summaryrefslogtreecommitdiff
path: root/main-loop.h
blob: e8059c3d0a72d4063ec5b2454684964eafd32348 (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
/*
 * QEMU System Emulator
 *
 * Copyright (c) 2003-2008 Fabrice Bellard
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#ifndef QEMU_MAIN_LOOP_H
#define QEMU_MAIN_LOOP_H 1

#include "block/aio.h"

#define SIG_IPI SIGUSR1

/**
 * qemu_init_main_loop: Set up the process so that it can run the main loop.
 *
 * This includes setting up signal handlers.  It should be called before
 * any other threads are created.  In addition, threads other than the
 * main one should block signals that are trapped by the main loop.
 * For simplicity, you can consider these signals to be safe: SIGUSR1,
 * SIGUSR2, thread signals (SIGFPE, SIGILL, SIGSEGV, SIGBUS) and real-time
 * signals if available.  Remember that Windows in practice does not have
 * signals, though.
 *
 * In the case of QEMU tools, this will also start/initialize timers.
 */
int qemu_init_main_loop(void);

/**
 * main_loop_wait: Run one iteration of the main loop.
 *
 * If @nonblocking is true, poll for events, otherwise suspend until
 * one actually occurs.  The main loop usually consists of a loop that
 * repeatedly calls main_loop_wait(false).
 *
 * Main loop services include file descriptor callbacks, bottom halves
 * and timers (defined in qemu-timer.h).  Bottom halves are similar to timers
 * that execute immediately, but have a lower overhead and scheduling them
 * is wait-free, thread-safe and signal-safe.
 *
 * It is sometimes useful to put a whole program in a coroutine.  In this
 * case, the coroutine actually should be started from within the main loop,
 * so that the main loop can run whenever the coroutine yields.  To do this,
 * you can use a bottom half to enter the coroutine as soon as the main loop
 * starts:
 *
 *     void enter_co_bh(void *opaque) {
 *         QEMUCoroutine *co = opaque;
 *         qemu_coroutine_enter(co, NULL);
 *     }
 *
 *     ...
 *     QEMUCoroutine *co = qemu_coroutine_create(coroutine_entry);
 *     QEMUBH *start_bh = qemu_bh_new(enter_co_bh, co);
 *     qemu_bh_schedule(start_bh);
 *     while (...) {
 *         main_loop_wait(false);
 *     }
 *
 * (In the future we may provide a wrapper for this).
 *
 * @nonblocking: Whether the caller should block until an event occurs.
 */
int main_loop_wait(int nonblocking);

/**
 * qemu_notify_event: Force processing of pending events.
 *
 * Similar to signaling a condition variable, qemu_notify_event forces
 * main_loop_wait to look at pending events and exit.  The caller of
 * main_loop_wait will usually call it again very soon, so qemu_notify_event
 * also has the side effect of recalculating the sets of file descriptors
 * that the main loop waits for.
 *
 * Calling qemu_notify_event is rarely necessary, because main loop
 * services (bottom halves and timers) call it themselves.  One notable
 * exception occurs when using qemu_set_fd_handler2 (see below).
 */
void qemu_notify_event(void);

#ifdef _WIN32
/* return TRUE if no sleep should be done afterwards */
typedef int PollingFunc(void *opaque);

/**
 * qemu_add_polling_cb: Register a Windows-specific polling callback
 *
 * Currently, under Windows some events are polled rather than waited for.
 * Polling callbacks do not ensure that @func is called timely, because
 * the main loop might wait for an arbitrarily long time.  If possible,
 * you should instead create a separate thread that does a blocking poll
 * and set a Win32 event object.  The event can then be passed to
 * qemu_add_wait_object.
 *
 * Polling callbacks really have nothing Windows specific in them, but
 * as they are a hack and are currently not necessary under POSIX systems,
 * they are only available when QEMU is running under Windows.
 *
 * @func: The function that does the polling, and returns 1 to force
 * immediate completion of main_loop_wait.
 * @opaque: A pointer-size value that is passed to @func.
 */
int qemu_add_polling_cb(PollingFunc *func, void *opaque);

/**
 * qemu_del_polling_cb: Unregister a Windows-specific polling callback
 *
 * This function removes a callback that was registered with
 * qemu_add_polling_cb.
 *
 * @func: The function that was passed to qemu_add_polling_cb.
 * @opaque: A pointer-size value that was passed to qemu_add_polling_cb.
 */
void qemu_del_polling_cb(PollingFunc *func, void *opaque);

/* Wait objects handling */
typedef void WaitObjectFunc(void *opaque);

/**
 * qemu_add_wait_object: Register a callback for a Windows handle
 *
 * Under Windows, the iohandler mechanism can only be used with sockets.
 * QEMU must use the WaitForMultipleObjects API to wait on other handles.
 * This function registers a #HANDLE with QEMU, so that it will be included
 * in the main loop's calls to WaitForMultipleObjects.  When the handle
 * is in a signaled state, QEMU will call @func.
 *
 * @handle: The Windows handle to be observed.
 * @func: A function to be called when @handle is in a signaled state.
 * @opaque: A pointer-size value that is passed to @func.
 */
int qemu_add_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque);

/**
 * qemu_del_wait_object: Unregister a callback for a Windows handle
 *
 * This function removes a callback that was registered with
 * qemu_add_wait_object.
 *
 * @func: The function that was passed to qemu_add_wait_object.
 * @opaque: A pointer-size value that was passed to qemu_add_wait_object.
 */
void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque);
#endif

