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main-loop: unify qemu_init_main_loop between QEMU and tools
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1 /*
2 * QEMU System Emulator
3 *
4 * Copyright (c) 2003-2008 Fabrice Bellard
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a copy
7 * of this software and associated documentation files (the "Software"), to deal
8 * in the Software without restriction, including without limitation the rights
9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10 * copies of the Software, and to permit persons to whom the Software is
11 * furnished to do so, subject to the following conditions:
12 *
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
22 * THE SOFTWARE.
23 */
24
25 #ifndef QEMU_MAIN_LOOP_H
26 #define QEMU_MAIN_LOOP_H 1
27
28 #define SIG_IPI SIGUSR1
29
30 /**
31 * qemu_init_main_loop: Set up the process so that it can run the main loop.
32 *
33 * This includes setting up signal handlers. It should be called before
34 * any other threads are created. In addition, threads other than the
35 * main one should block signals that are trapped by the main loop.
36 * For simplicity, you can consider these signals to be safe: SIGUSR1,
37 * SIGUSR2, thread signals (SIGFPE, SIGILL, SIGSEGV, SIGBUS) and real-time
38 * signals if available. Remember that Windows in practice does not have
39 * signals, though.
40 *
41 * In the case of QEMU tools, this will also start/initialize timers.
42 */
43 int qemu_init_main_loop(void);
44
45 /**
46 * main_loop_wait: Run one iteration of the main loop.
47 *
48 * If @nonblocking is true, poll for events, otherwise suspend until
49 * one actually occurs. The main loop usually consists of a loop that
50 * repeatedly calls main_loop_wait(false).
51 *
52 * Main loop services include file descriptor callbacks, bottom halves
53 * and timers (defined in qemu-timer.h). Bottom halves are similar to timers
54 * that execute immediately, but have a lower overhead and scheduling them
55 * is wait-free, thread-safe and signal-safe.
56 *
57 * It is sometimes useful to put a whole program in a coroutine. In this
58 * case, the coroutine actually should be started from within the main loop,
59 * so that the main loop can run whenever the coroutine yields. To do this,
60 * you can use a bottom half to enter the coroutine as soon as the main loop
61 * starts:
62 *
63 * void enter_co_bh(void *opaque) {
64 * QEMUCoroutine *co = opaque;
65 * qemu_coroutine_enter(co, NULL);
66 * }
67 *
68 * ...
69 * QEMUCoroutine *co = qemu_coroutine_create(coroutine_entry);
70 * QEMUBH *start_bh = qemu_bh_new(enter_co_bh, co);
71 * qemu_bh_schedule(start_bh);
72 * while (...) {
73 * main_loop_wait(false);
74 * }
75 *
76 * (In the future we may provide a wrapper for this).
77 *
78 * @nonblocking: Whether the caller should block until an event occurs.
79 */
80 int main_loop_wait(int nonblocking);
81
82 /**
83 * qemu_notify_event: Force processing of pending events.
84 *
85 * Similar to signaling a condition variable, qemu_notify_event forces
86 * main_loop_wait to look at pending events and exit. The caller of
87 * main_loop_wait will usually call it again very soon, so qemu_notify_event
88 * also has the side effect of recalculating the sets of file descriptors
89 * that the main loop waits for.
90 *
91 * Calling qemu_notify_event is rarely necessary, because main loop
92 * services (bottom halves and timers) call it themselves. One notable
93 * exception occurs when using qemu_set_fd_handler2 (see below).
94 */
95 void qemu_notify_event(void);
96
97 #ifdef _WIN32
98 /* return TRUE if no sleep should be done afterwards */
99 typedef int PollingFunc(void *opaque);
100
101 /**
102 * qemu_add_polling_cb: Register a Windows-specific polling callback
103 *
104 * Currently, under Windows some events are polled rather than waited for.
105 * Polling callbacks do not ensure that @func is called timely, because
106 * the main loop might wait for an arbitrarily long time. If possible,
107 * you should instead create a separate thread that does a blocking poll
108 * and set a Win32 event object. The event can then be passed to
109 * qemu_add_wait_object.
110 *
111 * Polling callbacks really have nothing Windows specific in them, but
112 * as they are a hack and are currently not necessary under POSIX systems,
113 * they are only available when QEMU is running under Windows.
114 *
115 * @func: The function that does the polling, and returns 1 to force
116 * immediate completion of main_loop_wait.
117 * @opaque: A pointer-size value that is passed to @func.
118 */
119 int qemu_add_polling_cb(PollingFunc *func, void *opaque);
120
121 /**
122 * qemu_del_polling_cb: Unregister a Windows-specific polling callback
123 *
124 * This function removes a callback that was registered with
125 * qemu_add_polling_cb.
