/// <summary>
/// Adds an element in the first available slot, beginning the search from the tail-to-head.
/// If no slots are available, the array is grown. The method doesn't return until successful.
/// </summary>
/// <param name="element">The element to add.</param>
/// <returns>Information about where the add happened, to enable O(1) deregistration.</returns>
internal SparselyPopulatedArrayAddInfo <T> Add(T element)
{
while (true)
{
// Get the tail, and ensure it's up to date.
SparselyPopulatedArrayFragment <T> tail = m_tail;
while (tail.m_next != null)
{
m_tail = (tail = tail.m_next);
}
// Search for a free index, starting from the tail.
SparselyPopulatedArrayFragment <T> curr = tail;
while (curr != null)
{
const int RE_SEARCH_THRESHOLD = -10; // Every 10 skips, force a search.
if (curr.m_freeCount < 1)
{
--curr.m_freeCount;
}
if (curr.m_freeCount > 0 || curr.m_freeCount < RE_SEARCH_THRESHOLD)
{
int c = curr.Length;
// We'll compute a start offset based on how many free slots we think there
// are. This optimizes for ordinary the LIFO deregistration pattern, and is
// far from perfect due to the non-threadsafe ++ and -- of the free counter.
int start = ((c - curr.m_freeCount) % c);
if (start < 0)
{
start = 0;
curr.m_freeCount--; // Too many free elements; fix up.
}
Contract.Assert(start >= 0 && start < c, "start is outside of bounds");
// Now walk the array until we find a free slot (or reach the end).
for (int i = 0; i < c; i++)
{
// If the slot is null, try to CAS our element into it.
int tryIndex = (start + i) % c;
Contract.Assert(tryIndex >= 0 && tryIndex < curr.m_elements.Length, "tryIndex is outside of bounds");
if (curr.m_elements[tryIndex] == null && Interlocked.CompareExchange(ref curr.m_elements[tryIndex], element, null) == null)
{
// We adjust the free count by --. Note: if this drops to 0, we will skip
// the fragment on the next search iteration. Searching threads will -- the
// count and force a search every so often, just in case fragmentation occurs.
int newFreeCount = curr.m_freeCount - 1;
curr.m_freeCount = newFreeCount > 0 ? newFreeCount : 0;
return(new SparselyPopulatedArrayAddInfo <T>(curr, tryIndex));
}
}
}
curr = curr.m_prev;
}
// If we got here, we need to add a new chunk to the tail and try again.
SparselyPopulatedArrayFragment <T> newTail = new SparselyPopulatedArrayFragment <T>(
tail.m_elements.Length == 4096 ? 4096 : tail.m_elements.Length * 2, tail);
if (Interlocked.CompareExchange(ref tail.m_next, newTail, null) == null)
{
m_tail = newTail;
}
}
}
/// <summary>
/// Blocks the current thread until it can enter the <see cref="SemaphoreSlim"/>,
/// using a 32-bit signed integer to measure the time interval,
/// while observing a <see cref="T:System.Threading.CancellationToken"/>.
/// </summary>
/// <param name="millisecondsTimeout">The number of milliseconds to wait, or <see cref="Timeout.Infinite"/>(-1) to
/// wait indefinitely.</param>
/// <param name="cancellationToken">The <see cref="T:System.Threading.CancellationToken"/> to observe.</param>
/// <returns>true if the current thread successfully entered the <see cref="SemaphoreSlim"/>; otherwise, false.</returns>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="millisecondsTimeout"/> is a negative number other than -1,
/// which represents an infinite time-out.</exception>
/// <exception cref="System.OperationCanceledException"><paramref name="cancellationToken"/> was canceled.</exception>
public bool Wait(int millisecondsTimeout, CancellationToken cancellationToken)
{
CheckDispose();
// Validate input
if (millisecondsTimeout < -1)
{
throw new ArgumentOutOfRangeException(
"totalMilliSeconds", millisecondsTimeout, GetResourceString("SemaphoreSlim_Wait_TimeoutWrong"));
}
cancellationToken.ThrowIfCancellationRequested();
long startTimeTicks = 0;
if (millisecondsTimeout != Timeout.Infinite && millisecondsTimeout > 0)
{
startTimeTicks = DateTime.UtcNow.Ticks;
}
bool lockTaken = false;
//Register for cancellation outside of the main lock.
