4
* Copyright Red Hat, Inc. 2013
7
* Stefan Hajnoczi <stefanha@redhat.com>
9
* This work is licensed under the terms of the GNU LGPL, version 2 or later.
10
* See the COPYING.LIB file in the top-level directory.
15
#include "qemu/rfifolock.h"
17
void rfifolock_init(RFifoLock *r, void (*cb)(void *), void *opaque)
19
qemu_mutex_init(&r->lock);
22
qemu_cond_init(&r->cond);
25
r->cb_opaque = opaque;
28
void rfifolock_destroy(RFifoLock *r)
30
qemu_cond_destroy(&r->cond);
31
qemu_mutex_destroy(&r->lock);
35
* Theory of operation:
37
* In order to ensure FIFO ordering, implement a ticketlock. Threads acquiring
38
* the lock enqueue themselves by incrementing the tail index. When the lock
39
* is unlocked, the head is incremented and waiting threads are notified.
41
* Recursive locking does not take a ticket since the head is only incremented
42
* when the outermost recursive caller unlocks.
44
void rfifolock_lock(RFifoLock *r)
46
qemu_mutex_lock(&r->lock);
49
unsigned int ticket = r->tail++;
51
if (r->nesting > 0 && qemu_thread_is_self(&r->owner_thread)) {
52
r->tail--; /* put ticket back, we're nesting */
54
while (ticket != r->head) {
55
/* Invoke optional contention callback */
59
qemu_cond_wait(&r->cond, &r->lock);
63
qemu_thread_get_self(&r->owner_thread);
65
qemu_mutex_unlock(&r->lock);
68
void rfifolock_unlock(RFifoLock *r)
70
qemu_mutex_lock(&r->lock);
71
assert(r->nesting > 0);
72
assert(qemu_thread_is_self(&r->owner_thread));
73
if (--r->nesting == 0) {
75
qemu_cond_broadcast(&r->cond);
77
qemu_mutex_unlock(&r->lock);