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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.Versioning;
namespace System.Threading
{
// ManualResetEventSlim wraps a manual-reset event internally with a little bit of
// spinning. When an event will be set imminently, it is often advantageous to avoid
// a 4k+ cycle context switch in favor of briefly spinning. Therefore we layer on to
// a brief amount of spinning that should, on the average, make using the slim event
// cheaper than using Win32 events directly. This can be reset manually, much like
// a Win32 manual-reset would be.
//
// Notes:
// We lazily allocate the Win32 event internally. Therefore, the caller should
// always call Dispose to clean it up, just in case. This API is a no-op of the
// event wasn't allocated, but if it was, ensures that the event goes away
// eagerly, instead of waiting for finalization.
/// <summary>
/// Provides a slimmed down version of <see cref="ManualResetEvent"/>.
/// </summary>
/// <remarks>
/// All public and protected members of <see cref="ManualResetEventSlim"/> are thread-safe and may be used
/// concurrently from multiple threads, with the exception of Dispose, which
/// must only be used when all other operations on the <see cref="ManualResetEventSlim"/> have
/// completed, and Reset, which should only be used when no other threads are
/// accessing the event.
/// </remarks>
[DebuggerDisplay("Set = {IsSet}")]
public class ManualResetEventSlim : IDisposable
{
// These are the default spin counts we use on single-proc and MP machines.
private const int DEFAULT_SPIN_SP = 1;
private object? m_lock;
// A lock used for waiting and pulsing. Lazily initialized via EnsureLockObjectCreated()
private volatile ManualResetEvent? m_eventObj; // A true Win32 event used for waiting.
// -- State -- //
// For a packed word a uint would seem better, but Interlocked.* doesn't support them as uint isn't CLS-compliant.
private volatile int m_combinedState; // ie a uint. Used for the state items listed below.
// 1-bit for signalled state
private const int SignalledState_BitMask = unchecked((int)0x80000000); // 1000 0000 0000 0000 0000 0000 0000 0000
private const int SignalledState_ShiftCount = 31;
// 1-bit for disposed state
private const int Dispose_BitMask = unchecked((int)0x40000000); // 0100 0000 0000 0000 0000 0000 0000 0000
// 11-bits for m_spinCount
private const int SpinCountState_BitMask = unchecked((int)0x3FF80000); // 0011 1111 1111 1000 0000 0000 0000 0000
private const int SpinCountState_ShiftCount = 19;
private const int SpinCountState_MaxValue = (1 << 11) - 1; // 2047
// 19-bits for m_waiters. This allows support of 512K threads waiting which should be ample
private const int NumWaitersState_BitMask = unchecked((int)0x0007FFFF); // 0000 0000 0000 0111 1111 1111 1111 1111
private const int NumWaitersState_ShiftCount = 0;
private const int NumWaitersState_MaxValue = (1 << 19) - 1; // 512K-1
// ----------- //
/// <summary>
/// Gets the underlying <see cref="Threading.WaitHandle"/> object for this <see
/// cref="ManualResetEventSlim"/>.
/// </summary>
/// <value>The underlying <see cref="Threading.WaitHandle"/> event object fore this <see
/// cref="ManualResetEventSlim"/>.</value>
/// <remarks>
/// Accessing this property forces initialization of an underlying event object if one hasn't
/// already been created. To simply wait on this <see cref="ManualResetEventSlim"/>,
/// the public Wait methods should be preferred.
/// </remarks>
public WaitHandle WaitHandle
{
get
{
ObjectDisposedException.ThrowIf(IsDisposed, this);
if (m_eventObj == null)
{
// Lazily initialize the event object if needed.
LazyInitializeEvent();
Debug.Assert(m_eventObj != null);
}
return m_eventObj;
}
}
/// <summary>
/// Gets whether the event is set.
/// </summary>
/// <value>true if the event has is set; otherwise, false.</value>
public bool IsSet
{
get => 0 != ExtractStatePortion(m_combinedState, SignalledState_BitMask);
private set => UpdateStateAtomically(((value) ? 1 : 0) << SignalledState_ShiftCount, SignalledState_BitMask);
}
/// <summary>
/// Gets the number of spin waits that will be occur before falling back to a true wait.
