main-loop: create main-loop.h

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 327 insertions, 0 deletions

diff --git a/main-loop.h b/main-loop.h
new file mode 100644
index 0000000000..a73b9c0bbe
--- /dev/null
+++ b/main-loop.h
@@ -0,0 +1,327 @@
+/*
+ * 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
+
+#ifdef SIGRTMIN
+#define SIG_IPI (SIGRTMIN+4)
+#else
+#define SIG_IPI SIGUSR1
+#endif
+
+/**
+ * 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.
+ */
+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 currenly 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);
+typedef void IOHandler(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);
+
+typedef struct QEMUBH QEMUBH;
+typedef void QEMUBHFunc(void *opaque);
+
+/**
+ * qemu_bh_new: Allocate a new bottom half structure.
+ *
+ * Bottom halves are lightweight callbacks whose invocation is guaranteed
+ * to be wait-free, thread-safe and signal-safe.  The #QEMUBH structure
+ * is opaque and must be allocated prior to its use.
+ */
+QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque);
+
+/**
+ * qemu_bh_schedule: Schedule a bottom half.
+ *
+ * Scheduling a bottom half interrupts the main loop and causes the
+ * execution of the callback that was passed to qemu_bh_new.
+ *
+ * Bottom halves that are scheduled from a bottom half handler are instantly
+ * invoked.  This can create an infinite loop if a bottom half handler
+ * schedules itself.
+ *
+ * @bh: The bottom half to be scheduled.
+ */
+void qemu_bh_schedule(QEMUBH *bh);
+
+/**
+ * qemu_bh_cancel: Cancel execution of a bottom half.
+ *
+ * Canceling execution of a bottom half undoes the effect of calls to
+ * qemu_bh_schedule without freeing its resources yet.  While cancellation
+ * itself is also wait-free and thread-safe, it can of course race with the
+ * loop that executes bottom halves unless you are holding the iothread
+ * mutex.  This makes it mostly useless if you are not holding the mutex.
+ *
+ * @bh: The bottom half to be canceled.
+ */
+void qemu_bh_cancel(QEMUBH *bh);
+
+/**
+ *qemu_bh_delete: Cancel execution of a bottom half and free its resources.
+ *
+ * Deleting a bottom half frees the memory that was allocated for it by
+ * qemu_bh_new.  It also implies canceling the bottom half if it was
+ * scheduled.
+ *
+ * @bh: The bottom half to be deleted.
+ */
+void qemu_bh_delete(QEMUBH *bh);
+
+#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
+
+/* internal interfaces */
+
+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);
+
+void qemu_bh_schedule_idle(QEMUBH *bh);
+int qemu_bh_poll(void);
+void qemu_bh_update_timeout(int *timeout);
+
+#endif