private static void Wait(int spinIndex)
{
Debug.Assert(SpinYieldThreshold < SpinSleep0Threshold);
if (spinIndex < SpinYieldThreshold)
{
RuntimeThread.SpinWait(1 << spinIndex);
return;
}
if (spinIndex < SpinSleep0Threshold && RuntimeThread.Yield())
{
return;
}
/// <see cref="RuntimeThread.Sleep(int)"/> is interruptible. The current operation may not allow thread interrupt
/// (for instance, <see cref="LowLevelLock.Acquire"/> as part of <see cref="EventWaitHandle.Set"/>). Use the
/// uninterruptible version of Sleep(0).
RuntimeThread.UninterruptibleSleep0();
// Don't want to Sleep(1) in this spin wait:
// - Don't want to spin for that long, since a proper wait will follow when the spin wait fails
// - Sleep(1) would put the thread into a wait state, and a proper wait will follow when the spin wait fails
// anyway (the intended use for this class), so it's preferable to put the thread into the proper wait state
}
public static void UninterruptibleSleep0()
{
// On Unix, a thread waits on a condition variable. The timeout time will have already elapsed at the time
// of the call. The documentation does not state whether the thread yields or does nothing before returning
// an error, and in some cases, suggests that doing nothing is acceptable. The behavior could also be
// different between distributions. Yield directly here.
RuntimeThread.Yield();
}
/// <summary>
/// Performs a single spin.
/// </summary>
/// <remarks>
/// This is typically called in a loop, and may change in behavior based on the number of times a
/// <see cref="SpinOnce"/> has been called thus far on this instance.
/// </remarks>
public void SpinOnce()
{
if (NextSpinWillYield)
{
//
// We must yield.
//
// We prefer to call Thread.Yield first, triggering a SwitchToThread. This
// unfortunately doesn't consider all runnable threads on all OS SKUs. In
// some cases, it may only consult the runnable threads whose ideal processor
// is the one currently executing code. Thus we ocassionally issue a call to
// Sleep(0), which considers all runnable threads at equal priority. Even this
// is insufficient since we may be spin waiting for lower priority threads to
// execute; we therefore must call Sleep(1) once in a while too, which considers
// all runnable threads, regardless of ideal processor and priority, but may
// remove the thread from the scheduler's queue for 10+ms, if the system is
// configured to use the (default) coarse-grained system timer.
//
int yieldsSoFar = (_count >= YIELD_THRESHOLD ? _count - YIELD_THRESHOLD : _count);
if ((yieldsSoFar % SLEEP_1_EVERY_HOW_MANY_TIMES) == (SLEEP_1_EVERY_HOW_MANY_TIMES - 1))
{
RuntimeThread.Sleep(1);
}
else if ((yieldsSoFar % SLEEP_0_EVERY_HOW_MANY_TIMES) == (SLEEP_0_EVERY_HOW_MANY_TIMES - 1))
{
RuntimeThread.Sleep(0);
}
else
{
RuntimeThread.Yield();
}
}
else
{
//
// Otherwise, we will spin.
//
// We do this using the CLR's SpinWait API, which is just a busy loop that
// issues YIELD/PAUSE instructions to ensure multi-threaded CPUs can react
// intelligently to avoid starving. (These are NOOPs on other CPUs.) We
// choose a number for the loop iteration count such that each successive
// call spins for longer, to reduce cache contention. We cap the total
// number of spins we are willing to tolerate to reduce delay to the caller,
// since we expect most callers will eventually block anyway.
//
RuntimeThread.SpinWait(4 << _count);
}
// Finally, increment our spin counter.
_count = (_count == int.MaxValue ? YIELD_THRESHOLD : _count + 1);
}
public static bool Yield() => RuntimeThread.Yield();
/// <summary>
/// Blocks the current thread until the current <see cref="ManualResetEventSlim"/> is set, 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 <see cref="System.Threading.ManualResetEventSlim"/> was set; otherwise,
/// false.</returns>
/// <exception cref="T:System.ArgumentOutOfRangeException"><paramref name="millisecondsTimeout"/> is a
/// negative number other than -1, which represents an infinite time-out.</exception>
/// <exception cref="T:System.InvalidOperationException">
/// The maximum number of waiters has been exceeded.