/// </summary>
public int SpinCount
{
get => ExtractStatePortionAndShiftRight(m_combinedState, SpinCountState_BitMask, SpinCountState_ShiftCount);
private set
{
Debug.Assert(value >= 0, "SpinCount is a restricted-width integer. The value supplied is outside the legal range.");
Debug.Assert(value <= SpinCountState_MaxValue, "SpinCount is a restricted-width integer. The value supplied is outside the legal range.");
// Don't worry about thread safety because it's set one time from the constructor
m_combinedState = (m_combinedState & ~SpinCountState_BitMask) | (value << SpinCountState_ShiftCount);
}
}
/// <summary>
/// How many threads are waiting.
/// </summary>
private int Waiters
{
get => ExtractStatePortionAndShiftRight(m_combinedState, NumWaitersState_BitMask, NumWaitersState_ShiftCount);
set
{
// setting to <0 would indicate an internal flaw, hence Assert is appropriate.
Debug.Assert(value >= 0, "NumWaiters should never be less than zero. This indicates an internal error.");
// it is possible for the max number of waiters to be exceeded via user-code, hence we use a real exception here.
if (value >= NumWaitersState_MaxValue)
throw new InvalidOperationException(SR.Format(SR.ManualResetEventSlim_ctor_TooManyWaiters, NumWaitersState_MaxValue));
UpdateStateAtomically(value << NumWaitersState_ShiftCount, NumWaitersState_BitMask);
}
}
//-----------------------------------------------------------------------------------
// Constructs a new event, optionally specifying the initial state and spin count.
// The defaults are that the event is unsignaled and some reasonable default spin.
//
/// <summary>
/// Initializes a new instance of the <see cref="ManualResetEventSlim"/>
/// class with an initial state of nonsignaled.
/// </summary>
public ManualResetEventSlim()
: this(false)
{
}
/// <summary>
/// Initializes a new instance of the <see cref="ManualResetEventSlim"/>
/// class with a boolean value indicating whether to set the initial state to signaled.
/// </summary>
/// <param name="initialState">true to set the initial state signaled; false to set the initial state
/// to nonsignaled.</param>
public ManualResetEventSlim(bool initialState)
{
// Specify the default spin count, and use default spin if we're
// on a multi-processor machine. Otherwise, we won't.
Initialize(initialState, SpinWait.SpinCountforSpinBeforeWait);
}
/// <summary>
/// Initializes a new instance of the <see cref="ManualResetEventSlim"/>
/// class with a Boolean value indicating whether to set the initial state to signaled and a specified
/// spin count.
/// </summary>
/// <param name="initialState">true to set the initial state to signaled; false to set the initial state
/// to nonsignaled.</param>
/// <param name="spinCount">The number of spin waits that will occur before falling back to a true
/// wait.</param>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="spinCount"/> is less than
/// 0 or greater than the maximum allowed value.</exception>
public ManualResetEventSlim(bool initialState, int spinCount)
{
ArgumentOutOfRangeException.ThrowIfNegative(spinCount);
ArgumentOutOfRangeException.ThrowIfGreaterThan(spinCount, SpinCountState_MaxValue);
// We will suppress default spin because the user specified a count.
Initialize(initialState, spinCount);
}
/// <summary>
/// Initializes the internal state of the event.
/// </summary>
/// <param name="initialState">Whether the event is set initially or not.</param>
/// <param name="spinCount">The spin count that decides when the event will block.</param>
private void Initialize(bool initialState, int spinCount)
{
m_combinedState = initialState ? (1 << SignalledState_ShiftCount) : 0;
// the spinCount argument has been validated by the ctors.
// but we now sanity check our predefined constants.
Debug.Assert(DEFAULT_SPIN_SP >= 0, "Internal error - DEFAULT_SPIN_SP is outside the legal range.");
Debug.Assert(DEFAULT_SPIN_SP <= SpinCountState_MaxValue, "Internal error - DEFAULT_SPIN_SP is outside the legal range.");
SpinCount = Environment.IsSingleProcessor ? DEFAULT_SPIN_SP : spinCount;
}
/// <summary>
/// Helper to ensure the lock object is created before first use.
