include/qemu/main-loop.h

   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
  27
  28 #include "block/aio.h"
  29
  30 #define SIG_IPI SIGUSR1
  31
  32 /**
  33  * qemu_init_main_loop: Set up the process so that it can run the main loop.
  34  *
  35  * This includes setting up signal handlers.  It should be called before
  36  * any other threads are created.  In addition, threads other than the
  37  * main one should block signals that are trapped by the main loop.
  38  * For simplicity, you can consider these signals to be safe: SIGUSR1,
  39  * SIGUSR2, thread signals (SIGFPE, SIGILL, SIGSEGV, SIGBUS) and real-time
  40  * signals if available.  Remember that Windows in practice does not have
  41  * signals, though.
  42  *
  43  * In the case of QEMU tools, this will also start/initialize timers.
  44  */
  45 int qemu_init_main_loop(Error **errp);
  46
  47 /**
  48  * main_loop_wait: Run one iteration of the main loop.
  49  *
  50  * If @nonblocking is true, poll for events, otherwise suspend until
  51  * one actually occurs.  The main loop usually consists of a loop that
  52  * repeatedly calls main_loop_wait(false).
  53  *
  54  * Main loop services include file descriptor callbacks, bottom halves
  55  * and timers (defined in qemu-timer.h).  Bottom halves are similar to timers
  56  * that execute immediately, but have a lower overhead and scheduling them
  57  * is wait-free, thread-safe and signal-safe.
  58  *
  59  * It is sometimes useful to put a whole program in a coroutine.  In this
  60  * case, the coroutine actually should be started from within the main loop,
  61  * so that the main loop can run whenever the coroutine yields.  To do this,
  62  * you can use a bottom half to enter the coroutine as soon as the main loop
  63  * starts:
  64  *
  65  *     void enter_co_bh(void *opaque) {
  66  *         QEMUCoroutine *co = opaque;
  67  *         qemu_coroutine_enter(co, NULL);
  68  *     }
  69  *
  70  *     ...
  71  *     QEMUCoroutine *co = qemu_coroutine_create(coroutine_entry);
  72  *     QEMUBH *start_bh = qemu_bh_new(enter_co_bh, co);
  73  *     qemu_bh_schedule(start_bh);
  74  *     while (...) {
  75  *         main_loop_wait(false);
  76  *     }
  77  *
  78  * (In the future we may provide a wrapper for this).
  79  *
  80  * @nonblocking: Whether the caller should block until an event occurs.
  81  */
  82 int main_loop_wait(int nonblocking);
  83
  84 /**
  85  * qemu_get_aio_context: Return the main loop's AioContext
  86  */
  87 AioContext *qemu_get_aio_context(void);
  88
  89 /**
  90  * qemu_notify_event: Force processing of pending events.
  91  *
  92  * Similar to signaling a condition variable, qemu_notify_event forces
  93  * main_loop_wait to look at pending events and exit.  The caller of
  94  * main_loop_wait will usually call it again very soon, so qemu_notify_event
  95  * also has the side effect of recalculating the sets of file descriptors
  96  * that the main loop waits for.
  97  *
  98  * Calling qemu_notify_event is rarely necessary, because main loop
  99  * services (bottom halves and timers) call it themselves.
 100  */
 101 void qemu_notify_event(void);
 102
 103 #ifdef _WIN32
 104 /* return TRUE if no sleep should be done afterwards */
 105 typedef int PollingFunc(void *opaque);
 106
 107 /**
 108  * qemu_add_polling_cb: Register a Windows-specific polling callback
 109  *
 110  * Currently, under Windows some events are polled rather than waited for.
 111  * Polling callbacks do not ensure that @func is called timely, because
 112  * the main loop might wait for an arbitrarily long time.  If possible,
 113  * you should instead create a separate thread that does a blocking poll
 114  * and set a Win32 event object.  The event can then be passed to
 115  * qemu_add_wait_object.
 116  *
 117  * Polling callbacks really have nothing Windows specific in them, but
 118  * as they are a hack and are currently not necessary under POSIX systems,
 119  * they are only available when QEMU is running under Windows.
 120  *
 121  * @func: The function that does the polling, and returns 1 to force
 122  * immediate completion of main_loop_wait.
 123  * @opaque: A pointer-size value that is passed to @func.
 124  */
 125 int qemu_add_polling_cb(PollingFunc *func, void *opaque);
 126
 127 /**
 128  * qemu_del_polling_cb: Unregister a Windows-specific polling callback
 129  *
 130  * This function removes a callback that was registered with
 131  * qemu_add_polling_cb.
 132  *
 133  * @func: The function that was passed to qemu_add_polling_cb.
 134  * @opaque: A pointer-size value that was passed to qemu_add_polling_cb.
 135  */
 136 void qemu_del_polling_cb(PollingFunc *func, void *opaque);
 137
 138 /* Wait objects handling */
 139 typedef void WaitObjectFunc(void *opaque);
 140
 141 /**
 142  * qemu_add_wait_object: Register a callback for a Windows handle
 143  *
 144  * Under Windows, the iohandler mechanism can only be used with sockets.
 145  * QEMU must use the WaitForMultipleObjects API to wait on other handles.
