// Entry point from unmanaged code
private static void EnsureGateThreadRunning()
{
Debug.Assert(UsePortableThreadPool);
Debug.Assert(!UsePortableThreadPoolForIO);
PortableThreadPool.EnsureGateThreadRunning();
}
/// <summary>
/// Reduce the number of working workers by one, but maybe add back a worker (possibily this thread) if a thread request comes in while we are marking this thread as not working.
/// </summary>
private static void RemoveWorkingWorker(PortableThreadPool threadPoolInstance)
{
ThreadCounts currentCounts = threadPoolInstance._separated.counts.VolatileRead();
while (true)
{
ThreadCounts newCounts = currentCounts;
newCounts.SubtractNumProcessingWork(1);
ThreadCounts oldCounts = threadPoolInstance._separated.counts.InterlockedCompareExchange(newCounts, currentCounts);
if (oldCounts == currentCounts)
{
break;
}
currentCounts = oldCounts;
}
// It's possible that we decided we had thread requests just before a request came in,
// but reduced the worker count *after* the request came in. In this case, we might
// miss the notification of a thread request. So we wake up a thread (maybe this one!)
// if there is work to do.
if (threadPoolInstance._separated.numRequestedWorkers > 0)
{
MaybeAddWorkingWorker(threadPoolInstance);
}
}
/// <summary>
/// Reduce the number of working workers by one, but maybe add back a worker (possibily this thread) if a thread request comes in while we are marking this thread as not working.
/// </summary>
private static void RemoveWorkingWorker(PortableThreadPool threadPoolInstance)
{
// A compare-exchange loop is used instead of Interlocked.Decrement or Interlocked.Add to defensively prevent
// NumProcessingWork from underflowing. See the setter for NumProcessingWork.
ThreadCounts counts = threadPoolInstance._separated.counts;
while (true)
{
ThreadCounts newCounts = counts;
newCounts.NumProcessingWork--;
ThreadCounts countsBeforeUpdate =
threadPoolInstance._separated.counts.InterlockedCompareExchange(newCounts, counts);
if (countsBeforeUpdate == counts)
{
break;
}
counts = countsBeforeUpdate;
}
// It's possible that we decided we had thread requests just before a request came in,
// but reduced the worker count *after* the request came in. In this case, we might
// miss the notification of a thread request. So we wake up a thread (maybe this one!)
// if there is work to do.
if (threadPoolInstance._separated.numRequestedWorkers > 0)
{
MaybeAddWorkingWorker(threadPoolInstance);
}
}
private static void CreateGateThread(PortableThreadPool threadPoolInstance)
{
bool created = false;
try
{
// Thread pool threads must start in the default execution context without transferring the context, so
// using UnsafeStart() instead of Start()
Thread gateThread = new Thread(GateThreadStart, SmallStackSizeBytes)
{
IsThreadPoolThread = true,
IsBackground = true,
Name = ".NET ThreadPool Gate"
};
gateThread.UnsafeStart();
created = true;
}
finally
{
if (!created)
{
Interlocked.Exchange(ref threadPoolInstance._separated.gateThreadRunningState, 0);
}
}
}
/// <summary>
/// Returns if the current thread should stop processing work on the thread pool.
/// A thread should stop processing work on the thread pool when work remains only when
/// there are more worker threads in the thread pool than we currently want.
/// </summary>
/// <returns>Whether or not this thread should stop processing work even if there is still work in the queue.</returns>
internal static bool ShouldStopProcessingWorkNow(PortableThreadPool threadPoolInstance)
{
ThreadCounts counts = threadPoolInstance._separated.counts;
while (true)
{
// When there are more threads processing work than the thread count goal, it may have been decided
// to decrease the number of threads. Stop processing if the counts can be updated. We may have more
// threads existing than the thread count goal and that is ok, the cold ones will eventually time out if
// the thread count goal is not increased again. This logic is a bit different from the original CoreCLR
// code from which this implementation was ported, which turns a processing thread into a retired thread
// and checks for pending requests like RemoveWorkingWorker. In this implementation there are
// no retired threads, so only the count of threads processing work is considered.
if (counts.NumProcessingWork <= counts.NumThreadsGoal)
{
return(false);
}
ThreadCounts newCounts = counts;
newCounts.NumProcessingWork--;
ThreadCounts oldCounts = threadPoolInstance._separated.counts.InterlockedCompareExchange(newCounts, counts);
if (oldCounts == counts)
{
return(true);
}
counts = oldCounts;
}
}
// This is called by a worker thread
internal static void EnsureRunning(PortableThreadPool threadPoolInstance)
{
// The callers ensure that this speculative load is sufficient to ensure that the gate thread is activated when
// it is needed
if (threadPoolInstance._separated.gateThreadRunningState != GetRunningStateForNumRuns(MaxRuns))
{
EnsureRunningSlow(threadPoolInstance);
}
}
internal static void EnsureRunningSlow(PortableThreadPool threadPoolInstance)
{
int numRunsMask = Interlocked.Exchange(ref threadPoolInstance._separated.gateThreadRunningState, GetRunningStateForNumRuns(MaxRuns));
if (numRunsMask == GetRunningStateForNumRuns(0))
{
s_runGateThreadEvent.Set();
}
else if ((numRunsMask & GateThreadRunningMask) == 0)
{
CreateGateThread(threadPoolInstance);
}
}
/// <summary>
/// Reduce the number of working workers by one, but maybe add back a worker (possibily this thread) if a thread request comes in while we are marking this thread as not working.
