[*] Harden WinXP-7 semaphores [2b0ed797
cont] [more paranoia]
[*] Dont overspin spurious modernnt condvar wakes [*] Revert 2943ffdb's add waiter, if under modern nt 1: While spuriously waking a blocked keyed event, don't leave the condition variable in a state where signals can be ignored.
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@ -151,8 +151,9 @@ namespace Aurora::Threading::Primitives
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}
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else
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{
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if (bIOU ||
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(bSpin ? this->CheckOut() : this->CheckOutNoSpin()))
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// Acquire our signal before spinning and potentially giving up on our timeslice.
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// If we were awoken, try to acquire before yielding to a contested mutex.
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if (bIOU || this->CheckOutNoSpin())
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{
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pMutex->Lock();
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return true;
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@ -160,10 +161,11 @@ namespace Aurora::Threading::Primitives
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if (!gUseNativeWaitCondvar)
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{
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// (NT 5-6.1) Unblocks one race condition, where another thread checks out our signal, and we return with nothing.
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// Normal execution of the blocked thread can continue, so long as we trigger the keyed event as though this thread was signaled.
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// This is only relevant in an edge case of multi-waiters spinning, rapid signaling, and the IOU being hit once. Do this instead of ticketing.
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this->SignalSpuriously();
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}
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this->AddWaiter();
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}
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}
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}
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@ -211,8 +213,7 @@ namespace Aurora::Threading::Primitives
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pNtWaitForKeyedEvent(gKeyedEventHandle, (void *)&this->wlist, 0, nullptr);
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}
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if (bIOU ||
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(bSpin ? this->CheckOut() : this->CheckOutNoSpin()))
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if (bIOU || this->CheckOutNoSpin())
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{
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pMutex->Lock();
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return bRet;
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@ -222,8 +223,6 @@ namespace Aurora::Threading::Primitives
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{
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this->SignalSpuriously();
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}
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this->AddWaiter();
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}
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}
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#else
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@ -344,20 +343,22 @@ namespace Aurora::Threading::Primitives
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if (expected)
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{
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// NOTE: missing this->signalCount atomic increment to force another AddWaiter under successful keyedevent return
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// INTENTIONAL: Missing this->signalCount atomic increment to force another AddWaiter under successful keyedevent return
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while (expected)
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{
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if (AuAtomicCompareExchange(&this->wlist, ((expected - 1) << kShiftCountByBits) /*intentional clear*/, original) == original)
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// INTENTIONAL: Removed the -1 so we dont have to rewatch the condvar, potentially missing a signal in the process
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if (AuAtomicCompareExchange(&this->wlist, (expected << kShiftCountByBits) /*intentional clear*/, original) == original)
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{
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if (gUseNativeWaitCondvar)
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{
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InternalLTSWakeOne((void *)&this->wlist);
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}
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else
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if (!gUseNativeWaitCondvar)
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{
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pNtReleaseKeyedEvent(gKeyedEventHandle, (void *)&this->wlist, FALSE, nullptr);
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}
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// INTENTIONAL: Removal of modernt branch. We err on the side of caution by failing awake, then its up to the last waking
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// thread up process to block again. So long as wlist represents all the waiting threads, it doesn't matter,
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// we will continue to be signalable withouts signal being lost or any thread blocking.
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return;
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}
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