Do not use the somewhat mysterious atomic_mb_read/atomic_mb_set, instead make sure that the operations on QemuEvent are annotated with the desired acquire and release semantics. In particular, qemu_event_set wakes up the waiting thread, so it must be a release from the POV of the waker (compare with qemu_mutex_unlock). And it actually needs a full barrier, because that's the only thing that provides something like a "load-release". Use smp_mb_acquire until we have atomic_load_acquire and atomic_store_release in atomic.h. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
488 lines
13 KiB
C
488 lines
13 KiB
C
/*
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* Win32 implementation for mutex/cond/thread functions
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*
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* Copyright Red Hat, Inc. 2010
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*
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* Author:
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* Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*
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*/
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#include "qemu/osdep.h"
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#include "qemu-common.h"
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#include "qemu/thread.h"
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#include "qemu/notify.h"
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#include <process.h>
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static bool name_threads;
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void qemu_thread_naming(bool enable)
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{
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/* But note we don't actually name them on Windows yet */
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name_threads = enable;
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fprintf(stderr, "qemu: thread naming not supported on this host\n");
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}
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static void error_exit(int err, const char *msg)
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{
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char *pstr;
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FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER,
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NULL, err, 0, (LPTSTR)&pstr, 2, NULL);
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fprintf(stderr, "qemu: %s: %s\n", msg, pstr);
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LocalFree(pstr);
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abort();
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}
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void qemu_mutex_init(QemuMutex *mutex)
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{
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mutex->owner = 0;
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InitializeCriticalSection(&mutex->lock);
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}
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void qemu_mutex_destroy(QemuMutex *mutex)
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{
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assert(mutex->owner == 0);
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DeleteCriticalSection(&mutex->lock);
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}
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void qemu_mutex_lock(QemuMutex *mutex)
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{
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EnterCriticalSection(&mutex->lock);
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/* Win32 CRITICAL_SECTIONs are recursive. Assert that we're not
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* using them as such.
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*/
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assert(mutex->owner == 0);
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mutex->owner = GetCurrentThreadId();
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}
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int qemu_mutex_trylock(QemuMutex *mutex)
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{
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int owned;
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owned = TryEnterCriticalSection(&mutex->lock);
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if (owned) {
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assert(mutex->owner == 0);
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mutex->owner = GetCurrentThreadId();
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}
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return !owned;
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}
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void qemu_mutex_unlock(QemuMutex *mutex)
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{
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assert(mutex->owner == GetCurrentThreadId());
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mutex->owner = 0;
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LeaveCriticalSection(&mutex->lock);
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}
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void qemu_cond_init(QemuCond *cond)
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{
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memset(cond, 0, sizeof(*cond));
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cond->sema = CreateSemaphore(NULL, 0, LONG_MAX, NULL);
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if (!cond->sema) {
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error_exit(GetLastError(), __func__);
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}
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cond->continue_event = CreateEvent(NULL, /* security */
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FALSE, /* auto-reset */
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FALSE, /* not signaled */
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NULL); /* name */
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if (!cond->continue_event) {
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error_exit(GetLastError(), __func__);
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}
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}
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void qemu_cond_destroy(QemuCond *cond)
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{
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BOOL result;
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result = CloseHandle(cond->continue_event);
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if (!result) {
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error_exit(GetLastError(), __func__);
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}
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cond->continue_event = 0;
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result = CloseHandle(cond->sema);
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if (!result) {
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error_exit(GetLastError(), __func__);
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}
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cond->sema = 0;
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}
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void qemu_cond_signal(QemuCond *cond)
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{
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DWORD result;
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/*
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* Signal only when there are waiters. cond->waiters is
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* incremented by pthread_cond_wait under the external lock,
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* so we are safe about that.
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*/
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if (cond->waiters == 0) {
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return;
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}
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/*
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* Waiting threads decrement it outside the external lock, but
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* only if another thread is executing pthread_cond_broadcast and
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* has the mutex. So, it also cannot be decremented concurrently
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* with this particular access.
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*/
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cond->target = cond->waiters - 1;
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result = SignalObjectAndWait(cond->sema, cond->continue_event,
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INFINITE, FALSE);
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if (result == WAIT_ABANDONED || result == WAIT_FAILED) {
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error_exit(GetLastError(), __func__);
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}
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}
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void qemu_cond_broadcast(QemuCond *cond)
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{
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BOOLEAN result;
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/*
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* As in pthread_cond_signal, access to cond->waiters and
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* cond->target is locked via the external mutex.
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*/
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if (cond->waiters == 0) {
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return;
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}
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cond->target = 0;
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result = ReleaseSemaphore(cond->sema, cond->waiters, NULL);
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if (!result) {
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error_exit(GetLastError(), __func__);
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}
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/*
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* At this point all waiters continue. Each one takes its
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* slice of the semaphore. Now it's our turn to wait: Since
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* the external mutex is held, no thread can leave cond_wait,
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* yet. For this reason, we can be sure that no thread gets
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* a chance to eat *more* than one slice. OTOH, it means
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* that the last waiter must send us a wake-up.
