#include "gslice.h"
#include "gmessages.h"
#include "gstrfuncs.h"
+#include "gmain.h"
#include <stdlib.h>
#include <stdio.h>
#include <windows.h>
#endif
+/* clang defines __ATOMIC_SEQ_CST but doesn't support the GCC extension */
+#if defined(HAVE_FUTEX) && defined(__ATOMIC_SEQ_CST) && !defined(__clang__)
+#define USE_NATIVE_MUTEX
+#endif
+
static void
g_thread_abort (gint status,
const gchar *function)
/* {{{1 GMutex */
+#if !defined(USE_NATIVE_MUTEX)
+
static pthread_mutex_t *
g_mutex_impl_new (void)
{
pthread_mutexattr_t *pattr = NULL;
pthread_mutex_t *mutex;
gint status;
+#ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
+ pthread_mutexattr_t attr;
+#endif
mutex = malloc (sizeof (pthread_mutex_t));
if G_UNLIKELY (mutex == NULL)
g_thread_abort (errno, "malloc");
#ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
- {
- pthread_mutexattr_t attr;
- pthread_mutexattr_init (&attr);
- pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_ADAPTIVE_NP);
- pattr = &attr;
- }
+ pthread_mutexattr_init (&attr);
+ pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_ADAPTIVE_NP);
+ pattr = &attr;
#endif
if G_UNLIKELY ((status = pthread_mutex_init (mutex, pattr)) != 0)
free (mutex);
}
-static pthread_mutex_t *
+static inline pthread_mutex_t *
g_mutex_get_impl (GMutex *mutex)
{
pthread_mutex_t *impl = g_atomic_pointer_get (&mutex->p);
* It is not necessary to initialize a mutex that has been
* statically allocated.
*
- * |[
+ * |[<!-- language="C" -->
* typedef struct {
* GMutex m;
* ...
* current thread will block until @mutex is unlocked by the other
* thread.
*
- * <note>#GMutex is neither guaranteed to be recursive nor to be
+ * #GMutex is neither guaranteed to be recursive nor to be
* non-recursive. As such, calling g_mutex_lock() on a #GMutex that has
* already been locked by the same thread results in undefined behaviour
- * (including but not limited to deadlocks).</note>
+ * (including but not limited to deadlocks).
*/
void
g_mutex_lock (GMutex *mutex)
* it immediately returns %FALSE. Otherwise it locks @mutex and returns
* %TRUE.
*
- * <note>#GMutex is neither guaranteed to be recursive nor to be
+ * #GMutex is neither guaranteed to be recursive nor to be
* non-recursive. As such, calling g_mutex_lock() on a #GMutex that has
* already been locked by the same thread results in undefined behaviour
* (including but not limited to deadlocks or arbitrary return values).
- * </note>
* Returns: %TRUE if @mutex could be locked
*/
return FALSE;
}
+#endif /* !defined(USE_NATIVE_MUTEX) */
+
/* {{{1 GRecMutex */
static pthread_mutex_t *
free (mutex);
}
-static pthread_mutex_t *
+static inline pthread_mutex_t *
g_rec_mutex_get_impl (GRecMutex *rec_mutex)
{
pthread_mutex_t *impl = g_atomic_pointer_get (&rec_mutex->p);
* It is not necessary to initialise a recursive mutex that has been
* statically allocated.
*
- * |[
+ * |[<!-- language="C" -->
* typedef struct {
* GRecMutex m;
* ...
free (rwlock);
}
-static pthread_rwlock_t *
+static inline pthread_rwlock_t *
g_rw_lock_get_impl (GRWLock *lock)
{
pthread_rwlock_t *impl = g_atomic_pointer_get (&lock->p);
* necessary to initialise a reader-writer lock that has been statically
* allocated.
*
- * |[
+ * |[<!-- language="C" -->
* typedef struct {
* GRWLock l;
* ...
/* {{{1 GCond */
+#if !defined(USE_NATIVE_MUTEX)
+
static pthread_cond_t *
g_cond_impl_new (void)
{
gint status;
pthread_condattr_init (&attr);
-#if defined (HAVE_PTHREAD_CONDATTR_SETCLOCK) && defined (CLOCK_MONOTONIC)
- pthread_condattr_setclock (&attr, CLOCK_MONOTONIC);
+
+#ifdef HAVE_PTHREAD_COND_TIMEDWAIT_RELATIVE_NP
+#elif defined (HAVE_PTHREAD_CONDATTR_SETCLOCK) && defined (CLOCK_MONOTONIC)
+ if G_UNLIKELY ((status = pthread_condattr_setclock (&attr, CLOCK_MONOTONIC)) != 0)
+ g_thread_abort (status, "pthread_condattr_setclock");
+#else
+#error Cannot support GCond on your platform.
#endif
cond = malloc (sizeof (pthread_cond_t));
free (cond);
}
-static pthread_cond_t *
+static inline pthread_cond_t *
g_cond_get_impl (GCond *cond)
{
pthread_cond_t *impl = g_atomic_pointer_get (&cond->p);
* passed.
