util/qemu-thread-win32.c - qemu - Git at Google

 /*
  * 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/osdep.h"
 #include "qemu/thread.h"
 #include "qemu/notify.h"
 #include "qemu-thread-common.h"
 #include <process.h>

 static bool name_threads;

 typedef HRESULT (WINAPI *pSetThreadDescription) (HANDLE hThread,
                                                  PCWSTR lpThreadDescription);
 static pSetThreadDescription SetThreadDescriptionFunc;
 static HMODULE kernel32_module;

 static bool load_set_thread_description(void)
 {
     static gsize _init_once = 0;

     if (g_once_init_enter(&_init_once)) {
         kernel32_module = LoadLibrary("kernel32.dll");
         if (kernel32_module) {
             SetThreadDescriptionFunc =
                 (pSetThreadDescription)GetProcAddress(kernel32_module,
                                                       "SetThreadDescription");
             if (!SetThreadDescriptionFunc) {
                 FreeLibrary(kernel32_module);
             }
         }
         g_once_init_leave(&_init_once, 1);
     }

     return !!SetThreadDescriptionFunc;
 }

 void qemu_thread_naming(bool enable)
 {
     name_threads = enable;

     if (enable && !load_set_thread_description()) {
         fprintf(stderr, "qemu: thread naming not supported on this host\n");
         name_threads = false;
     }
 }

 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);
     abort();
 }

 void qemu_mutex_init(QemuMutex *mutex)
 {
     InitializeSRWLock(&mutex->lock);
     qemu_mutex_post_init(mutex);
 }

 void qemu_mutex_destroy(QemuMutex *mutex)
 {
     assert(mutex->initialized);
     mutex->initialized = false;
     InitializeSRWLock(&mutex->lock);
 }

 void qemu_mutex_lock_impl(QemuMutex *mutex, const char *file, const int line)
 {
     assert(mutex->initialized);
     qemu_mutex_pre_lock(mutex, file, line);
     AcquireSRWLockExclusive(&mutex->lock);
     qemu_mutex_post_lock(mutex, file, line);
 }

 int qemu_mutex_trylock_impl(QemuMutex *mutex, const char *file, const int line)
 {
     int owned;

     assert(mutex->initialized);
     owned = TryAcquireSRWLockExclusive(&mutex->lock);
     if (owned) {
         qemu_mutex_post_lock(mutex, file, line);
         return 0;
     }
     return -EBUSY;
 }

 void qemu_mutex_unlock_impl(QemuMutex *mutex, const char *file, const int line)
 {
     assert(mutex->initialized);
     qemu_mutex_pre_unlock(mutex, file, line);
     ReleaseSRWLockExclusive(&mutex->lock);
 }

 void qemu_rec_mutex_init(QemuRecMutex *mutex)
 {
     InitializeCriticalSection(&mutex->lock);
     mutex->initialized = true;
 }

 void qemu_rec_mutex_destroy(QemuRecMutex *mutex)
 {
     assert(mutex->initialized);
     mutex->initialized = false;
     DeleteCriticalSection(&mutex->lock);
 }

 void qemu_rec_mutex_lock_impl(QemuRecMutex *mutex, const char *file, int line)
 {
     assert(mutex->initialized);
     EnterCriticalSection(&mutex->lock);
 }

 int qemu_rec_mutex_trylock_impl(QemuRecMutex *mutex, const char *file, int line)
 {
     assert(mutex->initialized);
     return !TryEnterCriticalSection(&mutex->lock);
 }

 void qemu_rec_mutex_unlock_impl(QemuRecMutex *mutex, const char *file, int line)
 {
     assert(mutex->initialized);
     LeaveCriticalSection(&mutex->lock);
 }

 void qemu_cond_init(QemuCond *cond)
 {
     memset(cond, 0, sizeof(*cond));
     InitializeConditionVariable(&cond->var);
     cond->initialized = true;
 }

 void qemu_cond_destroy(QemuCond *cond)
 {
     assert(cond->initialized);
     cond->initialized = false;
     InitializeConditionVariable(&cond->var);
 }

 void qemu_cond_signal(QemuCond *cond)
 {
     assert(cond->initialized);
     WakeConditionVariable(&cond->var);
 }

