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/* Commit an elided pthread lock.
Copyright (C) 2014-2017 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <pthreadP.h>
#include <lowlevellock.h>
#include <htm.h>
int
__lll_unlock_elision(int *futex, short *adapt_count, int private)
{
/* If the lock is free, we elided the lock earlier. This does not
necessarily mean that we are in a transaction, because the user code may
have closed the transaction, but that is impossible to detect reliably.
Relaxed MO access to futex is sufficient as we only need a hint, if we
started a transaction or acquired the futex in e.g. elision-lock.c. */
if (atomic_load_relaxed (futex) == 0)
{
__libc_tend ();
}
else
{
/* Update the adapt_count while unlocking before completing the critical
section. adapt_count is accessed concurrently outside of a
transaction or an aquired lock e.g. in elision-lock.c so we need to use
atomic accesses. However, the value of adapt_count is just a hint, so
relaxed MO accesses are sufficient.
If adapt_count would be decremented while locking, multiple
CPUs trying to lock the locked mutex will decrement adapt_count to
zero and another CPU will try to start a transaction, which will be
immediately aborted as the mutex is locked.
If adapt_count would be decremented while unlocking after completing
the critical section, possible waiters will be waked up before
decrementing the adapt_count. Those waked up waiters could have
destroyed and freed this mutex! */
short adapt_count_val = atomic_load_relaxed (adapt_count);
if (adapt_count_val > 0)
atomic_store_relaxed (adapt_count, adapt_count_val - 1);
lll_unlock ((*futex), private);
}
return 0;
}
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