mirror of
https://sourceware.org/git/glibc.git
synced 2025-11-02 09:33:31 +03:00
120 lines
3.9 KiB
C
120 lines
3.9 KiB
C
/* elide.h: Generic lock elision support.
|
|
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/>. */
|
|
#ifndef ELIDE_H
|
|
#define ELIDE_H 1
|
|
|
|
#include <hle.h>
|
|
#include <elision-conf.h>
|
|
#include <atomic.h>
|
|
|
|
|
|
/* Adapt elision with ADAPT_COUNT and STATUS and decide retries. */
|
|
|
|
static inline bool
|
|
elision_adapt(signed char *adapt_count, unsigned int status)
|
|
{
|
|
if (status & _XABORT_RETRY)
|
|
return false;
|
|
if ((status & _XABORT_EXPLICIT)
|
|
&& _XABORT_CODE (status) == _ABORT_LOCK_BUSY)
|
|
{
|
|
/* Right now we skip here. Better would be to wait a bit
|
|
and retry. This likely needs some spinning. Be careful
|
|
to avoid writing the lock.
|
|
Using relaxed MO and separate atomic accesses is sufficient because
|
|
adapt_count is just a hint. */
|
|
if (atomic_load_relaxed (adapt_count) != __elision_aconf.skip_lock_busy)
|
|
atomic_store_relaxed (adapt_count, __elision_aconf.skip_lock_busy);
|
|
}
|
|
/* Internal abort. There is no chance for retry.
|
|
Use the normal locking and next time use lock.
|
|
Be careful to avoid writing to the lock. See above for MO. */
|
|
else if (atomic_load_relaxed (adapt_count)
|
|
!= __elision_aconf.skip_lock_internal_abort)
|
|
atomic_store_relaxed (adapt_count,
|
|
__elision_aconf.skip_lock_internal_abort);
|
|
return true;
|
|
}
|
|
|
|
/* is_lock_free must be executed inside the transaction */
|
|
|
|
/* Returns true if lock defined by IS_LOCK_FREE was elided.
|
|
ADAPT_COUNT is a per-lock state variable; it must be accessed atomically
|
|
to avoid data races but is just a hint, so using relaxed MO and separate
|
|
atomic loads and stores instead of atomic read-modify-write operations is
|
|
sufficient. */
|
|
|
|
#define ELIDE_LOCK(adapt_count, is_lock_free) \
|
|
({ \
|
|
int ret = 0; \
|
|
\
|
|
if (atomic_load_relaxed (&(adapt_count)) <= 0) \
|
|
{ \
|
|
for (int i = __elision_aconf.retry_try_xbegin; i > 0; i--) \
|
|
{ \
|
|
unsigned int status; \
|
|
if ((status = _xbegin ()) == _XBEGIN_STARTED) \
|
|
{ \
|
|
if (is_lock_free) \
|
|
{ \
|
|
ret = 1; \
|
|
break; \
|
|
} \
|
|
_xabort (_ABORT_LOCK_BUSY); \
|
|
} \
|
|
if (!elision_adapt (&(adapt_count), status)) \
|
|
break; \
|
|
} \
|
|
} \
|
|
else \
|
|
atomic_store_relaxed (&(adapt_count), \
|
|
atomic_load_relaxed (&(adapt_count)) - 1); \
|
|
ret; \
|
|
})
|
|
|
|
/* Returns true if lock defined by IS_LOCK_FREE was try-elided.
|
|
ADAPT_COUNT is a per-lock state variable. */
|
|
|
|
#define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) ({ \
|
|
int ret = 0; \
|
|
if (__elision_aconf.retry_try_xbegin > 0) \
|
|
{ \
|
|
if (write) \
|
|
_xabort (_ABORT_NESTED_TRYLOCK); \
|
|
ret = ELIDE_LOCK (adapt_count, is_lock_free); \
|
|
} \
|
|
ret; \
|
|
})
|
|
|
|
/* Returns true if lock defined by IS_LOCK_FREE was elided. The call
|
|
to _xend crashes if the application incorrectly tries to unlock a
|
|
lock which has not been locked. */
|
|
|
|
#define ELIDE_UNLOCK(is_lock_free) \
|
|
({ \
|
|
int ret = 0; \
|
|
if (is_lock_free) \
|
|
{ \
|
|
_xend (); \
|
|
ret = 1; \
|
|
} \
|
|
ret; \
|
|
})
|
|
|
|
#endif
|