*
* The following code shows how to correctly perform a timed wait on a
- * condition variable (extended the example presented in the
+ * condition variable (extending the example presented in the
* documentation for #GCond):
*
- * |[
+ * |[<!-- language="C" -->
* gpointer
* pop_data_timed (void)
* {
struct timespec ts;
gint status;
- ts.tv_sec = end_time / 1000000;
- ts.tv_nsec = (end_time % 1000000) * 1000;
+#ifdef HAVE_PTHREAD_COND_TIMEDWAIT_RELATIVE_NP
+ /* end_time is given relative to the monotonic clock as returned by
+ * g_get_monotonic_time().
+ *
+ * Since this pthreads wants the relative time, convert it back again.
+ */
+ {
+ gint64 now = g_get_monotonic_time ();
+ gint64 relative;
-#if defined(HAVE_PTHREAD_COND_TIMEDWAIT_MONOTONIC)
- if ((status = pthread_cond_timedwait_monotonic (g_cond_get_impl (cond), g_mutex_get_impl (mutex), &ts)) == 0)
- return TRUE;
-#elif defined(HAVE_PTHREAD_COND_TIMEDWAIT_MONOTONIC_NP)
- if ((status = pthread_cond_timedwait_monotonic_np (g_cond_get_impl (cond), g_mutex_get_impl (mutex), &ts)) == 0)
- return TRUE;
+ if (end_time <= now)
+ return FALSE;
+
+ relative = end_time - now;
+
+ ts.tv_sec = relative / 1000000;
+ ts.tv_nsec = (relative % 1000000) * 1000;
+
+ if ((status = pthread_cond_timedwait_relative_np (g_cond_get_impl (cond), g_mutex_get_impl (mutex), &ts)) == 0)
+ return TRUE;
+ }
+#elif defined (HAVE_PTHREAD_CONDATTR_SETCLOCK) && defined (CLOCK_MONOTONIC)
+ /* This is the exact check we used during init to set the clock to
+ * monotonic, so if we're in this branch, timedwait() will already be
+ * expecting a monotonic clock.
+ */
+ {
+ ts.tv_sec = end_time / 1000000;
+ ts.tv_nsec = (end_time % 1000000) * 1000;
+
+ if ((status = pthread_cond_timedwait (g_cond_get_impl (cond), g_mutex_get_impl (mutex), &ts)) == 0)
+ return TRUE;
+ }
#else
- /* Pray that the cond is actually using the monotonic clock */
- if ((status = pthread_cond_timedwait (g_cond_get_impl (cond), g_mutex_get_impl (mutex), &ts)) == 0)
- return TRUE;
+#error Cannot support GCond on your platform.
#endif
if G_UNLIKELY (status != ETIMEDOUT)
return FALSE;
}
+#endif /* defined(USE_NATIVE_MUTEX) */
+
/* {{{1 GPrivate */
/**
* See G_PRIVATE_INIT() for a couple of examples.
*
* The #GPrivate structure should be considered opaque. It should only
- * be accessed via the <function>g_private_</function> functions.
+ * be accessed via the g_private_ functions.
*/
/**
* be properly initialised by default (ie: to all zeros). See the
* examples below.
*
- * |[
+ * |[<!-- language="C" -->
* static GPrivate name_key = G_PRIVATE_INIT (g_free);
*
* // return value should not be freed
free (key);
}
-static pthread_key_t *
+static inline pthread_key_t *
g_private_get_impl (GPrivate *key)
{
pthread_key_t *impl = g_atomic_pointer_get (&key->p);
#endif
}
-/* {{{1 Epilogue */
+/* {{{1 GMutex and GCond futex implementation */
+
+#if defined(USE_NATIVE_MUTEX)
+
+#include <linux/futex.h>
+#include <sys/syscall.h>
+
+/* We should expand the set of operations available in gatomic once we
+ * have better C11 support in GCC in common distributions (ie: 4.9).
+ *
+ * Before then, let's define a couple of useful things for our own
+ * purposes...
+ */
+
+#define exchange_acquire(ptr, new) \
+ __atomic_exchange_4((ptr), (new), __ATOMIC_ACQUIRE)
+#define compare_exchange_acquire(ptr, old, new) \
+ __atomic_compare_exchange_4((ptr), (old), (new), 0, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)
+
+#define exchange_release(ptr, new) \
+ __atomic_exchange_4((ptr), (new), __ATOMIC_RELEASE)
+#define store_release(ptr, new) \
+ __atomic_store_4((ptr), (new), __ATOMIC_RELEASE)
+
+/* Our strategy for the mutex is pretty simple:
+ *
+ * 0: not in use
+ *
+ * 1: acquired by one thread only, no contention
+ *
+ * > 1: contended
+ *
+ *
+ * As such, attempting to acquire the lock should involve an increment.