 void qemu_cond_broadcast(QemuCond *cond)
 {
     assert(cond->initialized);
     WakeAllConditionVariable(&cond->var);
 }

 void qemu_cond_wait_impl(QemuCond *cond, QemuMutex *mutex, const char *file, const int line)
 {
     assert(cond->initialized);
     qemu_mutex_pre_unlock(mutex, file, line);
     SleepConditionVariableSRW(&cond->var, &mutex->lock, INFINITE, 0);
     qemu_mutex_post_lock(mutex, file, line);
 }

 bool qemu_cond_timedwait_impl(QemuCond *cond, QemuMutex *mutex, int ms,
                               const char *file, const int line)
 {
     int rc = 0;

     assert(cond->initialized);
     trace_qemu_mutex_unlock(mutex, file, line);
     if (!SleepConditionVariableSRW(&cond->var, &mutex->lock, ms, 0)) {
         rc = GetLastError();
     }
     trace_qemu_mutex_locked(mutex, file, line);
     if (rc && rc != ERROR_TIMEOUT) {
         error_exit(rc, __func__);
     }
     return rc != ERROR_TIMEOUT;
 }

 void qemu_sem_init(QemuSemaphore *sem, int init)
 {
     /* Manual reset.  */
     sem->sema = CreateSemaphore(NULL, init, LONG_MAX, NULL);
     sem->initialized = true;
 }

 void qemu_sem_destroy(QemuSemaphore *sem)
 {
     assert(sem->initialized);
     sem->initialized = false;
     CloseHandle(sem->sema);
 }

 void qemu_sem_post(QemuSemaphore *sem)
 {
     assert(sem->initialized);
     ReleaseSemaphore(sem->sema, 1, NULL);
 }

 int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
 {
     int rc;

     assert(sem->initialized);
     rc = WaitForSingleObject(sem->sema, ms);
     if (rc == WAIT_OBJECT_0) {
         return 0;
     }
     if (rc != WAIT_TIMEOUT) {
         error_exit(GetLastError(), __func__);
     }
     return -1;
 }

 void qemu_sem_wait(QemuSemaphore *sem)
 {
     assert(sem->initialized);
     if (WaitForSingleObject(sem->sema, INFINITE) != WAIT_OBJECT_0) {
         error_exit(GetLastError(), __func__);
     }
 }

 /* Wrap a Win32 manual-reset event with a fast userspace path.  The idea
  * is to reset the Win32 event lazily, as part of a test-reset-test-wait
  * sequence.  Such a sequence is, indeed, how QemuEvents are used by
  * RCU and other subsystems!
  *
  * Valid transitions:
  * - free->set, when setting the event
  * - busy->set, when setting the event, followed by SetEvent
  * - set->free, when resetting the event
  * - free->busy, when waiting
  *
  * set->busy does not happen (it can be observed from the outside but
  * it really is set->free->busy).
  *
  * busy->free provably cannot happen; to enforce it, the set->free transition
  * is done with an OR, which becomes a no-op if the event has concurrently
  * transitioned to free or busy (and is faster than cmpxchg).
  */

 #define EV_SET         0
 #define EV_FREE        1
 #define EV_BUSY       -1

 void qemu_event_init(QemuEvent *ev, bool init)
 {
     /* Manual reset.  */
     ev->event = CreateEvent(NULL, TRUE, TRUE, NULL);
     ev->value = (init ? EV_SET : EV_FREE);
     ev->initialized = true;
 }

 void qemu_event_destroy(QemuEvent *ev)
 {
     assert(ev->initialized);
     ev->initialized = false;
     CloseHandle(ev->event);
 }

 void qemu_event_set(QemuEvent *ev)
 {
     assert(ev->initialized);
     /* qemu_event_set has release semantics, but because it *loads*
      * ev->value we need a full memory barrier here.
      */
     smp_mb();
     if (qatomic_read(&ev->value) != EV_SET) {
         if (qatomic_xchg(&ev->value, EV_SET) == EV_BUSY) {
             /* There were waiters, wake them up.  */
             SetEvent(ev->event);
         }
     }
 }

 void qemu_event_reset(QemuEvent *ev)
 {
     unsigned value;