//NOTE: Register/deregister inside the lock can deadlock as different lock acquisition orders could
// occur for (1)this.m_lockObj and (2)cts.internalLock
CancellationTokenRegistration cancellationTokenRegistration = cancellationToken.Register(s_cancellationTokenCanceledEventHandler, this);
try
{
// Perf: first spin wait for the count to be positive, but only up to the first planned yield.
// This additional amount of spinwaiting in addition
// to Monitor2.Enter()’s spinwaiting has shown measurable perf gains in test scenarios.
//
SpinWait spin = new SpinWait();
while (m_currentCount == 0 && !spin.NextSpinWillYield)
{
spin.SpinOnce();
}
// entering the lock and incrementing waiters must not suffer a thread-abort, else we cannot
// clean up m_waitCount correctly, which may lead to deadlock due to non-woken waiters.
try { }
finally
{
Monitor2.Enter(m_lockObj, ref lockTaken);
if (lockTaken)
{
m_waitCount++;
}
}
// If the count > 0 we are good to move on.
// If not, then wait if we were given allowed some wait duration
if (m_currentCount == 0)
{
if (millisecondsTimeout == 0)
{
return(false);
}
// Prepare for the main wait...
// wait until the count become greater than zero or the timeout is expired
if (!WaitUntilCountOrTimeout(millisecondsTimeout, startTimeTicks, cancellationToken))
{
return(false);
}
}
// At this point the count should be greater than zero
Contract.Assert(m_currentCount > 0);
m_currentCount--;
// Exposing wait handle which is lazily initialized if needed
if (m_waitHandle != null && m_currentCount == 0)
{
m_waitHandle.Reset();
}
}
finally
{
// Release the lock
if (lockTaken)
{
m_waitCount--;
Monitor.Exit(m_lockObj);
}
// Unregister the cancellation callback.
cancellationTokenRegistration.Dispose();
}
return(true);
}
internal void Reacquire(uint previousRecursionCount)
{
Acquire();
Contract.Assert(_recursionCount == 0);
_recursionCount = previousRecursionCount;
}
/// <summary>
/// Invoke the Canceled event.
/// </summary>
/// <remarks>
/// The handlers are invoked synchronously in LIFO order.
/// </remarks>
private void ExecuteCallbackHandlers(bool throwOnFirstException)
{
Contract.Assert(IsCancellationRequested, "ExecuteCallbackHandlers should only be called after setting IsCancellationRequested->true");
Contract.Assert(ThreadIDExecutingCallbacks != -1, "ThreadIDExecutingCallbacks should have been set.");
// Design decision: call the delegates in LIFO order so that callbacks fire 'deepest first'.
// This is intended to help with nesting scenarios so that child enlisters cancel before their parents.
List <Exception> exceptionList = null;
SparselyPopulatedArray <CancellationCallbackInfo>[] callbackLists = m_registeredCallbacksLists;
// If there are no callbacks to run, we can safely exit. Any races to lazy initialize it
// will see IsCancellationRequested and will then run the callback themselves.
if (callbackLists == null)
{
Interlocked.Exchange(ref m_state, NOTIFYINGCOMPLETE);
return;
}
try
{
for (int index = 0; index < callbackLists.Length; index++)
{
SparselyPopulatedArray <CancellationCallbackInfo> list = callbackLists[index];
if (list != null)
{
SparselyPopulatedArrayFragment <CancellationCallbackInfo> currArrayFragment = list.Tail;
while (currArrayFragment != null)
{
for (int i = currArrayFragment.Length - 1; i >= 0; i--)
{
// 1a. publish the indended callback, to ensure ctr.Dipose can tell if a wait is necessary.
