main-loop.c

/*
 * 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.
 */

#include "android/charpipe.h"
#include "android/log-rotate.h"
#include "android/snaphost-android.h"
#include "block/aio.h"
#include "exec/hax.h"
#include "hw/hw.h"
#include "monitor/monitor.h"
#include "net/net.h"
#include "qemu-common.h"
#include "qemu/sockets.h"
#include "qemu/timer.h"
#include "slirp-android/libslirp.h"
#include "sysemu/cpus.h"
#include "sysemu/sysemu.h"

#ifdef __linux__
#include <sys/ioctl.h>
#endif

#ifdef _WIN32
#include <windows.h>
#include <mmsystem.h>
#endif

int qemu_calculate_timeout(void);

/* Conversion factor from emulated instructions to virtual clock ticks.  */
int icount_time_shift;
/* Arbitrarily pick 1MIPS as the minimum allowable speed.  */
#define MAX_ICOUNT_SHIFT 10
/* Compensate for varying guest execution speed.  */
int64_t qemu_icount_bias;
static QEMUTimer *icount_rt_timer;
static QEMUTimer *icount_vm_timer;

#ifndef _WIN32
static int io_thread_fd = -1;

static void qemu_event_read(void *opaque)
{
    int fd = (unsigned long)opaque;
    ssize_t len;

    /* Drain the notify pipe */
    do {
        char buffer[512];
        len = read(fd, buffer, sizeof(buffer));
    } while ((len == -1 && errno == EINTR) || len > 0);
}

static int qemu_main_loop_event_init(void)
{
    int err;
    int fds[2];

    err = pipe(fds);
    if (err == -1)
        return -errno;

    err = fcntl_setfl(fds[0], O_NONBLOCK);
    if (err < 0)
        goto fail;

    err = fcntl_setfl(fds[1], O_NONBLOCK);
    if (err < 0)
        goto fail;

    qemu_set_fd_handler2(fds[0], NULL, qemu_event_read, NULL,
                         (void *)(unsigned long)fds[0]);

    io_thread_fd = fds[1];
    return 0;

fail:
    close(fds[0]);
    close(fds[1]);
    return err;
}
#else
HANDLE qemu_event_handle;

static void dummy_event_handler(void *opaque)
{
}

static int qemu_main_loop_event_init(void)
{
    qemu_event_handle = CreateEvent(NULL, FALSE, FALSE, NULL);
    if (!qemu_event_handle) {
        perror("Failed CreateEvent");
        return -1;
    }
    qemu_add_wait_object(qemu_event_handle, dummy_event_handler, NULL);
    return 0;
}
#endif

int qemu_init_main_loop(void)
{
    return qemu_main_loop_event_init();
}

#ifndef _WIN32

static inline void os_host_main_loop_wait(int *timeout)
{
}

#else  // _WIN32

/***********************************************************/
/* Polling handling */

typedef struct PollingEntry {
    PollingFunc *func;
    void *opaque;
    struct PollingEntry *next;
} PollingEntry;

static PollingEntry *first_polling_entry;

int qemu_add_polling_cb(PollingFunc *func, void *opaque)
{
    PollingEntry **ppe, *pe;
    pe = g_malloc0(sizeof(PollingEntry));
    pe->func = func;
    pe->opaque = opaque;
    for(ppe = &first_polling_entry; *ppe != NULL; ppe = &(*ppe)->next);
    *ppe = pe;
    return 0;
}

void qemu_del_polling_cb(PollingFunc *func, void *opaque)
{
    PollingEntry **ppe, *pe;
    for(ppe = &first_polling_entry; *ppe != NULL; ppe = &(*ppe)->next) {
        pe = *ppe;
        if (pe->func == func && pe->opaque == opaque) {
            *ppe = pe->next;
            g_free(pe);
            break;
        }
    }
}