     assert(ev->initialized);
     value = qatomic_read(&ev->value);
     smp_mb_acquire();
     if (value == EV_SET) {
         /* If there was a concurrent reset (or even reset+wait),
          * do nothing.  Otherwise change EV_SET->EV_FREE.
          */
         qatomic_or(&ev->value, EV_FREE);
     }
 }

 void qemu_event_wait(QemuEvent *ev)
 {
     unsigned value;

     assert(ev->initialized);
     value = qatomic_read(&ev->value);
     smp_mb_acquire();
     if (value != EV_SET) {
         if (value == EV_FREE) {
             /* qemu_event_set is not yet going to call SetEvent, but we are
              * going to do another check for EV_SET below when setting EV_BUSY.
              * At that point it is safe to call WaitForSingleObject.
              */
             ResetEvent(ev->event);

             /* Tell qemu_event_set that there are waiters.  No need to retry
              * because there cannot be a concurrent busy->free transition.
              * After the CAS, the event will be either set or busy.
              */
             if (qatomic_cmpxchg(&ev->value, EV_FREE, EV_BUSY) == EV_SET) {
                 value = EV_SET;
             } else {
                 value = EV_BUSY;
             }
         }
         if (value == EV_BUSY) {
             WaitForSingleObject(ev->event, INFINITE);
         }
     }
 }

 struct QemuThreadData {
     /* Passed to win32_start_routine.  */
     void             *(*start_routine)(void *);
     void             *arg;
     short             mode;
     NotifierList      exit;

     /* Only used for joinable threads. */
     bool              exited;
     void             *ret;
     CRITICAL_SECTION  cs;
 };

 static bool atexit_registered;
 static NotifierList main_thread_exit;

 static __thread QemuThreadData *qemu_thread_data;

 static void run_main_thread_exit(void)
 {
     notifier_list_notify(&main_thread_exit, NULL);
 }

 void qemu_thread_atexit_add(Notifier *notifier)
 {
     if (!qemu_thread_data) {
         if (!atexit_registered) {
             atexit_registered = true;
             atexit(run_main_thread_exit);
         }
         notifier_list_add(&main_thread_exit, notifier);
     } else {
         notifier_list_add(&qemu_thread_data->exit, notifier);
     }
 }

 void qemu_thread_atexit_remove(Notifier *notifier)
 {
     notifier_remove(notifier);
 }

 static unsigned __stdcall win32_start_routine(void *arg)
 {
     QemuThreadData *data = (QemuThreadData *) arg;
     void *(*start_routine)(void *) = data->start_routine;
     void *thread_arg = data->arg;

     qemu_thread_data = data;
     qemu_thread_exit(start_routine(thread_arg));
     abort();
 }

 void qemu_thread_exit(void *arg)
 {
     QemuThreadData *data = qemu_thread_data;

     notifier_list_notify(&data->exit, NULL);
     if (data->mode == QEMU_THREAD_JOINABLE) {
         data->ret = arg;
         EnterCriticalSection(&data->cs);
         data->exited = true;
         LeaveCriticalSection(&data->cs);
     } else {
         g_free(data);
     }
     _endthreadex(0);
 }

 void *qemu_thread_join(QemuThread *thread)
 {
     QemuThreadData *data;
     void *ret;
     HANDLE handle;

     data = thread->data;
     if (data->mode == QEMU_THREAD_DETACHED) {
         return NULL;
     }

     /*
      * Because multiple copies of the QemuThread can exist via
      * qemu_thread_get_self, we need to store a value that cannot
      * leak there.  The simplest, non racy way is to store the TID,
      * discard the handle that _beginthreadex gives back, and
      * get another copy of the handle here.
      */
     handle = qemu_thread_get_handle(thread);
     if (handle) {
         WaitForSingleObject(handle, INFINITE);
         CloseHandle(handle);
     }
     ret = data->ret;
     DeleteCriticalSection(&data->cs);
     g_free(data);
     return ret;
 }

 static bool set_thread_description(HANDLE h, const char *name)
 {
     HRESULT hr;
     g_autofree wchar_t *namew = NULL;

     if (!load_set_thread_description()) {
         return false;
     }

     namew = g_utf8_to_utf16(name, -1, NULL, NULL, NULL);
     if (!namew) {
         return false;
     }

     hr = SetThreadDescriptionFunc(h, namew);

