This patch adds support for spinlocks in Asterisk.
There are cases in Asterisk where it might be desirable to lock a short critical code section but not incur the context switch and yield penalty of a mutex or rwlock. The primary spinlock implementations execute exclusively in userspace and therefore don't incur those penalties. Spinlocks are NOT meant to be a general replacement for mutexes. They should be used only for protecting short blocks of critical code such as simple compares and assignments. Operations that may block, hold a lock, or cause the thread to give up it's timeslice should NEVER be attempted in a spinlock. The first use case for spinlocks is in astobj2 - internal_ao2_ref. Currently the manipulation of the reference counter is done with an ast_atomic_fetchadd_int which works fine. When weak reference containers are introduced however, there's an additional comparison and assignment that'll need to be done while the lock is held. A mutex would be way too expensive here, hence the spinlock. Given that lock contention in this situation would be infrequent, the overhead of the spinlock is only a few more machine instructions than the current ast_atomic_fetchadd_int call. ASTERISK-23553 #close Review: https://reviewboard.asterisk.org/r/3405/ ........ Merged revisions 412976 from http://svn.asterisk.org/svn/asterisk/branches/12 git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@412977 65c4cc65-6c06-0410-ace0-fbb531ad65f3
This commit is contained in:
George Joseph
parent
e6c4b97521
commit
64045f0b57
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@ -1,5 +1,5 @@
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#! /bin/sh
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# From configure.ac Revision: 406825 .
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# From configure.ac Revision.
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# Guess values for system-dependent variables and create Makefiles.
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# Generated by GNU Autoconf 2.69 for asterisk trunk.
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#
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@ -15862,6 +15862,60 @@ else
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
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$as_echo "no" >&6; }
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fi
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rm -f core conftest.err conftest.$ac_objext \
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conftest$ac_exeext conftest.$ac_ext
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{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for PTHREAD_MUTEX_ADAPTIVE_NP in pthread.h" >&5
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$as_echo_n "checking for PTHREAD_MUTEX_ADAPTIVE_NP in pthread.h... " >&6; }
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cat confdefs.h - <<_ACEOF >conftest.$ac_ext
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/* end confdefs.h. */
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#include <pthread.h>
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int
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main ()
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{
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int a = PTHREAD_MUTEX_ADAPTIVE_NP;
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;
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return 0;
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}
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_ACEOF
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if ac_fn_c_try_link "$LINENO"; then :
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
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$as_echo "yes" >&6; }
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$as_echo "#define HAVE_PTHREAD_MUTEX_ADAPTIVE_NP 1" >>confdefs.h
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else
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
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$as_echo "no" >&6; }
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fi
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rm -f core conftest.err conftest.$ac_objext \
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conftest$ac_exeext conftest.$ac_ext
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{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for pthread_spinlock_t in pthread.h" >&5
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$as_echo_n "checking for pthread_spinlock_t in pthread.h... " >&6; }
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cat confdefs.h - <<_ACEOF >conftest.$ac_ext
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/* end confdefs.h. */
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#include <pthread.h>
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int
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main ()
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{
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pthread_spinlock_t spin;
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;
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return 0;
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}
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_ACEOF
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if ac_fn_c_try_link "$LINENO"; then :
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
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$as_echo "yes" >&6; }
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$as_echo "#define HAVE_PTHREAD_SPINLOCK 1" >>confdefs.h
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else
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{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
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$as_echo "no" >&6; }
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fi
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rm -f core conftest.err conftest.$ac_objext \
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conftest$ac_exeext conftest.$ac_ext
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16
configure.ac
16
configure.ac
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@ -818,6 +818,22 @@ AC_DEFINE([HAVE_PTHREAD_MUTEX_RECURSIVE_NP], 1, [Define to 1 if your system defi
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AC_MSG_RESULT(no)
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)
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AC_MSG_CHECKING(for PTHREAD_MUTEX_ADAPTIVE_NP in pthread.h)
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AC_LINK_IFELSE(
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[AC_LANG_PROGRAM([#include <pthread.h>], [int a = PTHREAD_MUTEX_ADAPTIVE_NP;])],
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AC_MSG_RESULT(yes)
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AC_DEFINE([HAVE_PTHREAD_MUTEX_ADAPTIVE_NP], 1, [Define to 1 if your system defines PTHREAD_MUTEX_ADAPTIVE_NP in pthread.h]),
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AC_MSG_RESULT(no)
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)
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AC_MSG_CHECKING(for pthread_spinlock_t in pthread.h)
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AC_LINK_IFELSE(