/* async I/O support */

typedef void IOReadHandler(void *opaque, const uint8_t *buf, int size);
typedef int IOCanReadHandler(void *opaque);

/**
 * qemu_set_fd_handler2: Register a file descriptor with the main loop
 *
 * This function tells the main loop to wake up whenever one of the
 * following conditions is true:
 *
 * 1) if @fd_write is not %NULL, when the file descriptor is writable;
 *
 * 2) if @fd_read is not %NULL, when the file descriptor is readable.
 *
 * @fd_read_poll can be used to disable the @fd_read callback temporarily.
 * This is useful to avoid calling qemu_set_fd_handler2 every time the
 * client becomes interested in reading (or dually, stops being interested).
 * A typical example is when @fd is a listening socket and you want to bound
 * the number of active clients.  Remember to call qemu_notify_event whenever
 * the condition may change from %false to %true.
 *
 * The callbacks that are set up by qemu_set_fd_handler2 are level-triggered.
 * If @fd_read does not read from @fd, or @fd_write does not write to @fd
 * until its buffers are full, they will be called again on the next
 * iteration.
 *
 * @fd: The file descriptor to be observed.  Under Windows it must be
 * a #SOCKET.
 *
 * @fd_read_poll: A function that returns 1 if the @fd_read callback
 * should be fired.  If the function returns 0, the main loop will not
 * end its iteration even if @fd becomes readable.
 *
 * @fd_read: A level-triggered callback that is fired if @fd is readable
 * at the beginning of a main loop iteration, or if it becomes readable
 * during one.
 *
 * @fd_write: A level-triggered callback that is fired when @fd is writable
 * at the beginning of a main loop iteration, or if it becomes writable
 * during one.
 *
 * @opaque: A pointer-sized value that is passed to @fd_read_poll,
 * @fd_read and @fd_write.
 */
int qemu_set_fd_handler2(int fd,
                         IOCanReadHandler *fd_read_poll,
                         IOHandler *fd_read,
                         IOHandler *fd_write,
                         void *opaque);

/**
 * qemu_set_fd_handler: Register a file descriptor with the main loop
 *
 * This function tells the main loop to wake up whenever one of the
 * following conditions is true:
 *
 * 1) if @fd_write is not %NULL, when the file descriptor is writable;
 *
 * 2) if @fd_read is not %NULL, when the file descriptor is readable.
 *
 * The callbacks that are set up by qemu_set_fd_handler are level-triggered.
 * If @fd_read does not read from @fd, or @fd_write does not write to @fd
 * until its buffers are full, they will be called again on the next
 * iteration.
 *
 * @fd: The file descriptor to be observed.  Under Windows it must be
 * a #SOCKET.
 *
 * @fd_read: A level-triggered callback that is fired if @fd is readable
 * at the beginning of a main loop iteration, or if it becomes readable
 * during one.
 *
 * @fd_write: A level-triggered callback that is fired when @fd is writable
 * at the beginning of a main loop iteration, or if it becomes writable
 * during one.
 *
 * @opaque: A pointer-sized value that is passed to @fd_read and @fd_write.
 */
int qemu_set_fd_handler(int fd,
                        IOHandler *fd_read,
                        IOHandler *fd_write,
                        void *opaque);

#ifdef CONFIG_POSIX
/**
 * qemu_add_child_watch: Register a child process for reaping.
 *
 * Under POSIX systems, a parent process must read the exit status of
 * its child processes using waitpid, or the operating system will not
 * free some of the resources attached to that process.
 *
 * This function directs the QEMU main loop to observe a child process
 * and call waitpid as soon as it exits; the watch is then removed
 * automatically.  It is useful whenever QEMU forks a child process
 * but will find out about its termination by other means such as a
 * "broken pipe".
 *
 * @pid: The pid that QEMU should observe.
 */
int qemu_add_child_watch(pid_t pid);
#endif

/**
 * qemu_mutex_lock_iothread: Lock the main loop mutex.
 *
 * This function locks the main loop mutex.  The mutex is taken by
 * qemu_init_main_loop and always taken except while waiting on
 * external events (such as with select).  The mutex should be taken
 * by threads other than the main loop thread when calling
 * qemu_bh_new(), qemu_set_fd_handler() and basically all other
 * functions documented in this file.
 *
 * NOTE: tools currently are single-threaded and qemu_mutex_lock_iothread
 * is a no-op there.
 */
void qemu_mutex_lock_iothread(void);

/**
 * qemu_mutex_unlock_iothread: Unlock the main loop mutex.
 *
 * This function unlocks the main loop mutex.  The mutex is taken by
 * qemu_init_main_loop and always taken except while waiting on
 * external events (such as with select).  The mutex should be unlocked
 * as soon as possible by threads other than the main loop thread,
 * because it prevents the main loop from processing callbacks,
 * including timers and bottom halves.
 *
 * NOTE: tools currently are single-threaded and qemu_mutex_unlock_iothread
 * is a no-op there.
 */
void qemu_mutex_unlock_iothread(void);

/* internal interfaces */

void qemu_fd_register(int fd);
void qemu_iohandler_fill(int *pnfds, fd_set *readfds, fd_set *writefds, fd_set *xfds);
void qemu_iohandler_poll(fd_set *readfds, fd_set *writefds, fd_set *xfds, int rc);

QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque);
void qemu_bh_schedule_idle(QEMUBH *bh);

#endif