126 *
127 * @func: The function that was passed to qemu_add_polling_cb.
128 * @opaque: A pointer-size value that was passed to qemu_add_polling_cb.
129 */
130 void qemu_del_polling_cb(PollingFunc *func, void *opaque);
131
132 /* Wait objects handling */
133 typedef void WaitObjectFunc(void *opaque);
134
135 /**
136 * qemu_add_wait_object: Register a callback for a Windows handle
137 *
138 * Under Windows, the iohandler mechanism can only be used with sockets.
139 * QEMU must use the WaitForMultipleObjects API to wait on other handles.
140 * This function registers a #HANDLE with QEMU, so that it will be included
141 * in the main loop's calls to WaitForMultipleObjects. When the handle
142 * is in a signaled state, QEMU will call @func.
143 *
144 * @handle: The Windows handle to be observed.
145 * @func: A function to be called when @handle is in a signaled state.
146 * @opaque: A pointer-size value that is passed to @func.
147 */
148 int qemu_add_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque);
149
150 /**
151 * qemu_del_wait_object: Unregister a callback for a Windows handle
152 *
153 * This function removes a callback that was registered with
154 * qemu_add_wait_object.
155 *
156 * @func: The function that was passed to qemu_add_wait_object.
157 * @opaque: A pointer-size value that was passed to qemu_add_wait_object.
158 */
159 void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque);
160 #endif
161
162 /* async I/O support */
163
164 typedef void IOReadHandler(void *opaque, const uint8_t *buf, int size);
165 typedef int IOCanReadHandler(void *opaque);
166 typedef void IOHandler(void *opaque);
167
168 /**
169 * qemu_set_fd_handler2: Register a file descriptor with the main loop
170 *
171 * This function tells the main loop to wake up whenever one of the
172 * following conditions is true:
173 *
174 * 1) if @fd_write is not %NULL, when the file descriptor is writable;
175 *
176 * 2) if @fd_read is not %NULL, when the file descriptor is readable.
177 *
178 * @fd_read_poll can be used to disable the @fd_read callback temporarily.
179 * This is useful to avoid calling qemu_set_fd_handler2 every time the
180 * client becomes interested in reading (or dually, stops being interested).
181 * A typical example is when @fd is a listening socket and you want to bound
182 * the number of active clients. Remember to call qemu_notify_event whenever
183 * the condition may change from %false to %true.
184 *
185 * The callbacks that are set up by qemu_set_fd_handler2 are level-triggered.
186 * If @fd_read does not read from @fd, or @fd_write does not write to @fd
187 * until its buffers are full, they will be called again on the next
188 * iteration.
189 *
190 * @fd: The file descriptor to be observed. Under Windows it must be
191 * a #SOCKET.
192 *
193 * @fd_read_poll: A function that returns 1 if the @fd_read callback
194 * should be fired. If the function returns 0, the main loop will not
195 * end its iteration even if @fd becomes readable.
196 *
197 * @fd_read: A level-triggered callback that is fired if @fd is readable
198 * at the beginning of a main loop iteration, or if it becomes readable
199 * during one.
200 *
201 * @fd_write: A level-triggered callback that is fired when @fd is writable
202 * at the beginning of a main loop iteration, or if it becomes writable
203 * during one.
204 *
205 * @opaque: A pointer-sized value that is passed to @fd_read_poll,
206 * @fd_read and @fd_write.
207 */
208 int qemu_set_fd_handler2(int fd,
209 IOCanReadHandler *fd_read_poll,
210 IOHandler *fd_read,
211 IOHandler *fd_write,
212 void *opaque);
213
214 /**
215 * qemu_set_fd_handler: Register a file descriptor with the main loop
216 *
217 * This function tells the main loop to wake up whenever one of the
218 * following conditions is true:
219 *
220 * 1) if @fd_write is not %NULL, when the file descriptor is writable;
221 *
222 * 2) if @fd_read is not %NULL, when the file descriptor is readable.
223 *
224 * The callbacks that are set up by qemu_set_fd_handler are level-triggered.
225 * If @fd_read does not read from @fd, or @fd_write does not write to @fd
226 * until its buffers are full, they will be called again on the next
227 * iteration.
228 *
229 * @fd: The file descriptor to be observed. Under Windows it must be
230 * a #SOCKET.
231 *
232 * @fd_read: A level-triggered callback that is fired if @fd is readable
233 * at the beginning of a main loop iteration, or if it becomes readable
234 * during one.
235 *
236 * @fd_write: A level-triggered callback that is fired when @fd is writable
237 * at the beginning of a main loop iteration, or if it becomes writable
238 * during one.