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[AC_LANG_PROGRAM([#include <pthread.h>], [pthread_spinlock_t spin;])],
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AC_MSG_RESULT(yes)
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AC_DEFINE([HAVE_PTHREAD_SPINLOCK], 1, [Define to 1 if your system has pthread_spinlock_t in pthread.h]),
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AC_MSG_RESULT(no)
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)
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save_LIBS="$LIBS"
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save_CFLAGS="$CFLAGS"
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LIBS="$PTHREAD_LIBS $LIBS"
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@ -667,6 +667,10 @@
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/* Define if you have POSIX threads libraries and header files. */
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#undef HAVE_PTHREAD
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/* Define to 1 if your system defines PTHREAD_MUTEX_ADAPTIVE_NP in pthread.h
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*/
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#undef HAVE_PTHREAD_MUTEX_ADAPTIVE_NP
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/* Define to 1 if your system defines PTHREAD_MUTEX_RECURSIVE_NP in pthread.h
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*/
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#undef HAVE_PTHREAD_MUTEX_RECURSIVE_NP
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@ -685,6 +689,9 @@
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/* Define if your system has pthread_rwlock_timedwrlock() */
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#undef HAVE_PTHREAD_RWLOCK_TIMEDWRLOCK
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/* Define to 1 if your system has pthread_spinlock_t in pthread.h */
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#undef HAVE_PTHREAD_SPINLOCK
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/* Define to 1 if the system has the type `ptrdiff_t'. */
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#undef HAVE_PTRDIFF_T
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@ -0,0 +1,445 @@
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/*
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* Asterisk -- An open source telephony toolkit.
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*
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* Copyright (C) 2014, Fairview 5 Engineering, LLC
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*
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* George Joseph <george.joseph@fairview5.com>
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*
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* See http://www.asterisk.org for more information about
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* the Asterisk project. Please do not directly contact
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* any of the maintainers of this project for assistance;
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* the project provides a web site, mailing lists and IRC
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* channels for your use.
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*
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* This program is free software, distributed under the terms of
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* the GNU General Public License Version 2. See the LICENSE file
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* at the top of the source tree.
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*/
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/*! \file
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* \brief Spin Locks.
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*
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* In some atomic operation circumstances the __atomic calls are not quite
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* flexible enough but a full fledged mutex or rwlock is too expensive.
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*
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* Spin locks should be used only for protecting short blocks of critical
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* code such as simple compares and assignments. Operations that may block,
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* hold a lock, or cause the thread to give up it's timeslice should NEVER
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* be attempted in a spin lock.
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*
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* Because spinlocks must be as lightweight as possible, there are no
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* recursion or deadlock checks.
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*
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*/
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#ifndef _ASTERISK_SPINLOCK_H
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#define _ASTERISK_SPINLOCK_H
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#include <pthread.h>
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#include "asterisk/compiler.h"
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/*!
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* \brief Spinlock Implementation Types
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*
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* Not all implementations will be available on all platforms.
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*
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*/
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enum ast_spinlock_type {
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AST_SPINLOCK_TYPE_GCC_ATOMICS,
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AST_SPINLOCK_TYPE_GAS_X86,
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AST_SPINLOCK_TYPE_GAS_ARM,
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AST_SPINLOCK_TYPE_GAS_SPARC,
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AST_SPINLOCK_TYPE_OSX_ATOMICS,
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AST_SPINLOCK_TYPE_PTHREAD_SPINLOCK,
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AST_SPINLOCK_TYPE_PTHREAD_MUTEX,
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};
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/*!
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* \brief Implementation using GCC Atomics
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*
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* Specifically, __sync_lock_test_and_set is used to atomically
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* set/unset the lock variable.
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*
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* Most recent gcc implementations support this method and it's performance
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* is equal to or better than the assembly implementations hence it is the
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* most preferred implementation on all platforms.
