2014-07-15 22:23:06 +00:00
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/* Low-level lock implementation. Generic futex-based version.
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2020-01-01 00:14:33 +00:00
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Copyright (C) 2005-2020 Free Software Foundation, Inc.
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2014-07-15 22:23:06 +00:00
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library. If not, see
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Prefer https to http for gnu.org and fsf.org URLs
Also, change sources.redhat.com to sourceware.org.
This patch was automatically generated by running the following shell
script, which uses GNU sed, and which avoids modifying files imported
from upstream:
sed -ri '
s,(http|ftp)(://(.*\.)?(gnu|fsf|sourceware)\.org($|[^.]|\.[^a-z])),https\2,g
s,(http|ftp)(://(.*\.)?)sources\.redhat\.com($|[^.]|\.[^a-z]),https\2sourceware.org\4,g
' \
$(find $(git ls-files) -prune -type f \
! -name '*.po' \
! -name 'ChangeLog*' \
! -path COPYING ! -path COPYING.LIB \
! -path manual/fdl-1.3.texi ! -path manual/lgpl-2.1.texi \
! -path manual/texinfo.tex ! -path scripts/config.guess \
! -path scripts/config.sub ! -path scripts/install-sh \
! -path scripts/mkinstalldirs ! -path scripts/move-if-change \
! -path INSTALL ! -path locale/programs/charmap-kw.h \
! -path po/libc.pot ! -path sysdeps/gnu/errlist.c \
! '(' -name configure \
-execdir test -f configure.ac -o -f configure.in ';' ')' \
! '(' -name preconfigure \
-execdir test -f preconfigure.ac ';' ')' \
-print)
and then by running 'make dist-prepare' to regenerate files built
from the altered files, and then executing the following to cleanup:
chmod a+x sysdeps/unix/sysv/linux/riscv/configure
# Omit irrelevant whitespace and comment-only changes,
# perhaps from a slightly-different Autoconf version.
git checkout -f \
sysdeps/csky/configure \
sysdeps/hppa/configure \
sysdeps/riscv/configure \
sysdeps/unix/sysv/linux/csky/configure
# Omit changes that caused a pre-commit check to fail like this:
# remote: *** error: sysdeps/powerpc/powerpc64/ppc-mcount.S: trailing lines
git checkout -f \
sysdeps/powerpc/powerpc64/ppc-mcount.S \
sysdeps/unix/sysv/linux/s390/s390-64/syscall.S
# Omit change that caused a pre-commit check to fail like this:
# remote: *** error: sysdeps/sparc/sparc64/multiarch/memcpy-ultra3.S: last line does not end in newline
git checkout -f sysdeps/sparc/sparc64/multiarch/memcpy-ultra3.S
2019-09-07 05:40:42 +00:00
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<https://www.gnu.org/licenses/>. */
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2014-07-15 22:23:06 +00:00
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#ifndef _LOWLEVELLOCK_H
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#define _LOWLEVELLOCK_H 1
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#include <atomic.h>
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#include <lowlevellock-futex.h>
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2019-10-30 18:56:39 +00:00
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#include <time.h>
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2014-07-15 22:23:06 +00:00
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2014-12-15 21:49:29 +00:00
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/* Low-level locks use a combination of atomic operations (to acquire and
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release lock ownership) and futex operations (to block until the state
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of a lock changes). A lock can be in one of three states:
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0: not acquired,
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1: acquired with no waiters; no other threads are blocked or about to block
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for changes to the lock state,
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>1: acquired, possibly with waiters; there may be other threads blocked or
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about to block for changes to the lock state.
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We expect that the common case is an uncontended lock, so we just need
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to transition the lock between states 0 and 1; releasing the lock does
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not need to wake any other blocked threads. If the lock is contended
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and a thread decides to block using a futex operation, then this thread
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needs to first change the state to >1; if this state is observed during
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lock release, the releasing thread will wake one of the potentially
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blocked threads.