     return SUCCEEDED(hr);
 }

 void qemu_thread_create(QemuThread *thread, const char *name,
                        void *(*start_routine)(void *),
                        void *arg, int mode)
 {
     HANDLE hThread;
     struct QemuThreadData *data;

     data = g_malloc(sizeof *data);
     data->start_routine = start_routine;
     data->arg = arg;
     data->mode = mode;
     data->exited = false;
     notifier_list_init(&data->exit);

     if (data->mode != QEMU_THREAD_DETACHED) {
         InitializeCriticalSection(&data->cs);
     }

     hThread = (HANDLE) _beginthreadex(NULL, 0, win32_start_routine,
                                       data, 0, &thread->tid);
     if (!hThread) {
         error_exit(GetLastError(), __func__);
     }
     if (name_threads && name && !set_thread_description(hThread, name)) {
         fprintf(stderr, "qemu: failed to set thread description: %s\n", name);
     }
     CloseHandle(hThread);

     thread->data = data;
 }

 int qemu_thread_set_affinity(QemuThread *thread, unsigned long *host_cpus,
                              unsigned long nbits)
 {
     return -ENOSYS;
 }

 int qemu_thread_get_affinity(QemuThread *thread, unsigned long **host_cpus,
                              unsigned long *nbits)
 {
     return -ENOSYS;
 }

 void qemu_thread_get_self(QemuThread *thread)
 {
     thread->data = qemu_thread_data;
     thread->tid = GetCurrentThreadId();
 }

 HANDLE qemu_thread_get_handle(QemuThread *thread)
 {
     QemuThreadData *data;
     HANDLE handle;

     data = thread->data;
     if (data->mode == QEMU_THREAD_DETACHED) {
         return NULL;
     }

     EnterCriticalSection(&data->cs);
     if (!data->exited) {
         handle = OpenThread(SYNCHRONIZE | THREAD_SUSPEND_RESUME |
                             THREAD_SET_CONTEXT, FALSE, thread->tid);
     } else {
         handle = NULL;
     }
     LeaveCriticalSection(&data->cs);
     return handle;
 }

 bool qemu_thread_is_self(QemuThread *thread)
 {
     return GetCurrentThreadId() == thread->tid;
 }
	/*
	* 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/osdep.h"
	#include "qemu/thread.h"
	#include "qemu/notify.h"
	#include "qemu-thread-common.h"
	#include <process.h>

	static bool name_threads;

	typedef HRESULT (WINAPI *pSetThreadDescription) (HANDLE hThread,
	PCWSTR lpThreadDescription);
	static pSetThreadDescription SetThreadDescriptionFunc;
	static HMODULE kernel32_module;

	static bool load_set_thread_description(void)
	{
	static gsize _init_once = 0;

	if (g_once_init_enter(&_init_once)) {
	kernel32_module = LoadLibrary("kernel32.dll");
	if (kernel32_module) {
	SetThreadDescriptionFunc =
	(pSetThreadDescription)GetProcAddress(kernel32_module,
	"SetThreadDescription");
	if (!SetThreadDescriptionFunc) {
	FreeLibrary(kernel32_module);
	}
	}
	g_once_init_leave(&_init_once, 1);
	}

	return !!SetThreadDescriptionFunc;
	}

	void qemu_thread_naming(bool enable)
	{
	name_threads = enable;

	if (enable && !load_set_thread_description()) {
	fprintf(stderr, "qemu: thread naming not supported on this host\n");
	name_threads = false;
	}
	}

	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);
	abort();
	}

	void qemu_mutex_init(QemuMutex *mutex)
	{
	InitializeSRWLock(&mutex->lock);
	qemu_mutex_post_init(mutex);
	}

	void qemu_mutex_destroy(QemuMutex *mutex)
	{
	assert(mutex->initialized);
	mutex->initialized = false;
	InitializeSRWLock(&mutex->lock);
	}

	void qemu_mutex_lock_impl(QemuMutex mutex, const char file, const int line)
	{
	assert(mutex->initialized);
	qemu_mutex_pre_lock(mutex, file, line);
	AcquireSRWLockExclusive(&mutex->lock);
	qemu_mutex_post_lock(mutex, file, line);
	}