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*
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*/
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#ifdef HAVE_GCC_ATOMICS
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#define AST_SPINLOCK_TYPE AST_SPINLOCK_TYPE_GCC_ATOMICS
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#define AST_SPINLOCK_TYPE_LABEL "gcc_atomics"
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typedef volatile unsigned int ast_spinlock_t;
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static force_inline int ast_spinlock_init(ast_spinlock_t *lock)
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{
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*lock = 0;
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return 0;
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}
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static force_inline int ast_spinlock_lock(ast_spinlock_t *lock)
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{
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while (__sync_lock_test_and_set(lock, 1)) {
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while(*lock) {
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}
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}
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return 0;
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}
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static force_inline int ast_spinlock_trylock(ast_spinlock_t *lock)
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{
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return __sync_lock_test_and_set(lock, 1);
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}
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static force_inline int ast_spinlock_unlock(ast_spinlock_t *lock)
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{
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__sync_lock_release(lock);
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return 0;
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}
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#endif
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/*!
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* \brief Implementation using x86 Assembly
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*
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* For x86 implementations that don't support gcc atomics,
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* this is the next best method.
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*
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*/
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#if (defined(__x86_64__) || defined(__i386__)) && !defined(AST_SPINLOCK_TYPE)
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#define AST_SPINLOCK_TYPE AST_SPINLOCK_TYPE_GAS_X86
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#define AST_SPINLOCK_TYPE_LABEL "gas_x86"
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typedef volatile unsigned int ast_spinlock_t;
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static force_inline int ast_spinlock_init(ast_spinlock_t *lock)
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{
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*lock = 0;
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return 0;
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}
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static force_inline int x86chgl(ast_spinlock_t *p, unsigned int v)
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{
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__asm __volatile (
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" xchg %0, %1 ;"
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: "+r" (v), "=m" (*p)
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: "m" (*p)
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);
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return (v);
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}
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static force_inline int ast_spinlock_lock(ast_spinlock_t *lock)
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{
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while (x86chgl(lock, 1)) {
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while(*lock) {
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}
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}
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return 0;
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}
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static force_inline int ast_spinlock_trylock(ast_spinlock_t *lock)
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{
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return x86chgl(lock, 1);
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}
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static force_inline int ast_spinlock_unlock(ast_spinlock_t *lock)
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{
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x86chgl(lock, 0);
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return 0;
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}
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#endif
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/*!
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* \brief Implementation using ARM Assembly
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*
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* For ARM implementations that don't support gcc atomics,
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* this is the next best method.
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*
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*/
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#if defined(__arm__) && !defined(AST_SPINLOCK_TYPE)
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#define AST_SPINLOCK_TYPE AST_SPINLOCK_TYPE_GAS_ARM
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#define AST_SPINLOCK_TYPE_LABEL "gas_arm"
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typedef volatile unsigned int ast_spinlock_t;
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static force_inline int ast_spinlock_init(ast_spinlock_t *lock)
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{
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*lock = 0;
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return 0;
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}
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static force_inline int ast_spinlock_lock(ast_spinlock_t *lock)
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{
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unsigned int tmp;
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__asm __volatile (
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"1: ldrex %[tmp], %[lock];"
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" teq %[tmp], #0;"
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#if defined __ARM_ARCH && __ARM_ARCH >= 7
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" wfene;"
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#endif
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" strexeq %[tmp], %[c1], %[lock];"
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" teqeq %[tmp], #0;"
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" bne 1b;"
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: [tmp] "=&r" (tmp)
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: [lock] "m" (*lock) [c1] "r" (1)
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: "cc"
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);
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return tmp;
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}
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static force_inline int ast_spinlock_trylock(ast_spinlock_t *lock)
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{
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unsigned int tmp;
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__asm __volatile (
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" ldrex %[tmp], %[lock];"
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" teq %[tmp], #0;"
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#if defined __ARM_ARCH && __ARM_ARCH >= 7
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" wfene;"
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#endif
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" strexeq %[tmp], %[c1], %[lock];"
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: [tmp] "=&r" (tmp)
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: [lock] "m" (*lock) [c1] "r" (1)
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: "cc"
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);
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return tmp;
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}
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static force_inline int ast_spinlock_unlock(ast_spinlock_t *lock)
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{
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__asm __volatile (
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" dmb;"
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" str %[c0], %[lock];"
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#if defined __ARM_ARCH && __ARM_ARCH >= 7
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" dsb;"
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" sev;"
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#endif
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:
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: [lock] "m" (*lock) [c0] "r" (0)
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: "cc"
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);
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return 0;
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}
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#endif
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/*!
