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Merge libcxxrt commit f2e55091e2e878386c9f7974d4922bbdc4faed84
Fix unlock in two-word version and add missing comment.
Fixes #15
Fixes #16
This should fix the hangs in __cxa_guard_acquire() reported on i386 (and
possibly other 32-bit platforms).
Obtained from: https://github.com/libcxxrt/libcxxrt/commit/f2e5509
Fixes: 56aaed388b
MFC after: 2 weeks
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@ -69,7 +69,12 @@
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* progress). The bit to use depends on the byte order of the target.
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*
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* On many 32-bit platforms, 64-bit atomics are unavailable (or slow) and so we
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* treat the two halves of the 64-bit word as independent values and
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* treat the two halves of the 64-bit word as independent values and establish
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* an ordering on them such that the guard word is never modified unless the
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* lock word is in the locked state. This means that we can do double-checked
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* locking by loading the guard word and, if it is not initialised, trying to
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* transition the lock word from the unlocked to locked state, and then
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* manipulate the guard word.
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*/
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namespace
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{
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@ -227,7 +232,7 @@ namespace
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// If another thread did manage to initialise this, release
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// the lock and notify the caller that initialisation is
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// done.
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lock_word.store(initialised, memory_order::release);
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lock_word.store(0, memory_order::release);
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return GuardState::InitDone;
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}
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return GuardState::InitLockSucceeded;
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