aboutsummaryrefslogtreecommitdiff
path: root/async.c
blob: d4dd2cc799283ecbbcad2ddd3a271e77685863dc (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
/*
 * QEMU System Emulator
 *
 * Copyright (c) 2003-2008 Fabrice Bellard
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "qemu/osdep.h"
#include "qemu-common.h"
#include "block/aio.h"
#include "block/thread-pool.h"
#include "qemu/main-loop.h"
#include "qemu/atomic.h"

/***********************************************************/
/* bottom halves (can be seen as timers which expire ASAP) */

struct QEMUBH {
    AioContext *ctx;
    QEMUBHFunc *cb;
    void *opaque;
    QEMUBH *next;
    bool scheduled;
    bool idle;
    bool deleted;
};

QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
{
    QEMUBH *bh;
    bh = g_new(QEMUBH, 1);
    *bh = (QEMUBH){
        .ctx = ctx,
        .cb = cb,
        .opaque = opaque,
    };
    qemu_mutex_lock(&ctx->bh_lock);
    bh->next = ctx->first_bh;
    /* Make sure that the members are ready before putting bh into list */
    smp_wmb();
    ctx->first_bh = bh;
    qemu_mutex_unlock(&ctx->bh_lock);
    return bh;
}

void aio_bh_call(QEMUBH *bh)
{
    bh->cb(bh->opaque);
}

/* Multiple occurrences of aio_bh_poll cannot be called concurrently */
int aio_bh_poll(AioContext *ctx)
{
    QEMUBH *bh, **bhp, *next;
    int ret;

    ctx->walking_bh++;

    ret = 0;
    for (bh = ctx->first_bh; bh; bh = next) {
        /* Make sure that fetching bh happens before accessing its members */
        smp_read_barrier_depends();
        next = bh->next;
        /* The atomic_xchg is paired with the one in qemu_bh_schedule.  The
         * implicit memory barrier ensures that the callback sees all writes
         * done by the scheduling thread.  It also ensures that the scheduling
         * thread sees the zero before bh->cb has run, and thus will call
         * aio_notify again if necessary.
         */
        if (!bh->deleted && atomic_xchg(&bh->scheduled, 0)) {
            /* Idle BHs and the notify BH don't count as progress */
            if (!bh->idle && bh != ctx->notify_dummy_bh) {
                ret = 1;
            }
            bh->idle = 0;
            aio_bh_call(bh);
        }
    }

    ctx->walking_bh--;

    /* remove deleted bhs */
    if (!ctx->walking_bh) {
        qemu_mutex_lock(&ctx->bh_lock);
        bhp = &ctx->first_bh;
        while (*bhp) {
            bh = *bhp;
            if (bh->deleted) {
                *bhp = bh->next;
                g_free(bh);
            } else {
                bhp = &bh->next;
            }
        }
        qemu_mutex_unlock(&ctx->bh_lock);
    }

    return ret;
}

void qemu_bh_schedule_idle(QEMUBH *bh)
{
    bh->idle = 1;
    /* Make sure that idle & any writes needed by the callback are done
     * before the locations are read in the aio_bh_poll.
     */
    atomic_mb_set(&bh->scheduled, 1);
}

void qemu_bh_schedule(QEMUBH *bh)
{
    AioContext *ctx;

    ctx = bh->ctx;
    bh->idle = 0;
    /* The memory barrier implicit in atomic_xchg makes sure that:
     * 1. idle & any writes needed by the callback are done before the
     *    locations are read in the aio_bh_poll.
     * 2. ctx is loaded before scheduled is set and the callback has a chance
     *    to execute.
     */
    if (atomic_xchg(&bh->scheduled, 1) == 0) {
        aio_notify(ctx);
    }
}


/* This func is async.
 */
void qemu_bh_cancel(QEMUBH *bh)
{
    bh->scheduled = 0;
}

/* This func is async.The bottom half will do the delete action at the finial
 * end.
 */
void qemu_bh_delete(QEMUBH *bh)
{
    bh->scheduled = 0;
    bh->deleted = 1;
}

int64_t
aio_compute_timeout(AioContext *ctx)
{
    int64_t deadline;
    int timeout = -1;
    QEMUBH *bh;

    for (bh = ctx->first_bh; bh; bh = bh->next) {
        if (!bh->deleted && bh->scheduled) {
            if (bh->idle) {
                /* idle bottom halves will be polled at least
                 * every 10ms */
                timeout = 10000000;
            } else {
                /* non-idle bottom halves will be executed
                 * immediately */
                return 0;
            }
        }
    }

    deadline = timerlistgroup_deadline_ns(&ctx->tlg);
    if (deadline == 0) {
        return 0;
    } else {
        return qemu_soonest_timeout(timeout, deadline);
    }
}

static gboolean
aio_ctx_prepare(GSource *source, gint    *timeout)
{
    AioContext *ctx = (AioContext *) source;

    atomic_or(&ctx->notify_me, 1);