239 *
240 * @opaque: A pointer-sized value that is passed to @fd_read and @fd_write.
241 */
242 int qemu_set_fd_handler(int fd,
243 IOHandler *fd_read,
244 IOHandler *fd_write,
245 void *opaque);
246
247 typedef struct QEMUBH QEMUBH;
248 typedef void QEMUBHFunc(void *opaque);
249
250 /**
251 * qemu_bh_new: Allocate a new bottom half structure.
252 *
253 * Bottom halves are lightweight callbacks whose invocation is guaranteed
254 * to be wait-free, thread-safe and signal-safe. The #QEMUBH structure
255 * is opaque and must be allocated prior to its use.
256 */
257 QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque);
258
259 /**
260 * qemu_bh_schedule: Schedule a bottom half.
261 *
262 * Scheduling a bottom half interrupts the main loop and causes the
263 * execution of the callback that was passed to qemu_bh_new.
264 *
265 * Bottom halves that are scheduled from a bottom half handler are instantly
266 * invoked. This can create an infinite loop if a bottom half handler
267 * schedules itself.
268 *
269 * @bh: The bottom half to be scheduled.
270 */
271 void qemu_bh_schedule(QEMUBH *bh);
272
273 /**
274 * qemu_bh_cancel: Cancel execution of a bottom half.
275 *
276 * Canceling execution of a bottom half undoes the effect of calls to
277 * qemu_bh_schedule without freeing its resources yet. While cancellation
278 * itself is also wait-free and thread-safe, it can of course race with the
279 * loop that executes bottom halves unless you are holding the iothread
280 * mutex. This makes it mostly useless if you are not holding the mutex.
281 *
282 * @bh: The bottom half to be canceled.
283 */
284 void qemu_bh_cancel(QEMUBH *bh);
285
286 /**
287 *qemu_bh_delete: Cancel execution of a bottom half and free its resources.
288 *
289 * Deleting a bottom half frees the memory that was allocated for it by
290 * qemu_bh_new. It also implies canceling the bottom half if it was
291 * scheduled.
292 *
293 * @bh: The bottom half to be deleted.
294 */
295 void qemu_bh_delete(QEMUBH *bh);
296
297 #ifdef CONFIG_POSIX
298 /**
299 * qemu_add_child_watch: Register a child process for reaping.
300 *
301 * Under POSIX systems, a parent process must read the exit status of
302 * its child processes using waitpid, or the operating system will not
303 * free some of the resources attached to that process.
304 *
305 * This function directs the QEMU main loop to observe a child process
306 * and call waitpid as soon as it exits; the watch is then removed
307 * automatically. It is useful whenever QEMU forks a child process
308 * but will find out about its termination by other means such as a
309 * "broken pipe".
310 *
311 * @pid: The pid that QEMU should observe.
312 */
313 int qemu_add_child_watch(pid_t pid);
314 #endif
315
316 /**
317 * qemu_mutex_lock_iothread: Lock the main loop mutex.
318 *
319 * This function locks the main loop mutex. The mutex is taken by
320 * qemu_init_main_loop and always taken except while waiting on
321 * external events (such as with select). The mutex should be taken
322 * by threads other than the main loop thread when calling
323 * qemu_bh_new(), qemu_set_fd_handler() and basically all other
324 * functions documented in this file.
325 *
326 * NOTE: tools currently are single-threaded and qemu_mutex_lock_iothread
327 * is a no-op there.
328 */
329 void qemu_mutex_lock_iothread(void);
330
331 /**
332 * qemu_mutex_unlock_iothread: Unlock the main loop mutex.
333 *
334 * This function unlocks the main loop mutex. The mutex is taken by
335 * qemu_init_main_loop and always taken except while waiting on
336 * external events (such as with select). The mutex should be unlocked
337 * as soon as possible by threads other than the main loop thread,
338 * because it prevents the main loop from processing callbacks,
339 * including timers and bottom halves.
340 *
341 * NOTE: tools currently are single-threaded and qemu_mutex_unlock_iothread
342 * is a no-op there.
343 */
344 void qemu_mutex_unlock_iothread(void);
345
346 /* internal interfaces */
347
348 void qemu_fd_register(int fd);
349 void qemu_iohandler_fill(int *pnfds, fd_set *readfds, fd_set *writefds, fd_set *xfds);
350 void qemu_iohandler_poll(fd_set *readfds, fd_set *writefds, fd_set *xfds, int rc);
351
352 void qemu_bh_schedule_idle(QEMUBH *bh);
353 int qemu_bh_poll(void);
354 void qemu_bh_update_timeout(uint32_t *timeout);
355
356 #endif