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Remove some unnecessary spinning #21437

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jkotas merged 3 commits into from
Dec 8, 2018
Merged

Remove some unnecessary spinning #21437

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05d48bb
Remove some unnecessary spinning
stephentoub Dec 7, 2018
74af7ae
Address PR feedback
stephentoub Dec 7, 2018
7d93d80
Address more PR feedback
stephentoub Dec 7, 2018
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8 changes: 4 additions & 4 deletions src/System.Private.CoreLib/shared/System/Collections/Concurrent/ConcurrentQueueSegment.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -112,15 +112,15 @@ internal static int RoundUpToPowerOf2(int i)
_frozenForEnqueues = true;

// Increase the tail by FreezeOffset, spinning until we're successful in doing so.
var spinner = new SpinWait();
int tail = _headAndTail.Tail;
while (true)
{
int tail = Volatile.Read(ref _headAndTail.Tail);
if (Interlocked.CompareExchange(ref _headAndTail.Tail, tail + FreezeOffset, tail) == tail)
int oldTail = Interlocked.CompareExchange(ref _headAndTail.Tail, tail + FreezeOffset, tail);
if (oldTail == tail)
{
break;
}
spinner.SpinOnce();
tail = oldTail;
}
}
}
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29 changes: 14 additions & 15 deletions src/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -721,31 +721,31 @@ internal bool AtomicStateUpdate(int newBits, int illegalBits)

private bool AtomicStateUpdateSlow(int newBits, int illegalBits)
{
var sw = new SpinWait();
int flags = m_stateFlags;
do
{
int oldFlags = m_stateFlags;
if ((oldFlags & illegalBits) != 0) return false;
if (Interlocked.CompareExchange(ref m_stateFlags, oldFlags | newBits, oldFlags) == oldFlags)
if ((flags & illegalBits) != 0) return false;
int oldFlags = Interlocked.CompareExchange(ref m_stateFlags, flags | newBits, flags);
if (oldFlags == flags)
{
return true;
}
sw.SpinOnce();
flags = oldFlags;
} while (true);
}

internal bool AtomicStateUpdate(int newBits, int illegalBits, ref int oldFlags)
{
SpinWait sw = new SpinWait();
int flags = oldFlags = m_stateFlags;
do
{
oldFlags = m_stateFlags;
if ((oldFlags & illegalBits) != 0) return false;
if (Interlocked.CompareExchange(ref m_stateFlags, oldFlags | newBits, oldFlags) == oldFlags)
if ((flags & illegalBits) != 0) return false;
oldFlags = Interlocked.CompareExchange(ref m_stateFlags, flags | newBits, flags);
if (oldFlags == flags)
{
return true;
}
sw.SpinOnce();
flags = oldFlags;
} while (true);
}

Expand All @@ -772,13 +772,12 @@ internal void SetNotificationForWaitCompletion(bool enabled)
else
{
// Atomically clear the END_AWAIT_NOTIFICATION bit
SpinWait sw = new SpinWait();
int flags = m_stateFlags;
while (true)
{
int oldFlags = m_stateFlags;
int newFlags = oldFlags & (~TASK_STATE_WAIT_COMPLETION_NOTIFICATION);
if (Interlocked.CompareExchange(ref m_stateFlags, newFlags, oldFlags) == oldFlags) break;
sw.SpinOnce();
int oldFlags = Interlocked.CompareExchange(ref m_stateFlags, flags & (~TASK_STATE_WAIT_COMPLETION_NOTIFICATION), flags);
if (oldFlags == flags) break;
flags = oldFlags;
}
}
}
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