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add futex semaphore support derived from hutchinson port #50

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Merged
merged 1 commit into from
Feb 25, 2016
Merged

add futex semaphore support derived from hutchinson port #50

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5 changes: 5 additions & 0 deletions configure.ac
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Original file line number Diff line number Diff line change
Expand Up @@ -276,6 +276,8 @@ AC_CHECK_FUNC([sem_init],
[have_sem_init=true], [have_sem_init=false]
)

AC_CHECK_HEADER(linux/futex.h, [have_futex=true], [have_futex=false])

#
# We support both Mach semaphores and POSIX semaphores; if the former are
# available, prefer them.
Expand All @@ -284,6 +286,9 @@ AC_MSG_CHECKING([what semaphore type to use]);
AS_IF([test "x$have_mach" = "xtrue"],
[AC_DEFINE(USE_MACH_SEM, 1, [Define to use Mach semaphores])
AC_MSG_RESULT([Mach semaphores])],
[test "x$have_futex" = "xtrue"],
[AC_DEFINE(USE_FUTEX_SEM, 1, [Define to use Futex semaphores])
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USE_FUTEX sounds better, Futexes are not semaphores, it's more like "[Define to use futex(7) when appropriate]"

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What I mean is that I can tell you'll want to use FUTEX for other things, so I wouldn't make this scoped to "semaphores" only.

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In this particular case we want to be symmetric on the USE_xxxxx_SEM, so that should stay.
Will see whether we can be more generic here from which we derive USE_FUTEX_SEM.

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fair enough

AC_MSG_RESULT([Futex semaphores])],
[test "x$have_sem_init" = "xtrue"],
[AC_DEFINE(USE_POSIX_SEM, 1, [Define to use POSIX semaphores])
AC_MSG_RESULT([POSIX semaphores])],
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23 changes: 23 additions & 0 deletions src/internal.h
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Expand Up @@ -228,9 +228,14 @@ DISPATCH_EXPORT DISPATCH_NOTHROW void dispatch_atfork_child(void);
#endif
#include <limits.h>
#include <search.h>
#if USE_FUTEX_SEM
#include <sys/syscall.h>
#include <linux/futex.h>
#endif
#if USE_POSIX_SEM
#include <semaphore.h>
#endif

#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
Expand All @@ -242,6 +247,24 @@ DISPATCH_EXPORT DISPATCH_NOTHROW void dispatch_atfork_child(void);
#include <unistd.h>
#endif

#if defined(__APPLE__)
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#define DISPATCH_LITTLE_ENDIAN
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
#define DISPATCH_BIG_ENDIAN
#endif
#else
#include <endian.h>
#if __BYTE_ORDER == __LITTLE_ENDIAN
#define DISPATCH_LITTLE_ENDIAN
#elif __BYTE_ORDER == __BIG_ENDIAN
#define DISPATCH_BIG_ENDIAN
#else
#error "please define DISPATCH_LITTLE_ENDIAN or DISPATCH_BIG_ENDIAN for your architecture / platform"
#endif
#endif /* defined(__APPLE__) */


#ifndef __has_builtin
#define __has_builtin(x) 0
#endif
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2 changes: 2 additions & 0 deletions src/queue.c
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Expand Up @@ -879,6 +879,8 @@ _dispatch_root_queue_init_pthread_pool(dispatch_root_queue_context_t qc,
/* XXXRW: POSIX semaphores don't support LIFO? */
int ret = sem_init(&(pqc->dpq_thread_mediator.dsema_sem), 0, 0);
(void)dispatch_assume_zero(ret);
#elif USE_FUTEX_SEM
pqc->dpq_thread_mediator.dsema_futex = DISPATCH_FUTEX_INIT;
#endif
}
#endif // DISPATCH_USE_PTHREAD_POOL
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