Refactor some hax related codes.
[sdk/emulator/qemu.git] / thread-pool.c
1 /*
2  * QEMU block layer thread pool
3  *
4  * Copyright IBM, Corp. 2008
5  * Copyright Red Hat, Inc. 2012
6  *
7  * Authors:
8  *  Anthony Liguori   <aliguori@us.ibm.com>
9  *  Paolo Bonzini     <pbonzini@redhat.com>
10  *
11  * This work is licensed under the terms of the GNU GPL, version 2.  See
12  * the COPYING file in the top-level directory.
13  *
14  * Contributions after 2012-01-13 are licensed under the terms of the
15  * GNU GPL, version 2 or (at your option) any later version.
16  */
17 #include "qemu-common.h"
18 #include "qemu/queue.h"
19 #include "qemu/thread.h"
20 #include "qemu/osdep.h"
21 #include "block/coroutine.h"
22 #include "trace.h"
23 #include "block/block_int.h"
24 #include "qemu/event_notifier.h"
25 #include "block/thread-pool.h"
26
27 static void do_spawn_thread(ThreadPool *pool);
28
29 typedef struct ThreadPoolElement ThreadPoolElement;
30
31 enum ThreadState {
32     THREAD_QUEUED,
33     THREAD_ACTIVE,
34     THREAD_DONE,
35     THREAD_CANCELED,
36 };
37
38 struct ThreadPoolElement {
39     BlockDriverAIOCB common;
40     ThreadPool *pool;
41     ThreadPoolFunc *func;
42     void *arg;
43
44     /* Moving state out of THREAD_QUEUED is protected by lock.  After
45      * that, only the worker thread can write to it.  Reads and writes
46      * of state and ret are ordered with memory barriers.
47      */
48     enum ThreadState state;
49     int ret;
50
51     /* Access to this list is protected by lock.  */
52     QTAILQ_ENTRY(ThreadPoolElement) reqs;
53
54     /* Access to this list is protected by the global mutex.  */
55     QLIST_ENTRY(ThreadPoolElement) all;
56 };
57
58 struct ThreadPool {
59     EventNotifier notifier;
60     AioContext *ctx;
61     QemuMutex lock;
62     QemuCond check_cancel;
63     QemuCond worker_stopped;
64     QemuSemaphore sem;
65     int max_threads;
66     QEMUBH *new_thread_bh;
67
68     /* The following variables are only accessed from one AioContext. */
69     QLIST_HEAD(, ThreadPoolElement) head;
70
71     /* The following variables are protected by lock.  */
72     QTAILQ_HEAD(, ThreadPoolElement) request_list;
73     int cur_threads;
74     int idle_threads;
75     int new_threads;     /* backlog of threads we need to create */
76     int pending_threads; /* threads created but not running yet */
77     int pending_cancellations; /* whether we need a cond_broadcast */
78     bool stopping;
79 };
80
81 static void *worker_thread(void *opaque)
82 {
83     ThreadPool *pool = opaque;
84
85     qemu_mutex_lock(&pool->lock);
86     pool->pending_threads--;
87     do_spawn_thread(pool);
88
89     while (!pool->stopping) {
90         ThreadPoolElement *req;
91         int ret;
92
93         do {
94             pool->idle_threads++;
95             qemu_mutex_unlock(&pool->lock);
96             ret = qemu_sem_timedwait(&pool->sem, 10000);
97             qemu_mutex_lock(&pool->lock);
98             pool->idle_threads--;
99         } while (ret == -1 && !QTAILQ_EMPTY(&pool->request_list));
100         if (ret == -1 || pool->stopping) {
101             break;
102         }
103
104         req = QTAILQ_FIRST(&pool->request_list);
105         QTAILQ_REMOVE(&pool->request_list, req, reqs);
106         req->state = THREAD_ACTIVE;
107         qemu_mutex_unlock(&pool->lock);
108
109         ret = req->func(req->arg);
110
111         req->ret = ret;
112         /* Write ret before state.  */
113         smp_wmb();
114         req->state = THREAD_DONE;
115
116         qemu_mutex_lock(&pool->lock);
117         if (pool->pending_cancellations) {
118             qemu_cond_broadcast(&pool->check_cancel);
119         }
120
121         event_notifier_set(&pool->notifier);
122     }
123
124     pool->cur_threads--;
125     qemu_cond_signal(&pool->worker_stopped);
126     qemu_mutex_unlock(&pool->lock);
127     return NULL;
128 }
129
130 static void do_spawn_thread(ThreadPool *pool)
131 {
132     QemuThread t;
133
134     /* Runs with lock taken.  */
135     if (!pool->new_threads) {
136         return;
137     }
138
139     pool->new_threads--;
140     pool->pending_threads++;
141
142     qemu_thread_create(&t, worker_thread, pool, QEMU_THREAD_DETACHED);
143 }
144
145 static void spawn_thread_bh_fn(void *opaque)
146 {
147     ThreadPool *pool = opaque;
148
149     qemu_mutex_lock(&pool->lock);
150     do_spawn_thread(pool);
151     qemu_mutex_unlock(&pool->lock);
152 }
153
154 static void spawn_thread(ThreadPool *pool)
155 {
156     pool->cur_threads++;
157     pool->new_threads++;
158     /* If there are threads being created, they will spawn new workers, so
159      * we don't spend time creating many threads in a loop holding a mutex or
160      * starving the current vcpu.