/// </summary>
private static void RemoveWorkingWorker(PortableThreadPool threadPoolInstance)
{
threadPoolInstance._separated.counts.InterlockedDecrementNumProcessingWork();
// It's possible that we decided we had thread requests just before a request came in,
// but reduced the worker count *after* the request came in. In this case, we might
// miss the notification of a thread request. So we wake up a thread (maybe this one!)
// if there is work to do.
if (threadPoolInstance._separated.numRequestedWorkers > 0)
{
MaybeAddWorkingWorker(threadPoolInstance);
}
}
private static bool TakeActiveRequest(PortableThreadPool threadPoolInstance)
{
int count = threadPoolInstance._separated.numRequestedWorkers;
while (count > 0)
{
int prevCount = Interlocked.CompareExchange(ref threadPoolInstance._separated.numRequestedWorkers, count - 1, count);
if (prevCount == count)
{
return(true);
}
count = prevCount;
}
return(false);
}
// called by logic to spawn new worker threads, return true if it's been too long
// since the last dequeue operation - takes number of worker threads into account
// in deciding "too long"
private static bool SufficientDelaySinceLastDequeue(PortableThreadPool threadPoolInstance)
{
uint delay = (uint)(Environment.TickCount - threadPoolInstance._separated.lastDequeueTime);
uint minimumDelay;
if (threadPoolInstance._cpuUtilization < CpuUtilizationLow)
{
minimumDelay = GateActivitiesPeriodMs;
}
else
{
minimumDelay = (uint)threadPoolInstance._separated.numThreadsGoal * DequeueDelayThresholdMs;
}
return(delay > minimumDelay);
}
// called by logic to spawn new worker threads, return true if it's been too long
// since the last dequeue operation - takes number of worker threads into account
// in deciding "too long"
private static bool SufficientDelaySinceLastDequeue(PortableThreadPool threadPoolInstance)
{
int delay = Environment.TickCount - Volatile.Read(ref threadPoolInstance._separated.lastDequeueTime);
int minimumDelay;
if (threadPoolInstance._cpuUtilization < CpuUtilizationLow)
{
minimumDelay = GateThreadDelayMs;
}
else
{
ThreadCounts counts = threadPoolInstance._separated.counts.VolatileRead();
int numThreads = counts.NumThreadsGoal;
minimumDelay = numThreads * DequeueDelayThresholdMs;
}
return(delay > minimumDelay);
}
/// <summary>
/// Reduce the number of working workers by one, but maybe add back a worker (possibily this thread) if a thread request comes in while we are marking this thread as not working.
/// </summary>
private static void RemoveWorkingWorker(PortableThreadPool threadPoolInstance)
{
ThreadCounts currentCounts = threadPoolInstance._separated.counts.VolatileRead();
while (true)
{
ThreadCounts newCounts = currentCounts;
newCounts.SubtractNumProcessingWork(1);
ThreadCounts oldCounts = threadPoolInstance._separated.counts.InterlockedCompareExchange(newCounts, currentCounts);
if (oldCounts == currentCounts)
{
break;
}
currentCounts = oldCounts;
}
if (currentCounts.NumProcessingWork > 1)
{
// In highly bursty cases with short bursts of work, especially in the portable thread pool implementation,
// worker threads are being released and entering Dispatch very quickly, not finding much work in Dispatch,
// and soon afterwards going back to Dispatch, causing extra thrashing on data and some interlocked
// operations. If this is not the last thread to stop processing work, introduce a slight delay to help
// other threads make more efficient progress. The spin-wait is mainly for when the sleep is not effective
// due to there being no other threads to schedule.
Thread.UninterruptibleSleep0();
if (!Environment.IsSingleProcessor)
{
Thread.SpinWait(1);
}
}
// It's possible that we decided we had thread requests just before a request came in,
// but reduced the worker count *after* the request came in. In this case, we might
// miss the notification of a thread request. So we wake up a thread (maybe this one!)
// if there is work to do.
if (threadPoolInstance._separated.numRequestedWorkers > 0)
{
MaybeAddWorkingWorker(threadPoolInstance);
}
}
private static void CreateGateThread(PortableThreadPool threadPoolInstance)
{
bool created = false;
try
{
Thread gateThread = new Thread(GateThreadStart, SmallStackSizeBytes);
gateThread.IsThreadPoolThread = true;
gateThread.IsBackground = true;
gateThread.Name = ".NET ThreadPool Gate";
gateThread.Start();
created = true;
}
finally
{
if (!created)
{
Interlocked.Exchange(ref threadPoolInstance._separated.gateThreadRunningState, 0);
}
}
}
/// <summary>
/// Unregister a wait handle.
/// </summary>
/// <param name="handle">The wait handle to unregister.</param>
/// <param name="blocking">Should the unregistration block at all.</param>
private void UnregisterWait(RegisteredWaitHandle handle, bool blocking)
{
bool pendingRemoval = false;
// TODO: Optimization: Try to unregister wait directly if it isn't being waited on.
PortableThreadPool threadPoolInstance = ThreadPoolInstance;
threadPoolInstance._waitThreadLock.Acquire();
try
{
// If this handle is not already pending removal and hasn't already been removed
if (Array.IndexOf(_registeredWaits, handle) != -1)
{
if (Array.IndexOf(_pendingRemoves, handle) == -1)
{
_pendingRemoves[_numPendingRemoves++] = handle;
_changeHandlesEvent.Set(); // Tell the wait thread that there are changes pending.
