summaryrefslogtreecommitdiff
path: root/thread-pool.c
blob: 23888dcfc4d74d9c9343462271dd15cb6eaa926d (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
/*
 * QEMU block layer thread pool
 *
 * Copyright IBM, Corp. 2008
 * Copyright Red Hat, Inc. 2012
 *
 * Authors:
 *  Anthony Liguori   <aliguori@us.ibm.com>
 *  Paolo Bonzini     <pbonzini@redhat.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2.  See
 * the COPYING file in the top-level directory.
 *
 * Contributions after 2012-01-13 are licensed under the terms of the
 * GNU GPL, version 2 or (at your option) any later version.
 */
#include "qemu-common.h"
#include "qemu/queue.h"
#include "qemu/thread.h"
#include "qemu/osdep.h"
#include "block/coroutine.h"
#include "trace.h"
#include "block/block_int.h"
#include "block/thread-pool.h"
#include "qemu/main-loop.h"

static void do_spawn_thread(ThreadPool *pool);

typedef struct ThreadPoolElement ThreadPoolElement;

enum ThreadState {
    THREAD_QUEUED,
    THREAD_ACTIVE,
    THREAD_DONE,
    THREAD_CANCELED,
};

struct ThreadPoolElement {
    BlockDriverAIOCB common;
    ThreadPool *pool;
    ThreadPoolFunc *func;
    void *arg;

    /* Moving state out of THREAD_QUEUED is protected by lock.  After
     * that, only the worker thread can write to it.  Reads and writes
     * of state and ret are ordered with memory barriers.
     */
    enum ThreadState state;
    int ret;

    /* Access to this list is protected by lock.  */
    QTAILQ_ENTRY(ThreadPoolElement) reqs;

    /* Access to this list is protected by the global mutex.  */
    QLIST_ENTRY(ThreadPoolElement) all;
};

struct ThreadPool {
    AioContext *ctx;
    QEMUBH *completion_bh;
    QemuMutex lock;
    QemuCond check_cancel;
    QemuCond worker_stopped;
    QemuSemaphore sem;
    int max_threads;
    QEMUBH *new_thread_bh;

    /* The following variables are only accessed from one AioContext. */
    QLIST_HEAD(, ThreadPoolElement) head;

    /* The following variables are protected by lock.  */
    QTAILQ_HEAD(, ThreadPoolElement) request_list;
    int cur_threads;
    int idle_threads;
    int new_threads;     /* backlog of threads we need to create */
    int pending_threads; /* threads created but not running yet */
    int pending_cancellations; /* whether we need a cond_broadcast */
    bool stopping;
};

static void *worker_thread(void *opaque)
{
    ThreadPool *pool = opaque;

    qemu_mutex_lock(&pool->lock);
    pool->pending_threads--;
    do_spawn_thread(pool);

    while (!pool->stopping) {
        ThreadPoolElement *req;
        int ret;

        do {
            pool->idle_threads++;
            qemu_mutex_unlock(&pool->lock);
            ret = qemu_sem_timedwait(&pool->sem, 10000);
            qemu_mutex_lock(&pool->lock);
            pool->idle_threads--;
        } while (ret == -1 && !QTAILQ_EMPTY(&pool->request_list));
        if (ret == -1 || pool->stopping) {
            break;
        }

        req = QTAILQ_FIRST(&pool->request_list);
        QTAILQ_REMOVE(&pool->request_list, req, reqs);
        req->state = THREAD_ACTIVE;
        qemu_mutex_unlock(&pool->lock);

        ret = req->func(req->arg);

        req->ret = ret;
        /* Write ret before state.  */
        smp_wmb();
        req->state = THREAD_DONE;

        qemu_mutex_lock(&pool->lock);
        if (pool->pending_cancellations) {
            qemu_cond_broadcast(&pool->check_cancel);
        }

        qemu_bh_schedule(pool->completion_bh);
    }

    pool->cur_threads--;
    qemu_cond_signal(&pool->worker_stopped);
    qemu_mutex_unlock(&pool->lock);
    return NULL;
}

static void do_spawn_thread(ThreadPool *pool)
{
    QemuThread t;

    /* Runs with lock taken.  */
    if (!pool->new_threads) {
        return;
    }

    pool->new_threads--;
    pool->pending_threads++;

    qemu_thread_create(&t, "worker", worker_thread, pool, QEMU_THREAD_DETACHED);
}

static void spawn_thread_bh_fn(void *opaque)
{
    ThreadPool *pool = opaque;

    qemu_mutex_lock(&pool->lock);
    do_spawn_thread(pool);
    qemu_mutex_unlock(&pool->lock);
}

static void spawn_thread(ThreadPool *pool)
{
    pool->cur_threads++;
    pool->new_threads++;
    /* If there are threads being created, they will spawn new workers, so
     * we don't spend time creating many threads in a loop holding a mutex or
     * starving the current vcpu.
     *
     * If there are no idle threads, ask the main thread to create one, so we
     * inherit the correct affinity instead of the vcpu affinity.
     */
    if (!pool->pending_threads) {
        qemu_bh_schedule(pool->new_thread_bh);
    }
}

static void thread_pool_completion_bh(void *opaque)
{
    ThreadPool *pool = opaque;
    ThreadPoolElement *elem, *next;

restart:
    QLIST_FOREACH_SAFE(elem, &pool->head, all, next) {
        if (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
            continue;
        }
        if (elem->state == THREAD_DONE) {
            trace_thread_pool_complete(pool, elem, elem->common.opaque,
                                       elem->ret);
        }
        if (elem->state == THREAD_DONE && elem->common.cb) {
            QLIST_REMOVE(elem, all);
            /* Read state before ret.  */
            smp_rmb();

