path: root/qemu-thread-win32.c

/*
 * Win32 implementation for mutex/cond/thread functions
 *
 * Copyright Red Hat, Inc. 2010
 *
 * Author:
 *  Paolo Bonzini <pbonzini@redhat.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or later.
 * See the COPYING file in the top-level directory.
 *
 */
#include "qemu-common.h"
#include "qemu-thread.h"
#include <process.h>
#include <assert.h>
#include <limits.h>

static void error_exit(int err, const char *msg)
{
    char *pstr;

    FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER,
                  NULL, err, 0, (LPTSTR)&pstr, 2, NULL);
    fprintf(stderr, "qemu: %s: %s\n", msg, pstr);
    LocalFree(pstr);
    exit(1);
}

void qemu_mutex_init(QemuMutex *mutex)
{
    mutex->owner = 0;
    InitializeCriticalSection(&mutex->lock);
}

void qemu_mutex_lock(QemuMutex *mutex)
{
    EnterCriticalSection(&mutex->lock);

    /* Win32 CRITICAL_SECTIONs are recursive.  Assert that we're not
     * using them as such.
     */
    assert(mutex->owner == 0);
    mutex->owner = GetCurrentThreadId();
}

int qemu_mutex_trylock(QemuMutex *mutex)
{
    int owned;

    owned = TryEnterCriticalSection(&mutex->lock);
    if (owned) {
        assert(mutex->owner == 0);
        mutex->owner = GetCurrentThreadId();
    }
    return !owned;
}

void qemu_mutex_unlock(QemuMutex *mutex)
{
    assert(mutex->owner == GetCurrentThreadId());
    mutex->owner = 0;
    LeaveCriticalSection(&mutex->lock);
}

void qemu_cond_init(QemuCond *cond)
{
    memset(cond, 0, sizeof(*cond));

    cond->sema = CreateSemaphore(NULL, 0, LONG_MAX, NULL);
    if (!cond->sema) {
        error_exit(GetLastError(), __func__);
    }
    cond->continue_event = CreateEvent(NULL,    /* security */
                                       FALSE,   /* auto-reset */
                                       FALSE,   /* not signaled */
                                       NULL);   /* name */
    if (!cond->continue_event) {
        error_exit(GetLastError(), __func__);
    }
}

void qemu_cond_signal(QemuCond *cond)
{
    DWORD result;

    /*
     * Signal only when there are waiters.  cond->waiters is
     * incremented by pthread_cond_wait under the external lock,
     * so we are safe about that.
     */
    if (cond->waiters == 0) {
        return;
    }

    /*
     * Waiting threads decrement it outside the external lock, but
     * only if another thread is executing pthread_cond_broadcast and
     * has the mutex.  So, it also cannot be decremented concurrently
     * with this particular access.
     */
    cond->target = cond->waiters - 1;
    result = SignalObjectAndWait(cond->sema, cond->continue_event,
                                 INFINITE, FALSE);
    if (result == WAIT_ABANDONED || result == WAIT_FAILED) {
        error_exit(GetLastError(), __func__);
    }
}

void qemu_cond_broadcast(QemuCond *cond)
{
    BOOLEAN result;
    /*
     * As in pthread_cond_signal, access to cond->waiters and
     * cond->target is locked via the external mutex.
     */
    if (cond->waiters == 0) {
        return;
    }

    cond->target = 0;
    result = ReleaseSemaphore(cond->sema, cond->waiters, NULL);
    if (!result) {
        error_exit(GetLastError(), __func__);
    }

    /*
     * At this point all waiters continue. Each one takes its
     * slice of the semaphore. Now it's our turn to wait: Since
     * the external mutex is held, no thread can leave cond_wait,
     * yet. For this reason, we can be sure that no thread gets
     * a chance to eat *more* than one slice. OTOH, it means
     * that the last waiter must send us a wake-up.
     */
    WaitForSingleObject(cond->continue_event, INFINITE);
}

void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
{
    /*
     * This access is protected under the mutex.
     */
    cond->waiters++;