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* \brief Implementation using Sparc Assembly
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*
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* For Sparc implementations that don't support gcc atomics,
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* this is the next best method.
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*
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*/
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#if defined(__sparc__) && !defined(AST_SPINLOCK_TYPE)
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#define AST_SPINLOCK_TYPE AST_SPINLOCK_TYPE_GAS_SPARC
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#define AST_SPINLOCK_TYPE_LABEL "gas_sparc"
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typedef volatile unsigned char ast_spinlock_t;
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static force_inline int ast_spinlock_init(ast_spinlock_t *lock)
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{
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*lock = 0;
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return 0;
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}
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static force_inline int ast_spinlock_lock(ast_spinlock_t *lock)
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{
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unsigned char tmp;
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__asm__ __volatile__(
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"1: ldstub %[lock], %[tmp]\n"
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" brnz,pn %[tmp], 2f\n"
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" nop\n"
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" .subsection 2\n"
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"2: ldub %[lock], %[tmp]\n"
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" brnz,pt %[tmp], 2b\n"
|
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" nop\n"
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" ba,a,pt %%xcc, 1b\n"
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" .previous"
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: [tmp] "=&r" (tmp)
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: [lock] "m" (*lock)
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: "memory"
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);
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return 0;
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}
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static force_inline int ast_spinlock_trylock(ast_spinlock_t *lock)
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{
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unsigned long result = 1;
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__asm__ __volatile__(
|
||||
" ldstub %[lock], %[result]\n"
|
||||
: [result] "=&r" (result)
|
||||
: [lock] "m" (*lock)
|
||||
: "memory", "cc"
|
||||
);
|
||||
|
||||
return (result != 0);
|
||||
}
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||||
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static force_inline int ast_spinlock_unlock(ast_spinlock_t *lock)
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{
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__asm__ __volatile__(
|
||||
" stb %%g0, %[lock]"
|
||||
:
|
||||
: [lock] "m" (*lock)
|
||||
: "memory", "cc"
|
||||
);
|
||||
|
||||
return 0;
|
||||
}
|
||||
#endif
|
||||
|
||||
/*!
|
||||
* \brief Implementation using pthread_spinlock
|
||||
*
|
||||
* pthread_spinlocks are not supported on all platforms
|
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* but if for some reason none of the previous implementations are
|
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* available, it can be used with reasonable performance.
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*
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*/
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#if defined (HAVE_PTHREAD_SPINLOCK) && !defined(AST_SPINLOCK_TYPE)
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#define AST_SPINLOCK_TYPE AST_SPINLOCK_TYPE_PTHREAD_SPINLOCK
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#define AST_SPINLOCK_TYPE_LABEL "pthread_spinlock"
|
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typedef pthread_spinlock_t ast_spinlock_t;
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||||
|
||||
static force_inline int ast_spinlock_init(ast_spinlock_t *lock)
|
||||
{
|
||||
return pthread_spin_init(lock, PTHREAD_PROCESS_PRIVATE);
|
||||
}
|
||||
|
||||
static force_inline int ast_spinlock_lock(ast_spinlock_t *lock)
|
||||
{
|
||||
return pthread_spin_lock(lock);
|
||||
}
|
||||
|
||||
static force_inline int ast_spinlock_trylock(ast_spinlock_t *lock)
|
||||
{
|
||||
return pthread_spin_trylock(lock);
|
||||
}
|
||||
|
||||
static force_inline int ast_spinlock_unlock(ast_spinlock_t *lock)
|
||||
{
|
||||
return pthread_spin_unlock(lock);
|
||||
}
|
||||
#endif
|
||||
|
||||
/*!
|
||||
* \brief Implementation using OSX Atomics
|
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*
|
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* The Darwin/Mac OSX platform has its own atomics
|
||||
* implementation but it uses more kernel time than
|
||||
* GCC atomics and x86 assembly. It is included
|
||||
* as an unlikely fallback.