    /* We assume there is no timeout already supplied */
    *timeout = qemu_timeout_ns_to_ms(aio_compute_timeout(ctx));

    if (aio_prepare(ctx)) {
        *timeout = 0;
    }

    return *timeout == 0;
}

static gboolean
aio_ctx_check(GSource *source)
{
    AioContext *ctx = (AioContext *) source;
    QEMUBH *bh;

    atomic_and(&ctx->notify_me, ~1);
    aio_notify_accept(ctx);

    for (bh = ctx->first_bh; bh; bh = bh->next) {
        if (!bh->deleted && bh->scheduled) {
            return true;
	}
    }
    return aio_pending(ctx) || (timerlistgroup_deadline_ns(&ctx->tlg) == 0);
}

static gboolean
aio_ctx_dispatch(GSource     *source,
                 GSourceFunc  callback,
                 gpointer     user_data)
{
    AioContext *ctx = (AioContext *) source;

    assert(callback == NULL);
    aio_dispatch(ctx);
    return true;
}

static void
aio_ctx_finalize(GSource     *source)
{
    AioContext *ctx = (AioContext *) source;

    qemu_bh_delete(ctx->notify_dummy_bh);
    thread_pool_free(ctx->thread_pool);

    qemu_mutex_lock(&ctx->bh_lock);
    while (ctx->first_bh) {
        QEMUBH *next = ctx->first_bh->next;

        /* qemu_bh_delete() must have been called on BHs in this AioContext */
        assert(ctx->first_bh->deleted);

        g_free(ctx->first_bh);
        ctx->first_bh = next;
    }
    qemu_mutex_unlock(&ctx->bh_lock);

    aio_set_event_notifier(ctx, &ctx->notifier, false, NULL);
    event_notifier_cleanup(&ctx->notifier);
    rfifolock_destroy(&ctx->lock);
    qemu_mutex_destroy(&ctx->bh_lock);
    timerlistgroup_deinit(&ctx->tlg);
}

static GSourceFuncs aio_source_funcs = {
    aio_ctx_prepare,
    aio_ctx_check,
    aio_ctx_dispatch,
    aio_ctx_finalize
};

GSource *aio_get_g_source(AioContext *ctx)
{
    g_source_ref(&ctx->source);
    return &ctx->source;
}

ThreadPool *aio_get_thread_pool(AioContext *ctx)
{
    if (!ctx->thread_pool) {
        ctx->thread_pool = thread_pool_new(ctx);
    }
    return ctx->thread_pool;
}

void aio_notify(AioContext *ctx)
{
    /* Write e.g. bh->scheduled before reading ctx->notify_me.  Pairs
     * with atomic_or in aio_ctx_prepare or atomic_add in aio_poll.
     */
    smp_mb();
    if (ctx->notify_me) {
        event_notifier_set(&ctx->notifier);
        atomic_mb_set(&ctx->notified, true);
    }
}

void aio_notify_accept(AioContext *ctx)
{
    if (atomic_xchg(&ctx->notified, false)) {
        event_notifier_test_and_clear(&ctx->notifier);
    }
}

static void aio_timerlist_notify(void *opaque)
{
    aio_notify(opaque);
}

static void aio_rfifolock_cb(void *opaque)
{
    AioContext *ctx = opaque;

    /* Kick owner thread in case they are blocked in aio_poll() */
    qemu_bh_schedule(ctx->notify_dummy_bh);
}

static void notify_dummy_bh(void *opaque)
{
    /* Do nothing, we were invoked just to force the event loop to iterate */
}

static void event_notifier_dummy_cb(EventNotifier *e)
{
}

AioContext *aio_context_new(Error **errp)
{
    int ret;
    AioContext *ctx;
    Error *local_err = NULL;

    ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
    aio_context_setup(ctx, &local_err);
    if (local_err) {
        error_propagate(errp, local_err);
        goto fail;
    }
    ret = event_notifier_init(&ctx->notifier, false);
    if (ret < 0) {
        error_setg_errno(errp, -ret, "Failed to initialize event notifier");
        goto fail;
    }
    g_source_set_can_recurse(&ctx->source, true);
    aio_set_event_notifier(ctx, &ctx->notifier,
                           false,
                           (EventNotifierHandler *)
                           event_notifier_dummy_cb);
    ctx->thread_pool = NULL;
    qemu_mutex_init(&ctx->bh_lock);
    rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
    timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);

    ctx->notify_dummy_bh = aio_bh_new(ctx, notify_dummy_bh, NULL);

    return ctx;
fail:
    g_source_destroy(&ctx->source);
    return NULL;
}

void aio_context_ref(AioContext *ctx)
{
    g_source_ref(&ctx->source);
}

void aio_context_unref(AioContext *ctx)
{
    g_source_unref(&ctx->source);
}

void aio_context_acquire(AioContext *ctx)
{
    rfifolock_lock(&ctx->lock);
}

void aio_context_release(AioContext *ctx)
{
    rfifolock_unlock(&ctx->lock);
}