}
pendingRemoval = true;
}
}
finally
{
threadPoolInstance._waitThreadLock.Release();
}
if (blocking)
{
if (handle.IsBlocking)
{
handle.WaitForCallbacks();
}
else if (pendingRemoval)
{
handle.WaitForRemoval();
}
}
}
internal static void MaybeAddWorkingWorker(PortableThreadPool threadPoolInstance)
{
ThreadCounts counts = threadPoolInstance._separated.counts;
short numExistingThreads, numProcessingWork, newNumExistingThreads, newNumProcessingWork;
while (true)
{
numProcessingWork = counts.NumProcessingWork;
if (numProcessingWork >= counts.NumThreadsGoal)
{
return;
}
newNumProcessingWork = (short)(numProcessingWork + 1);
numExistingThreads = counts.NumExistingThreads;
newNumExistingThreads = Math.Max(numExistingThreads, newNumProcessingWork);
ThreadCounts newCounts = counts;
newCounts.NumProcessingWork = newNumProcessingWork;
newCounts.NumExistingThreads = newNumExistingThreads;
ThreadCounts oldCounts = threadPoolInstance._separated.counts.InterlockedCompareExchange(newCounts, counts);
if (oldCounts == counts)
{
break;
}
counts = oldCounts;
}
int toCreate = newNumExistingThreads - numExistingThreads;
int toRelease = newNumProcessingWork - numProcessingWork;
if (toRelease > 0)
{
s_semaphore.Release(toRelease);
}
while (toCreate > 0)
{
if (TryCreateWorkerThread())
{
toCreate--;
continue;
}
counts = threadPoolInstance._separated.counts;
while (true)
{
ThreadCounts newCounts = counts;
newCounts.NumProcessingWork -= (short)toCreate;
newCounts.NumExistingThreads -= (short)toCreate;
ThreadCounts oldCounts = threadPoolInstance._separated.counts.InterlockedCompareExchange(newCounts, counts);
if (oldCounts == counts)
{
break;
}
counts = oldCounts;
}
break;
}
}
public static void Wake(PortableThreadPool threadPoolInstance)
{
DelayEvent.Set();
EnsureRunning(threadPoolInstance);
}
public (int newThreadCount, int newSampleMs) Update(int currentThreadCount, double sampleDurationSeconds, int numCompletions)
{
//
// If someone changed the thread count without telling us, update our records accordingly.
//
if (currentThreadCount != _lastThreadCount)
{
ForceChange(currentThreadCount, StateOrTransition.Initializing);
}
//
// Update the cumulative stats for this thread count
//
_secondsElapsedSinceLastChange += sampleDurationSeconds;
_completionsSinceLastChange += numCompletions;
//
// Add in any data we've already collected about this sample
//
sampleDurationSeconds += _accumulatedSampleDurationSeconds;
numCompletions += _accumulatedCompletionCount;
//
// We need to make sure we're collecting reasonably accurate data. Since we're just counting the end
// of each work item, we are goinng to be missing some data about what really happened during the
// sample interval. The count produced by each thread includes an initial work item that may have
// started well before the start of the interval, and each thread may have been running some new
// work item for some time before the end of the interval, which did not yet get counted. So
// our count is going to be off by +/- threadCount workitems.
//
// The exception is that the thread that reported to us last time definitely wasn't running any work
// at that time, and the thread that's reporting now definitely isn't running a work item now. So
// we really only need to consider threadCount-1 threads.
//
// Thus the percent error in our count is +/- (threadCount-1)/numCompletions.
//
// We cannot rely on the frequency-domain analysis we'll be doing later to filter out this error, because
// of the way it accumulates over time. If this sample is off by, say, 33% in the negative direction,
// then the next one likely will be too. The one after that will include the sum of the completions
// we missed in the previous samples, and so will be 33% positive. So every three samples we'll have
// two "low" samples and one "high" sample. This will appear as periodic variation right in the frequency
// range we're targeting, which will not be filtered by the frequency-domain translation.
//
if (_totalSamples > 0 && ((currentThreadCount - 1.0) / numCompletions) >= _maxSampleError)
{
// not accurate enough yet. Let's accumulate the data so far, and tell the ThreadPool
// to collect a little more.
_accumulatedSampleDurationSeconds = sampleDurationSeconds;
_accumulatedCompletionCount = numCompletions;
return(currentThreadCount, 10);
}
//
// We've got enouugh data for our sample; reset our accumulators for next time.
//
_accumulatedSampleDurationSeconds = 0;
_accumulatedCompletionCount = 0;
//
// Add the current thread count and throughput sample to our history
//
double throughput = numCompletions / sampleDurationSeconds;
if (NativeRuntimeEventSource.Log.IsEnabled())
{
NativeRuntimeEventSource.Log.ThreadPoolWorkerThreadAdjustmentSample(throughput);
}
int sampleIndex = (int)(_totalSamples % _samplesToMeasure);
_samples[sampleIndex] = throughput;
_threadCounts[sampleIndex] = currentThreadCount;
_totalSamples++;
//
// Set up defaults for our metrics
//
Complex threadWaveComponent = default;
Complex throughputWaveComponent = default;
double throughputErrorEstimate = 0;
Complex ratio = default;
double confidence = 0;
StateOrTransition state = StateOrTransition.Warmup;
//
// How many samples will we use? It must be at least the three wave periods we're looking for, and it must also be a whole
// multiple of the primary wave's period; otherwise the frequency we're looking for will fall between two frequency bands
// in the Fourier analysis, and we won't be able to measure it accurately.
//
int sampleCount = ((int)Math.Min(_totalSamples - 1, _samplesToMeasure)) / _wavePeriod * _wavePeriod;
if (sampleCount > _wavePeriod)
{
//
// Average the throughput and thread count samples, so we can scale the wave magnitudes later.