 146  * This function registers a #HANDLE with QEMU, so that it will be included
 147  * in the main loop's calls to WaitForMultipleObjects.  When the handle
 148  * is in a signaled state, QEMU will call @func.
 149  *
 150  * @handle: The Windows handle to be observed.
 151  * @func: A function to be called when @handle is in a signaled state.
 152  * @opaque: A pointer-size value that is passed to @func.
 153  */
 154 int qemu_add_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque);
 155
 156 /**
 157  * qemu_del_wait_object: Unregister a callback for a Windows handle
 158  *
 159  * This function removes a callback that was registered with
 160  * qemu_add_wait_object.
 161  *
 162  * @func: The function that was passed to qemu_add_wait_object.
 163  * @opaque: A pointer-size value that was passed to qemu_add_wait_object.
 164  */
 165 void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque);
 166 #endif
 167
 168 /* async I/O support */
 169
 170 typedef void IOReadHandler(void *opaque, const uint8_t *buf, int size);
 171 typedef int IOCanReadHandler(void *opaque);
 172
 173 /**
 174  * qemu_set_fd_handler: Register a file descriptor with the main loop
 175  *
 176  * This function tells the main loop to wake up whenever one of the
 177  * following conditions is true:
 178  *
 179  * 1) if @fd_write is not %NULL, when the file descriptor is writable;
 180  *
 181  * 2) if @fd_read is not %NULL, when the file descriptor is readable.
 182  *
 183  * The callbacks that are set up by qemu_set_fd_handler are level-triggered.
 184  * If @fd_read does not read from @fd, or @fd_write does not write to @fd
 185  * until its buffers are full, they will be called again on the next
 186  * iteration.
 187  *
 188  * @fd: The file descriptor to be observed.  Under Windows it must be
 189  * a #SOCKET.
 190  *
 191  * @fd_read: A level-triggered callback that is fired if @fd is readable
 192  * at the beginning of a main loop iteration, or if it becomes readable
 193  * during one.
 194  *
 195  * @fd_write: A level-triggered callback that is fired when @fd is writable
 196  * at the beginning of a main loop iteration, or if it becomes writable
 197  * during one.
 198  *
 199  * @opaque: A pointer-sized value that is passed to @fd_read and @fd_write.
 200  */
 201 void qemu_set_fd_handler(int fd,
 202                          IOHandler *fd_read,
 203                          IOHandler *fd_write,
 204                          void *opaque);
 205
 206 GSource *iohandler_get_g_source(void);
 207 AioContext *iohandler_get_aio_context(void);
 208 #ifdef CONFIG_POSIX
 209 /**
 210  * qemu_add_child_watch: Register a child process for reaping.
 211  *
 212  * Under POSIX systems, a parent process must read the exit status of
 213  * its child processes using waitpid, or the operating system will not
 214  * free some of the resources attached to that process.
 215  *
 216  * This function directs the QEMU main loop to observe a child process
 217  * and call waitpid as soon as it exits; the watch is then removed
 218  * automatically.  It is useful whenever QEMU forks a child process
 219  * but will find out about its termination by other means such as a
 220  * "broken pipe".
 221  *
 222  * @pid: The pid that QEMU should observe.
 223  */
 224 int qemu_add_child_watch(pid_t pid);
 225 #endif
 226
 227 /**
 228  * qemu_mutex_iothread_locked: Return lock status of the main loop mutex.
 229  *
 230  * The main loop mutex is the coarsest lock in QEMU, and as such it
 231  * must always be taken outside other locks.  This function helps
 232  * functions take different paths depending on whether the current
 233  * thread is running within the main loop mutex.
 234  */
 235 bool qemu_mutex_iothread_locked(void);
 236
 237 /**
 238  * qemu_mutex_lock_iothread: Lock the main loop mutex.
 239  *
 240  * This function locks the main loop mutex.  The mutex is taken by
 241  * qemu_init_main_loop and always taken except while waiting on
 242  * external events (such as with select).  The mutex should be taken
 243  * by threads other than the main loop thread when calling
 244  * qemu_bh_new(), qemu_set_fd_handler() and basically all other
 245  * functions documented in this file.
 246  *
 247  * NOTE: tools currently are single-threaded and qemu_mutex_lock_iothread
 248  * is a no-op there.
 249  */
 250 void qemu_mutex_lock_iothread(void);
 251
 252 /**
 253  * qemu_mutex_unlock_iothread: Unlock the main loop mutex.
 254  *
 255  * This function unlocks the main loop mutex.  The mutex is taken by
 256  * qemu_init_main_loop and always taken except while waiting on
 257  * external events (such as with select).  The mutex should be unlocked
 258  * as soon as possible by threads other than the main loop thread,
 259  * because it prevents the main loop from processing callbacks,
 260  * including timers and bottom halves.
 261  *
 262  * NOTE: tools currently are single-threaded and qemu_mutex_unlock_iothread
 263  * is a no-op there.
 264  */
 265 void qemu_mutex_unlock_iothread(void);
 266
 267 /* internal interfaces */
 268
 269 void qemu_fd_register(int fd);
 270
 271 QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque);
 272 void qemu_bh_schedule_idle(QEMUBH *bh);
 273
 274 #endif