/// </summary>
[MemberNotNull(nameof(m_lock))]
private void EnsureLockObjectCreated()
{
if (m_lock is null)
{
Interlocked.CompareExchange(ref m_lock, new object(), null); // failure is benign. Someone else set the value.
}
}
/// <summary>
/// This method lazily initializes the event object. It uses CAS to guarantee that
/// many threads racing to call this at once don't result in more than one event
/// being stored and used. The event will be signaled or unsignaled depending on
/// the state of the thin-event itself, with synchronization taken into account.
/// </summary>
private void LazyInitializeEvent()
{
bool preInitializeIsSet = IsSet;
ManualResetEvent newEventObj = new ManualResetEvent(preInitializeIsSet);
// We have to CAS this in case we are racing with another thread. We must
// guarantee only one event is actually stored in this field.
if (Interlocked.CompareExchange(ref m_eventObj, newEventObj, null) != null)
{
// Someone else set the value due to a race condition. Destroy the garbage event.
newEventObj.Dispose();
}
else
{
// Now that the event is published, verify that the state hasn't changed since
// we snapped the preInitializeState. Another thread could have done that
// between our initial observation above and here. The barrier incurred from
// the CAS above (in addition to m_state being volatile) prevents this read
// from moving earlier and being collapsed with our original one.
bool currentIsSet = IsSet;
if (currentIsSet != preInitializeIsSet)
{
Debug.Assert(currentIsSet,
"The only safe concurrent transition is from unset->set: detected set->unset.");
// We saw it as unsignaled, but it has since become set.
lock (newEventObj)
{
// If our event hasn't already been disposed of, we must set it.
if (m_eventObj == newEventObj)
{
newEventObj.Set();
}
}
}
}
}
/// <summary>
/// Sets the state of the event to signaled, which allows one or more threads waiting on the event to
/// proceed.
/// </summary>
public void Set()
{
Set(false);
}
/// <summary>
/// Private helper to actually perform the Set.
/// </summary>
/// <param name="duringCancellation">Indicates whether we are calling Set() during cancellation.</param>
/// <exception cref="OperationCanceledException">The object has been canceled.</exception>
private void Set(bool duringCancellation)
{
// We need to ensure that IsSet=true does not get reordered past the read of m_eventObj
// This would be a legal movement according to the .NET memory model.
// The code is safe as IsSet involves an Interlocked.CompareExchange which provides a full memory barrier.
IsSet = true;
// If there are waiting threads, we need to pulse them.
if (Waiters > 0)
{
Debug.Assert(m_lock != null); // if waiters>0, then m_lock has already been created.
lock (m_lock)
{
Monitor.PulseAll(m_lock);
}
}
ManualResetEvent? eventObj = m_eventObj;
// Design-decision: do not set the event if we are in cancellation -> better to deadlock than to wake up waiters incorrectly
// It would be preferable to wake up the event and have it throw OCE. This requires MRE to implement cancellation logic
if (eventObj != null && !duringCancellation)
{
// We must surround this call to Set in a lock. The reason is fairly subtle.
// Sometimes a thread will issue a Wait and wake up after we have set m_state,
// but before we have gotten around to setting m_eventObj (just below). That's
// because Wait first checks m_state and will only access the event if absolutely
// necessary. However, the coding pattern { event.Wait(); event.Dispose() } is
// quite common, and we must support it. If the waiter woke up and disposed of
// the event object before the setter has finished, however, we would try to set a
// now-disposed Win32 event. Crash! To deal with this race condition, we use a lock to
// protect access to the event object when setting and disposing of it. We also
// double-check that the event has not become null in the meantime when in the lock.
lock (eventObj)
{
// If somebody is waiting, we must set the event.
m_eventObj?.Set();
}
}
}
/// <summary>
/// Sets the state of the event to nonsignaled, which causes threads to block.