	int qemu_mutex_trylock_impl(QemuMutex mutex, const char file, const int line)
	{
	int owned;

	assert(mutex->initialized);
	owned = TryAcquireSRWLockExclusive(&mutex->lock);
	if (owned) {
	qemu_mutex_post_lock(mutex, file, line);
	return 0;
	}
	return -EBUSY;
	}

	void qemu_mutex_unlock_impl(QemuMutex mutex, const char file, const int line)
	{
	assert(mutex->initialized);
	qemu_mutex_pre_unlock(mutex, file, line);
	ReleaseSRWLockExclusive(&mutex->lock);
	}

	void qemu_rec_mutex_init(QemuRecMutex *mutex)
	{
	InitializeCriticalSection(&mutex->lock);
	mutex->initialized = true;
	}

	void qemu_rec_mutex_destroy(QemuRecMutex *mutex)
	{
	assert(mutex->initialized);
	mutex->initialized = false;
	DeleteCriticalSection(&mutex->lock);
	}

	void qemu_rec_mutex_lock_impl(QemuRecMutex mutex, const char file, int line)
	{
	assert(mutex->initialized);
	EnterCriticalSection(&mutex->lock);
	}

	int qemu_rec_mutex_trylock_impl(QemuRecMutex mutex, const char file, int line)
	{
	assert(mutex->initialized);
	return !TryEnterCriticalSection(&mutex->lock);
	}

	void qemu_rec_mutex_unlock_impl(QemuRecMutex mutex, const char file, int line)
	{
	assert(mutex->initialized);
	LeaveCriticalSection(&mutex->lock);
	}

	void qemu_cond_init(QemuCond *cond)
	{
	memset(cond, 0, sizeof(*cond));
	InitializeConditionVariable(&cond->var);
	cond->initialized = true;
	}

	void qemu_cond_destroy(QemuCond *cond)
	{
	assert(cond->initialized);
	cond->initialized = false;
	InitializeConditionVariable(&cond->var);
	}

	void qemu_cond_signal(QemuCond *cond)
	{
	assert(cond->initialized);
	WakeConditionVariable(&cond->var);
	}

	void qemu_cond_broadcast(QemuCond *cond)
	{
	assert(cond->initialized);
	WakeAllConditionVariable(&cond->var);
	}

	void qemu_cond_wait_impl(QemuCond cond, QemuMutex mutex, const char *file, const int line)
	{
	assert(cond->initialized);
	qemu_mutex_pre_unlock(mutex, file, line);
	SleepConditionVariableSRW(&cond->var, &mutex->lock, INFINITE, 0);
	qemu_mutex_post_lock(mutex, file, line);
	}

	bool qemu_cond_timedwait_impl(QemuCond cond, QemuMutex mutex, int ms,
	const char *file, const int line)
	{
	int rc = 0;

	assert(cond->initialized);
	trace_qemu_mutex_unlock(mutex, file, line);
	if (!SleepConditionVariableSRW(&cond->var, &mutex->lock, ms, 0)) {
	rc = GetLastError();
	}
	trace_qemu_mutex_locked(mutex, file, line);
	if (rc && rc != ERROR_TIMEOUT) {
	error_exit(rc, __func__);
	}
	return rc != ERROR_TIMEOUT;
	}

	void qemu_sem_init(QemuSemaphore *sem, int init)
	{
	/* Manual reset. */
	sem->sema = CreateSemaphore(NULL, init, LONG_MAX, NULL);
	sem->initialized = true;
	}

	void qemu_sem_destroy(QemuSemaphore *sem)
	{
	assert(sem->initialized);
	sem->initialized = false;
	CloseHandle(sem->sema);
	}

	void qemu_sem_post(QemuSemaphore *sem)
	{
	assert(sem->initialized);
	ReleaseSemaphore(sem->sema, 1, NULL);
	}

	int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
	{
	int rc;

	assert(sem->initialized);
	rc = WaitForSingleObject(sem->sema, ms);
	if (rc == WAIT_OBJECT_0) {
	return 0;
	}
	if (rc != WAIT_TIMEOUT) {
	error_exit(GetLastError(), __func__);
	}
	return -1;
	}

	void qemu_sem_wait(QemuSemaphore *sem)
	{
	assert(sem->initialized);
	if (WaitForSingleObject(sem->sema, INFINITE) != WAIT_OBJECT_0) {
	error_exit(GetLastError(), __func__);
	}
	}

