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 #include "qemu/atomic.h"
  30
  31 /***********************************************************/
  32 /* bottom halves (can be seen as timers which expire ASAP) */
  33
  34 struct QEMUBH {
  35     AioContext *ctx;
  36     QEMUBHFunc *cb;
  37     void *opaque;
  38     QEMUBH *next;
  39     bool scheduled;
  40     bool idle;
  41     bool deleted;
  42 };
  43
  44 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
  45 {
  46     QEMUBH *bh;
  47     bh = g_malloc0(sizeof(QEMUBH));
  48     bh->ctx = ctx;
  49     bh->cb = cb;
  50     bh->opaque = opaque;
  51     qemu_mutex_lock(&ctx->bh_lock);
  52     bh->next = ctx->first_bh;
  53     /* Make sure that the members are ready before putting bh into list */
  54     smp_wmb();
  55     ctx->first_bh = bh;
  56     qemu_mutex_unlock(&ctx->bh_lock);
  57     return bh;
  58 }
  59
  60 /* Multiple occurrences of aio_bh_poll cannot be called concurrently */
  61 int aio_bh_poll(AioContext *ctx)
  62 {
  63     QEMUBH *bh, **bhp, *next;
  64     int ret;
  65
  66     ctx->walking_bh++;
  67
  68     ret = 0;
  69     for (bh = ctx->first_bh; bh; bh = next) {
  70         /* Make sure that fetching bh happens before accessing its members */
  71         smp_read_barrier_depends();
  72         next = bh->next;
  73         if (!bh->deleted && bh->scheduled) {
  74             bh->scheduled = 0;
  75             /* Paired with write barrier in bh schedule to ensure reading for
  76              * idle & callbacks coming after bh's scheduling.
  77              */
  78             smp_rmb();
  79             if (!bh->idle)
  80                 ret = 1;
  81             bh->idle = 0;
  82             bh->cb(bh->opaque);
  83         }
  84     }
  85
  86     ctx->walking_bh--;
  87
  88     /* remove deleted bhs */
  89     if (!ctx->walking_bh) {
  90         qemu_mutex_lock(&ctx->bh_lock);
  91         bhp = &ctx->first_bh;
  92         while (*bhp) {
  93             bh = *bhp;
  94             if (bh->deleted) {
  95                 *bhp = bh->next;
  96                 g_free(bh);
  97             } else {
  98                 bhp = &bh->next;
  99             }
 100         }
 101         qemu_mutex_unlock(&ctx->bh_lock);
 102     }
 103
 104     return ret;
 105 }
 106
 107 void qemu_bh_schedule_idle(QEMUBH *bh)
 108 {
 109     if (bh->scheduled)
 110         return;
 111     bh->idle = 1;
 112     /* Make sure that idle & any writes needed by the callback are done
 113      * before the locations are read in the aio_bh_poll.
 114      */
 115     smp_wmb();
 116     bh->scheduled = 1;
 117 }
 118
 119 void qemu_bh_schedule(QEMUBH *bh)
 120 {
 121     AioContext *ctx;
 122
 123     if (bh->scheduled)
 124         return;
 125     ctx = bh->ctx;
 126     bh->idle = 0;
 127     /* Make sure that:
 128      * 1. idle & any writes needed by the callback are done before the
 129      *    locations are read in the aio_bh_poll.
 130      * 2. ctx is loaded before scheduled is set and the callback has a chance
 131      *    to execute.
 132      */
 133     smp_mb();
 134     bh->scheduled = 1;
 135     aio_notify(ctx);
 136 }
 137
 138
 139 /* This func is async.
 140  */
 141 void qemu_bh_cancel(QEMUBH *bh)
 142 {
 143     bh->scheduled = 0;
 144 }
 145
 146 /* This func is async.The bottom half will do the delete action at the finial
 147  * end.
