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