161      *
162      * If there are no idle threads, ask the main thread to create one, so we
163      * inherit the correct affinity instead of the vcpu affinity.
164      */
165     if (!pool->pending_threads) {
166         qemu_bh_schedule(pool->new_thread_bh);
167     }
168 }
169
170 static void event_notifier_ready(EventNotifier *notifier)
171 {
172     ThreadPool *pool = container_of(notifier, ThreadPool, notifier);
173     ThreadPoolElement *elem, *next;
174
175     event_notifier_test_and_clear(notifier);
176 restart:
177     QLIST_FOREACH_SAFE(elem, &pool->head, all, next) {
178         if (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
179             continue;
180         }
181         if (elem->state == THREAD_DONE) {
182             trace_thread_pool_complete(pool, elem, elem->common.opaque,
183                                        elem->ret);
184         }
185         if (elem->state == THREAD_DONE && elem->common.cb) {
186             QLIST_REMOVE(elem, all);
187             /* Read state before ret.  */
188             smp_rmb();
189             elem->common.cb(elem->common.opaque, elem->ret);
190             qemu_aio_release(elem);
191             goto restart;
192         } else {
193             /* remove the request */
194             QLIST_REMOVE(elem, all);
195             qemu_aio_release(elem);
196         }
197     }
198 }
199
200 static int thread_pool_active(EventNotifier *notifier)
201 {
202     ThreadPool *pool = container_of(notifier, ThreadPool, notifier);
203     return !QLIST_EMPTY(&pool->head);
204 }
205
206 static void thread_pool_cancel(BlockDriverAIOCB *acb)
207 {
208     ThreadPoolElement *elem = (ThreadPoolElement *)acb;
209     ThreadPool *pool = elem->pool;
210
211     trace_thread_pool_cancel(elem, elem->common.opaque);
212
213     qemu_mutex_lock(&pool->lock);
214     if (elem->state == THREAD_QUEUED &&
215         /* No thread has yet started working on elem. we can try to "steal"
216          * the item from the worker if we can get a signal from the
217          * semaphore.  Because this is non-blocking, we can do it with
218          * the lock taken and ensure that elem will remain THREAD_QUEUED.
