async.c

   1 /*
   2  * QEMU System Emulator
   3  *
   4  * Copyright (c) 2003-2008 Fabrice Bellard
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to deal
   8  * in the Software without restriction, including without limitation the rights
   9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10  * copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  22  * THE SOFTWARE.
  23  */
  24
  25 #include "qemu-common.h"
  26 #include "block/aio.h"
  27 #include "block/thread-pool.h"
  28 #include "qemu/main-loop.h"
  29
  30 /***********************************************************/
  31 /* bottom halves (can be seen as timers which expire ASAP) */
  32
  33 struct QEMUBH {
  34     AioContext *ctx;
  35     QEMUBHFunc *cb;
  36     void *opaque;
  37     QEMUBH *next;
  38     bool scheduled;
  39     bool idle;
  40     bool deleted;
  41 };
  42
  43 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  44 {
  45     QEMUBH *bh;
  46     bh = g_malloc0(sizeof(QEMUBH));
  47     bh->ctx = ctx;
  48     bh->cb = cb;
  49     bh->opaque = opaque;
  50     qemu_mutex_lock(&ctx->bh_lock);
  51     bh->next = ctx->first_bh;
  52     /* Make sure that the members are ready before putting bh into list */
  53     smp_wmb();
  54     ctx->first_bh = bh;
  55     qemu_mutex_unlock(&ctx->bh_lock);
  56     return bh;
  57 }
  58
  59 /* Multiple occurrences of aio_bh_poll cannot be called concurrently */
  60 int aio_bh_poll(AioContext *ctx)
  61 {
  62     QEMUBH *bh, **bhp, *next;
  63     int ret;
  64
  65     ctx->walking_bh++;
  66
  67     ret = 0;
  68     for (bh = ctx->first_bh; bh; bh = next) {
  69         /* Make sure that fetching bh happens before accessing its members */
  70         smp_read_barrier_depends();
  71         next = bh->next;
  72         if (!bh->deleted && bh->scheduled) {
  73             bh->scheduled = 0;
  74             /* Paired with write barrier in bh schedule to ensure reading for
  75              * idle & callbacks coming after bh's scheduling.
  76              */
  77             smp_rmb();
  78             if (!bh->idle)
  79                 ret = 1;
  80             bh->idle = 0;
  81             bh->cb(bh->opaque);
  82         }
  83     }
  84
  85     ctx->walking_bh--;
  86
  87     /* remove deleted bhs */
  88     if (!ctx->walking_bh) {
  89         qemu_mutex_lock(&ctx->bh_lock);
  90         bhp = &ctx->first_bh;
  91         while (*bhp) {
  92             bh = *bhp;
  93             if (bh->deleted) {
  94                 *bhp = bh->next;
  95                 g_free(bh);
  96             } else {
  97                 bhp = &bh->next;
  98             }
  99         }
 100         qemu_mutex_unlock(&ctx->bh_lock);
 101     }
 102
 103     return ret;
 104 }
 105
 106 void qemu_bh_schedule_idle(QEMUBH *bh)
 107 {
 108     if (bh->scheduled)
 109         return;
 110     bh->idle = 1;
 111     /* Make sure that idle & any writes needed by the callback are done
 112      * before the locations are read in the aio_bh_poll.
 113      */
 114     smp_wmb();
 115     bh->scheduled = 1;
 116 }
 117
 118 void qemu_bh_schedule(QEMUBH *bh)
 119 {
 120     if (bh->scheduled)
 121         return;
 122     bh->idle = 0;
 123     /* Make sure that idle & any writes needed by the callback are done
 124      * before the locations are read in the aio_bh_poll.
 125      */
 126     smp_wmb();
 127     bh->scheduled = 1;
 128     aio_notify(bh->ctx);
 129 }
 130
 131
 132 /* This func is async.
