/// <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 oc----ionally 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. // #if !FEATURE_PAL && !FEATURE_CORECLR // PAL doesn't support eventing, and we don't compile CDS providers for Coreclr CdsSyncEtwBCLProvider.Log.SpinWait_NextSpinWillYield(); #endif int yieldsSoFar = (m_count >= YIELD_THRESHOLD ? m_count - YIELD_THRESHOLD : m_count); if ((yieldsSoFar % SLEEP_1_EVERY_HOW_MANY_TIMES) == (SLEEP_1_EVERY_HOW_MANY_TIMES - 1)) { Thread.Sleep(1); } else if ((yieldsSoFar % SLEEP_0_EVERY_HOW_MANY_TIMES) == (SLEEP_0_EVERY_HOW_MANY_TIMES - 1)) { Thread.Sleep(0); } else { #if PFX_LEGACY_3_5 Platform.Yield(); #else Thread.Yield(); #endif } } 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. // Thread.SpinWait(4 << m_count); } // Finally, increment our spin counter. m_count = (m_count == int.MaxValue ? YIELD_THRESHOLD : m_count + 1); }
/// <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) { long startTicks = 0; if (millisecondsTimeout != Timeout.Infinite && millisecondsTimeout != 0) { startTicks = DateTime.UtcNow.Ticks; } #if !FEATURE_PAL && !FEATURE_CORECLR // PAL doesn't support eventing, and we don't compile CDS providers for Coreclr if (CdsSyncEtwBCLProvider.Log.IsEnabled()) { CdsSyncEtwBCLProvider.Log.SpinLock_FastPathFailed(m_owner); } #endif if (IsThreadOwnerTrackingEnabled) { // Slow path for enabled thread tracking mode ContinueTryEnterWithThreadTracking(millisecondsTimeout, startTicks, 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 increaes 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; //***Step 1, take the lock or update the waiters // try to acquire the lock directly if possoble or update the waiters count SpinWait spinner = new SpinWait(); while (true) { observedOwner = m_owner; if ((observedOwner & LOCK_ANONYMOUS_OWNED) == LOCK_UNOWNED) { #if !FEATURE_CORECLR Thread.BeginCriticalRegion(); #endif #if PFX_LEGACY_3_5 if (Interlocked.CompareExchange(ref m_owner, observedOwner | 1, observedOwner) == observedOwner) { lockTaken = true; return; } #else if (Interlocked.CompareExchange(ref m_owner, observedOwner | 1, observedOwner, ref lockTaken) == observedOwner) { return; } #endif #if !FEATURE_CORECLR Thread.EndCriticalRegion(); #endif } 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 || Interlocked.CompareExchange(ref m_owner, observedOwner + 2, observedOwner) == observedOwner) { break; } spinner.SpinOnce(); } // Check the timeout. if (millisecondsTimeout == 0 || (millisecondsTimeout != Timeout.Infinite && TimeoutExpired(startTicks, millisecondsTimeout))) { DecrementWaiters(); return; } //***Step 2. Spinning //lock acquired failed and waiters updated int turn = ((observedOwner + 2) & WAITERS_MASK) / 2; int processorCount = PlatformHelper.ProcessorCount; if (turn < processorCount) { int processFactor = 1; for (int i = 1; i <= turn * SPINNING_FACTOR; i++) { Thread.SpinWait((turn + i) * SPINNING_FACTOR * processFactor); if (processFactor < processorCount) { processFactor++; } observedOwner = m_owner; if ((observedOwner & LOCK_ANONYMOUS_OWNED) == LOCK_UNOWNED) { #if !FEATURE_CORECLR Thread.BeginCriticalRegion(); #endif 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 Contract.Assert((newOwner & WAITERS_MASK) >= 0); #if PFX_LEGACY_3_5 if (Interlocked.CompareExchange(ref m_owner, newOwner, observedOwner) == observedOwner) { lockTaken = true; return; } #else if (Interlocked.CompareExchange(ref m_owner, newOwner, observedOwner, ref lockTaken) == observedOwner) { return; } #endif #if !FEATURE_CORECLR Thread.EndCriticalRegion(); #endif } } } // Check the timeout. if (millisecondsTimeout != Timeout.Infinite && TimeoutExpired(startTicks, millisecondsTimeout)) { 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) { #if !FEATURE_CORECLR Thread.BeginCriticalRegion(); #endif 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 Contract.Assert((newOwner & WAITERS_MASK) >= 0); #if PFX_LEGACY_3_5 if (Interlocked.CompareExchange(ref m_owner, newOwner, observedOwner) == observedOwner) { lockTaken = true; return; } #else if (Interlocked.CompareExchange(ref m_owner, newOwner, observedOwner, ref lockTaken) == observedOwner) { return; } #endif #if !FEATURE_CORECLR Thread.EndCriticalRegion(); #endif } if (yieldsoFar % SLEEP_ONE_FREQUENCY == 0) { Thread.Sleep(1); } else if (yieldsoFar % SLEEP_ZERO_FREQUENCY == 0) { Thread.Sleep(0); } else { #if PFX_LEGACY_3_5 Platform.Yield(); #else Thread.Yield(); #endif } if (yieldsoFar % TIMEOUT_CHECK_FREQUENCY == 0) { //Check the timeout. if (millisecondsTimeout != Timeout.Infinite && TimeoutExpired(startTicks, millisecondsTimeout)) { DecrementWaiters(); return; } } yieldsoFar++; } }
/// <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("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) { #if PFX_LEGACY_3_5 Platform.Yield(); #else Thread.Yield(); #endif } else { Thread.SpinWait(PlatformHelper.ProcessorCount * (4 << i)); } } else if (i % HOW_MANY_YIELD_EVERY_SLEEP_1 == 0) { Thread.Sleep(1); } else if (i % HOW_MANY_YIELD_EVERY_SLEEP_0 == 0) { Thread.Sleep(0); } else { #if PFX_LEGACY_3_5 Platform.Yield(); #else Thread.Yield(); #endif } 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)) { lock (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 ---- 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 (!Monitor.Wait(m_lock, 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. }