219          */
220         qemu_sem_timedwait(&pool->sem, 0) == 0) {
221         QTAILQ_REMOVE(&pool->request_list, elem, reqs);
222         elem->state = THREAD_CANCELED;
223         event_notifier_set(&pool->notifier);
224     } else {
225         pool->pending_cancellations++;
226         while (elem->state != THREAD_CANCELED && elem->state != THREAD_DONE) {
227             qemu_cond_wait(&pool->check_cancel, &pool->lock);
228         }
229         pool->pending_cancellations--;
230     }
231     qemu_mutex_unlock(&pool->lock);
232 }
233
234 static const AIOCBInfo thread_pool_aiocb_info = {
235     .aiocb_size         = sizeof(ThreadPoolElement),
236     .cancel             = thread_pool_cancel,
237 };
238
239 BlockDriverAIOCB *thread_pool_submit_aio(ThreadPool *pool,
240         ThreadPoolFunc *func, void *arg,
241         BlockDriverCompletionFunc *cb, void *opaque)
242 {
243     ThreadPoolElement *req;
244
245     req = qemu_aio_get(&thread_pool_aiocb_info, NULL, cb, opaque);
246     req->func = func;
247     req->arg = arg;
248     req->state = THREAD_QUEUED;
249     req->pool = pool;
250
251     QLIST_INSERT_HEAD(&pool->head, req, all);
252
253     trace_thread_pool_submit(pool, req, arg);
254
255     qemu_mutex_lock(&pool->lock);
256     if (pool->idle_threads == 0 && pool->cur_threads < pool->max_threads) {
257         spawn_thread(pool);
258     }
259     QTAILQ_INSERT_TAIL(&pool->request_list, req, reqs);
260     qemu_mutex_unlock(&pool->lock);
261     qemu_sem_post(&pool->sem);
262     return &req->common;
263 }
264
265 typedef struct ThreadPoolCo {
266     Coroutine *co;
267     int ret;
268 } ThreadPoolCo;
269
270 static void thread_pool_co_cb(void *opaque, int ret)
271 {
272     ThreadPoolCo *co = opaque;
273
274     co->ret = ret;
275     qemu_coroutine_enter(co->co, NULL);
276 }
277
278 int coroutine_fn thread_pool_submit_co(ThreadPool *pool, ThreadPoolFunc *func,
279                                        void *arg)
280 {
281     ThreadPoolCo tpc = { .co = qemu_coroutine_self(), .ret = -EINPROGRESS };
282     assert(qemu_in_coroutine());
283     thread_pool_submit_aio(pool, func, arg, thread_pool_co_cb, &tpc);
284     qemu_coroutine_yield();
285     return tpc.ret;
286 }
287
288 void thread_pool_submit(ThreadPool *pool, ThreadPoolFunc *func, void *arg)
289 {
290     thread_pool_submit_aio(pool, func, arg, NULL, NULL);
291 }
292
293 static void thread_pool_init_one(ThreadPool *pool, AioContext *ctx)
294 {
295     if (!ctx) {
296         ctx = qemu_get_aio_context();
297     }
298
299     memset(pool, 0, sizeof(*pool));
300     event_notifier_init(&pool->notifier, false);
301     pool->ctx = ctx;
302     qemu_mutex_init(&pool->lock);
303     qemu_cond_init(&pool->check_cancel);
304     qemu_cond_init(&pool->worker_stopped);
305     qemu_sem_init(&pool->sem, 0);
306     pool->max_threads = 64;
307     pool->new_thread_bh = aio_bh_new(ctx, spawn_thread_bh_fn, pool);
308
309     QLIST_INIT(&pool->head);
310     QTAILQ_INIT(&pool->request_list);
311
312     aio_set_event_notifier(ctx, &pool->notifier, event_notifier_ready,
313                            thread_pool_active);
314 }
315
316 ThreadPool *thread_pool_new(AioContext *ctx)
317 {
318     ThreadPool *pool = g_new(ThreadPool, 1);
319     thread_pool_init_one(pool, ctx);
320     return pool;
321 }
322
323 void thread_pool_free(ThreadPool *pool)
324 {
325     if (!pool) {
326         return;
327     }
328
329     assert(QLIST_EMPTY(&pool->head));
330
331     qemu_mutex_lock(&pool->lock);
332
333     /* Stop new threads from spawning */
334     qemu_bh_delete(pool->new_thread_bh);
335     pool->cur_threads -= pool->new_threads;
336     pool->new_threads = 0;
337
338     /* Wait for worker threads to terminate */
339     pool->stopping = true;
340     while (pool->cur_threads > 0) {
341         qemu_sem_post(&pool->sem);
342         qemu_cond_wait(&pool->worker_stopped, &pool->lock);
343     }
344
345     qemu_mutex_unlock(&pool->lock);
346
347     aio_set_event_notifier(pool->ctx, &pool->notifier, NULL, NULL);
348     qemu_sem_destroy(&pool->sem);
349     qemu_cond_destroy(&pool->check_cancel);
350     qemu_cond_destroy(&pool->worker_stopped);
351     qemu_mutex_destroy(&pool->lock);
352     event_notifier_cleanup(&pool->notifier);
353     g_free(pool);
354 }