/***********************************************************/
/* Wait objects support */
typedef struct WaitObjects {
    int num;
    HANDLE events[MAXIMUM_WAIT_OBJECTS + 1];
    WaitObjectFunc *func[MAXIMUM_WAIT_OBJECTS + 1];
    void *opaque[MAXIMUM_WAIT_OBJECTS + 1];
} WaitObjects;

static WaitObjects wait_objects = {0};

int qemu_add_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
{
    WaitObjects *w = &wait_objects;

    if (w->num >= MAXIMUM_WAIT_OBJECTS)
        return -1;
    w->events[w->num] = handle;
    w->func[w->num] = func;
    w->opaque[w->num] = opaque;
    w->num++;
    return 0;
}

void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
{
    int i, found;
    WaitObjects *w = &wait_objects;

    found = 0;
    for (i = 0; i < w->num; i++) {
        if (w->events[i] == handle)
            found = 1;
        if (found) {
            w->events[i] = w->events[i + 1];
            w->func[i] = w->func[i + 1];
            w->opaque[i] = w->opaque[i + 1];
        }
    }
    if (found)
        w->num--;
}

void os_host_main_loop_wait(int *timeout)
{
    int ret, ret2, i;
    PollingEntry *pe;

    /* XXX: need to suppress polling by better using win32 events */
    ret = 0;
    for(pe = first_polling_entry; pe != NULL; pe = pe->next) {
        ret |= pe->func(pe->opaque);
    }
    if (ret == 0) {
        int err;
        WaitObjects *w = &wait_objects;

        qemu_mutex_unlock_iothread();
        ret = WaitForMultipleObjects(w->num, w->events, FALSE, *timeout);
        qemu_mutex_lock_iothread();
        if (WAIT_OBJECT_0 + 0 <= ret && ret <= WAIT_OBJECT_0 + w->num - 1) {
            if (w->func[ret - WAIT_OBJECT_0])
                w->func[ret - WAIT_OBJECT_0](w->opaque[ret - WAIT_OBJECT_0]);

            /* Check for additional signaled events */
            for(i = (ret - WAIT_OBJECT_0 + 1); i < w->num; i++) {

                /* Check if event is signaled */
                ret2 = WaitForSingleObject(w->events[i], 0);
                if(ret2 == WAIT_OBJECT_0) {
                    if (w->func[i])
                        w->func[i](w->opaque[i]);
                } else if (ret2 == WAIT_TIMEOUT) {
                } else {
                    err = GetLastError();
                    fprintf(stderr, "WaitForSingleObject error %d %d\n", i, err);
                }
            }
        } else if (ret == WAIT_TIMEOUT) {
        } else {
            err = GetLastError();
            fprintf(stderr, "WaitForMultipleObjects error %d %d\n", ret, err);
        }
    }

    *timeout = 0;
}

#endif  // _WIN32

static void qemu_run_alarm_timer(void);  // forward

void main_loop_wait(int timeout)
{
    fd_set rfds, wfds, xfds;
    int ret, nfds;
    struct timeval tv;

    qemu_bh_update_timeout(&timeout);

    os_host_main_loop_wait(&timeout);

    tv.tv_sec = timeout / 1000;
    tv.tv_usec = (timeout % 1000) * 1000;

    /* poll any events */

    /* XXX: separate device handlers from system ones */
    nfds = -1;
    FD_ZERO(&rfds);
    FD_ZERO(&wfds);
    FD_ZERO(&xfds);
    qemu_iohandler_fill(&nfds, &rfds, &wfds, &xfds);
    if (slirp_is_inited()) {
        slirp_select_fill(&nfds, &rfds, &wfds, &xfds);
    }

    qemu_mutex_unlock_iothread();
    ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv);
    qemu_mutex_lock_iothread();
    qemu_iohandler_poll(&rfds, &wfds, &xfds, ret);
    if (slirp_is_inited()) {
        if (ret < 0) {
            FD_ZERO(&rfds);
            FD_ZERO(&wfds);
            FD_ZERO(&xfds);
        }
        slirp_select_poll(&rfds, &wfds, &xfds);
    }
    charpipe_poll();

    qemu_clock_run_all_timers();

    qemu_run_alarm_timer();

    /* Check bottom-halves last in case any of the earlier events triggered
       them.  */
    qemu_bh_poll();

}

void main_loop(void)
{
    int r;

#ifdef CONFIG_HAX
    if (hax_enabled())
        hax_sync_vcpus();
#endif

    for (;;) {
        do {
#ifdef CONFIG_PROFILER
            int64_t ti;
#endif
            tcg_cpu_exec();
#ifdef CONFIG_PROFILER
            ti = profile_getclock();
#endif
            main_loop_wait(qemu_calculate_timeout());
#ifdef CONFIG_PROFILER
            dev_time += profile_getclock() - ti;
#endif

            qemu_log_rotation_poll();