// 1b. transition to the target syncContext and continue there..
// On the target SyncContext.
// 2. actually remove the callback
// 3. execute the callback
// re:#2 we do the remove on the syncCtx so that we can be sure we have control of the syncCtx before
// grabbing the callback. This prevents a deadlock if ctr.Dispose() might run on the syncCtx too.
m_executingCallback = currArrayFragment[i];
if (m_executingCallback != null)
{
//Transition to the target sync context (if necessary), and continue our work there.
CancellationCallbackCoreWorkArguments args = new CancellationCallbackCoreWorkArguments(currArrayFragment, i);
// marshal exceptions: either aggregate or perform an immediate rethrow
// We assume that syncCtx.Send() has forwarded on user exceptions when appropriate.
try
{
if (m_executingCallback.TargetSyncContext != null)
{
#pragma warning disable 0618 // This API isn't available in Metro, but we never run in metro.
m_executingCallback.TargetSyncContext.Send(CancellationCallbackCoreWork_OnSyncContext, args);
#pragma warning restore 0618
// CancellationCallbackCoreWork_OnSyncContext may have altered ThreadIDExecutingCallbacks, so reset it.
ThreadIDExecutingCallbacks = Thread.CurrentThread.ManagedThreadId;
}
else
{
CancellationCallbackCoreWork_OnSyncContext(args);
}
}
catch (Exception ex)
{
if (throwOnFirstException)
{
throw;
}
// Otherwise, log it and proceed.
if (exceptionList == null)
{
exceptionList = new List <Exception>();
}
exceptionList.Add(ex);
}
}
}
currArrayFragment = currArrayFragment.Prev;
}
}
}
}
finally
{
m_state = NOTIFYINGCOMPLETE;
m_executingCallback = null;
Thread.MemoryBarrier(); // for safety, prevent reorderings crossing this point and seeing inconsistent state.
}
if (exceptionList != null)
{
Contract.Assert(exceptionList.Count > 0, "Expected exception count > 0");
throw new AggregateException(exceptionList);
}
}
private bool TryAcquireContended(int currentThreadId, int millisecondsTimeout)
{
//
// If we already own the lock, just increment the recursion count.
//
if (_owningThreadId == currentThreadId)
{
checked { _recursionCount++; }
return(true);
}
//
// We've already made one lock attempt at this point, so bail early if the timeout is zero.
//
if (millisecondsTimeout == 0)
{
return(false);
}
int spins = 1;
if (s_maxSpinCount < 0)
{
s_maxSpinCount = (Environment.ProcessorCount > 1) ? 10000 : 0;
}
while (true)
{
//
// Try to grab the lock. We may take the lock here even if there are existing waiters. This creates the possibility
// of starvation of waiters, but it also prevents lock convoys from destroying perf.
// The starvation issue is largely mitigated by the priority boost the OS gives to a waiter when we set
// the event, after we release the lock. Eventually waiters will be boosted high enough to preempt this thread.
//
int oldState = _state;
if ((oldState & Locked) == 0 && Interlocked.CompareExchange(ref _state, oldState | Locked, oldState) == oldState)
{
goto GotTheLock;
}
//
// Back off by a factor of 2 for each attempt, up to MaxSpinCount
//
if (spins <= s_maxSpinCount)
{
System.Runtime.RuntimeImports.RhSpinWait(spins);
spins *= 2;
}
else
{
//
// We reached our spin limit, and need to wait. Increment the waiter count.
// Note that we do not do any overflow checking on this increment. In order to overflow,
// we'd need to have about 1 billion waiting threads, which is inconceivable anytime in the
// forseeable future.
//
int newState = (oldState + WaiterCountIncrement) & ~WaiterWoken;
if (Interlocked.CompareExchange(ref _state, newState, oldState) == oldState)
{
break;
}
}
}
//
// Now we wait.
