizationContext.Current))
{
SynchronizationContext.SetSynchronizationContext(SingleThreadedTestSynchronizationContext.New());
}
SingleThreadedTestSynchronizationContext.IFrame?frame = SingleThreadedTestSynchronizationContext.NewFrame();
Exception?failure = null;
SynchronizationContext.Current !.Post(
async _ =>
{
try
{
await action();
}
catch (Exception ex)
{
failure = ex;
}
finally
{
frame.Continue = false;
}
},
null);
SingleThreadedTestSynchronizationContext.PushFrame(SynchronizationContext.Current, frame);
if (failure is object)
{
ExceptionDispatchInfo.Capture(failure).Throw();
}
}
/// <summary>
/// Runs a given scenario many times to observe memory characteristics and assert that they can satisfy given conditions.
/// </summary>
/// <param name="scenario">The delegate to invoke.</param>
/// <param name="maxBytesAllocated">The maximum number of bytes allowed to be allocated by one run of the scenario. Use -1 to indicate no limit.</param>
/// <param name="iterations">The number of times to invoke <paramref name="scenario"/> in a row before measuring average memory impact.</param>
/// <param name="allowedAttempts">The number of times the (scenario * iterations) loop repeats with a failing result before ultimately giving up.</param>
/// <param name="completeSynchronously"><c>true</c> to synchronously complete instead of yielding.</param>
/// <returns>A task that captures the result of the operation.</returns>
protected async Task CheckGCPressureAsync(Func <Task> scenario, int maxBytesAllocated, int iterations = 100, int allowedAttempts = GCAllocationAttempts, bool completeSynchronously = false)
{
const int quietPeriodMaxAttempts = 3;
const int shortDelayDuration = 250;
const int quietThreshold = 1200;
// prime the pump
for (int i = 0; i < 2; i++)
{
await MaybeShouldBeComplete(scenario(), completeSynchronously);
}
long waitForQuietMemory1, waitForQuietMemory2, waitPeriodAllocations, waitForQuietAttemptCount = 0;
do
{
waitForQuietMemory1 = GC.GetTotalMemory(true);
await MaybeShouldBlock(Task.Delay(shortDelayDuration), completeSynchronously);
waitForQuietMemory2 = GC.GetTotalMemory(true);
waitPeriodAllocations = Math.Abs(waitForQuietMemory2 - waitForQuietMemory1);
this.Logger.WriteLine("Bytes allocated during quiet wait period: {0}", waitPeriodAllocations);
}while (waitPeriodAllocations > quietThreshold || ++waitForQuietAttemptCount >= quietPeriodMaxAttempts);
if (waitPeriodAllocations > quietThreshold)
{
this.Logger.WriteLine("WARNING: Unable to establish a quiet period.");
}
// This test is rather rough. So we're willing to try it a few times in order to observe the desired value.
bool attemptWithNoLeakObserved = false;
bool attemptWithinMemoryLimitsObserved = false;
for (int attempt = 1; attempt <= allowedAttempts; attempt++)
{
this.Logger?.WriteLine("Iteration {0}", attempt);
int[] gcCountBefore = new int[GC.MaxGeneration + 1];
int[] gcCountAfter = new int[GC.MaxGeneration + 1];
long initialMemory = GC.GetTotalMemory(true);
GC.TryStartNoGCRegion(8 * 1024 * 1024);
for (int i = 0; i <= GC.MaxGeneration; i++)
{
gcCountBefore[i] = GC.CollectionCount(i);
}
for (int i = 0; i < iterations; i++)
{
await MaybeShouldBeComplete(scenario(), completeSynchronously);
}
for (int i = 0; i < gcCountAfter.Length; i++)
{
gcCountAfter[i] = GC.CollectionCount(i);
}
long allocated = (GC.GetTotalMemory(false) - initialMemory) / iterations;
GC.EndNoGCRegion();
attemptWithinMemoryLimitsObserved |= maxBytesAllocated == -1 || allocated <= maxBytesAllocated;
long leaked = long.MaxValue;
for (int leakCheck = 0; leakCheck < 3; leakCheck++)
{
// Allow the message queue to drain.
if (completeSynchronously)
{
// If there is a dispatcher sync context, let it run for a bit.
// This allows any posted messages that are now obsolete to be released.
if (SingleThreadedTestSynchronizationContext.IsSingleThreadedSyncContext(SynchronizationContext.Current))
{
SingleThreadedTestSynchronizationContext.IFrame?frame = SingleThreadedTestSynchronizationContext.NewFrame();
SynchronizationContext.Current.Post(state => frame.Continue = false, null);
SingleThreadedTestSynchronizationContext.PushFrame(SynchronizationContext.Current, frame);
}
}
else
{
await Task.Yield();
}
leaked = (GC.GetTotalMemory(true) - initialMemory) / iterations;
attemptWithNoLeakObserved |= leaked <= 3 * IntPtr.Size; // any real leak would be an object, which is at least this size.
if (attemptWithNoLeakObserved)
{
break;
}
await MaybeShouldBlock(Task.Delay(shortDelayDuration), completeSynchronously);
}
this.Logger?.WriteLine("{0} bytes leaked per iteration.", leaked);
this.Logger?.WriteLine("{0} bytes allocated per iteration ({1} allowed).", allocated, maxBytesAllocated);
for (int i = 0; i <= GC.MaxGeneration; i++)
{
Assert.False(gcCountAfter[i] > gcCountBefore[i], $"WARNING: Gen {i} GC occurred {gcCountAfter[i] - gcCountBefore[i]} times during testing. Results are probably totally wrong.");
}
if (attemptWithNoLeakObserved && attemptWithinMemoryLimitsObserved)
{
// Don't keep looping. We got what we needed.
break;
}
// give the system a bit of cool down time to increase the odds we'll pass next time.
GC.Collect();
await MaybeShouldBlock(Task.Delay(shortDelayDuration), completeSynchronously);
}
Assert.True(attemptWithNoLeakObserved, "Leaks observed in every iteration.");
Assert.True(attemptWithinMemoryLimitsObserved, "Excess memory allocations in every iteration.");
}