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 
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 
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. */
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 
69 void coroutine_fn co_get_from_shres(SharedResource *s, uint64_t n)
70 {
71     assert(n <= s->total);
72     QEMU_LOCK_GUARD(&s->lock);
73     while (!co_try_get_from_shres_locked(s, n)) {
74         qemu_co_queue_wait(&s->queue, &s->lock);
75     }
76 }
77 
78 void coroutine_fn co_put_to_shres(SharedResource *s, uint64_t n)
79 {
80     QEMU_LOCK_GUARD(&s->lock);
81     assert(s->total - s->available >= n);
82     s->available += n;
83     qemu_co_queue_restart_all(&s->queue);
84 }
85