        } while (vm_can_run());

        if (qemu_debug_requested())
            vm_stop(EXCP_DEBUG);
        if (qemu_shutdown_requested()) {
            if (no_shutdown) {
                vm_stop(0);
                no_shutdown = 0;
            } else {
                if (savevm_on_exit != NULL) {
                  /* Prior to saving VM to the snapshot file, save HW config
                   * settings for that VM, so we can match them when VM gets
                   * loaded from the snapshot. */
                  snaphost_save_config(savevm_on_exit);
                  do_savevm(cur_mon, savevm_on_exit);
                }
                break;
            }
        }
        if (qemu_reset_requested()) {
            pause_all_vcpus();
            qemu_system_reset();
            resume_all_vcpus();
        }
        if (qemu_powerdown_requested())
            qemu_system_powerdown();
        if ((r = qemu_vmstop_requested()))
            vm_stop(r);
    }
    pause_all_vcpus();
}

/* Correlation between real and virtual time is always going to be
   fairly approximate, so ignore small variation.
   When the guest is idle real and virtual time will be aligned in
   the IO wait loop.  */
#define ICOUNT_WOBBLE (get_ticks_per_sec() / 10)

static void icount_adjust(void)
{
    int64_t cur_time;
    int64_t cur_icount;
    int64_t delta;
    static int64_t last_delta;
    /* If the VM is not running, then do nothing.  */
    if (!vm_running)
        return;

    cur_time = cpu_get_clock();
    cur_icount = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
    delta = cur_icount - cur_time;
    /* FIXME: This is a very crude algorithm, somewhat prone to oscillation.  */
    if (delta > 0
        && last_delta + ICOUNT_WOBBLE < delta * 2
        && icount_time_shift > 0) {
        /* The guest is getting too far ahead.  Slow time down.  */
        icount_time_shift--;
    }
    if (delta < 0
        && last_delta - ICOUNT_WOBBLE > delta * 2
        && icount_time_shift < MAX_ICOUNT_SHIFT) {
        /* The guest is getting too far behind.  Speed time up.  */
        icount_time_shift++;
    }
    last_delta = delta;
    qemu_icount_bias = cur_icount - (qemu_icount << icount_time_shift);
}

static void icount_adjust_rt(void * opaque)
{
    timer_mod(icount_rt_timer,
                   qemu_clock_get_ms(QEMU_CLOCK_REALTIME) + 1000);
    icount_adjust();
}

static void icount_adjust_vm(void * opaque)
{
    timer_mod(icount_vm_timer,
                   qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + get_ticks_per_sec() / 10);
    icount_adjust();
}
extern void qemu_timer_register_savevm(void);

void configure_icount(const char *option)
{
    qemu_timer_register_savevm();

    if (!option)
        return;

    if (strcmp(option, "auto") != 0) {
        icount_time_shift = strtol(option, NULL, 0);
        use_icount = 1;
        return;
    }

    use_icount = 2;

    /* 125MIPS seems a reasonable initial guess at the guest speed.
       It will be corrected fairly quickly anyway.  */
    icount_time_shift = 3;

    /* Have both realtime and virtual time triggers for speed adjustment.
       The realtime trigger catches emulated time passing too slowly,
       the virtual time trigger catches emulated time passing too fast.
       Realtime triggers occur even when idle, so use them less frequently
       than VM triggers.  */
    icount_rt_timer = timer_new(QEMU_CLOCK_REALTIME, SCALE_MS, icount_adjust_rt, NULL);
    timer_mod(icount_rt_timer,
                   qemu_clock_get_ms(QEMU_CLOCK_REALTIME) + 1000);
    icount_vm_timer = timer_new(QEMU_CLOCK_VIRTUAL, SCALE_NS, icount_adjust_vm, NULL);
    timer_mod(icount_vm_timer,
                   qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + get_ticks_per_sec() / 10);
}

