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 1
  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.  One notable
 100  * exception occurs when using qemu_set_fd_handler2 (see below).
 101  */
 102 void qemu_notify_event(void);
 103
 104 #ifdef _WIN32
 105 /* return TRUE if no sleep should be done afterwards */
 106 typedef int PollingFunc(void *opaque);
 107
 108 /**
 109  * qemu_add_polling_cb: Register a Windows-specific polling callback
 110  *
 111  * Currently, under Windows some events are polled rather than waited for.
 112  * Polling callbacks do not ensure that @func is called timely, because
 113  * the main loop might wait for an arbitrarily long time.  If possible,
 114  * you should instead create a separate thread that does a blocking poll
 115  * and set a Win32 event object.  The event can then be passed to
 116  * qemu_add_wait_object.
 117  *
 118  * Polling callbacks really have nothing Windows specific in them, but
 119  * as they are a hack and are currently not necessary under POSIX systems,
 120  * they are only available when QEMU is running under Windows.
 121  *
 122  * @func: The function that does the polling, and returns 1 to force
 123  * immediate completion of main_loop_wait.
 124  * @opaque: A pointer-size value that is passed to @func.
 125  */
 126 int qemu_add_polling_cb(PollingFunc *func, void *opaque);
 127
 128 /**
 129  * qemu_del_polling_cb: Unregister a Windows-specific polling callback
 130  *
 131  * This function removes a callback that was registered with
 132  * qemu_add_polling_cb.
 133  *
 134  * @func: The function that was passed to qemu_add_polling_cb.
 135  * @opaque: A pointer-size value that was passed to qemu_add_polling_cb.
 136  */
 137 void qemu_del_polling_cb(PollingFunc *func, void *opaque);
 138
 139 /* Wait objects handling */
 140 typedef void WaitObjectFunc(void *opaque);
 141
 142 /**
 143  * qemu_add_wait_object: Register a callback for a Windows handle
 144  *
 145  * Under Windows, the iohandler mechanism can only be used with sockets.
 146  * QEMU must use the WaitForMultipleObjects API to wait on other handles.
 147  * This function registers a #HANDLE with QEMU, so that it will be included
 148  * in the main loop's calls to WaitForMultipleObjects.  When the handle
 149  * is in a signaled state, QEMU will call @func.
 150  *
 151  * @handle: The Windows handle to be observed.
 152  * @func: A function to be called when @handle is in a signaled state.
 153  * @opaque: A pointer-size value that is passed to @func.
 154  */
 155 int qemu_add_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque);
 156
 157 /**
 158  * qemu_del_wait_object: Unregister a callback for a Windows handle
 159  *
 160  * This function removes a callback that was registered with
 161  * qemu_add_wait_object.
 162  *
 163  * @func: The function that was passed to qemu_add_wait_object.
 164  * @opaque: A pointer-size value that was passed to qemu_add_wait_object.
 165  */
 166 void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque);
 167 #endif
 168
 169 /* async I/O support */
 170
 171 typedef void IOReadHandler(void *opaque, const uint8_t *buf, int size);
 172 typedef int IOCanReadHandler(void *opaque);
 173
 174 /**
 175  * qemu_set_fd_handler2: Register a file descriptor with the main loop
 176  *
 177  * This function tells the main loop to wake up whenever one of the
 178  * following conditions is true:
 179  *
 180  * 1) if @fd_write is not %NULL, when the file descriptor is writable;
 181  *
 182  * 2) if @fd_read is not %NULL, when the file descriptor is readable.
 183  *
 184  * @fd_read_poll can be used to disable the @fd_read callback temporarily.
 185  * This is useful to avoid calling qemu_set_fd_handler2 every time the
 186  * client becomes interested in reading (or dually, stops being interested).
 187  * A typical example is when @fd is a listening socket and you want to bound
 188  * the number of active clients.  Remember to call qemu_notify_event whenever
 189  * the condition may change from %false to %true.
 190  *
 191  * The callbacks that are set up by qemu_set_fd_handler2 are level-triggered.
 192  * If @fd_read does not read from @fd, or @fd_write does not write to @fd
 193  * until its buffers are full, they will be called again on the next
 194  * iteration.
 195  *
 196  * @fd: The file descriptor to be observed.  Under Windows it must be
 197  * a #SOCKET.
 198  *
 199  * @fd_read_poll: A function that returns 1 if the @fd_read callback
 200  * should be fired.  If the function returns 0, the main loop will not
 201  * end its iteration even if @fd becomes readable.