 133  */
 134 void qemu_bh_cancel(QEMUBH *bh)
 135 {
 136     bh->scheduled = 0;
 137 }
 138
 139 /* This func is async.The bottom half will do the delete action at the finial
 140  * end.
 141  */
 142 void qemu_bh_delete(QEMUBH *bh)
 143 {
 144     bh->scheduled = 0;
 145     bh->deleted = 1;
 146 }
 147
 148 static gboolean
 149 aio_ctx_prepare(GSource *source, gint    *timeout)
 150 {
 151     AioContext *ctx = (AioContext *) source;
 152     QEMUBH *bh;
 153
 154     for (bh = ctx->first_bh; bh; bh = bh->next) {
 155         if (!bh->deleted && bh->scheduled) {
 156             if (bh->idle) {
 157                 /* idle bottom halves will be polled at least
 158                  * every 10ms */
 159                 *timeout = 10;
 160             } else {
 161                 /* non-idle bottom halves will be executed
 162                  * immediately */
 163                 *timeout = 0;
 164                 return true;
 165             }
 166         }
 167     }
 168
 169     return false;
 170 }
 171
 172 static gboolean
 173 aio_ctx_check(GSource *source)
 174 {
 175     AioContext *ctx = (AioContext *) source;
 176     QEMUBH *bh;
 177
 178     for (bh = ctx->first_bh; bh; bh = bh->next) {
 179         if (!bh->deleted && bh->scheduled) {
 180             return true;
 181         }
 182     }
 183     return aio_pending(ctx);
 184 }
 185
 186 static gboolean
 187 aio_ctx_dispatch(GSource     *source,
 188                  GSourceFunc  callback,
 189                  gpointer     user_data)
 190 {
 191     AioContext *ctx = (AioContext *) source;
 192
 193     assert(callback == NULL);
 194     aio_poll(ctx, false);
 195     return true;
 196 }
 197
 198 static void
 199 aio_ctx_finalize(GSource     *source)
 200 {
 201     AioContext *ctx = (AioContext *) source;
 202
 203     thread_pool_free(ctx->thread_pool);
 204     aio_set_event_notifier(ctx, &ctx->notifier, NULL, NULL);
 205     event_notifier_cleanup(&ctx->notifier);
 206     qemu_mutex_destroy(&ctx->bh_lock);
 207     g_array_free(ctx->pollfds, TRUE);
 208 }
 209
 210 static GSourceFuncs aio_source_funcs = {
 211     aio_ctx_prepare,
 212     aio_ctx_check,
 213     aio_ctx_dispatch,
 214     aio_ctx_finalize
 215 };
 216
 217 GSource *aio_get_g_source(AioContext *ctx)
 218 {
 219     g_source_ref(&ctx->source);
 220     return &ctx->source;
 221 }
 222
 223 ThreadPool *aio_get_thread_pool(AioContext *ctx)
 224 {
 225     if (!ctx->thread_pool) {
 226         ctx->thread_pool = thread_pool_new(ctx);
 227     }
 228     return ctx->thread_pool;
 229 }
 230
 231 void aio_notify(AioContext *ctx)
 232 {
 233     event_notifier_set(&ctx->notifier);
 234 }
 235
 236 AioContext *aio_context_new(void)
 237 {
 238     AioContext *ctx;
 239     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
 240     ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
 241     ctx->thread_pool = NULL;
 242     qemu_mutex_init(&ctx->bh_lock);
 243     event_notifier_init(&ctx->notifier, false);
 244     aio_set_event_notifier(ctx, &ctx->notifier,
 245                            (EventNotifierHandler *)
 246                            event_notifier_test_and_clear, NULL);
 247
 248     return ctx;
 249 }
 250
 251 void aio_context_ref(AioContext *ctx)
 252 {
 253     g_source_ref(&ctx->source);
 254 }
 255
 256 void aio_context_unref(AioContext *ctx)
 257 {
 258     g_source_unref(&ctx->source);
 259 }