//
double sampleSum = 0;
double threadSum = 0;
for (int i = 0; i < sampleCount; i++)
{
sampleSum += _samples[(_totalSamples - sampleCount + i) % _samplesToMeasure];
threadSum += _threadCounts[(_totalSamples - sampleCount + i) % _samplesToMeasure];
}
double averageThroughput = sampleSum / sampleCount;
double averageThreadCount = threadSum / sampleCount;
if (averageThroughput > 0 && averageThreadCount > 0)
{
//
// Calculate the periods of the adjacent frequency bands we'll be using to measure noise levels.
// We want the two adjacent Fourier frequency bands.
//
double adjacentPeriod1 = sampleCount / (((double)sampleCount / _wavePeriod) + 1);
double adjacentPeriod2 = sampleCount / (((double)sampleCount / _wavePeriod) - 1);
//
// Get the the three different frequency components of the throughput (scaled by average
// throughput). Our "error" estimate (the amount of noise that might be present in the
// frequency band we're really interested in) is the average of the adjacent bands.
//
throughputWaveComponent = GetWaveComponent(_samples, sampleCount, _wavePeriod) / averageThroughput;
throughputErrorEstimate = (GetWaveComponent(_samples, sampleCount, adjacentPeriod1) / averageThroughput).Abs();
if (adjacentPeriod2 <= sampleCount)
{
throughputErrorEstimate = Math.Max(throughputErrorEstimate, (GetWaveComponent(_samples, sampleCount, adjacentPeriod2) / averageThroughput).Abs());
}
//
// Do the same for the thread counts, so we have something to compare to. We don't measure thread count
// noise, because there is none; these are exact measurements.
//
threadWaveComponent = GetWaveComponent(_threadCounts, sampleCount, _wavePeriod) / averageThreadCount;
//
// Update our moving average of the throughput noise. We'll use this later as feedback to
// determine the new size of the thread wave.
//
if (_averageThroughputNoise == 0)
{
_averageThroughputNoise = throughputErrorEstimate;
}
else
{
_averageThroughputNoise = (_throughputErrorSmoothingFactor * throughputErrorEstimate) + ((1.0 - _throughputErrorSmoothingFactor) * _averageThroughputNoise);
}
if (threadWaveComponent.Abs() > 0)
{
//
// Adjust the throughput wave so it's centered around the target wave, and then calculate the adjusted throughput/thread ratio.
//
ratio = (throughputWaveComponent - (_targetThroughputRatio * threadWaveComponent)) / threadWaveComponent;
state = StateOrTransition.ClimbingMove;
}
else
{
ratio = new Complex(0, 0);
state = StateOrTransition.Stabilizing;
}
//
// Calculate how confident we are in the ratio. More noise == less confident. This has
// the effect of slowing down movements that might be affected by random noise.
//
double noiseForConfidence = Math.Max(_averageThroughputNoise, throughputErrorEstimate);
if (noiseForConfidence > 0)
{
confidence = (threadWaveComponent.Abs() / noiseForConfidence) / _targetSignalToNoiseRatio;
}
else
{
confidence = 1.0; //there is no noise!
}
}
}
//
// We use just the real part of the complex ratio we just calculated. If the throughput signal
// is exactly in phase with the thread signal, this will be the same as taking the magnitude of
// the complex move and moving that far up. If they're 180 degrees out of phase, we'll move
// backward (because this indicates that our changes are having the opposite of the intended effect).
// If they're 90 degrees out of phase, we won't move at all, because we can't tell whether we're
// having a negative or positive effect on throughput.
//
double move = Math.Min(1.0, Math.Max(-1.0, ratio.Real));
//
// Apply our confidence multiplier.
//
move *= Math.Min(1.0, Math.Max(0.0, confidence));
//
// Now apply non-linear gain, such that values around zero are attenuated, while higher values
// are enhanced. This allows us to move quickly if we're far away from the target, but more slowly
// if we're getting close, giving us rapid ramp-up without wild oscillations around the target.
//
double gain = _maxChangePerSecond * sampleDurationSeconds;
move = Math.Pow(Math.Abs(move), _gainExponent) * (move >= 0.0 ? 1 : -1) * gain;
move = Math.Min(move, _maxChangePerSample);
//
// If the result was positive, and CPU is > 95%, refuse the move.
//
PortableThreadPool threadPoolInstance = ThreadPoolInstance;
if (move > 0.0 && threadPoolInstance._cpuUtilization > CpuUtilizationHigh)
{
move = 0.0;
}
//
// Apply the move to our control setting
//
_currentControlSetting += move;
//
// Calculate the new thread wave magnitude, which is based on the moving average we've been keeping of
// the throughput error. This average starts at zero, so we'll start with a nice safe little wave at first.
//
int newThreadWaveMagnitude = (int)(0.5 + (_currentControlSetting * _averageThroughputNoise * _targetSignalToNoiseRatio * _threadMagnitudeMultiplier * 2.0));
newThreadWaveMagnitude = Math.Min(newThreadWaveMagnitude, _maxThreadWaveMagnitude);
newThreadWaveMagnitude = Math.Max(newThreadWaveMagnitude, 1);
//
// Make sure our control setting is within the ThreadPool's limits
//
int maxThreads = threadPoolInstance._maxThreads;
int minThreads = threadPoolInstance._minThreads;
_currentControlSetting = Math.Min(maxThreads - newThreadWaveMagnitude, _currentControlSetting);
_currentControlSetting = Math.Max(minThreads, _currentControlSetting);
//
// Calculate the new thread count (control setting + square wave)
//
int newThreadCount = (int)(_currentControlSetting + newThreadWaveMagnitude * ((_totalSamples / (_wavePeriod / 2)) % 2));
//
// Make sure the new thread count doesn't exceed the ThreadPool's limits
//
newThreadCount = Math.Min(maxThreads, newThreadCount);
newThreadCount = Math.Max(minThreads, newThreadCount);
//
// Record these numbers for posterity
//
if (NativeRuntimeEventSource.Log.IsEnabled())
{
NativeRuntimeEventSource.Log.ThreadPoolWorkerThreadAdjustmentStats(sampleDurationSeconds, throughput, threadWaveComponent.Real, throughputWaveComponent.Real,
throughputErrorEstimate, _averageThroughputNoise, ratio.Real, confidence, _currentControlSetting, (ushort)newThreadWaveMagnitude);
}
//
// If all of this caused an actual change in thread count, log that as well.