struct qemu_alarm_timer {
    char const *name;
    int (*start)(struct qemu_alarm_timer *t);
    void (*stop)(struct qemu_alarm_timer *t);
    void (*rearm)(struct qemu_alarm_timer *t);
#if defined(__linux__)
    int fd;
    timer_t timer;
#elif defined(_WIN32)
    HANDLE timer;
#endif
    char expired;
};

static struct qemu_alarm_timer *alarm_timer;

static inline int alarm_has_dynticks(struct qemu_alarm_timer *t)
{
    return t->rearm != NULL;
}

static void qemu_rearm_alarm_timer(struct qemu_alarm_timer *t)
{
    if (t->rearm) {
        t->rearm(t);
    }
}

static void qemu_run_alarm_timer(void) {
    /* rearm timer, if not periodic */
    if (alarm_timer->expired) {
        alarm_timer->expired = 0;
        qemu_rearm_alarm_timer(alarm_timer);
    }
}

/* TODO: MIN_TIMER_REARM_NS should be optimized */
#define MIN_TIMER_REARM_NS 250000

#ifdef _WIN32

static int mm_start_timer(struct qemu_alarm_timer *t);
static void mm_stop_timer(struct qemu_alarm_timer *t);
static void mm_rearm_timer(struct qemu_alarm_timer *t);

static int win32_start_timer(struct qemu_alarm_timer *t);
static void win32_stop_timer(struct qemu_alarm_timer *t);
static void win32_rearm_timer(struct qemu_alarm_timer *t);

#else

static int unix_start_timer(struct qemu_alarm_timer *t);
static void unix_stop_timer(struct qemu_alarm_timer *t);

#ifdef __linux__

static int dynticks_start_timer(struct qemu_alarm_timer *t);
static void dynticks_stop_timer(struct qemu_alarm_timer *t);
static void dynticks_rearm_timer(struct qemu_alarm_timer *t);

#endif /* __linux__ */

#endif /* _WIN32 */

int64_t qemu_icount_round(int64_t count)
{
    return (count + (1 << icount_time_shift) - 1) >> icount_time_shift;
}

static struct qemu_alarm_timer alarm_timers[] = {
#ifndef _WIN32
    {"unix", unix_start_timer, unix_stop_timer, NULL},
#ifdef __linux__
    /* on Linux, the 'dynticks' clock sometimes doesn't work
     * properly. this results in the UI freezing while emulation
     * continues, for several seconds... So move it to the end
     * of the list. */
    {"dynticks", dynticks_start_timer,
     dynticks_stop_timer, dynticks_rearm_timer},
#endif
#else
    {"mmtimer", mm_start_timer, mm_stop_timer, NULL},
    {"mmtimer2", mm_start_timer, mm_stop_timer, mm_rearm_timer},
    {"dynticks", win32_start_timer, win32_stop_timer, win32_rearm_timer},
    {"win32", win32_start_timer, win32_stop_timer, NULL},
#endif
    {NULL, }
};

static void show_available_alarms(void)
{
    int i;

    printf("Available alarm timers, in order of precedence:\n");
    for (i = 0; alarm_timers[i].name; i++)
        printf("%s\n", alarm_timers[i].name);
}

void configure_alarms(char const *opt)
{
    int i;
    int cur = 0;
    int count = ARRAY_SIZE(alarm_timers) - 1;
    char *arg;
    char *name;
    struct qemu_alarm_timer tmp;

    if (!strcmp(opt, "?")) {
        show_available_alarms();
        exit(0);
    }

    arg = g_strdup(opt);

    /* Reorder the array */
    name = strtok(arg, ",");
    while (name) {
        for (i = 0; i < count && alarm_timers[i].name; i++) {
            if (!strcmp(alarm_timers[i].name, name))
                break;
        }

        if (i == count) {
            fprintf(stderr, "Unknown clock %s\n", name);
            goto next;
        }

        if (i < cur)
            /* Ignore */
            goto next;

        /* Swap */
        tmp = alarm_timers[i];
        alarm_timers[i] = alarm_timers[cur];
        alarm_timers[cur] = tmp;

        cur++;
next:
        name = strtok(NULL, ",");
    }

    g_free(arg);

    if (cur) {
        /* Disable remaining timers */
        for (i = cur; i < count; i++)
            alarm_timers[i].name = NULL;
    } else {
        show_available_alarms();
        exit(1);
    }
}