/// </summary>
/// <remarks>
/// Unlike most of the members of <see cref="ManualResetEventSlim"/>, <see cref="Reset()"/> is not
/// thread-safe and may not be used concurrently with other members of this instance.
/// </remarks>
public void Reset()
{
ObjectDisposedException.ThrowIf(IsDisposed, this);
// If there's an event, reset it.
m_eventObj?.Reset();
// There is a race condition here. If another thread Sets the event, we will get into a state
// where m_state will be unsignaled, yet the Win32 event object will have been signaled.
// This could cause waiting threads to wake up even though the event is in an
// unsignaled state. This is fine -- those that are calling Reset concurrently are
// responsible for doing "the right thing" -- e.g. rechecking the condition and
// resetting the event manually.
// And finally set our state back to unsignaled.
IsSet = false;
}
/// <summary>
/// Blocks the current thread until the current <see cref="ManualResetEventSlim"/> is set.
/// </summary>
/// <exception cref="InvalidOperationException">
/// The maximum number of waiters has been exceeded.
/// </exception>
/// <remarks>
/// The caller of this method blocks indefinitely until the current instance is set. The caller will
/// return immediately if the event is currently in a set state.
/// </remarks>
#if !FEATURE_WASM_MANAGED_THREADS
[UnsupportedOSPlatform("browser")]
#endif
public void Wait()
{
Wait(Timeout.Infinite, CancellationToken.None);
}
/// <summary>
/// Blocks the current thread until the current <see cref="ManualResetEventSlim"/> receives a signal,
/// while observing a <see cref="CancellationToken"/>.
/// </summary>
/// <param name="cancellationToken">The <see cref="CancellationToken"/> to
/// observe.</param>
/// <exception cref="InvalidOperationException">
/// The maximum number of waiters has been exceeded.
/// </exception>
/// <exception cref="OperationCanceledException"><paramref name="cancellationToken"/> was
/// canceled.</exception>
/// <remarks>
/// The caller of this method blocks indefinitely until the current instance is set. The caller will
/// return immediately if the event is currently in a set state.
/// </remarks>
#if !FEATURE_WASM_MANAGED_THREADS
[UnsupportedOSPlatform("browser")]
#endif
public void Wait(CancellationToken cancellationToken)
{
Wait(Timeout.Infinite, cancellationToken);
}
/// <summary>
/// Blocks the current thread until the current <see cref="ManualResetEventSlim"/> is set, using a
/// <see cref="TimeSpan"/> to measure the time interval.
/// </summary>
/// <param name="timeout">A <see cref="TimeSpan"/> that represents the number of milliseconds
/// to wait, or a <see cref="TimeSpan"/> that represents -1 milliseconds to wait indefinitely.
/// </param>
/// <returns>true if the <see cref="ManualResetEventSlim"/> was set; otherwise,
/// false.</returns>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="timeout"/> is a negative
/// number other than -1 milliseconds, which represents an infinite time-out -or- timeout is greater
/// than <see cref="int.MaxValue"/>.</exception>
/// <exception cref="InvalidOperationException">
/// The maximum number of waiters has been exceeded.
/// </exception>
#if !FEATURE_WASM_MANAGED_THREADS
[UnsupportedOSPlatform("browser")]
#endif
public bool Wait(TimeSpan timeout)
{
long totalMilliseconds = (long)timeout.TotalMilliseconds;
ArgumentOutOfRangeException.ThrowIfLessThan(totalMilliseconds, -1, nameof(timeout));
ArgumentOutOfRangeException.ThrowIfGreaterThan(totalMilliseconds, int.MaxValue, nameof(timeout));
return Wait((int)totalMilliseconds, CancellationToken.None);
}
/// <summary>
/// Blocks the current thread until the current <see cref="ManualResetEventSlim"/> is set, using a
/// <see cref="TimeSpan"/> to measure the time interval, while observing a <see
/// cref="CancellationToken"/>.
/// </summary>
/// <param name="timeout">A <see cref="TimeSpan"/> that represents the number of milliseconds
/// to wait, or a <see cref="TimeSpan"/> that represents -1 milliseconds to wait indefinitely.
