xref: /qemu/include/qemu/main-loop.h (revision 7c754c78)

/*
 * 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

#include "block/aio.h"
#include "qom/object.h"
#include "sysemu/event-loop-base.h"

#define SIG_IPI SIGUSR1

#define TYPE_MAIN_LOOP  "main-loop"
OBJECT_DECLARE_TYPE(MainLoop, MainLoopClass, MAIN_LOOP)

struct MainLoop {
    EventLoopBase parent_obj;
};
typedef struct MainLoop MainLoop;

/**
 * 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(Error **errp);

/**
 * 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);
 *     }
 *
 *     ...
 *     QEMUCoroutine *co = qemu_coroutine_create(coroutine_entry, NULL);
 *     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.
 */
void main_loop_wait(int nonblocking);

/**
 * qemu_get_aio_context: Return the main loop's AioContext
 */
AioContext *qemu_get_aio_context(void);

/**
 * 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.
 */
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.
 *
 * If the same HANDLE is added twice, this function returns -1.
 *
 * @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);

/**
 * IOCanReadHandler: Return the number of bytes that #IOReadHandler can accept
 *
 * This function reports how many bytes #IOReadHandler is prepared to accept.
 * #IOReadHandler may be invoked with up to this number of bytes.  If this
 * function returns 0 then #IOReadHandler is not invoked.
 *
 * This function is typically called from an event loop.  If the number of
 * bytes changes outside the event loop (e.g. because a vcpu thread drained the
 * buffer), then it is necessary to kick the event loop so that this function
 * is called again.  aio_notify() or qemu_notify_event() can be used to kick
 * the event loop.
 */
typedef int IOCanReadHandler(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.
 */
void qemu_set_fd_handler(int fd,
                         IOHandler *fd_read,
                         IOHandler *fd_write,
                         void *opaque);


/**
 * event_notifier_set_handler: Register an EventNotifier with the main loop
 *
 * This function tells the main loop to wake up whenever the
 * #EventNotifier was set.
 *
 * @e: The #EventNotifier to be observed.
 *
 * @handler: A level-triggered callback that is fired when @e
 * has been set.  @e is passed to it as a parameter.
 */
void event_notifier_set_handler(EventNotifier *e,
                                EventNotifierHandler *handler);

GSource *iohandler_get_g_source(void);
AioContext *iohandler_get_aio_context(void);

/**
 * bql_locked: Return lock status of the Big QEMU Lock (BQL)
 *
 * The Big QEMU Lock (BQL) is the coarsest lock in QEMU, and as such it
 * must always be taken outside other locks.  This function helps
 * functions take different paths depending on whether the current
 * thread is running within the BQL.
 *
 * This function should never be used in the block layer, because
 * unit tests, block layer tools and qemu-storage-daemon do not
 * have a BQL.
 * Please instead refer to qemu_in_main_thread().
 */
bool bql_locked(void);

/**
 * qemu_in_main_thread: return whether it's possible to safely access
 * the global state of the block layer.
 *
 * Global state of the block layer is not accessible from I/O threads
 * or worker threads; only from threads that "own" the default
 * AioContext that qemu_get_aio_context() returns.  For tests, block
 * layer tools and qemu-storage-daemon there is a designated thread that
 * runs the event loop for qemu_get_aio_context(), and that is the
 * main thread.
 *
 * For emulators, however, any thread that holds the BQL can act
 * as the block layer main thread; this will be any of the actual
 * main thread, the vCPU threads or the RCU thread.
 *
 * For clarity, do not use this function outside the block layer.
 */
bool qemu_in_main_thread(void);

/*
 * Mark and check that the function is part of the Global State API.
 * Please refer to include/block/block-global-state.h for more
 * information about GS API.
 */
#define GLOBAL_STATE_CODE()                                         \
    do {                                                            \
        assert(qemu_in_main_thread());                              \
    } while (0)

/*
 * Mark and check that the function is part of the I/O API.
 * Please refer to include/block/block-io.h for more
 * information about IO API.
 */
#define IO_CODE()                                                   \
    do {                                                            \
        /* nop */                                                   \
    } while (0)

/*
 * Mark and check that the function is part of the "I/O OR GS" API.
 * Please refer to include/block/block-io.h for more
 * information about "IO or GS" API.
 */
#define IO_OR_GS_CODE()                                             \
    do {                                                            \
        /* nop */                                                   \
    } while (0)

/**
 * bql_lock: Lock the Big QEMU Lock (BQL).
 *
 * This function locks the Big QEMU Lock (BQL).  The lock is taken by
 * main() in vl.c and always taken except while waiting on
 * external events (such as with select).  The lock 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 bql_lock
 * is a no-op there.
 */
#define bql_lock() bql_lock_impl(__FILE__, __LINE__)
void bql_lock_impl(const char *file, int line);

/**
 * bql_unlock: Unlock the Big QEMU Lock (BQL).
 *
 * This function unlocks the Big QEMU Lock.  The lock is taken by
 * main() in vl.c and always taken except while waiting on
 * external events (such as with select).  The lock 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 bql_unlock
 * is a no-op there.
 */
void bql_unlock(void);

/**
 * BQL_LOCK_GUARD
 *
 * Wrap a block of code in a conditional bql_{lock,unlock}.
 */
typedef struct BQLLockAuto BQLLockAuto;

static inline BQLLockAuto *bql_auto_lock(const char *file, int line)
{
    if (bql_locked()) {
        return NULL;
    }
    bql_lock_impl(file, line);
    /* Anything non-NULL causes the cleanup function to be called */
    return (BQLLockAuto *)(uintptr_t)1;
}

static inline void bql_auto_unlock(BQLLockAuto *l)
{
    bql_unlock();
}

G_DEFINE_AUTOPTR_CLEANUP_FUNC(BQLLockAuto, bql_auto_unlock)

#define BQL_LOCK_GUARD() \
    g_autoptr(BQLLockAuto) _bql_lock_auto __attribute__((unused)) \
        = bql_auto_lock(__FILE__, __LINE__)

/*
 * qemu_cond_wait_bql: Wait on condition for the Big QEMU Lock (BQL)
 *
 * This function atomically releases the Big QEMU Lock (BQL) and causes
 * the calling thread to block on the condition.
 */
void qemu_cond_wait_bql(QemuCond *cond);

/*
 * qemu_cond_timedwait_bql: like the previous, but with timeout
 */
void qemu_cond_timedwait_bql(QemuCond *cond, int ms);

/* internal interfaces */

#define qemu_bh_new_guarded(cb, opaque, guard) \
    qemu_bh_new_full((cb), (opaque), (stringify(cb)), guard)
#define qemu_bh_new(cb, opaque) \
    qemu_bh_new_full((cb), (opaque), (stringify(cb)), NULL)
QEMUBH *qemu_bh_new_full(QEMUBHFunc *cb, void *opaque, const char *name,
                         MemReentrancyGuard *reentrancy_guard);
void qemu_bh_schedule_idle(QEMUBH *bh);

enum {
    MAIN_LOOP_POLL_FILL,
    MAIN_LOOP_POLL_ERR,
    MAIN_LOOP_POLL_OK,
};

typedef struct MainLoopPoll {
    int state;
    uint32_t timeout;
    GArray *pollfds;
} MainLoopPoll;

void main_loop_poll_add_notifier(Notifier *notify);
void main_loop_poll_remove_notifier(Notifier *notify);

#endif