// This variable is used to notify the qemu_timer_alarm_pending() caller
// (really tcg_cpu_exec()) that an alarm has expired. It is set in the
// timer callback, which can be a signal handler on non-Windows platforms.
static volatile sig_atomic_t timer_alarm_pending = 1;

int qemu_timer_alarm_pending(void)
{
    int ret = timer_alarm_pending;
    timer_alarm_pending = 0;
    return ret;
}

#if defined(__linux__) || defined(_WIN32)
// Compute the next alarm deadline, return a timeout in nanoseconds.
// NOTE: This function cannot be called from a signal handler since
// it calls qemu-timer.c functions that acquire/release global mutexes.
static int64_t qemu_next_alarm_deadline(void)
{
    int64_t delta = INT32_MAX;
    if (!use_icount) {
        delta = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL);
    }
    int64_t hdelta = qemu_clock_deadline_ns_all(QEMU_CLOCK_HOST);
    if (hdelta < delta) {
        delta = hdelta;
    }
    int64_t rtdelta = qemu_clock_deadline_ns_all(QEMU_CLOCK_REALTIME);
    if (rtdelta < delta) {
        delta = rtdelta;
    }
    return delta;
}
#endif  // __linux__ || _WIN32

#ifdef _WIN32
static void CALLBACK host_alarm_handler(PVOID lpParam, BOOLEAN unused)
#else
static void host_alarm_handler(int host_signum)
#endif
{
    struct qemu_alarm_timer *t = alarm_timer;
    if (!t)
        return;

    // It's not possible to call qemu_next_alarm_deadline() to know
    // if a timer has really expired, in the case of non-dynamic alarms,
    // so just signal and let the main loop thread do the checks instead.
    timer_alarm_pending = 1;

    // Ensure a dynamic alarm will be properly rescheduled.
    if (alarm_has_dynticks(t))
        t->expired = 1;

    // This forces a cpu_exit() call that will end the current CPU
    // execution ASAP.
    qemu_notify_event();
}

#if defined(__linux__)

static int dynticks_start_timer(struct qemu_alarm_timer *t)
{
    struct sigevent ev;
    timer_t host_timer;
    struct sigaction act;

    sigfillset(&act.sa_mask);
    act.sa_flags = 0;
    act.sa_handler = host_alarm_handler;

    sigaction(SIGALRM, &act, NULL);

    /*
     * Initialize ev struct to 0 to avoid valgrind complaining
     * about uninitialized data in timer_create call
     */
    memset(&ev, 0, sizeof(ev));
    ev.sigev_value.sival_int = 0;
    ev.sigev_notify = SIGEV_SIGNAL;
    ev.sigev_signo = SIGALRM;

    if (timer_create(CLOCK_REALTIME, &ev, &host_timer)) {
        perror("timer_create");

        /* disable dynticks */
        fprintf(stderr, "Dynamic Ticks disabled\n");

        return -1;
    }

    t->timer = host_timer;

    return 0;
}

static void dynticks_stop_timer(struct qemu_alarm_timer *t)
{
    timer_t host_timer = t->timer;

    timer_delete(host_timer);
}

static void dynticks_rearm_timer(struct qemu_alarm_timer *t)
{
    timer_t host_timer = t->timer;
    struct itimerspec timeout;
    int64_t nearest_delta_ns = INT64_MAX;
    int64_t current_ns;

    assert(alarm_has_dynticks(t));
    if (!qemu_clock_has_timers(QEMU_CLOCK_REALTIME) &&
        !qemu_clock_has_timers(QEMU_CLOCK_VIRTUAL) &&
        !qemu_clock_has_timers(QEMU_CLOCK_HOST))
        return;

    nearest_delta_ns = qemu_next_alarm_deadline();
    if (nearest_delta_ns < MIN_TIMER_REARM_NS)
        nearest_delta_ns = MIN_TIMER_REARM_NS;

