/// <summary>
/// Acquires the lock in shared mode, blocking
/// if necessary.
/// </summary>
/// <remarks>
/// Exclusive acquires are given precedence over shared
/// acquires.
/// </remarks>
public void AcquireShared()
{
int value;
int i = 0;
#if ENABLE_STATISTICS
Interlocked.Increment(ref _acqShrdCount);
#endif
while (true)
{
value = _value;
// Case 1: lock not owned AND no exclusive waiter is waking up AND
// there are no shared owners AND there are no exclusive waiters
if ((value & (
LockOwned |
(LockSharedOwnersMask << LockSharedOwnersShift) |
ExclusiveMask
)) == 0)
{
if (Interlocked.CompareExchange(
ref _value,
value + LockOwned + LockSharedOwnersIncrement,
value
) == value)
{
break;
}
}
// Case 2: lock is owned AND no exclusive waiter is waking up AND
// there are shared owners AND there are no exclusive waiters
else if (
(value & LockOwned) != 0 &&
((value >> LockSharedOwnersShift) & LockSharedOwnersMask) != 0 &&
(value & ExclusiveMask) == 0
)
{
if (Interlocked.CompareExchange(
ref _value,
value + LockSharedOwnersIncrement,
value
) == value)
{
break;
}
}
// Other cases.
else if (i >= SpinCount)
{
#if DEFER_EVENT_CREATION
this.EnsureEventCreated(ref _sharedWakeEvent);
#endif
if (Interlocked.CompareExchange(
ref _value,
value + LockSharedWaitersIncrement,
value
) == value)
{
#if ENABLE_STATISTICS
Interlocked.Increment(ref _acqShrdSlpCount);
int shrdWtrsCount = (value >> LockSharedWaitersShift) & LockSharedWaitersMask;
Interlocked2.Set(
ref _peakShrdWtrsCount,
(p) => p < shrdWtrsCount,
(p) => shrdWtrsCount
);
#endif
// Go to sleep.
if (NativeMethods.WaitForSingleObject(
_sharedWakeEvent,
Timeout.Infinite
) != NativeMethods.WaitObject0)
{
UtilsBreak("Utils.MsgFailedToWaitIndefinitely");
}
// Go back and try again.
continue;
}
}
#if ENABLE_STATISTICS
Interlocked.Increment(ref _acqShrdContCount);
#endif
i++;
}
}
/// <summary>
/// Acquires the lock in exclusive mode, blocking
/// if necessary.
/// </summary>
/// <remarks>
/// Exclusive acquires are given precedence over shared
/// acquires.
/// </remarks>
public void AcquireExclusive()
{
int value;
int i = 0;
#if ENABLE_STATISTICS
Interlocked.Increment(ref _acqExclCount);
#endif
while (true)
{
value = _value;
// Case 1: lock not owned AND an exclusive waiter is not waking up.
// Here we don't have to check if there are exclusive waiters, because
// if there are the lock would be owned, and we are checking that anyway.
if ((value & (LockOwned | LockExclusiveWaking)) == 0)
{
#if RIGOROUS_CHECKS
System.Diagnostics.Trace.Assert(((value >> LockSharedOwnersShift) & LockSharedOwnersMask) == 0);
System.Diagnostics.Trace.Assert(((value >> LockExclusiveWaitersShift) & LockExclusiveWaitersMask) == 0);
#endif
if (Interlocked.CompareExchange(
ref _value,
value + LockOwned,
value
) == value)
{
break;
}
}
// Case 2: lock owned OR lock not owned and an exclusive waiter is waking up.
// The second case means an exclusive waiter has just been woken up and is
// going to acquire the lock. We have to go to sleep to make sure we don't
// steal the lock.
else if (i >= SpinCount)
{
#if DEFER_EVENT_CREATION
// This call must go *before* the next operation. Otherwise,
// we will have a race condition between potential releasers
// and us.
this.EnsureEventCreated(ref _exclusiveWakeEvent);
#endif
if (Interlocked.CompareExchange(
ref _value,
value + LockExclusiveWaitersIncrement,
value
) == value)
{
#if ENABLE_STATISTICS
Interlocked.Increment(ref _acqExclSlpCount);
int exclWtrsCount = (value >> LockExclusiveWaitersShift) & LockExclusiveWaitersMask;
Interlocked2.Set(
ref _peakExclWtrsCount,
(p) => p < exclWtrsCount,
(p) => exclWtrsCount
);
#endif
// Go to sleep.
if (NativeMethods.WaitForSingleObject(
_exclusiveWakeEvent,
Timeout.Infinite
) != NativeMethods.WaitObject0)
{
UtilsBreak("Utils.MsgFailedToWaitIndefinitely");
}
// Acquire the lock.
// At this point *no one* should be able to steal the lock from us.
do
{
value = _value;
#if RIGOROUS_CHECKS
System.Diagnostics.Trace.Assert((value & LockOwned) == 0);
System.Diagnostics.Trace.Assert((value & LockExclusiveWaking) != 0);
#endif
} while(Interlocked.CompareExchange(
ref _value,
value + LockOwned - LockExclusiveWaking,
value
) != value);
break;
}
}
#if ENABLE_STATISTICS
Interlocked.Increment(ref _acqExclContCount);
#endif
i++;
}
}