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Much of this code takes a 'private' parameter. This may be:
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LLL_PRIVATE: lock only shared within a process
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LLL_SHARED: lock may be shared across processes.
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Condition variables contain an optimization for broadcasts that requeues
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waiting threads on a lock's futex. Therefore, there is a special
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variant of the locks (whose name contains "cond") that makes sure to
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always set the lock state to >1 and not just 1.
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Robust locks set the lock to the id of the owner. This allows detection
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of the case where the owner exits without releasing the lock. Flags are
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OR'd with the owner id to record additional information about lock state.
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Therefore the states of robust locks are:
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0: not acquired
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id: acquired (by user identified by id & FUTEX_TID_MASK)
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The following flags may be set in the robust lock value:
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FUTEX_WAITERS - possibly has waiters
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FUTEX_OWNER_DIED - owning user has exited without releasing the futex. */
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/* If LOCK is 0 (not acquired), set to 1 (acquired with no waiters) and return
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0. Otherwise leave lock unchanged and return non-zero to indicate that the
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lock was not acquired. */
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2019-02-21 16:33:54 +00:00
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#define __lll_trylock(lock) \
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__glibc_unlikely (atomic_compare_and_exchange_bool_acq ((lock), 1, 0))
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2014-07-15 22:23:06 +00:00
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#define lll_trylock(lock) \
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2019-02-21 16:33:54 +00:00
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__lll_trylock (&(lock))
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2014-07-15 22:23:06 +00:00
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2014-12-15 21:49:29 +00:00
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/* If LOCK is 0 (not acquired), set to 2 (acquired, possibly with waiters) and
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return 0. Otherwise leave lock unchanged and return non-zero to indicate
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that the lock was not acquired. */
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2014-07-15 22:23:06 +00:00
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#define lll_cond_trylock(lock) \
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2017-02-06 12:44:23 +00:00
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__glibc_unlikely (atomic_compare_and_exchange_bool_acq (&(lock), 2, 0))
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2014-07-15 22:23:06 +00:00
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extern void __lll_lock_wait_private (int *futex) attribute_hidden;
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extern void __lll_lock_wait (int *futex, int private) attribute_hidden;
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/* This is an expression rather than a statement even though its value is
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void, so that it can be used in a comma expression or as an expression
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that's cast to void. */
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2014-12-15 21:49:29 +00:00
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/* The inner conditional compiles to a call to __lll_lock_wait_private if
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private is known at compile time to be LLL_PRIVATE, and to a call to
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__lll_lock_wait otherwise. */
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/* If FUTEX is 0 (not acquired), set to 1 (acquired with no waiters) and
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return. Otherwise, ensure that it is >1 (acquired, possibly with waiters)
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and then block until we acquire the lock, at which point FUTEX will still be
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>1. The lock is always acquired on return. */
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2014-07-15 22:23:06 +00:00
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#define __lll_lock(futex, private) \
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((void) \
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({ \
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int *__futex = (futex); \
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if (__glibc_unlikely \
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(atomic_compare_and_exchange_bool_acq (__futex, 1, 0))) \
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{ \
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if (__builtin_constant_p (private) && (private) == LLL_PRIVATE) \
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__lll_lock_wait_private (__futex); \
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else \
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__lll_lock_wait (__futex, private); \
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} \
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}))
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#define lll_lock(futex, private) \
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__lll_lock (&(futex), private)
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/* This is an expression rather than a statement even though its value is
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void, so that it can be used in a comma expression or as an expression
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that's cast to void. */
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2014-12-15 21:49:29 +00:00
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/* Unconditionally set FUTEX to 2 (acquired, possibly with waiters). If FUTEX
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was 0 (not acquired) then return. Otherwise, block until the lock is
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acquired, at which point FUTEX is 2 (acquired, possibly with waiters). The
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lock is always acquired on return. */
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2014-07-15 22:23:06 +00:00
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#define __lll_cond_lock(futex, private) \
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((void) \