    /*
     * Unlock external mutex and wait for signal.
     * NOTE: we've held mutex locked long enough to increment
     * waiters count above, so there's no problem with
     * leaving mutex unlocked before we wait on semaphore.
     */
    qemu_mutex_unlock(mutex);
    WaitForSingleObject(cond->sema, INFINITE);

    /* Now waiters must rendez-vous with the signaling thread and
     * let it continue.  For cond_broadcast this has heavy contention
     * and triggers thundering herd.  So goes life.
     *
     * Decrease waiters count.  The mutex is not taken, so we have
     * to do this atomically.
     *
     * All waiters contend for the mutex at the end of this function
     * until the signaling thread relinquishes it.  To ensure
     * each waiter consumes exactly one slice of the semaphore,
     * the signaling thread stops until it is told by the last
     * waiter that it can go on.
     */
    if (InterlockedDecrement(&cond->waiters) == cond->target) {
        SetEvent(cond->continue_event);
    }

    qemu_mutex_lock(mutex);
}

struct QemuThreadData {
    QemuThread *thread;
    void *(*start_routine)(void *);
    void *arg;
};

static int qemu_thread_tls_index = TLS_OUT_OF_INDEXES;

static unsigned __stdcall win32_start_routine(void *arg)
{
    struct QemuThreadData data = *(struct QemuThreadData *) arg;
    QemuThread *thread = data.thread;

    free(arg);
    TlsSetValue(qemu_thread_tls_index, thread);

    /*
     * Use DuplicateHandle instead of assigning thread->thread in the
     * creating thread to avoid races.  It's simpler this way than with
     * synchronization.
     */
    DuplicateHandle(GetCurrentProcess(), GetCurrentThread(),
                    GetCurrentProcess(), &thread->thread,
                    0, FALSE, DUPLICATE_SAME_ACCESS);

    qemu_thread_exit(data.start_routine(data.arg));
    abort();
}

void qemu_thread_exit(void *arg)
{
    QemuThread *thread = TlsGetValue(qemu_thread_tls_index);
    thread->ret = arg;
    CloseHandle(thread->thread);
    thread->thread = NULL;
    ExitThread(0);
}

static inline void qemu_thread_init(void)
{
    if (qemu_thread_tls_index == TLS_OUT_OF_INDEXES) {
        qemu_thread_tls_index = TlsAlloc();
        if (qemu_thread_tls_index == TLS_OUT_OF_INDEXES) {
            error_exit(ERROR_NO_SYSTEM_RESOURCES, __func__);
        }
    }
}


void qemu_thread_create(QemuThread *thread,
                       void *(*start_routine)(void *),
                       void *arg)
{
    HANDLE hThread;

    struct QemuThreadData *data;
    qemu_thread_init();
    data = qemu_malloc(sizeof *data);
    data->thread = thread;
    data->start_routine = start_routine;
    data->arg = arg;

    hThread = (HANDLE) _beginthreadex(NULL, 0, win32_start_routine,
                                      data, 0, NULL);
    if (!hThread) {
        error_exit(GetLastError(), __func__);
    }
    CloseHandle(hThread);
}

void qemu_thread_get_self(QemuThread *thread)
{
    if (!thread->thread) {
        /* In the main thread of the process.  Initialize the QemuThread
           pointer in TLS, and use the dummy GetCurrentThread handle as
           the identifier for qemu_thread_is_self.  */
        qemu_thread_init();
        TlsSetValue(qemu_thread_tls_index, thread);
        thread->thread = GetCurrentThread();
    }
}

int qemu_thread_is_self(QemuThread *thread)
{
    QemuThread *this_thread = TlsGetValue(qemu_thread_tls_index);
    return this_thread->thread == thread->thread;
}