//
if (newThreadCount != currentThreadCount)
{
ChangeThreadCount(newThreadCount, state);
}
//
// Return the new thread count and sample interval. This is randomized to prevent correlations with other periodic
// changes in throughput. Among other things, this prevents us from getting confused by Hill Climbing instances
// running in other processes.
//
// If we're at minThreads, and we seem to be hurting performance by going higher, we can't go any lower to fix this. So
// we'll simply stay at minThreads much longer, and only occasionally try a higher value.
//
int newSampleInterval;
if (ratio.Real < 0.0 && newThreadCount == minThreads)
{
newSampleInterval = (int)(0.5 + _currentSampleMs * (10.0 * Math.Min(-ratio.Real, 1.0)));
}
else
{
newSampleInterval = _currentSampleMs;
}
return(newThreadCount, newSampleInterval);
}
/// <summary>
/// Go through the <see cref="_pendingRemoves"/> array and remove those registered wait handles from the <see cref="_registeredWaits"/>
/// and <see cref="_waitHandles"/> arrays, filling the holes along the way.
/// </summary>
private int ProcessRemovals()
{
PortableThreadPool threadPoolInstance = ThreadPoolInstance;
threadPoolInstance._waitThreadLock.Acquire();
try
{
Debug.Assert(_numPendingRemoves >= 0);
Debug.Assert(_numPendingRemoves <= _pendingRemoves.Length);
Debug.Assert(_numUserWaits >= 0);
Debug.Assert(_numUserWaits <= _registeredWaits.Length);
Debug.Assert(_numPendingRemoves <= _numUserWaits, $"Num removals {_numPendingRemoves} should be less than or equal to num user waits {_numUserWaits}");
if (_numPendingRemoves == 0 || _numUserWaits == 0)
{
return(_numUserWaits); // return the value taken inside the lock for the caller
}
int originalNumUserWaits = _numUserWaits;
int originalNumPendingRemoves = _numPendingRemoves;
// This is O(N^2), but max(N) = 63 and N will usually be very low
for (int i = 0; i < _numPendingRemoves; i++)
{
RegisteredWaitHandle waitHandleToRemove = _pendingRemoves[i] !;
int numUserWaits = _numUserWaits;
int j = 0;
for (; j < numUserWaits && waitHandleToRemove != _registeredWaits[j]; j++)
{
}
Debug.Assert(j < numUserWaits);
waitHandleToRemove.OnRemoveWait();
if (j + 1 < numUserWaits)
{
// Not removing the last element. Due to the possibility of there being duplicate system wait
// objects in the wait array, perhaps even with different handle values due to the use of
// DuplicateHandle(), don't reorder handles for fairness. When there are duplicate system wait
// objects in the wait array and the wait object gets signaled, the system may release the wait in
// in deterministic order based on the order in the wait array. Instead, shift the array.
int removeAt = j;
int count = numUserWaits;
Array.Copy(_registeredWaits, removeAt + 1, _registeredWaits, removeAt, count - (removeAt + 1));
_registeredWaits[count - 1] = null !;
// Corresponding elements in the wait handles array are shifted up by one
removeAt++;
count++;
Array.Copy(_waitHandles, removeAt + 1, _waitHandles, removeAt, count - (removeAt + 1));
_waitHandles[count - 1] = null !;
}
else
{
// Removing the last element
_registeredWaits[j] = null !;
_waitHandles[j + 1] = null !;
}
_numUserWaits = numUserWaits - 1;
_pendingRemoves[i] = null;
waitHandleToRemove.Handle.DangerousRelease();
}
_numPendingRemoves = 0;
Debug.Assert(originalNumUserWaits - originalNumPendingRemoves == _numUserWaits,
$"{originalNumUserWaits} - {originalNumPendingRemoves} == {_numUserWaits}");
return(_numUserWaits); // return the value taken inside the lock for the caller
}
finally
{
threadPoolInstance._waitThreadLock.Release();
}
}
void IThreadPoolWorkItem.Execute() => PortableThreadPool.CompleteWait(_registeredWaitHandle, _timedOut);
// Entry point from unmanaged code
private void CompleteWait()
{
Debug.Assert(ThreadPool.UsePortableThreadPool);
PortableThreadPool.CompleteWait(_registeredWaitHandle, _timedOut);
}
private static void WorkerThreadStart()
{
Thread.CurrentThread.SetThreadPoolWorkerThreadName();
PortableThreadPool threadPoolInstance = ThreadPoolInstance;
if (PortableThreadPoolEventSource.Log.IsEnabled(EventLevel.Informational, PortableThreadPoolEventSource.Keywords.ThreadingKeyword))
{
PortableThreadPoolEventSource.Log.ThreadPoolWorkerThreadStart(
(uint)threadPoolInstance._separated.counts.VolatileRead().NumExistingThreads);
}
LowLevelLock hillClimbingThreadAdjustmentLock = threadPoolInstance._hillClimbingThreadAdjustmentLock;
LowLevelLifoSemaphore semaphore = s_semaphore;
while (true)
{
bool spinWait = true;
while (semaphore.Wait(ThreadPoolThreadTimeoutMs, spinWait))
{
bool alreadyRemovedWorkingWorker = false;
while (TakeActiveRequest(threadPoolInstance))
{
Volatile.Write(ref threadPoolInstance._separated.lastDequeueTime, Environment.TickCount);
if (!ThreadPoolWorkQueue.Dispatch())
{
// ShouldStopProcessingWorkNow() caused the thread to stop processing work, and it would have
// already removed this working worker in the counts. This typically happens when hill climbing
// decreases the worker thread count goal.