	/* Wrap a Win32 manual-reset event with a fast userspace path. The idea
	* is to reset the Win32 event lazily, as part of a test-reset-test-wait
	* sequence. Such a sequence is, indeed, how QemuEvents are used by
	* RCU and other subsystems!
	*
	* Valid transitions:
	* - free->set, when setting the event
	* - busy->set, when setting the event, followed by SetEvent
	* - set->free, when resetting the event
	* - free->busy, when waiting
	*
	* set->busy does not happen (it can be observed from the outside but
	* it really is set->free->busy).
	*
	* busy->free provably cannot happen; to enforce it, the set->free transition
	* is done with an OR, which becomes a no-op if the event has concurrently
	* transitioned to free or busy (and is faster than cmpxchg).
	*/

	#define EV_SET 0
	#define EV_FREE 1
	#define EV_BUSY -1

	void qemu_event_init(QemuEvent *ev, bool init)
	{
	/* Manual reset. */
	ev->event = CreateEvent(NULL, TRUE, TRUE, NULL);
	ev->value = (init ? EV_SET : EV_FREE);
	ev->initialized = true;
	}

	void qemu_event_destroy(QemuEvent *ev)
	{
	assert(ev->initialized);
	ev->initialized = false;
	CloseHandle(ev->event);
	}

	void qemu_event_set(QemuEvent *ev)
	{
	assert(ev->initialized);
	/* qemu_event_set has release semantics, but because it loads
	* ev->value we need a full memory barrier here.
	*/
	smp_mb();
	if (qatomic_read(&ev->value) != EV_SET) {
	if (qatomic_xchg(&ev->value, EV_SET) == EV_BUSY) {
	/* There were waiters, wake them up. */
	SetEvent(ev->event);
	}
	}
	}

	void qemu_event_reset(QemuEvent *ev)
	{
	unsigned value;

	assert(ev->initialized);
	value = qatomic_read(&ev->value);
	smp_mb_acquire();
	if (value == EV_SET) {
	/* If there was a concurrent reset (or even reset+wait),
	* do nothing. Otherwise change EV_SET->EV_FREE.
	*/
	qatomic_or(&ev->value, EV_FREE);
	}
	}

	void qemu_event_wait(QemuEvent *ev)
	{
	unsigned value;

	assert(ev->initialized);
	value = qatomic_read(&ev->value);
	smp_mb_acquire();
	if (value != EV_SET) {
	if (value == EV_FREE) {
	/* qemu_event_set is not yet going to call SetEvent, but we are
	* going to do another check for EV_SET below when setting EV_BUSY.
	* At that point it is safe to call WaitForSingleObject.
	*/
	ResetEvent(ev->event);

	/* Tell qemu_event_set that there are waiters. No need to retry
	* because there cannot be a concurrent busy->free transition.
	* After the CAS, the event will be either set or busy.
	*/
	if (qatomic_cmpxchg(&ev->value, EV_FREE, EV_BUSY) == EV_SET) {
	value = EV_SET;
	} else {
	value = EV_BUSY;
	}
	}
	if (value == EV_BUSY) {
	WaitForSingleObject(ev->event, INFINITE);
	}
	}
	}

	struct QemuThreadData {
	/* Passed to win32_start_routine. */
	void (start_routine)(void *);
	void *arg;
	short mode;
	NotifierList exit;

	/* Only used for joinable threads. */
	bool exited;
	void *ret;
	CRITICAL_SECTION cs;
	};

	static bool atexit_registered;
	static NotifierList main_thread_exit;

	static __thread QemuThreadData *qemu_thread_data;

	static void run_main_thread_exit(void)
	{
	notifier_list_notify(&main_thread_exit, NULL);
	}

	void qemu_thread_atexit_add(Notifier *notifier)
	{
	if (!qemu_thread_data) {
	if (!atexit_registered) {
	atexit_registered = true;
	atexit(run_main_thread_exit);
	}
	notifier_list_add(&main_thread_exit, notifier);
	} else {
	notifier_list_add(&qemu_thread_data->exit, notifier);
	}
	}