 148  */
 149 void qemu_bh_delete(QEMUBH *bh)
 150 {
 151     bh->scheduled = 0;
 152     bh->deleted = 1;
 153 }
 154
 155 static gboolean
 156 aio_ctx_prepare(GSource *source, gint    *timeout)
 157 {
 158     AioContext *ctx = (AioContext *) source;
 159     QEMUBH *bh;
 160     int deadline;
 161
 162     /* We assume there is no timeout already supplied */
 163     *timeout = -1;
 164     for (bh = ctx->first_bh; bh; bh = bh->next) {
 165         if (!bh->deleted && bh->scheduled) {
 166             if (bh->idle) {
 167                 /* idle bottom halves will be polled at least
 168                  * every 10ms */
 169                 *timeout = 10;
 170             } else {
 171                 /* non-idle bottom halves will be executed
 172                  * immediately */
 173                 *timeout = 0;
 174                 return true;
 175             }
 176         }
 177     }
 178
 179     deadline = qemu_timeout_ns_to_ms(timerlistgroup_deadline_ns(&ctx->tlg));
 180     if (deadline == 0) {
 181         *timeout = 0;
 182         return true;
 183     } else {
 184         *timeout = qemu_soonest_timeout(*timeout, deadline);
 185     }
 186
 187     return false;
 188 }
 189
 190 static gboolean
 191 aio_ctx_check(GSource *source)
 192 {
 193     AioContext *ctx = (AioContext *) source;
 194     QEMUBH *bh;
 195
 196     for (bh = ctx->first_bh; bh; bh = bh->next) {
 197         if (!bh->deleted && bh->scheduled) {
 198             return true;
 199         }
 200     }
 201     return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
 202 }
 203
 204 static gboolean
 205 aio_ctx_dispatch(GSource     *source,
 206                  GSourceFunc  callback,
 207                  gpointer     user_data)
 208 {
 209     AioContext *ctx = (AioContext *) source;
 210
 211     assert(callback == NULL);
 212     aio_poll(ctx, false);
 213     return true;
 214 }
 215
 216 static void
 217 aio_ctx_finalize(GSource     *source)
 218 {
 219     AioContext *ctx = (AioContext *) source;
 220
 221     thread_pool_free(ctx->thread_pool);
 222     aio_set_event_notifier(ctx, &ctx->notifier, NULL);
 223     event_notifier_cleanup(&ctx->notifier);
 224     rfifolock_destroy(&ctx->lock);
 225     qemu_mutex_destroy(&ctx->bh_lock);
 226     g_array_free(ctx->pollfds, TRUE);
 227     timerlistgroup_deinit(&ctx->tlg);
 228 }
 229
 230 static GSourceFuncs aio_source_funcs = {
 231     aio_ctx_prepare,
 232     aio_ctx_check,
 233     aio_ctx_dispatch,
 234     aio_ctx_finalize
 235 };
 236
 237 GSource *aio_get_g_source(AioContext *ctx)
 238 {
 239     g_source_ref(&ctx->source);
 240     return &ctx->source;
 241 }
 242
 243 ThreadPool *aio_get_thread_pool(AioContext *ctx)
 244 {
 245     if (!ctx->thread_pool) {
 246         ctx->thread_pool = thread_pool_new(ctx);
 247     }
 248     return ctx->thread_pool;
 249 }
 250
 251 void aio_set_dispatching(AioContext *ctx, bool dispatching)
 252 {
 253     ctx->dispatching = dispatching;
 254     if (!dispatching) {
 255         /* Write ctx->dispatching before reading e.g. bh->scheduled.
 256          * Optimization: this is only needed when we're entering the "unsafe"
 257          * phase where other threads must call event_notifier_set.
 258          */
 259         smp_mb();
 260     }
 261 }
 262
 263 void aio_notify(AioContext *ctx)
 264 {
 265     /* Write e.g. bh->scheduled before reading ctx->dispatching.  */
 266     smp_mb();
 267     if (!ctx->dispatching) {
 268         event_notifier_set(&ctx->notifier);
 269     }
 270 }
 271
 272 static void aio_timerlist_notify(void *opaque)
 273 {
 274     aio_notify(opaque);
 275 }
 276
 277 static void aio_rfifolock_cb(void *opaque)
 278 {
 279     /* Kick owner thread in case they are blocked in aio_poll() */
 280     aio_notify(opaque);
 281 }
 282
 283 AioContext *aio_context_new(void)
 284 {
 285     AioContext *ctx;
 286     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
 287     ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
 288     ctx->thread_pool = NULL;
 289     qemu_mutex_init(&ctx->bh_lock);
 290     rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
 291     event_notifier_init(&ctx->notifier, false);
 292     aio_set_event_notifier(ctx, &ctx->notifier,
 293                            (EventNotifierHandler *)
 294                            event_notifier_test_and_clear);
 295     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
 296
 297     return ctx;
 298 }
 299
 300 void aio_context_ref(AioContext *ctx)
 301 {
 302     g_source_ref(&ctx->source);
 303 }
 304
 305 void aio_context_unref(AioContext *ctx)
 306 {
 307     g_source_unref(&ctx->source);
 308 }
 309
 310 void aio_context_acquire(AioContext *ctx)
 311 {
 312     rfifolock_lock(&ctx->lock);
 313 }
 314
 315 void aio_context_release(AioContext *ctx)
 316 {
 317     rfifolock_unlock(&ctx->lock);
 318 }