util/qemu-co-shared-resource.c

   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 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
  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
  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 }