trap signals for "-serial mon:stdio"
[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 }