    /* check whether a timer is already running */
    if (timer_gettime(host_timer, &timeout)) {
        perror("gettime");
        fprintf(stderr, "Internal timer error: aborting\n");
        exit(1);
    }
    current_ns = timeout.it_value.tv_sec * 1000000000LL + timeout.it_value.tv_nsec;
    if (current_ns && current_ns <= nearest_delta_ns)
        return;

    timeout.it_interval.tv_sec = 0;
    timeout.it_interval.tv_nsec = 0; /* 0 for one-shot timer */
    timeout.it_value.tv_sec =  nearest_delta_ns / 1000000000;
    timeout.it_value.tv_nsec = nearest_delta_ns % 1000000000;
    if (timer_settime(host_timer, 0 /* RELATIVE */, &timeout, NULL)) {
        perror("settime");
        fprintf(stderr, "Internal timer error: aborting\n");
        exit(1);
    }
}

#endif /* defined(__linux__) */

#if !defined(_WIN32)

static int unix_start_timer(struct qemu_alarm_timer *t)
{
    struct sigaction act;
    struct itimerval itv;
    int err;

    /* timer signal */
    sigfillset(&act.sa_mask);
    act.sa_flags = 0;
    act.sa_handler = host_alarm_handler;

    sigaction(SIGALRM, &act, NULL);

    itv.it_interval.tv_sec = 0;
    /* for i386 kernel 2.6 to get 1 ms */
    itv.it_interval.tv_usec = 999;
    itv.it_value.tv_sec = 0;
    itv.it_value.tv_usec = 10 * 1000;

    err = setitimer(ITIMER_REAL, &itv, NULL);
    if (err)
        return -1;

    return 0;
}

static void unix_stop_timer(struct qemu_alarm_timer *t)
{
    struct itimerval itv;

    memset(&itv, 0, sizeof(itv));
    setitimer(ITIMER_REAL, &itv, NULL);
}

#endif /* !defined(_WIN32) */


#ifdef _WIN32

static MMRESULT mm_timer;
static unsigned mm_period;

static void CALLBACK mm_alarm_handler(UINT uTimerID, UINT uMsg,
                                      DWORD_PTR dwUser, DWORD_PTR dw1,
                                      DWORD_PTR dw2)
{
    struct qemu_alarm_timer *t = alarm_timer;
    if (!t) {
        return;
    }
    // We can actually call qemu_next_alarm_deadline() here since this
    // doesn't run in a signal handler, but a different thread.
    if (alarm_has_dynticks(t) || qemu_next_alarm_deadline() <= 0) {
        t->expired = 1;
        timer_alarm_pending = 1;
        qemu_notify_event();
    }
}

static int mm_start_timer(struct qemu_alarm_timer *t)
{
    TIMECAPS tc;
    UINT flags;

    memset(&tc, 0, sizeof(tc));
    timeGetDevCaps(&tc, sizeof(tc));

    mm_period = tc.wPeriodMin;
    timeBeginPeriod(mm_period);

    flags = TIME_CALLBACK_FUNCTION;
    if (alarm_has_dynticks(t)) {
        flags |= TIME_ONESHOT;
    } else {
        flags |= TIME_PERIODIC;
    }

    mm_timer = timeSetEvent(1,                  /* interval (ms) */
                            mm_period,          /* resolution */
                            mm_alarm_handler,   /* function */
                            (DWORD_PTR)t,       /* parameter */
                        flags);

    if (!mm_timer) {
        fprintf(stderr, "Failed to initialize win32 alarm timer: %ld\n",
                GetLastError());
        timeEndPeriod(mm_period);
        return -1;
    }

    return 0;
}

static void mm_stop_timer(struct qemu_alarm_timer *t)
{
    timeKillEvent(mm_timer);
    timeEndPeriod(mm_period);
}

static void mm_rearm_timer(struct qemu_alarm_timer *t)
{
    int nearest_delta_ms;

    assert(alarm_has_dynticks(t));
    if (!qemu_clock_has_timers(QEMU_CLOCK_REALTIME) &&
        !qemu_clock_has_timers(QEMU_CLOCK_VIRTUAL) &&
        !qemu_clock_has_timers(QEMU_CLOCK_HOST)) {
        return;
    }

    timeKillEvent(mm_timer);

    nearest_delta_ms = (qemu_next_alarm_deadline() + 999999) / 1000000;
    if (nearest_delta_ms < 1) {
        nearest_delta_ms = 1;
    }
    mm_timer = timeSetEvent(nearest_delta_ms,
                            mm_period,
                            mm_alarm_handler,
                            (DWORD_PTR)t,
                            TIME_ONESHOT | TIME_CALLBACK_FUNCTION);

    if (!mm_timer) {
        fprintf(stderr, "Failed to re-arm win32 alarm timer %ld\n",
                GetLastError());

        timeEndPeriod(mm_period);
        exit(1);
    }
}

static int win32_start_timer(struct qemu_alarm_timer *t)
{
    HANDLE hTimer;
    BOOLEAN success;