alreadyRemovedWorkingWorker = true;
break;
}
}
// Don't spin-wait on the semaphore next time if the thread was actively stopped from processing work,
// as it's unlikely that the worker thread count goal would be increased again so soon afterwards that
// the semaphore would be released within the spin-wait window
spinWait = !alreadyRemovedWorkingWorker;
if (!alreadyRemovedWorkingWorker)
{
// If we woke up but couldn't find a request, or ran out of work items to process, we need to update
// the number of working workers to reflect that we are done working for now
RemoveWorkingWorker(threadPoolInstance);
}
}
hillClimbingThreadAdjustmentLock.Acquire();
try
{
// At this point, the thread's wait timed out. We are shutting down this thread.
// We are going to decrement the number of exisiting threads to no longer include this one
// and then change the max number of threads in the thread pool to reflect that we don't need as many
// as we had. Finally, we are going to tell hill climbing that we changed the max number of threads.
ThreadCounts counts = threadPoolInstance._separated.counts.VolatileRead();
while (true)
{
// Since this thread is currently registered as an existing thread, if more work comes in meanwhile,
// this thread would be expected to satisfy the new work. Ensure that NumExistingThreads is not
// decreased below NumProcessingWork, as that would be indicative of such a case.
short numExistingThreads = counts.NumExistingThreads;
if (numExistingThreads <= counts.NumProcessingWork)
{
// In this case, enough work came in that this thread should not time out and should go back to work.
break;
}
ThreadCounts newCounts = counts;
newCounts.SubtractNumExistingThreads(1);
short newNumExistingThreads = (short)(numExistingThreads - 1);
short newNumThreadsGoal = Math.Max(threadPoolInstance._minThreads, Math.Min(newNumExistingThreads, newCounts.NumThreadsGoal));
newCounts.NumThreadsGoal = newNumThreadsGoal;
ThreadCounts oldCounts = threadPoolInstance._separated.counts.InterlockedCompareExchange(newCounts, counts);
if (oldCounts == counts)
{
HillClimbing.ThreadPoolHillClimber.ForceChange(newNumThreadsGoal, HillClimbing.StateOrTransition.ThreadTimedOut);
if (PortableThreadPoolEventSource.Log.IsEnabled(EventLevel.Informational, PortableThreadPoolEventSource.Keywords.ThreadingKeyword))
{
PortableThreadPoolEventSource.Log.ThreadPoolWorkerThreadStop((uint)newNumExistingThreads);
}
return;
}
counts = oldCounts;
}
}
finally
{
hillClimbingThreadAdjustmentLock.Release();
}
}
}
private static void GateThreadStart()
{
bool disableStarvationDetection =
AppContextConfigHelper.GetBooleanConfig("System.Threading.ThreadPool.DisableStarvationDetection", false);
bool debuggerBreakOnWorkStarvation =
AppContextConfigHelper.GetBooleanConfig("System.Threading.ThreadPool.DebugBreakOnWorkerStarvation", false);
// The first reading is over a time range other than what we are focusing on, so we do not use the read other
// than to send it to any runtime-specific implementation that may also use the CPU utilization.
CpuUtilizationReader cpuUtilizationReader = default;
_ = cpuUtilizationReader.CurrentUtilization;
PortableThreadPool threadPoolInstance = ThreadPoolInstance;
LowLevelLock threadAdjustmentLock = threadPoolInstance._threadAdjustmentLock;
DelayHelper delayHelper = default;
if (BlockingConfig.IsCooperativeBlockingEnabled)
{
// Initialize memory usage and limits, and register to update them on gen 2 GCs
threadPoolInstance.OnGen2GCCallback();
Gen2GcCallback.Register(threadPoolInstance.OnGen2GCCallback);
}
while (true)
{
RunGateThreadEvent.WaitOne();
int currentTimeMs = Environment.TickCount;
delayHelper.SetGateActivitiesTime(currentTimeMs);
while (true)
{
bool wasSignaledToWake = DelayEvent.WaitOne((int)delayHelper.GetNextDelay(currentTimeMs));
currentTimeMs = Environment.TickCount;
// Thread count adjustment for cooperative blocking
do
{
PendingBlockingAdjustment pendingBlockingAdjustment = threadPoolInstance._pendingBlockingAdjustment;
if (pendingBlockingAdjustment == PendingBlockingAdjustment.None)
{
delayHelper.ClearBlockingAdjustmentDelay();
break;
}
bool previousDelayElapsed = false;
if (delayHelper.HasBlockingAdjustmentDelay)
{
previousDelayElapsed =
delayHelper.HasBlockingAdjustmentDelayElapsed(currentTimeMs, wasSignaledToWake);
if (pendingBlockingAdjustment == PendingBlockingAdjustment.WithDelayIfNecessary &&
!previousDelayElapsed)
{
break;
}
}
uint nextDelayMs = threadPoolInstance.PerformBlockingAdjustment(previousDelayElapsed);
if (nextDelayMs <= 0)
{
delayHelper.ClearBlockingAdjustmentDelay();
}
else
{
delayHelper.SetBlockingAdjustmentTimeAndDelay(currentTimeMs, nextDelayMs);
}
} while (false);
//
// Periodic gate activities
//
if (!delayHelper.ShouldPerformGateActivities(currentTimeMs, wasSignaledToWake))
{
continue;
}
if (ThreadPool.EnableWorkerTracking && NativeRuntimeEventSource.Log.IsEnabled())
{
NativeRuntimeEventSource.Log.ThreadPoolWorkingThreadCount(
(uint)threadPoolInstance.GetAndResetHighWatermarkCountOfThreadsProcessingUserCallbacks());
}
int cpuUtilization = cpuUtilizationReader.CurrentUtilization;
threadPoolInstance._cpuUtilization = cpuUtilization;
bool needGateThreadForRuntime = ThreadPool.PerformRuntimeSpecificGateActivities(cpuUtilization);
if (!disableStarvationDetection &&
threadPoolInstance._pendingBlockingAdjustment == PendingBlockingAdjustment.None &&
threadPoolInstance._separated.numRequestedWorkers > 0 &&
SufficientDelaySinceLastDequeue(threadPoolInstance))
{
bool addWorker = false;
threadAdjustmentLock.Acquire();
try
{
// Don't add a thread if we're at max or if we are already in the process of adding threads.
