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threads: use FUTEX_WAIT_PRIVATE and FUTEX_WAKE_PRIVATE if possible

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This avoids some expensive code paths in the kernel, see
http://lwn.net/Articles/229668/

https://bugzilla.gnome.org/show_bug.cgi?id=741442
This commit is contained in:
Tim-Philipp Müller 2014-12-12 01:38:24 +00:00 committed by Ryan Lortie
parent 6fffce2588
commit 627a145e16
2 changed files with 18 additions and 8 deletions
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9
glib/gbitlock.c
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@ -52,6 +52,11 @@ static GSList *g_futex_address_list = NULL;
#include <sys/syscall.h>
#include <unistd.h>
#ifndef FUTEX_WAIT_PRIVATE
#define FUTEX_WAIT_PRIVATE FUTEX_WAIT
#define FUTEX_WAKE_PRIVATE FUTEX_WAKE
#endif
/* < private >
* g_futex_wait:
* @address: a pointer to an integer
@ -73,7 +78,7 @@ static void
g_futex_wait (const volatile gint *address,
gint value)
{
syscall (__NR_futex, address, (gsize) FUTEX_WAIT, (gsize) value, NULL);
syscall (__NR_futex, address, (gsize) FUTEX_WAIT_PRIVATE, (gsize) value, NULL);
}
/* < private >
@ -90,7 +95,7 @@ g_futex_wait (const volatile gint *address,
static void
g_futex_wake (const volatile gint *address)
{
syscall (__NR_futex, address, (gsize) FUTEX_WAKE, (gsize) 1, NULL);
syscall (__NR_futex, address, (gsize) FUTEX_WAKE_PRIVATE, (gsize) 1, NULL);
}
#else

17
glib/gthread-posix.c
View File

@ -1239,6 +1239,11 @@ g_system_thread_set_name (const gchar *name)
#include <linux/futex.h>
#include <sys/syscall.h>
#ifndef FUTEX_WAIT_PRIVATE
#define FUTEX_WAIT_PRIVATE FUTEX_WAIT
#define FUTEX_WAKE_PRIVATE FUTEX_WAKE
#endif
/* We should expand the set of operations available in gatomic once we
* have better C11 support in GCC in common distributions (ie: 4.9).
*
@ -1305,7 +1310,7 @@ g_mutex_lock_slowpath (GMutex *mutex)
* Otherwise, sleep for as long as the 2 remains...
*/
while (exchange_acquire (&mutex->i[0], 2) != 0)
syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAIT, (gsize) 2, NULL);
syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAIT_PRIVATE, (gsize) 2, NULL);
}
static void __attribute__((noinline))
@ -1321,7 +1326,7 @@ g_mutex_unlock_slowpath (GMutex *mutex,
abort ();
}
syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAKE, (gsize) 1, NULL);
syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAKE_PRIVATE, (gsize) 1, NULL);
}
void
@ -1387,7 +1392,7 @@ g_cond_wait (GCond *cond,
guint sampled = g_atomic_int_get (&cond->i[0]);
g_mutex_unlock (mutex);
syscall (__NR_futex, &cond->i[0], (gsize) FUTEX_WAIT, (gsize) sampled, NULL);
syscall (__NR_futex, &cond->i[0], (gsize) FUTEX_WAIT_PRIVATE, (gsize) sampled, NULL);
g_mutex_lock (mutex);
}
@ -1396,7 +1401,7 @@ g_cond_signal (GCond *cond)
{
g_atomic_int_inc (&cond->i[0]);
syscall (__NR_futex, &cond->i[0], (gsize) FUTEX_WAKE, (gsize) 1, NULL);
syscall (__NR_futex, &cond->i[0], (gsize) FUTEX_WAKE_PRIVATE, (gsize) 1, NULL);
}
void
@ -1404,7 +1409,7 @@ g_cond_broadcast (GCond *cond)
{
g_atomic_int_inc (&cond->i[0]);
syscall (__NR_futex, &cond->i[0], (gsize) FUTEX_WAKE, (gsize) INT_MAX, NULL);
syscall (__NR_futex, &cond->i[0], (gsize) FUTEX_WAKE_PRIVATE, (gsize) INT_MAX, NULL);
}
gboolean
@ -1434,7 +1439,7 @@ g_cond_wait_until (GCond *cond,
sampled = cond->i[0];
g_mutex_unlock (mutex);
res = syscall (__NR_futex, &cond->i[0], (gsize) FUTEX_WAIT, (gsize) sampled, &span);
res = syscall (__NR_futex, &cond->i[0], (gsize) FUTEX_WAIT_PRIVATE, (gsize) sampled, &span);
g_mutex_lock (mutex);
return (res < 0 && errno == ETIMEDOUT) ? FALSE : TRUE;