/// </exception>
/// <exception cref="T:System.Threading.OperationCanceledException"><paramref
/// name="cancellationToken"/> was canceled.</exception>
public bool Wait(int millisecondsTimeout, CancellationToken cancellationToken)
{
ThrowIfDisposed();
cancellationToken.ThrowIfCancellationRequested(); // an early convenience check
if (millisecondsTimeout < -1)
{
throw new ArgumentOutOfRangeException(nameof(millisecondsTimeout));
}
if (!IsSet)
{
if (millisecondsTimeout == 0)
{
// For 0-timeouts, we just return immediately.
return(false);
}
// We spin briefly before falling back to allocating and/or waiting on a true event.
uint startTime = 0;
bool bNeedTimeoutAdjustment = false;
int realMillisecondsTimeout = millisecondsTimeout; //this will be adjusted if necessary.
if (millisecondsTimeout != Timeout.Infinite)
{
// We will account for time spent spinning, so that we can decrement it from our
// timeout. In most cases the time spent in this section will be negligible. But
// we can't discount the possibility of our thread being switched out for a lengthy
// period of time. The timeout adjustments only take effect when and if we actually
// decide to block in the kernel below.
startTime = TimeoutHelper.GetTime();
bNeedTimeoutAdjustment = true;
}
//spin
int HOW_MANY_SPIN_BEFORE_YIELD = 10;
int HOW_MANY_YIELD_EVERY_SLEEP_0 = 5;
int HOW_MANY_YIELD_EVERY_SLEEP_1 = 20;
int spinCount = SpinCount;
for (int i = 0; i < spinCount; i++)
{
if (IsSet)
{
return(true);
}
else if (i < HOW_MANY_SPIN_BEFORE_YIELD)
{
if (i == HOW_MANY_SPIN_BEFORE_YIELD / 2)
{
RuntimeThread.Yield();
}
else
{
RuntimeThread.SpinWait(PlatformHelper.ProcessorCount * (4 << i));
}
}
else if (i % HOW_MANY_YIELD_EVERY_SLEEP_1 == 0)
{
RuntimeThread.Sleep(1);
}
else if (i % HOW_MANY_YIELD_EVERY_SLEEP_0 == 0)
{
RuntimeThread.Sleep(0);
}
else
{
RuntimeThread.Yield();
}
if (i >= 100 && i % 10 == 0) // check the cancellation token if the user passed a very large spin count
{
cancellationToken.ThrowIfCancellationRequested();
}
}
// Now enter the lock and wait.
EnsureLockObjectCreated();
// We must register and deregister the token outside of the lock, to avoid deadlocks.
using (cancellationToken.InternalRegisterWithoutEC(s_cancellationTokenCallback, this))
{
using (LockHolder.Hold(m_lock))
{
// Loop to cope with spurious wakeups from other waits being canceled
while (!IsSet)
{
// If our token was canceled, we must throw and exit.
cancellationToken.ThrowIfCancellationRequested();
//update timeout (delays in wait commencement are due to spinning and/or spurious wakeups from other waits being canceled)
if (bNeedTimeoutAdjustment)
{
realMillisecondsTimeout = TimeoutHelper.UpdateTimeOut(startTime, millisecondsTimeout);
if (realMillisecondsTimeout <= 0)
{
return(false);
}
}
// There is a race that Set will fail to see that there are waiters as Set does not take the lock,
// so after updating waiters, we must check IsSet again.
// Also, we must ensure there cannot be any reordering of the assignment to Waiters and the
// read from IsSet. This is guaranteed as Waiters{set;} involves an Interlocked.CompareExchange
// operation which provides a full memory barrier.
// If we see IsSet=false, then we are guaranteed that Set() will see that we are
// waiting and will pulse the monitor correctly.
Waiters = Waiters + 1;
if (IsSet) //This check must occur after updating Waiters.
{
Waiters--; //revert the increment.
return(true);
}
// Now finally perform the wait.
try
{
// ** the actual wait **
if (!m_condition.Wait(realMillisecondsTimeout))
{
return(false); //return immediately if the timeout has expired.
}
}
finally
{
// Clean up: we're done waiting.
Waiters = Waiters - 1;
}
// Now just loop back around, and the right thing will happen. Either:
// 1. We had a spurious wake-up due to some other wait being canceled via a different cancellationToken (rewait)
// or 2. the wait was successful. (the loop will break)
}
}
}
} // automatically disposes (and deregisters) the callback
return(true); //done. The wait was satisfied.