// This logic is slightly different from the native implementation in CoreCLR because there are
// no retired threads. In the native implementation, when hill climbing reduces the thread count
// goal, threads that are stopped from processing work are switched to "retired" state, and they
// don't count towards the equivalent existing thread count. In this implementation, the
// existing thread count includes any worker thread that has not yet exited, including those
// stopped from working by hill climbing, so here the number of threads processing work, instead
// of the number of existing threads, is compared with the goal. There may be alternative
// solutions, for now this is only to maintain consistency in behavior.
ThreadCounts counts = threadPoolInstance._separated.counts;
if (counts.NumProcessingWork < threadPoolInstance._maxThreads &&
counts.NumProcessingWork >= threadPoolInstance._separated.numThreadsGoal)
{
if (debuggerBreakOnWorkStarvation)
{
Debugger.Break();
}
short newNumThreadsGoal = (short)(counts.NumProcessingWork + 1);
threadPoolInstance._separated.numThreadsGoal = newNumThreadsGoal;
HillClimbing.ThreadPoolHillClimber.ForceChange(
newNumThreadsGoal,
HillClimbing.StateOrTransition.Starvation);
addWorker = true;
}
}
finally
{
threadAdjustmentLock.Release();
}
if (addWorker)
{
WorkerThread.MaybeAddWorkingWorker(threadPoolInstance);
}
}
if (!needGateThreadForRuntime &&
threadPoolInstance._separated.numRequestedWorkers <= 0 &&
threadPoolInstance._pendingBlockingAdjustment == PendingBlockingAdjustment.None &&
Interlocked.Decrement(ref threadPoolInstance._separated.gateThreadRunningState) <= GetRunningStateForNumRuns(0))
{
break;
}
}
}
}
// Entry point from unmanaged code
private void CompleteWait()
{
PortableThreadPool.CompleteWait(_registeredWaitHandle, _timedOut);
}
private static void WorkerThreadStart()
{
Thread.CurrentThread.SetThreadPoolWorkerThreadName();
PortableThreadPool threadPoolInstance = ThreadPoolInstance;
if (NativeRuntimeEventSource.Log.IsEnabled())
{
NativeRuntimeEventSource.Log.ThreadPoolWorkerThreadStart(
(uint)threadPoolInstance._separated.counts.VolatileRead().NumExistingThreads);
}
LowLevelLock threadAdjustmentLock = threadPoolInstance._threadAdjustmentLock;
LowLevelLifoSemaphore semaphore = s_semaphore;
while (true)
{
bool spinWait = true;
while (semaphore.Wait(ThreadPoolThreadTimeoutMs, spinWait))
{
bool alreadyRemovedWorkingWorker = false;
while (TakeActiveRequest(threadPoolInstance))
{
threadPoolInstance._separated.lastDequeueTime = Environment.TickCount;
if (!ThreadPoolWorkQueue.Dispatch())
{
// ShouldStopProcessingWorkNow() caused the thread to stop processing work, and it would have
// already removed this working worker in the counts. This typically happens when hill climbing
// decreases the worker thread count goal.
alreadyRemovedWorkingWorker = true;
break;
}
if (threadPoolInstance._separated.numRequestedWorkers <= 0)
{
break;
}
// In highly bursty cases with short bursts of work, especially in the portable thread pool
// implementation, worker threads are being released and entering Dispatch very quickly, not finding
// much work in Dispatch, and soon afterwards going back to Dispatch, causing extra thrashing on
// data and some interlocked operations, and similarly when the thread pool runs out of work. Since
// there is a pending request for work, introduce a slight delay before serving the next request.
// The spin-wait is mainly for when the sleep is not effective due to there being no other threads
// to schedule.
Thread.UninterruptibleSleep0();
if (!Environment.IsSingleProcessor)
{
Thread.SpinWait(1);
}
}
// Don't spin-wait on the semaphore next time if the thread was actively stopped from processing work,
// as it's unlikely that the worker thread count goal would be increased again so soon afterwards that
// the semaphore would be released within the spin-wait window
spinWait = !alreadyRemovedWorkingWorker;
if (!alreadyRemovedWorkingWorker)
{
// If we woke up but couldn't find a request, or ran out of work items to process, we need to update
// the number of working workers to reflect that we are done working for now
RemoveWorkingWorker(threadPoolInstance);
}
}
threadAdjustmentLock.Acquire();
try
{
// At this point, the thread's wait timed out. We are shutting down this thread.