//
TimeoutTracker timeoutTracker = TimeoutTracker.Start(millisecondsTimeout);
AutoResetEvent ev = Event;
while (true)
{
Contract.Assert(_state >= WaiterCountIncrement);
bool waitSucceeded = ev.WaitOne(timeoutTracker.Remaining);
while (true)
{
int oldState = _state;
Contract.Assert(oldState >= WaiterCountIncrement);
// Clear the "waiter woken" bit.
int newState = oldState & ~WaiterWoken;
if ((oldState & Locked) == 0)
{
// The lock is available, try to get it.
newState |= Locked;
newState -= WaiterCountIncrement;
if (Interlocked.CompareExchange(ref _state, newState, oldState) == oldState)
{
goto GotTheLock;
}
}
else if (!waitSucceeded)
{
// The lock is not available, and we timed out. We're not going to wait agin.
newState -= WaiterCountIncrement;
if (Interlocked.CompareExchange(ref _state, newState, oldState) == oldState)
{
return(false);
}
}
else
{
// The lock is not available, and we didn't time out. We're going to wait again.
if (Interlocked.CompareExchange(ref _state, newState, oldState) == oldState)
{
break;
}
}
}
}
GotTheLock:
Contract.Assert((_state | Locked) != 0);
Contract.Assert(_owningThreadId == 0);
Contract.Assert(_recursionCount == 0);
_owningThreadId = currentThreadId;
return(true);
}
//
// Fire any timers that have expired, and update the native timer to schedule the rest of them.
//
private void FireNextTimers()
{
//
// we fire the first timer on this thread; any other timers that might have fired are queued
// to the ThreadPool.
//
TimerQueueTimer timerToFireOnThisThread = null;
lock (this)
{
// prevent ThreadAbort while updating state
try { }
finally
{
//
// since we got here, that means our previous timer has fired.
//
m_isAppDomainTimerScheduled = false;
bool haveTimerToSchedule = false;
uint nextAppDomainTimerDuration = uint.MaxValue;
int nowTicks = TickCount;
//
// Sweep through all timers. The ones that have reached their due time
// will fire. We will calculate the next native timer due time from the
// other timers.
//
TimerQueueTimer timer = m_timers;
while (timer != null)
{
Contract.Assert(timer.m_dueTime != Timeout.UnsignedInfinite);
uint elapsed = (uint)(nowTicks - timer.m_startTicks);
if (elapsed >= timer.m_dueTime)
{
//
// Remember the next timer in case we delete this one
//
TimerQueueTimer nextTimer = timer.m_next;
if (timer.m_period != Timeout.UnsignedInfinite)
{
timer.m_startTicks = nowTicks;
timer.m_dueTime = timer.m_period;
//
// This is a repeating timer; schedule it to run again.
//
if (timer.m_dueTime < nextAppDomainTimerDuration)
{
haveTimerToSchedule = true;
nextAppDomainTimerDuration = timer.m_dueTime;
}
}
else
{
//
// Not repeating; remove it from the queue
//
DeleteTimer(timer);
}
//
// If this is the first timer, we'll fire it on this thread. Otherwise, queue it
// to the ThreadPool.
//
if (timerToFireOnThisThread == null)
{
timerToFireOnThisThread = timer;
}
else
{
QueueTimerCompletion(timer);
}
timer = nextTimer;
}
else
{
//
// This timer hasn't fired yet. Just update the next time the native timer fires.
//
uint remaining = timer.m_dueTime - elapsed;
if (remaining < nextAppDomainTimerDuration)
{
haveTimerToSchedule = true;
nextAppDomainTimerDuration = remaining;
}
timer = timer.m_next;
}
}
if (haveTimerToSchedule)
{
EnsureAppDomainTimerFiresBy(nextAppDomainTimerDuration);
}
}
}
//
// Fire the user timer outside of the lock!
