mips: Ensure PC update with MTC0 single-stepping
[qemu.git] / util / rfifolock.c
1 /*
2 * Recursive FIFO lock
3 *
4 * Copyright Red Hat, Inc. 2013
5 *
6 * Authors:
7 * Stefan Hajnoczi <stefanha@redhat.com>
8 *
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.
11 *
12 */
13
14 #include <assert.h>
15 #include "qemu/rfifolock.h"
16
17 void rfifolock_init(RFifoLock *r, void (*cb)(void *), void *opaque)
18 {
19 qemu_mutex_init(&r->lock);
20 r->head = 0;
21 r->tail = 0;
22 qemu_cond_init(&r->cond);
23 r->nesting = 0;
24 r->cb = cb;
25 r->cb_opaque = opaque;
26 }
27
28 void rfifolock_destroy(RFifoLock *r)
29 {
30 qemu_cond_destroy(&r->cond);
31 qemu_mutex_destroy(&r->lock);
32 }
33
34 /*
35 * Theory of operation:
36 *
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.
40 *
41 * Recursive locking does not take a ticket since the head is only incremented
42 * when the outermost recursive caller unlocks.
43 */
44 void rfifolock_lock(RFifoLock *r)
45 {
46 qemu_mutex_lock(&r->lock);
47
48 /* Take a ticket */
49 unsigned int ticket = r->tail++;
50
51 if (r->nesting > 0 && qemu_thread_is_self(&r->owner_thread)) {
52 r->tail--; /* put ticket back, we're nesting */
53 } else {
54 while (ticket != r->head) {
55 /* Invoke optional contention callback */
56 if (r->cb) {
57 r->cb(r->cb_opaque);
58 }
59 qemu_cond_wait(&r->cond, &r->lock);
60 }
61 }
62
63 qemu_thread_get_self(&r->owner_thread);
64 r->nesting++;
65 qemu_mutex_unlock(&r->lock);
66 }
67
68 void rfifolock_unlock(RFifoLock *r)
69 {
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) {
74 r->head++;
75 qemu_cond_broadcast(&r->cond);
76 }
77 qemu_mutex_unlock(&r->lock);
78 }