// We are going to decrement the number of existing threads to no longer include this one
// and then change the max number of threads in the thread pool to reflect that we don't need as many
// as we had. Finally, we are going to tell hill climbing that we changed the max number of threads.
ThreadCounts counts = threadPoolInstance._separated.counts;
while (true)
{
// Since this thread is currently registered as an existing thread, if more work comes in meanwhile,
// this thread would be expected to satisfy the new work. Ensure that NumExistingThreads is not
// decreased below NumProcessingWork, as that would be indicative of such a case.
if (counts.NumExistingThreads <= counts.NumProcessingWork)
{
// In this case, enough work came in that this thread should not time out and should go back to work.
break;
}
ThreadCounts newCounts = counts;
short newNumExistingThreads = --newCounts.NumExistingThreads;
short newNumThreadsGoal =
Math.Max(
threadPoolInstance.MinThreadsGoal,
Math.Min(newNumExistingThreads, counts.NumThreadsGoal));
newCounts.NumThreadsGoal = newNumThreadsGoal;
ThreadCounts oldCounts =
threadPoolInstance._separated.counts.InterlockedCompareExchange(newCounts, counts);
if (oldCounts == counts)
{
HillClimbing.ThreadPoolHillClimber.ForceChange(
newNumThreadsGoal,
HillClimbing.StateOrTransition.ThreadTimedOut);
if (NativeRuntimeEventSource.Log.IsEnabled())
{
NativeRuntimeEventSource.Log.ThreadPoolWorkerThreadStop((uint)newNumExistingThreads);
}
return;
}
counts = oldCounts;
}
}
finally
{
threadAdjustmentLock.Release();
}
}
}
private static void GateThreadStart()
{
bool disableStarvationDetection =
AppContextConfigHelper.GetBooleanConfig("System.Threading.ThreadPool.DisableStarvationDetection", false);
bool debuggerBreakOnWorkStarvation =
AppContextConfigHelper.GetBooleanConfig("System.Threading.ThreadPool.DebugBreakOnWorkerStarvation", false);
// The first reading is over a time range other than what we are focusing on, so we do not use the read other
// than to send it to any runtime-specific implementation that may also use the CPU utilization.
CpuUtilizationReader cpuUtilizationReader = default;
_ = cpuUtilizationReader.CurrentUtilization;
PortableThreadPool threadPoolInstance = ThreadPoolInstance;
LowLevelLock hillClimbingThreadAdjustmentLock = threadPoolInstance._hillClimbingThreadAdjustmentLock;
while (true)
{
s_runGateThreadEvent.WaitOne();
bool needGateThreadForRuntime;
do
{
Thread.Sleep(GateThreadDelayMs);
if (ThreadPool.EnableWorkerTracking && PortableThreadPoolEventSource.Log.IsEnabled())
{
PortableThreadPoolEventSource.Log.ThreadPoolWorkingThreadCount(
(uint)threadPoolInstance.GetAndResetHighWatermarkCountOfThreadsProcessingUserCallbacks());
}
int cpuUtilization = cpuUtilizationReader.CurrentUtilization;
threadPoolInstance._cpuUtilization = cpuUtilization;
needGateThreadForRuntime = ThreadPool.PerformRuntimeSpecificGateActivities(cpuUtilization);
if (!disableStarvationDetection &&
threadPoolInstance._separated.numRequestedWorkers > 0 &&
SufficientDelaySinceLastDequeue(threadPoolInstance))
{
try
{
hillClimbingThreadAdjustmentLock.Acquire();
ThreadCounts counts = threadPoolInstance._separated.counts.VolatileRead();
// Don't add a thread if we're at max or if we are already in the process of adding threads.
// This logic is slightly different from the native implementation in CoreCLR because there are
// no retired threads. In the native implementation, when hill climbing reduces the thread count
// goal, threads that are stopped from processing work are switched to "retired" state, and they
// don't count towards the equivalent existing thread count. In this implementation, the
// existing thread count includes any worker thread that has not yet exited, including those
// stopped from working by hill climbing, so here the number of threads processing work, instead
// of the number of existing threads, is compared with the goal. There may be alternative
// solutions, for now this is only to maintain consistency in behavior.
while (
counts.NumExistingThreads < threadPoolInstance._maxThreads &&
counts.NumProcessingWork >= counts.NumThreadsGoal)
{
if (debuggerBreakOnWorkStarvation)
{
Debugger.Break();
}
ThreadCounts newCounts = counts;
short newNumThreadsGoal = (short)(counts.NumProcessingWork + 1);
newCounts.NumThreadsGoal = newNumThreadsGoal;
ThreadCounts oldCounts = threadPoolInstance._separated.counts.InterlockedCompareExchange(newCounts, counts);
if (oldCounts == counts)
{
HillClimbing.ThreadPoolHillClimber.ForceChange(newNumThreadsGoal, HillClimbing.StateOrTransition.Starvation);
WorkerThread.MaybeAddWorkingWorker(threadPoolInstance);
break;
}
counts = oldCounts;
}
}
finally
{
hillClimbingThreadAdjustmentLock.Release();
}
}
} while (
needGateThreadForRuntime ||
threadPoolInstance._separated.numRequestedWorkers > 0 ||
Interlocked.Decrement(ref threadPoolInstance._separated.gateThreadRunningState) > GetRunningStateForNumRuns(0));
}
}