    /* If you call ChangeTimerQueueTimer on a one-shot timer (its period
       is zero) that has already expired, the timer is not updated.  Since
       creating a new timer is relatively expensive, set a bogus one-hour
       interval in the dynticks case.  */
    success = CreateTimerQueueTimer(&hTimer,
                          NULL,
                          host_alarm_handler,
                          t,
                          1,
                          alarm_has_dynticks(t) ? 3600000 : 1,
                          WT_EXECUTEINTIMERTHREAD);

    if (!success) {
        fprintf(stderr, "Failed to initialize win32 alarm timer: %ld\n",
                GetLastError());
        return -1;
    }

    t->timer = hTimer;
    return 0;
}

static void win32_stop_timer(struct qemu_alarm_timer *t)
{
    HANDLE hTimer = t->timer;

    if (hTimer) {
        DeleteTimerQueueTimer(NULL, hTimer, NULL);
    }
}

static void win32_rearm_timer(struct qemu_alarm_timer *t)
{
    HANDLE hTimer = t->timer;
    int nearest_delta_ms;
    BOOLEAN success;

    assert(alarm_has_dynticks(t));
    if (!qemu_clock_has_timers(QEMU_CLOCK_REALTIME) &&
        !qemu_clock_has_timers(QEMU_CLOCK_VIRTUAL) &&
        !qemu_clock_has_timers(QEMU_CLOCK_HOST)) {
        return;
    }
    nearest_delta_ms = (qemu_next_alarm_deadline() + 999999) / 1000000;
    if (nearest_delta_ms < 1) {
        nearest_delta_ms = 1;
    }
    success = ChangeTimerQueueTimer(NULL,
                                    hTimer,
                                    nearest_delta_ms,
                                    3600000);

    if (!success) {
        fprintf(stderr, "Failed to rearm win32 alarm timer: %ld\n",
                GetLastError());
        exit(-1);
    }
}

#endif /* _WIN32 */

static void alarm_timer_on_change_state_rearm(void *opaque,
                                              int running,
                                              int reason)
{
    if (running)
        qemu_rearm_alarm_timer((struct qemu_alarm_timer *) opaque);
}

int init_timer_alarm(void)
{
    struct qemu_alarm_timer *t = NULL;
    int i, err = -1;

    for (i = 0; alarm_timers[i].name; i++) {
        t = &alarm_timers[i];

        err = t->start(t);
        if (!err)
            break;
    }

    if (err) {
        err = -ENOENT;
        goto fail;
    }

    /* first event is at time 0 */
    alarm_timer = t;
    timer_alarm_pending = 1;
    qemu_add_vm_change_state_handler(alarm_timer_on_change_state_rearm, t);

    return 0;

fail:
    return err;
}

void quit_timers(void)
{
    struct qemu_alarm_timer *t = alarm_timer;
    alarm_timer = NULL;
    t->stop(t);
}

int qemu_calculate_timeout(void)
{
    int timeout;

    if (!vm_running)
        timeout = 5000;
    else if (tcg_has_work())
        timeout = 0;
    else {
#ifdef WIN32
        /* This corresponds to the case where the emulated system is
         * totally idle and waiting for i/o. The problem is that on
         * Windows, the default value will prevent Windows user events
         * to be delivered in less than 5 seconds.
         *
         * Upstream contains a different way to handle this, for now
         * this hack should be sufficient until we integrate it into
         * our tree.
         */
        timeout = 1000/15;  /* deliver user events every 15/th of second */
#else
        timeout = 5000;
#endif
        int64_t timeout_ns = (int64_t)timeout * 1000000LL;
        timeout_ns = qemu_soonest_timeout(
                timeout_ns, timerlistgroup_deadline_ns(&main_loop_tlg));
        timeout = (int)((timeout_ns + 999999LL) / 1000000LL);
    }

    return timeout;
}