            /* Schedule ourselves in case elem->common.cb() calls aio_poll() to
             * wait for another request that completed at the same time.
             */
            qemu_bh_schedule(pool->completion_bh);

            elem->common.cb(elem->common.opaque, elem->ret);
            qemu_aio_release(elem);
            goto restart;
        } else {
            /* remove the request */
            QLIST_REMOVE(elem, all);
            qemu_aio_release(elem);
        }
    }
}

static void thread_pool_cancel(BlockDriverAIOCB *acb)
{
    ThreadPoolElement *elem = (ThreadPoolElement *)acb;
    ThreadPool *pool = elem->pool;

    trace_thread_pool_cancel(elem, elem->common.opaque);

    qemu_mutex_lock(&pool->lock);
    if (elem->state == THREAD_QUEUED &&
        /* No thread has yet started working on elem. we can try to "steal"
         * the item from the worker if we can get a signal from the
         * semaphore.  Because this is non-blocking, we can do it with
         * the lock taken and ensure that elem will remain THREAD_QUEUED.
         */
        qemu_sem_timedwait(&pool->sem, 0) == 0) {
        QTAILQ_REMOVE(&pool->request_list, elem, reqs);
        elem->state = THREAD_CANCELED;
        qemu_bh_schedule(pool->completion_bh);
    } else {
        pool->pending_cancellations++;
        while (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
            qemu_cond_wait(&pool->check_cancel, &pool->lock);
        }
        pool->pending_cancellations--;
    }
    qemu_mutex_unlock(&pool->lock);
    thread_pool_completion_bh(pool);
}

static const AIOCBInfo thread_pool_aiocb_info = {
    .aiocb_size         = sizeof(ThreadPoolElement),
    .cancel             = thread_pool_cancel,
};

BlockDriverAIOCB *thread_pool_submit_aio(ThreadPool *pool,
        ThreadPoolFunc *func, void *arg,
        BlockDriverCompletionFunc *cb, void *opaque)
{
    ThreadPoolElement *req;

    req = qemu_aio_get(&thread_pool_aiocb_info, NULL, cb, opaque);
    req->func = func;
    req->arg = arg;
    req->state = THREAD_QUEUED;
    req->pool = pool;

    QLIST_INSERT_HEAD(&pool->head, req, all);

    trace_thread_pool_submit(pool, req, arg);

    qemu_mutex_lock(&pool->lock);
    if (pool->idle_threads == 0 && pool->cur_threads < pool->max_threads) {
        spawn_thread(pool);
    }
    QTAILQ_INSERT_TAIL(&pool->request_list, req, reqs);
    qemu_mutex_unlock(&pool->lock);
    qemu_sem_post(&pool->sem);
    return &req->common;
}

typedef struct ThreadPoolCo {
    Coroutine *co;
    int ret;
} ThreadPoolCo;

static void thread_pool_co_cb(void *opaque, int ret)
{
    ThreadPoolCo *co = opaque;

    co->ret = ret;
    qemu_coroutine_enter(co->co, NULL);
}

int coroutine_fn thread_pool_submit_co(ThreadPool *pool, ThreadPoolFunc *func,
                                       void *arg)
{
    ThreadPoolCo tpc = { .co = qemu_coroutine_self(), .ret = -EINPROGRESS };
    assert(qemu_in_coroutine());
    thread_pool_submit_aio(pool, func, arg, thread_pool_co_cb, &tpc);
    qemu_coroutine_yield();
    return tpc.ret;
}

void thread_pool_submit(ThreadPool *pool, ThreadPoolFunc *func, void *arg)
{
    thread_pool_submit_aio(pool, func, arg, NULL, NULL);
}

static void thread_pool_init_one(ThreadPool *pool, AioContext *ctx)
{
    if (!ctx) {
        ctx = qemu_get_aio_context();
    }

    memset(pool, 0, sizeof(*pool));
    pool->ctx = ctx;
    pool->completion_bh = aio_bh_new(ctx, thread_pool_completion_bh, pool);
    qemu_mutex_init(&pool->lock);
    qemu_cond_init(&pool->check_cancel);
    qemu_cond_init(&pool->worker_stopped);
    qemu_sem_init(&pool->sem, 0);
    pool->max_threads = 64;
    pool->new_thread_bh = aio_bh_new(ctx, spawn_thread_bh_fn, pool);

    QLIST_INIT(&pool->head);
    QTAILQ_INIT(&pool->request_list);
}

ThreadPool *thread_pool_new(AioContext *ctx)
{
    ThreadPool *pool = g_new(ThreadPool, 1);
    thread_pool_init_one(pool, ctx);
    return pool;
}

void thread_pool_free(ThreadPool *pool)
{
    if (!pool) {
        return;
    }

    assert(QLIST_EMPTY(&pool->head));

    qemu_mutex_lock(&pool->lock);

    /* Stop new threads from spawning */
    qemu_bh_delete(pool->new_thread_bh);
    pool->cur_threads -= pool->new_threads;
    pool->new_threads = 0;

    /* Wait for worker threads to terminate */
    pool->stopping = true;
    while (pool->cur_threads > 0) {
        qemu_sem_post(&pool->sem);
        qemu_cond_wait(&pool->worker_stopped, &pool->lock);
    }

    qemu_mutex_unlock(&pool->lock);

    qemu_bh_delete(pool->completion_bh);
    qemu_sem_destroy(&pool->sem);
    qemu_cond_destroy(&pool->check_cancel);
    qemu_cond_destroy(&pool->worker_stopped);
    qemu_mutex_destroy(&pool->lock);
    g_free(pool);
}