Archipelago » qemu

/*

 * 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_destroy(QemuMutex *mutex)

{

    assert(mutex->owner == 0);

    DeleteCriticalSection(&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_destroy(QemuCond *cond)

{

    BOOL result;

    result = CloseHandle(cond->continue_event);

    if (!result) {

        error_exit(GetLastError(), __func__);

    }

    cond->continue_event = 0;

    result = CloseHandle(cond->sema);

    if (!result) {

        error_exit(GetLastError(), __func__);

    }

    cond->sema = 0;

}

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;

}