+ * If we find that the previous value was 0 then we can return
+ * immediately.
+ *
+ * On unlock, we always store 0 to indicate that the lock is available.
+ * If the value there was 1 before then we didn't have contention and
+ * can return immediately. If the value was something other than 1 then
+ * we have the contended case and need to wake a waiter.
+ *
+ * If it was not 0 then there is another thread holding it and we must
+ * wait. We must always ensure that we mark a value >1 while we are
+ * waiting in order to instruct the holder to do a wake operation on
+ * unlock.
+ */
+
+void
+g_mutex_init (GMutex *mutex)
+{
+ mutex->i[0] = 0;
+}
+
+void
+g_mutex_clear (GMutex *mutex)
+{
+ if G_UNLIKELY (mutex->i[0] != 0)
+ {
+ fprintf (stderr, "g_mutex_clear() called on uninitialised or locked mutex\n");
+ abort ();
+ }
+}
+
+static void __attribute__((noinline))
+g_mutex_lock_slowpath (GMutex *mutex)
+{
+ /* Set to 2 to indicate contention. If it was zero before then we
+ * just acquired the lock.
+ *
+ * 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);
+}
+
+static void __attribute__((noinline))
+g_mutex_unlock_slowpath (GMutex *mutex,
+ guint prev)
+{
+ /* We seem to get better code for the uncontended case by splitting
+ * this out...
+ */
+ if G_UNLIKELY (prev == 0)
+ {
+ fprintf (stderr, "Attempt to unlock mutex that was not locked\n");
+ abort ();
+ }
+
+ syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAKE, (gsize) 1, NULL);
+}
+
+void
+g_mutex_lock (GMutex *mutex)
+{
+ /* 0 -> 1 and we're done. Anything else, and we need to wait... */
+ if G_UNLIKELY (g_atomic_int_add (&mutex->i[0], 1) != 0)
+ g_mutex_lock_slowpath (mutex);
+}
+
+void
+g_mutex_unlock (GMutex *mutex)
+{
+ guint prev;
+
+ prev = exchange_release (&mutex->i[0], 0);
+
+ /* 1-> 0 and we're done. Anything else and we need to signal... */
+ if G_UNLIKELY (prev != 1)
+ g_mutex_unlock_slowpath (mutex, prev);
+}
+
+gboolean
+g_mutex_trylock (GMutex *mutex)
+{
+ guint zero = 0;
+
+ /* We don't want to touch the value at all unless we can move it from
+ * exactly 0 to 1.
+ */
+ return compare_exchange_acquire (&mutex->i[0], &zero, 1);
+}
+
+/* Condition variables are implemented in a rather simple way as well.
+ * In many ways, futex() as an abstraction is even more ideally suited
+ * to condition variables than it is to mutexes.
+ *
+ * We store a generation counter. We sample it with the lock held and
+ * unlock before sleeping on the futex.
+ *
+ * Signalling simply involves increasing the counter and making the
+ * appropriate futex call.
+ *
+ * The only thing that is the slightest bit complicated is timed waits
+ * because we must convert our absolute time to relative.
+ */
+
+void
+g_cond_init (GCond *cond)
+{
+ cond->i[0] = 0;
+}
+
+void
+g_cond_clear (GCond *cond)
+{
+}
+
+void
+g_cond_wait (GCond *cond,
+ GMutex *mutex)
+{
+ 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);
+ g_mutex_lock (mutex);
+}
+
+void
+g_cond_signal (GCond *cond)
+{
+ g_atomic_int_inc (&cond->i[0]);
+
+ syscall (__NR_futex, &cond->i[0], (gsize) FUTEX_WAKE, (gsize) 1, NULL);
+}
+
+void
+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);
+}
+
+gboolean
+g_cond_wait_until (GCond *cond,
+ GMutex *mutex,
+ gint64 end_time)
+{
+ struct timespec now;
+ struct timespec span;
+ guint sampled;
+ int res;
+
+ if (end_time < 0)
+ return FALSE;
+
+ clock_gettime (CLOCK_MONOTONIC, &now);
+ span.tv_sec = (end_time / 1000000) - now.tv_sec;
+ span.tv_nsec = ((end_time % 1000000) * 1000) - now.tv_nsec;
+ if (span.tv_nsec < 0)
+ {
+ span.tv_nsec += 1000000000;
+ span.tv_sec--;
+ }
+
+ if (span.tv_sec < 0)
+ return FALSE;
+
+ sampled = cond->i[0];
+ g_mutex_unlock (mutex);
+ res = syscall (__NR_futex, &cond->i[0], (gsize) FUTEX_WAIT, (gsize) sampled, &span);
+ g_mutex_lock (mutex);
+
+ return (res < 0 && errno == ETIMEDOUT) ? FALSE : TRUE;
+}
+
+#endif
+
+ /* {{{1 Epilogue */
/* vim:set foldmethod=marker: */
projects / platform / upstream / glib.git / blobdiff