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This patch adds support for spinlocks in Asterisk.

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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
2014-04-23 20:13:30 +00:00
parent e6c4b97521
commit 64045f0b57
4 changed files with 523 additions and 1 deletions
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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
AC_MSG_RESULT(no)
)
AC_MSG_CHECKING(for PTHREAD_MUTEX_ADAPTIVE_NP in pthread.h)
AC_LINK_IFELSE(
[AC_LANG_PROGRAM([#include <pthread.h>], [int a = PTHREAD_MUTEX_ADAPTIVE_NP;])],
AC_MSG_RESULT(yes)
AC_DEFINE([HAVE_PTHREAD_MUTEX_ADAPTIVE_NP], 1, [Define to 1 if your system defines PTHREAD_MUTEX_ADAPTIVE_NP in pthread.h]),
AC_MSG_RESULT(no)
)
AC_MSG_CHECKING(for pthread_spinlock_t in pthread.h)
AC_LINK_IFELSE(
[AC_LANG_PROGRAM([#include <pthread.h>], [pthread_spinlock_t spin;])],
AC_MSG_RESULT(yes)
AC_DEFINE([HAVE_PTHREAD_SPINLOCK], 1, [Define to 1 if your system has pthread_spinlock_t in pthread.h]),
AC_MSG_RESULT(no)
)
save_LIBS="$LIBS"
save_CFLAGS="$CFLAGS"
LIBS="$PTHREAD_LIBS $LIBS"