	void qemu_thread_atexit_remove(Notifier *notifier)
	{
	notifier_remove(notifier);
	}

	static unsigned __stdcall win32_start_routine(void *arg)
	{
	QemuThreadData data = (QemuThreadData ) arg;
	void (start_routine)(void *) = data->start_routine;
	void *thread_arg = data->arg;

	qemu_thread_data = data;
	qemu_thread_exit(start_routine(thread_arg));
	abort();
	}

	void qemu_thread_exit(void *arg)
	{
	QemuThreadData *data = qemu_thread_data;

	notifier_list_notify(&data->exit, NULL);
	if (data->mode == QEMU_THREAD_JOINABLE) {
	data->ret = arg;
	EnterCriticalSection(&data->cs);
	data->exited = true;
	LeaveCriticalSection(&data->cs);
	} else {
	g_free(data);
	}
	_endthreadex(0);
	}

	void qemu_thread_join(QemuThread thread)
	{
	QemuThreadData *data;
	void *ret;
	HANDLE handle;

	data = thread->data;
	if (data->mode == QEMU_THREAD_DETACHED) {
	return NULL;
	}

	/*
	* Because multiple copies of the QemuThread can exist via
	* qemu_thread_get_self, we need to store a value that cannot
	* leak there. The simplest, non racy way is to store the TID,
	* discard the handle that _beginthreadex gives back, and
	* get another copy of the handle here.
	*/
	handle = qemu_thread_get_handle(thread);
	if (handle) {
	WaitForSingleObject(handle, INFINITE);
	CloseHandle(handle);
	}
	ret = data->ret;
	DeleteCriticalSection(&data->cs);
	g_free(data);
	return ret;
	}

	static bool set_thread_description(HANDLE h, const char *name)
	{
	HRESULT hr;
	g_autofree wchar_t *namew = NULL;

	if (!load_set_thread_description()) {
	return false;
	}

	namew = g_utf8_to_utf16(name, -1, NULL, NULL, NULL);
	if (!namew) {
	return false;
	}

	hr = SetThreadDescriptionFunc(h, namew);

	return SUCCEEDED(hr);
	}

	void qemu_thread_create(QemuThread thread, const char name,
	void (start_routine)(void *),
	void *arg, int mode)
	{
	HANDLE hThread;
	struct QemuThreadData *data;

	data = g_malloc(sizeof *data);
	data->start_routine = start_routine;
	data->arg = arg;
	data->mode = mode;
	data->exited = false;
	notifier_list_init(&data->exit);

	if (data->mode != QEMU_THREAD_DETACHED) {
	InitializeCriticalSection(&data->cs);
	}

	hThread = (HANDLE) _beginthreadex(NULL, 0, win32_start_routine,
	data, 0, &thread->tid);
	if (!hThread) {
	error_exit(GetLastError(), __func__);
	}
	if (name_threads && name && !set_thread_description(hThread, name)) {
	fprintf(stderr, "qemu: failed to set thread description: %s\n", name);
	}
	CloseHandle(hThread);

	thread->data = data;
	}

	int qemu_thread_set_affinity(QemuThread thread, unsigned long host_cpus,
	unsigned long nbits)
	{
	return -ENOSYS;
	}

	int qemu_thread_get_affinity(QemuThread thread, unsigned long *host_cpus,
	unsigned long *nbits)
	{
	return -ENOSYS;
	}

	void qemu_thread_get_self(QemuThread *thread)
	{
	thread->data = qemu_thread_data;
	thread->tid = GetCurrentThreadId();
	}

	HANDLE qemu_thread_get_handle(QemuThread *thread)
	{
	QemuThreadData *data;
	HANDLE handle;

	data = thread->data;
	if (data->mode == QEMU_THREAD_DETACHED) {
	return NULL;
	}

	EnterCriticalSection(&data->cs);
	if (!data->exited) {
	handle = OpenThread(SYNCHRONIZE \| THREAD_SUSPEND_RESUME \|
	THREAD_SET_CONTEXT, FALSE, thread->tid);
	} else {
	handle = NULL;
	}
	LeaveCriticalSection(&data->cs);
	return handle;
	}

	bool qemu_thread_is_self(QemuThread *thread)
	{
	return GetCurrentThreadId() == thread->tid;
	}