/// </param>
/// <param name="cancellationToken">The <see cref="CancellationToken"/> to
/// observe.</param>
/// <returns>true if the <see cref="ManualResetEventSlim"/> was set; otherwise,
/// false.</returns>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="timeout"/> is a negative
/// number other than -1 milliseconds, which represents an infinite time-out -or- timeout is greater
/// than <see cref="int.MaxValue"/>.</exception>
/// <exception cref="OperationCanceledException"><paramref
/// name="cancellationToken"/> was canceled.</exception>
/// <exception cref="InvalidOperationException">
/// The maximum number of waiters has been exceeded.
/// </exception>
#if !FEATURE_WASM_MANAGED_THREADS
[UnsupportedOSPlatform("browser")]
#endif
public bool Wait(TimeSpan timeout, CancellationToken cancellationToken)
{
long totalMilliseconds = (long)timeout.TotalMilliseconds;
ArgumentOutOfRangeException.ThrowIfLessThan(totalMilliseconds, -1, nameof(timeout));
ArgumentOutOfRangeException.ThrowIfGreaterThan(totalMilliseconds, int.MaxValue, nameof(timeout));
return Wait((int)totalMilliseconds, cancellationToken);
}
/// <summary>
/// Blocks the current thread until the current <see cref="ManualResetEventSlim"/> is set, using a
/// 32-bit signed integer to measure the time interval.
/// </summary>
/// <param name="millisecondsTimeout">The number of milliseconds to wait, or <see
/// cref="Timeout.Infinite"/>(-1) to wait indefinitely.</param>
/// <returns>true if the <see cref="ManualResetEventSlim"/> was set; 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="InvalidOperationException">
/// The maximum number of waiters has been exceeded.
/// </exception>
#if !FEATURE_WASM_MANAGED_THREADS
[UnsupportedOSPlatform("browser")]
#endif
public bool Wait(int millisecondsTimeout)
{
return Wait(millisecondsTimeout, CancellationToken.None);
}
/// <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="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="CancellationToken"/> to
/// observe.</param>
/// <returns>true if the <see cref="ManualResetEventSlim"/> was set; 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="InvalidOperationException">
/// The maximum number of waiters has been exceeded.
/// </exception>
/// <exception cref="OperationCanceledException"><paramref
/// name="cancellationToken"/> was canceled.</exception>
#if !FEATURE_WASM_MANAGED_THREADS
[UnsupportedOSPlatform("browser")]
#endif
public bool Wait(int millisecondsTimeout, CancellationToken cancellationToken)
{
ObjectDisposedException.ThrowIf(IsDisposed, this);
cancellationToken.ThrowIfCancellationRequested(); // an early convenience check
ArgumentOutOfRangeException.ThrowIfLessThan(millisecondsTimeout, -1);
#if FEATURE_WASM_MANAGED_THREADS
Thread.AssureBlockingPossible();
#endif
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 spinCount = SpinCount;
SpinWait spinner = default;
while (spinner.Count < spinCount)
{
spinner.SpinOnce(sleep1Threshold: -1);
if (IsSet)
{
return true;
}
if (spinner.Count >= 100 && spinner.Count % 10 == 0) // check the cancellation token if the user passed a very large spin count
cancellationToken.ThrowIfCancellationRequested();
}
// Now enter the lock and wait. Must be created before registering the cancellation callback,
// which will try to take this lock.
EnsureLockObjectCreated();
// We must register and unregister the token outside of the lock, to avoid deadlocks.
using (cancellationToken.UnsafeRegister(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 race condition 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++;
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--;
}
// 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 unregisters) the callback
return true; // done. The wait was satisfied.
}
/// <summary>
/// Releases all resources used by the current instance of <see cref="ManualResetEventSlim"/>.
/// </summary>
/// <remarks>
/// Unlike most of the members of <see cref="ManualResetEventSlim"/>, <see cref="Dispose()"/> is not
/// thread-safe and may not be used concurrently with other members of this instance.
/// </remarks>
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
/// <summary>
/// When overridden in a derived class, releases the unmanaged resources used by the
/// <see cref="ManualResetEventSlim"/>, and optionally releases the managed resources.