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({ \
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int *__futex = (futex); \
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if (__glibc_unlikely (atomic_exchange_acq (__futex, 2) != 0)) \
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__lll_lock_wait (__futex, private); \
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}))
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#define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private)
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2019-10-30 18:56:39 +00:00
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extern int __lll_clocklock_wait (int *futex, int val, clockid_t,
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2019-06-24 13:08:25 +00:00
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const struct timespec *,
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2014-07-15 22:23:06 +00:00
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int private) attribute_hidden;
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2019-10-30 18:56:39 +00:00
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#define lll_timedwait(futex, val, clockid, abstime, private) \
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__lll_clocklock_wait (futex, val, clockid, abstime, private)
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2014-12-15 21:49:29 +00:00
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2019-06-24 13:08:25 +00:00
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/* As __lll_lock, but with an absolute timeout measured against the clock
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specified in CLOCKID. If the timeout occurs then return ETIMEDOUT. If
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ABSTIME is invalid, return EINVAL. */
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#define __lll_clocklock(futex, clockid, abstime, private) \
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2014-07-15 22:23:06 +00:00
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({ \
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int *__futex = (futex); \
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int __val = 0; \
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\
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2014-08-11 14:26:48 +00:00
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if (__glibc_unlikely \
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(atomic_compare_and_exchange_bool_acq (__futex, 1, 0))) \
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2019-10-30 18:56:39 +00:00
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{ \
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while (atomic_exchange_acq (futex, 2) != 0) \
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{ \
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__val = __lll_clocklock_wait (__futex, 2, clockid, \
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abstime, private); \
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if (__val == EINVAL || __val == ETIMEDOUT) \
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break; \
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} \
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} \
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2014-07-15 22:23:06 +00:00
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__val; \
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})
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2019-06-24 13:08:25 +00:00
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#define lll_clocklock(futex, clockid, abstime, private) \
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__lll_clocklock (&(futex), clockid, abstime, private)
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2014-07-15 22:23:06 +00:00
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/* This is an expression rather than a statement even though its value is
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void, so that it can be used in a comma expression or as an expression
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that's cast to void. */
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2014-12-15 21:49:29 +00:00
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/* Unconditionally set FUTEX to 0 (not acquired), releasing the lock. If FUTEX
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was >1 (acquired, possibly with waiters), then wake any waiters. The waiter
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2015-07-14 19:58:34 +00:00
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that acquires the lock will set FUTEX to >1.
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Evaluate PRIVATE before releasing the lock so that we do not violate the
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mutex destruction requirements. Specifically, we need to ensure that
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another thread can destroy the mutex (and reuse its memory) once it
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acquires the lock and when there will be no further lock acquisitions;
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thus, we must not access the lock after releasing it, or those accesses
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could be concurrent with mutex destruction or reuse of the memory. */
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2014-07-15 22:23:06 +00:00
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#define __lll_unlock(futex, private) \
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((void) \
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({ \
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int *__futex = (futex); \
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2015-07-14 19:58:34 +00:00
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int __private = (private); \
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2014-07-15 22:23:06 +00:00
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int __oldval = atomic_exchange_rel (__futex, 0); \
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if (__glibc_unlikely (__oldval > 1)) \
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2015-07-14 19:58:34 +00:00
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lll_futex_wake (__futex, 1, __private); \
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2014-07-15 22:23:06 +00:00
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}))
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#define lll_unlock(futex, private) \
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__lll_unlock (&(futex), private)
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#define lll_islocked(futex) \
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((futex) != LLL_LOCK_INITIALIZER)
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/* Our internal lock implementation is identical to the binary-compatible
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mutex implementation. */
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/* Initializers for lock. */
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#define LLL_LOCK_INITIALIZER (0)
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#define LLL_LOCK_INITIALIZER_LOCKED (1)
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#endif /* lowlevellock.h */
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