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gthread-posix: Use named states to manage the mutex states

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We used to use raw numbers to control the mutex state, we can use a
nicer enum to avoid dealing with pure numbers.
This commit is contained in:
Marco Trevisan (Treviño) 2022-06-23 06:26:34 +02:00
parent 15d2053122
commit 8d98617297
1 changed files with 29 additions and 17 deletions
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46
glib/gthread-posix.c
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@ -1449,9 +1449,16 @@ g_system_thread_set_name (const gchar *name)
*
* 1: acquired by one thread only, no contention
*
* > 1: contended
*
*
* 2: contended
*/
typedef enum {
G_MUTEX_STATE_EMPTY = 0,
G_MUTEX_STATE_OWNED,
G_MUTEX_STATE_CONTENDED,
} GMutexState;
/*
* 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.
@ -1470,13 +1477,13 @@ g_system_thread_set_name (const gchar *name)
void
g_mutex_init (GMutex *mutex)
{
mutex->i[0] = 0;
mutex->i[0] = G_MUTEX_STATE_EMPTY;
}
void
g_mutex_clear (GMutex *mutex)
{
if G_UNLIKELY (mutex->i[0] != 0)
if G_UNLIKELY (mutex->i[0] != G_MUTEX_STATE_EMPTY)
{
fprintf (stderr, "g_mutex_clear() called on uninitialised or locked mutex\n");
g_abort ();
@ -1486,13 +1493,16 @@ g_mutex_clear (GMutex *mutex)
static void __attribute__((noinline))
g_mutex_lock_slowpath (GMutex *mutex)
{
/* Set to 2 to indicate contention. If it was zero before then we
/* Set to contended. If it was empty before then we
* just acquired the lock.
*
* Otherwise, sleep for as long as the 2 remains...
* Otherwise, sleep for as long as the contended state remains...
*/
while (exchange_acquire (&mutex->i[0], 2) != 0)
syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAIT_PRIVATE, (gsize) 2, NULL);
while (exchange_acquire (&mutex->i[0], G_MUTEX_STATE_CONTENDED) != G_MUTEX_STATE_EMPTY)
{
syscall (__NR_futex, &mutex->i[0], (gsize) FUTEX_WAIT_PRIVATE,
G_MUTEX_STATE_CONTENDED, NULL);
}
}
static void __attribute__((noinline))
@ -1502,7 +1512,7 @@ g_mutex_unlock_slowpath (GMutex *mutex,
/* We seem to get better code for the uncontended case by splitting
* this out...
*/
if G_UNLIKELY (prev == 0)
if G_UNLIKELY (prev == G_MUTEX_STATE_EMPTY)
{
fprintf (stderr, "Attempt to unlock mutex that was not locked\n");
g_abort ();
@ -1514,8 +1524,10 @@ g_mutex_unlock_slowpath (GMutex *mutex,
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)
/* empty -> owned and we're done. Anything else, and we need to wait... */
if G_UNLIKELY (!g_atomic_int_compare_and_exchange (&mutex->i[0],
G_MUTEX_STATE_EMPTY,
G_MUTEX_STATE_OWNED))
g_mutex_lock_slowpath (mutex);
}
@ -1524,22 +1536,22 @@ g_mutex_unlock (GMutex *mutex)
{
guint prev;
prev = exchange_release (&mutex->i[0], 0);
prev = exchange_release (&mutex->i[0], G_MUTEX_STATE_EMPTY);
/* 1-> 0 and we're done. Anything else and we need to signal... */
if G_UNLIKELY (prev != 1)
if G_UNLIKELY (prev != G_MUTEX_STATE_OWNED)
g_mutex_unlock_slowpath (mutex, prev);
}
gboolean
g_mutex_trylock (GMutex *mutex)
{
guint zero = 0;
GMutexState empty = G_MUTEX_STATE_EMPTY;
/* We don't want to touch the value at all unless we can move it from
* exactly 0 to 1.
* exactly empty to owned.
*/
return compare_exchange_acquire (&mutex->i[0], &zero, 1);
return compare_exchange_acquire (&mutex->i[0], &empty, G_MUTEX_STATE_OWNED);
}
/* Condition variables are implemented in a rather simple way as well.