 202  *
 203  * @fd_read: A level-triggered callback that is fired if @fd is readable
 204  * at the beginning of a main loop iteration, or if it becomes readable
 205  * during one.
 206  *
 207  * @fd_write: A level-triggered callback that is fired when @fd is writable
 208  * at the beginning of a main loop iteration, or if it becomes writable
 209  * during one.
 210  *
 211  * @opaque: A pointer-sized value that is passed to @fd_read_poll,
 212  * @fd_read and @fd_write.
 213  */
 214 int qemu_set_fd_handler2(int fd,
 215                          IOCanReadHandler *fd_read_poll,
 216                          IOHandler *fd_read,
 217                          IOHandler *fd_write,
 218                          void *opaque);
 219
 220 /**
 221  * qemu_set_fd_handler: Register a file descriptor with the main loop
 222  *
 223  * This function tells the main loop to wake up whenever one of the
 224  * following conditions is true:
 225  *
 226  * 1) if @fd_write is not %NULL, when the file descriptor is writable;
 227  *
 228  * 2) if @fd_read is not %NULL, when the file descriptor is readable.
 229  *
 230  * The callbacks that are set up by qemu_set_fd_handler are level-triggered.
 231  * If @fd_read does not read from @fd, or @fd_write does not write to @fd
 232  * until its buffers are full, they will be called again on the next
 233  * iteration.
 234  *
 235  * @fd: The file descriptor to be observed.  Under Windows it must be
 236  * a #SOCKET.
 237  *
 238  * @fd_read: A level-triggered callback that is fired if @fd is readable
 239  * at the beginning of a main loop iteration, or if it becomes readable
 240  * during one.
 241  *
 242  * @fd_write: A level-triggered callback that is fired when @fd is writable
 243  * at the beginning of a main loop iteration, or if it becomes writable
 244  * during one.
 245  *
 246  * @opaque: A pointer-sized value that is passed to @fd_read and @fd_write.
 247  */
 248 int qemu_set_fd_handler(int fd,
 249                         IOHandler *fd_read,
 250                         IOHandler *fd_write,
 251                         void *opaque);
 252
 253 #ifdef CONFIG_POSIX
 254 /**
 255  * qemu_add_child_watch: Register a child process for reaping.
 256  *
 257  * Under POSIX systems, a parent process must read the exit status of
 258  * its child processes using waitpid, or the operating system will not
 259  * free some of the resources attached to that process.
 260  *
 261  * This function directs the QEMU main loop to observe a child process
 262  * and call waitpid as soon as it exits; the watch is then removed
 263  * automatically.  It is useful whenever QEMU forks a child process
 264  * but will find out about its termination by other means such as a
 265  * "broken pipe".
 266  *
 267  * @pid: The pid that QEMU should observe.
 268  */
 269 int qemu_add_child_watch(pid_t pid);
 270 #endif
 271
 272 /**
 273  * qemu_mutex_lock_iothread: Lock the main loop mutex.
 274  *
 275  * This function locks the main loop mutex.  The mutex is taken by
 276  * qemu_init_main_loop and always taken except while waiting on
 277  * external events (such as with select).  The mutex should be taken
 278  * by threads other than the main loop thread when calling
 279  * qemu_bh_new(), qemu_set_fd_handler() and basically all other
 280  * functions documented in this file.
 281  *
 282  * NOTE: tools currently are single-threaded and qemu_mutex_lock_iothread
 283  * is a no-op there.
 284  */
 285 void qemu_mutex_lock_iothread(void);
 286
 287 /**
 288  * qemu_mutex_unlock_iothread: Unlock the main loop mutex.
 289  *
 290  * This function unlocks the main loop mutex.  The mutex is taken by
 291  * qemu_init_main_loop and always taken except while waiting on
 292  * external events (such as with select).  The mutex should be unlocked
 293  * as soon as possible by threads other than the main loop thread,
 294  * because it prevents the main loop from processing callbacks,
 295  * including timers and bottom halves.
 296  *
 297  * NOTE: tools currently are single-threaded and qemu_mutex_unlock_iothread
 298  * is a no-op there.
 299  */
 300 void qemu_mutex_unlock_iothread(void);
 301
 302 /* internal interfaces */
 303
 304 void qemu_fd_register(int fd);
 305 void qemu_iohandler_fill(GArray *pollfds);
 306 void qemu_iohandler_poll(GArray *pollfds, int rc);
 307
 308 QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque);
 309 void qemu_bh_schedule_idle(QEMUBH *bh);
 310
 311 #endif