//
if (timerToFireOnThisThread != null)
{
timerToFireOnThisThread.Fire();
}
}
internal void Resume()
{
//
// Update timers to adjust their due-time to accomodate Pause/Resume
//
lock (this)
{
// prevent ThreadAbort while updating state
try { }
finally
{
int pauseTicks = m_pauseTicks;
m_pauseTicks = 0; // Set this to 0 so that now timers can be scheduled
int resumedTicks = TickCount;
int pauseDuration = resumedTicks - pauseTicks;
bool haveTimerToSchedule = false;
uint nextAppDomainTimerDuration = uint.MaxValue;
TimerQueueTimer timer = m_timers;
while (timer != null)
{
Contract.Assert(timer.m_dueTime != Timeout.UnsignedInfinite);
Contract.Assert(resumedTicks >= timer.m_startTicks);
uint elapsed; // How much of the timer dueTime has already elapsed
// Timers started before the paused event has to be sufficiently delayed to accomodate
// for the Pause time. However, timers started after the Paused event shouldnt be adjusted.
// E.g. ones created by the app in its Activated event should fire when it was designated.
// The Resumed event which is where this routine is executing is after this Activated and hence
// shouldn't delay this timer
if (timer.m_startTicks <= pauseTicks)
{
elapsed = (uint)(pauseTicks - timer.m_startTicks);
}
else
{
elapsed = (uint)(resumedTicks - timer.m_startTicks);
}
// Handling the corner cases where a Timer was already due by the time Resume is happening,
// We shouldn't delay those timers.
// Example is a timer started in App's Activated event with a very small duration
timer.m_dueTime = (timer.m_dueTime > elapsed) ? timer.m_dueTime - elapsed : 0;;
timer.m_startTicks = resumedTicks; // re-baseline
if (timer.m_dueTime < nextAppDomainTimerDuration)
{
haveTimerToSchedule = true;
nextAppDomainTimerDuration = timer.m_dueTime;
}
timer = timer.m_next;
}
if (haveTimerToSchedule)
{
EnsureAppDomainTimerFiresBy(nextAppDomainTimerDuration);
}
}
}
}
private bool EnsureAppDomainTimerFiresBy(uint requestedDuration)
{
//
// The VM's timer implementation does not work well for very long-duration timers.
// See kb 950807.
// So we'll limit our native timer duration to a "small" value.
// This may cause us to attempt to fire timers early, but that's ok -
// we'll just see that none of our timers has actually reached its due time,
// and schedule the native timer again.
//
const uint maxPossibleDuration = 0x0fffffff;
uint actualDuration = Math.Min(requestedDuration, maxPossibleDuration);
if (m_isAppDomainTimerScheduled)
{
uint elapsed = (uint)(TickCount - m_currentAppDomainTimerStartTicks);
if (elapsed >= m_currentAppDomainTimerDuration)
{
return(true); //the timer's about to fire
}
uint remainingDuration = m_currentAppDomainTimerDuration - elapsed;
if (actualDuration >= remainingDuration)
{
return(true); //the timer will fire earlier than this request
}
}
// If Pause is underway then do not schedule the timers
// A later update during resume will re-schedule
if (m_pauseTicks != 0)
{
Contract.Assert(!m_isAppDomainTimerScheduled);
Contract.Assert(m_appDomainTimer == null);
return(true);
}
if (m_appDomainTimer == null || m_appDomainTimer.IsInvalid)
{
Contract.Assert(!m_isAppDomainTimerScheduled);
m_appDomainTimer = CreateAppDomainTimer(actualDuration);
if (!m_appDomainTimer.IsInvalid)
{
m_isAppDomainTimerScheduled = true;
m_currentAppDomainTimerStartTicks = TickCount;
m_currentAppDomainTimerDuration = actualDuration;
return(true);
}
else
{
return(false);
}
}
else
{
if (ChangeAppDomainTimer(m_appDomainTimer, actualDuration))
{
m_isAppDomainTimerScheduled = true;
m_currentAppDomainTimerStartTicks = TickCount;
m_currentAppDomainTimerDuration = actualDuration;
return(true);
}
else
{
return(false);
}
}
}
void IThreadPoolWorkItem.ExecuteWorkItem()
{
bool setSuccessfully = TrySetResult(true);
Contract.Assert(setSuccessfully, "Should have been able to complete task");
}