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Remove dependency on sys_membarrier on linux #277

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Merged
merged 1 commit into from
Jul 14, 2017
Merged

Remove dependency on sys_membarrier on linux #277

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12 changes: 12 additions & 0 deletions dispatch/once.h
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,14 @@ __BEGIN_DECLS
DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
typedef long dispatch_once_t;

#if defined(__x86_64__) || defined(__i386__) || defined(__s390x__)
#define DISPATCH_ONCE_INLINE_FASTPATH 1
#elif defined(__APPLE__)
#define DISPATCH_ONCE_INLINE_FASTPATH 1
#else
#define DISPATCH_ONCE_INLINE_FASTPATH 0
#endif

/*!
* @function dispatch_once
*
Expand All @@ -65,6 +73,7 @@ void
dispatch_once(dispatch_once_t *predicate,
DISPATCH_NOESCAPE dispatch_block_t block);

#if DISPATCH_ONCE_INLINE_FASTPATH
DISPATCH_INLINE DISPATCH_ALWAYS_INLINE DISPATCH_NONNULL_ALL DISPATCH_NOTHROW
DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
void
Expand All @@ -81,6 +90,7 @@ _dispatch_once(dispatch_once_t *predicate,
#undef dispatch_once
#define dispatch_once _dispatch_once
#endif
#endif // DISPATCH_ONCE_INLINE_FASTPATH

API_AVAILABLE(macos(10.6), ios(4.0))
DISPATCH_EXPORT DISPATCH_NONNULL1 DISPATCH_NONNULL3 DISPATCH_NOTHROW
Expand All @@ -89,6 +99,7 @@ void
dispatch_once_f(dispatch_once_t *predicate, void *_Nullable context,
dispatch_function_t function);

#if DISPATCH_ONCE_INLINE_FASTPATH
DISPATCH_INLINE DISPATCH_ALWAYS_INLINE DISPATCH_NONNULL1 DISPATCH_NONNULL3
DISPATCH_NOTHROW
DISPATCH_SWIFT3_UNAVAILABLE("Use lazily initialized globals instead")
Expand All @@ -105,6 +116,7 @@ _dispatch_once_f(dispatch_once_t *predicate, void *_Nullable context,
}
#undef dispatch_once_f
#define dispatch_once_f _dispatch_once_f
#endif // DISPATCH_ONCE_INLINE_FASTPATH

__END_DECLS

Expand Down
24 changes: 21 additions & 3 deletions src/once.c
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Expand Up @@ -40,9 +40,15 @@ dispatch_once(dispatch_once_t *val, dispatch_block_t block)
}
#endif

DISPATCH_NOINLINE
void
dispatch_once_f(dispatch_once_t *val, void *ctxt, dispatch_function_t func)
#if DISPATCH_ONCE_INLINE_FASTPATH
#define DISPATCH_ONCE_SLOW_INLINE inline DISPATCH_ALWAYS_INLINE
#else
#define DISPATCH_ONCE_SLOW_INLINE DISPATCH_NOINLINE
#endif // DISPATCH_ONCE_INLINE_FASTPATH

DISPATCH_ONCE_SLOW_INLINE
static void
dispatch_once_f_slow(dispatch_once_t *val, void *ctxt, dispatch_function_t func)
{
#if DISPATCH_GATE_USE_FOR_DISPATCH_ONCE
dispatch_once_gate_t l = (dispatch_once_gate_t)val;
Expand Down Expand Up @@ -95,3 +101,15 @@ dispatch_once_f(dispatch_once_t *val, void *ctxt, dispatch_function_t func)
}
#endif
}

DISPATCH_NOINLINE
void
dispatch_once_f(dispatch_once_t *val, void *ctxt, dispatch_function_t func)
{
#if !DISPATCH_ONCE_INLINE_FASTPATH
if (likely(os_atomic_load(val, acquire) == DLOCK_ONCE_DONE)) {
return;
}
#endif // !DISPATCH_ONCE_INLINE_FASTPATH
return dispatch_once_f_slow(val, ctxt, func);
}
24 changes: 0 additions & 24 deletions src/shims/lock.h
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Original file line number Diff line number Diff line change
Expand Up @@ -59,9 +59,6 @@ _dispatch_lock_owner(dispatch_lock lock_value)
#elif defined(__linux__)

#include <linux/futex.h>
#if !defined(__x86_64__) && !defined(__i386__) && !defined(__s390x__)
#include <linux/membarrier.h>
#endif
#include <unistd.h>
#include <sys/syscall.h> /* For SYS_xxx definitions */

Expand Down Expand Up @@ -473,28 +470,7 @@ DISPATCH_ALWAYS_INLINE
static inline dispatch_once_t
_dispatch_once_xchg_done(dispatch_once_t *pred)
{
#if defined(__i386__) || defined(__x86_64__) || defined(__s390x__)
// On Intel, any load is a load-acquire, so we don't need to be fancy
// same for s390x
return os_atomic_xchg(pred, DLOCK_ONCE_DONE, release);
#elif defined(__linux__)
if (unlikely(syscall(__NR_membarrier, MEMBARRIER_CMD_SHARED, 0) < 0)) {
/*
* sys_membarrier not supported
*
* Ideally we would call DISPATCH_INTERNAL_CRASH() here, but
* due to ordering constraints in internal.h required by Darwin
* the macro is undefined when this header is included.
* Instead, open-code what would be a call to
* _dispatch_hardware_crash() inside DISPATCH_INTERNAL_CRASH().
*/
__asm__("");
__builtin_trap();
}
return os_atomic_xchg(pred, DLOCK_ONCE_DONE, relaxed);
#else
# error dispatch_once algorithm not available for this port
#endif
}

DISPATCH_ALWAYS_INLINE
Expand Down