|
||||
*
|
||||
*/
|
||||
#if defined(HAVE_OSX_ATOMICS) && !defined(AST_SPINLOCK_TYPE)
|
||||
#include <libkern/OSAtomic.h>
|
||||
#define AST_SPINLOCK_TYPE AST_SPINLOCK_TYPE_OSX_ATOMICS
|
||||
#define AST_SPINLOCK_TYPE_LABEL "osx_atomics"
|
||||
typedef OSSpinLock ast_spinlock_t;
|
||||
|
||||
static force_inline int ast_spinlock_init(ast_spinlock_t *lock)
|
||||
{
|
||||
*lock = OS_SPINLOCK_INIT;
|
||||
return 0;
|
||||
}
|
||||
|
||||
static force_inline int ast_spinlock_lock(ast_spinlock_t *lock)
|
||||
{
|
||||
OSSpinLockLock(lock);
|
||||
return 0;
|
||||
}
|
||||
|
||||
static force_inline int ast_spinlock_trylock(ast_spinlock_t *lock)
|
||||
{
|
||||
return !OSSpinLockTry(lock);
|
||||
}
|
||||
|
||||
static force_inline int ast_spinlock_unlock(ast_spinlock_t *lock)
|
||||
{
|
||||
OSSpinLockUnlock(lock);
|
||||
return 0;
|
||||
}
|
||||
#endif
|
||||
|
||||
/*!
|
||||
* \brief Implementation using pthread_mutex
|
||||
*
|
||||
* pthread_mutex is supported on all platforms but
|
||||
* it is also the worst performing. It is included
|
||||
* as an unlikely fallback.
|
||||
*
|
||||
*/
|
||||
#if !defined(AST_SPINLOCK_TYPE)
|
||||
#define AST_SPINLOCK_TYPE AST_SPINLOCK_TYPE_PTHREAD_MUTEX
|
||||
#define AST_SPINLOCK_TYPE_LABEL "pthread_mutex"
|
||||
typedef pthread_mutex_t ast_spinlock_t;
|
||||
|
||||
static force_inline int ast_spinlock_init(ast_spinlock_t *lock)
|
||||
{
|
||||
pthread_mutex_init(lock, NULL);
|
||||
return 0;
|
||||
}
|
||||
|
||||
static force_inline int ast_spinlock_lock(ast_spinlock_t *lock)
|
||||
{
|
||||
return pthread_mutex_lock(lock);
|
||||
}
|
||||
|
||||
static force_inline int ast_spinlock_trylock(ast_spinlock_t *lock)
|
||||
{
|
||||
return pthread_mutex_trylock(lock);
|
||||
}
|
||||
|
||||
static force_inline int ast_spinlock_unlock(ast_spinlock_t *lock)
|
||||
{
|
||||
return pthread_mutex_unlock(lock);
|
||||
}
|
||||
#endif
|
||||
|
||||
#if !defined(AST_SPINLOCK_TYPE)
|
||||
#error "No spinlock implementation could be found."
|
||||
#endif
|
||||
|
||||
/* Prototypes are declared here to insure that each implementation provides
|
||||
* the same API and to act as placeholders for the documentation.
|
||||
*/
|
||||
|
||||
/*!
|
||||
* \brief Initialize a spin lock
|
||||
* \param lock Address of the lock
|
||||
* \retval 0 Success
|
||||
* \retval other Failure
|
||||
*/
|
||||
static force_inline int ast_spinlock_init(ast_spinlock_t *lock);
|
||||
|
||||
/*!
|
||||
* \brief Lock a spin lock
|
||||
* \param lock Address of the lock
|
||||
* \retval 0 Success
|
||||
* \retval other Failure
|
||||
*/
|
||||
static force_inline int ast_spinlock_lock(ast_spinlock_t *lock);
|
||||
|
||||
/*!
|
||||
* \brief Try to lock a spin lock
|
||||
*
|
||||
* Attempt to gain a lock. Return immediately
|
||||
* regardless of result.
|
||||
*
|
||||
* \param lock Address of the lock
|
||||
* \retval 0 Success
|
||||
* \retval other Lock was not obtained
|
||||
*/
|
||||
static force_inline int ast_spinlock_trylock(ast_spinlock_t *lock);
|
||||
|
||||
/*!
|
||||
* \brief Unlock a spin lock
|
||||
* \param lock Address of the lock
|
||||
* \retval 0 Success
|
||||
* \retval other Failure
|
||||
*/
|
||||
static force_inline int ast_spinlock_unlock(ast_spinlock_t *lock);
|
||||
|
||||
#endif /* _ASTERISK_SPINLOCK_H */
|
||||
Loading…
Reference in New Issue