1 /*
2 * Helper functionality for distributing a fixed total amount of
3 * an abstract resource among multiple coroutines.
4 *
5 * Copyright (c) 2019 Virtuozzo International GmbH
6 *
7 * Permission is hereby granted, free of charge, to any person obtaining a copy
8 * of this software and associated documentation files (the "Software"), to deal
9 * in the Software without restriction, including without limitation the rights
10 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
11 * copies of the Software, and to permit persons to whom the Software is
12 * furnished to do so, subject to the following conditions:
13 *
14 * The above copyright notice and this permission notice shall be included in
15 * all copies or substantial portions of the Software.
16 *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
18 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
20 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
21 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
22 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
23 * THE SOFTWARE.
24 */
25
26 #include "qemu/osdep.h"
27 #include "qemu/coroutine.h"
28 #include "qemu/co-shared-resource.h"
29
30 struct SharedResource {
31 uint64_t total; /* Set in shres_create() and not changed anymore */
32
33 /* State fields protected by lock */
34 uint64_t available;
35 CoQueue queue;
36
37 QemuMutex lock;
38 };
39
shres_create(uint64_t total)40 SharedResource *shres_create(uint64_t total)
41 {
42 SharedResource *s = g_new0(SharedResource, 1);
43
44 s->total = s->available = total;
45 qemu_co_queue_init(&s->queue);
46 qemu_mutex_init(&s->lock);
47
48 return s;
49 }
50
shres_destroy(SharedResource * s)51 void shres_destroy(SharedResource *s)
52 {
53 assert(s->available == s->total);
54 qemu_mutex_destroy(&s->lock);
55 g_free(s);
56 }
57
58 /* Called with lock held. */
co_try_get_from_shres_locked(SharedResource * s,uint64_t n)59 static bool co_try_get_from_shres_locked(SharedResource *s, uint64_t n)
60 {
61 if (s->available >= n) {
62 s->available -= n;
63 return true;
64 }
65
66 return false;
67 }
68
co_try_get_from_shres(SharedResource * s,uint64_t n)69 bool co_try_get_from_shres(SharedResource *s, uint64_t n)
70 {
71 QEMU_LOCK_GUARD(&s->lock);
72 return co_try_get_from_shres_locked(s, n);
73 }
74
co_get_from_shres(SharedResource * s,uint64_t n)75 void coroutine_fn co_get_from_shres(SharedResource *s, uint64_t n)
76 {
77 assert(n <= s->total);
78 QEMU_LOCK_GUARD(&s->lock);
79 while (!co_try_get_from_shres_locked(s, n)) {
80 qemu_co_queue_wait(&s->queue, &s->lock);
81 }
82 }
83
co_put_to_shres(SharedResource * s,uint64_t n)84 void coroutine_fn co_put_to_shres(SharedResource *s, uint64_t n)
85 {
86 QEMU_LOCK_GUARD(&s->lock);
87 assert(s->total - s->available >= n);
88 s->available += n;
89 qemu_co_queue_restart_all(&s->queue);
90 }
91