/// </summary>
/// <param name="disposing">true to release both managed and unmanaged resources;
/// false to release only unmanaged resources.</param>
/// <remarks>
/// Unlike most of the members of <see cref="ManualResetEventSlim"/>, <see cref="Dispose(bool)"/> is not
/// thread-safe and may not be used concurrently with other members of this instance.
/// </remarks>
protected virtual void Dispose(bool disposing)
{
if ((m_combinedState & Dispose_BitMask) != 0)
return; // already disposed
m_combinedState |= Dispose_BitMask; // set the dispose bit
if (disposing)
{
// We will dispose of the event object. We do this under a lock to protect
// against the race condition outlined in the Set method above.
ManualResetEvent? eventObj = m_eventObj;
if (eventObj != null)
{
lock (eventObj)
{
eventObj.Dispose();
m_eventObj = null;
}
}
}
}
private bool IsDisposed => (m_combinedState & Dispose_BitMask) != 0;
/// <summary>
/// Private helper method to wake up waiters when a cancellationToken gets canceled.
/// </summary>
private static readonly Action<object?> s_cancellationTokenCallback = new Action<object?>(CancellationTokenCallback);
private static void CancellationTokenCallback(object? obj)
{
Debug.Assert(obj is ManualResetEventSlim, "Expected a ManualResetEventSlim");
ManualResetEventSlim mre = (ManualResetEventSlim)obj;
Debug.Assert(mre.m_lock != null); // the lock should have been created before this callback is registered for use.
lock (mre.m_lock)
{
Monitor.PulseAll(mre.m_lock); // awaken all waiters
}
}
/// <summary>
/// Private helper method for updating parts of a bit-string state value.
/// Mainly called from the IsSet and Waiters properties setters
/// </summary>
/// <remarks>
/// Note: the parameter types must be int as CompareExchange cannot take a Uint
/// </remarks>
/// <param name="newBits">The new value</param>
/// <param name="updateBitsMask">The mask used to set the bits</param>
private void UpdateStateAtomically(int newBits, int updateBitsMask)
{
SpinWait sw = default;
Debug.Assert((newBits | updateBitsMask) == updateBitsMask, "newBits do not fall within the updateBitsMask.");
while (true)
{
int oldState = m_combinedState; // cache the old value for testing in CAS
// Procedure:(1) zero the updateBits. eg oldState = [11111111] flag= [00111000] newState = [11000111]
// then (2) map in the newBits. eg [11000111] newBits=00101000, newState=[11101111]
int newState = (oldState & ~updateBitsMask) | newBits;
if (Interlocked.CompareExchange(ref m_combinedState, newState, oldState) == oldState)
{
return;
}
sw.SpinOnce(sleep1Threshold: -1);
}
}
/// <summary>
/// Private helper method - performs Mask and shift, particular helpful to extract a field from a packed word.
/// eg ExtractStatePortionAndShiftRight(0x12345678, 0xFF000000, 24) => 0x12, ie extracting the top 8-bits as a simple integer
///
/// ?? is there a common place to put this rather than being private to MRES?
/// </summary>
/// <param name="state"></param>
/// <param name="mask"></param>
/// <param name="rightBitShiftCount"></param>
/// <returns></returns>
private static int ExtractStatePortionAndShiftRight(int state, int mask, int rightBitShiftCount)
{
// convert to uint before shifting so that right-shift does not replicate the sign-bit,
// then convert back to int.
return unchecked((int)(((uint)(state & mask)) >> rightBitShiftCount));
}
/// <summary>
/// Performs a Mask operation, but does not perform the shift.
/// This is acceptable for boolean values for which the shift is unnecessary
/// eg (val & Mask) != 0 is an appropriate way to extract a boolean rather than using
/// ((val & Mask) >> shiftAmount) == 1
///
/// ?? is there a common place to put this rather than being private to MRES?
/// </summary>
/// <param name="state"></param>
/// <param name="mask"></param>
private static int ExtractStatePortion(int state, int mask)
{
return state & mask;
}
}
}
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