}
/// <summary>
/// Try acquire the lock with long path, this is usually called after the first path in Enter and
/// TryEnter failed The reason for short path is to make it inline in the run time which improves the
/// performance. This method assumed that the parameter are validated in Enter ir TryENter method
/// </summary>
/// <param name="millisecondsTimeout">The timeout milliseconds</param>
/// <param name="lockTaken">The lockTaken param</param>
private void ContinueTryEnter(int millisecondsTimeout, ref bool lockTaken)
{
// The fast path doesn't throw any exception, so we have to validate the parameters here
if (lockTaken)
{
lockTaken = false;
throw new System.ArgumentException(SR.SpinLock_TryReliableEnter_ArgumentException);
}
if (millisecondsTimeout < -1)
{
throw new ArgumentOutOfRangeException(
nameof(millisecondsTimeout), millisecondsTimeout, SR.SpinLock_TryEnter_ArgumentOutOfRange);
}
uint startTime = 0;
if (millisecondsTimeout != Timeout.Infinite && millisecondsTimeout != 0)
{
startTime = TimeoutHelper.GetTime();
}
if (SpinLockTrace.Enabled)
{
SpinLockTrace.SpinLock_FastPathFailed(m_owner);
}
if (IsThreadOwnerTrackingEnabled)
{
// Slow path for enabled thread tracking mode
ContinueTryEnterWithThreadTracking(millisecondsTimeout, startTime, ref lockTaken);
return;
}
// then thread tracking is disabled
// In this case there are three ways to acquire the lock
// 1- the first way the thread either tries to get the lock if it's free or updates the waiters, if the turn >= the processors count then go to 3 else go to 2
// 2- In this step the waiter threads spins and tries to acquire the lock, the number of spin iterations and spin count is dependent on the thread turn
// the late the thread arrives the more it spins and less frequent it check the lock avilability
// Also the spins count is increases each iteration
// If the spins iterations finished and failed to acquire the lock, go to step 3
// 3- This is the yielding step, there are two ways of yielding Thread.Yield and Sleep(1)
// If the timeout is expired in after step 1, we need to decrement the waiters count before returning
int observedOwner;
int turn = int.MaxValue;
//***Step 1, take the lock or update the waiters
// try to acquire the lock directly if possible or update the waiters count
observedOwner = m_owner;
if ((observedOwner & LOCK_ANONYMOUS_OWNED) == LOCK_UNOWNED)
{
if (CompareExchange(ref m_owner, observedOwner | 1, observedOwner, ref lockTaken) == observedOwner)
{
// Aquired lock
return;
}
if (millisecondsTimeout == 0)
{
// Did not aquire lock in CompareExchange and timeout is 0 so fail fast
return;
}
}
else if (millisecondsTimeout == 0)
{
// Did not aquire lock as owned and timeout is 0 so fail fast
return;
}
else //failed to acquire the lock,then try to update the waiters. If the waiters count reached the maximum, jsut break the loop to avoid overflow
{
if ((observedOwner & WAITERS_MASK) != MAXIMUM_WAITERS)
{
turn = (Interlocked.Add(ref m_owner, 2) & WAITERS_MASK) >> 1;
}
}
//***Step 2. Spinning
//lock acquired failed and waiters updated
int processorCount = PlatformHelper.ProcessorCount;
if (turn < processorCount)
{
int processFactor = 1;
for (int i = 1; i <= turn * SPINNING_FACTOR; i++)
{
RuntimeThread.SpinWait((turn + i) * SPINNING_FACTOR * processFactor);
if (processFactor < processorCount)
{
processFactor++;
}
observedOwner = m_owner;
if ((observedOwner & LOCK_ANONYMOUS_OWNED) == LOCK_UNOWNED)
{
int newOwner = (observedOwner & WAITERS_MASK) == 0 ? // Gets the number of waiters, if zero
observedOwner | 1 // don't decrement it. just set the lock bit, it is zzero because a previous call of Exit(false) ehich corrupted the waiters
: (observedOwner - 2) | 1; // otherwise decrement the waiters and set the lock bit
Debug.Assert((newOwner & WAITERS_MASK) >= 0);
if (CompareExchange(ref m_owner, newOwner, observedOwner, ref lockTaken) == observedOwner)
{
return;
}
}
}
// Check the timeout.
if (millisecondsTimeout != Timeout.Infinite && TimeoutHelper.UpdateTimeOut(startTime, millisecondsTimeout) <= 0)
{
DecrementWaiters();
return;
}
}
//*** Step 3, Yielding
//Sleep(1) every 50 yields
int yieldsoFar = 0;
while (true)
{
observedOwner = m_owner;
if ((observedOwner & LOCK_ANONYMOUS_OWNED) == LOCK_UNOWNED)
{
int newOwner = (observedOwner & WAITERS_MASK) == 0 ? // Gets the number of waiters, if zero
observedOwner | 1 // don't decrement it. just set the lock bit, it is zzero because a previous call of Exit(false) ehich corrupted the waiters
: (observedOwner - 2) | 1; // otherwise decrement the waiters and set the lock bit
Debug.Assert((newOwner & WAITERS_MASK) >= 0);
if (CompareExchange(ref m_owner, newOwner, observedOwner, ref lockTaken) == observedOwner)
{
return;
}
}
if (yieldsoFar % SLEEP_ONE_FREQUENCY == 0)
{
RuntimeThread.Sleep(1);
}
else if (yieldsoFar % SLEEP_ZERO_FREQUENCY == 0)
{
RuntimeThread.Sleep(0);
}
else
{
RuntimeThread.Yield();
}
if (yieldsoFar % TIMEOUT_CHECK_FREQUENCY == 0)
{
//Check the timeout.
if (millisecondsTimeout != Timeout.Infinite && TimeoutHelper.UpdateTimeOut(startTime, millisecondsTimeout) <= 0)
{
DecrementWaiters();
return;
}
}
yieldsoFar++;
}
}