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*/
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WaitForSingleObject(cond->continue_event, INFINITE);
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}
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void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
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{
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/*
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* This access is protected under the mutex.
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*/
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cond->waiters++;
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/*
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* Unlock external mutex and wait for signal.
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* NOTE: we've held mutex locked long enough to increment
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* waiters count above, so there's no problem with
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* leaving mutex unlocked before we wait on semaphore.
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*/
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qemu_mutex_unlock(mutex);
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WaitForSingleObject(cond->sema, INFINITE);
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/* Now waiters must rendez-vous with the signaling thread and
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* let it continue. For cond_broadcast this has heavy contention
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* and triggers thundering herd. So goes life.
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*
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* Decrease waiters count. The mutex is not taken, so we have
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* to do this atomically.
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*
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* All waiters contend for the mutex at the end of this function
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* until the signaling thread relinquishes it. To ensure
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* each waiter consumes exactly one slice of the semaphore,
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* the signaling thread stops until it is told by the last
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* waiter that it can go on.
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*/
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if (InterlockedDecrement(&cond->waiters) == cond->target) {
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SetEvent(cond->continue_event);
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}
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qemu_mutex_lock(mutex);
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}
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void qemu_sem_init(QemuSemaphore *sem, int init)
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{
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/* Manual reset. */
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sem->sema = CreateSemaphore(NULL, init, LONG_MAX, NULL);
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}
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void qemu_sem_destroy(QemuSemaphore *sem)
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{
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CloseHandle(sem->sema);
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}
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void qemu_sem_post(QemuSemaphore *sem)
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{
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ReleaseSemaphore(sem->sema, 1, NULL);
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}
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int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
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{
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int rc = WaitForSingleObject(sem->sema, ms);
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if (rc == WAIT_OBJECT_0) {
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return 0;
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}
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if (rc != WAIT_TIMEOUT) {
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error_exit(GetLastError(), __func__);
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}
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return -1;
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}
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void qemu_sem_wait(QemuSemaphore *sem)
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{
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if (WaitForSingleObject(sem->sema, INFINITE) != WAIT_OBJECT_0) {
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error_exit(GetLastError(), __func__);
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}
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}
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/* Wrap a Win32 manual-reset event with a fast userspace path. The idea
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* is to reset the Win32 event lazily, as part of a test-reset-test-wait
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* sequence. Such a sequence is, indeed, how QemuEvents are used by
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* RCU and other subsystems!
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*
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* Valid transitions:
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* - free->set, when setting the event
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* - busy->set, when setting the event, followed by futex_wake
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* - set->free, when resetting the event
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* - free->busy, when waiting
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*
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* set->busy does not happen (it can be observed from the outside but
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* it really is set->free->busy).
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*
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* busy->free provably cannot happen; to enforce it, the set->free transition
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* is done with an OR, which becomes a no-op if the event has concurrently
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* transitioned to free or busy (and is faster than cmpxchg).
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*/
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#define EV_SET 0
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#define EV_FREE 1
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#define EV_BUSY -1
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void qemu_event_init(QemuEvent *ev, bool init)
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{
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/* Manual reset. */
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ev->event = CreateEvent(NULL, TRUE, TRUE, NULL);
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ev->value = (init ? EV_SET : EV_FREE);
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}
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void qemu_event_destroy(QemuEvent *ev)
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{
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CloseHandle(ev->event);
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}
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void qemu_event_set(QemuEvent *ev)
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{
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/* qemu_event_set has release semantics, but because it *loads*
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* ev->value we need a full memory barrier here.
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*/
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smp_mb();
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if (atomic_read(&ev->value) != EV_SET) {
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if (atomic_xchg(&ev->value, EV_SET) == EV_BUSY) {
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/* There were waiters, wake them up. */
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SetEvent(ev->event);
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}
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}
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}
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void qemu_event_reset(QemuEvent *ev)
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{
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unsigned value;
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value = atomic_read(&ev->value);
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smp_mb_acquire();
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if (value == EV_SET) {
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/* If there was a concurrent reset (or even reset+wait),
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* do nothing. Otherwise change EV_SET->EV_FREE.
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*/
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atomic_or(&ev->value, EV_FREE);
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}
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}
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void qemu_event_wait(QemuEvent *ev)
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{
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unsigned value;
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value = atomic_read(&ev->value);
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smp_mb_acquire();
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if (value != EV_SET) {
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if (value == EV_FREE) {
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/* qemu_event_set is not yet going to call SetEvent, but we are
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* going to do another check for EV_SET below when setting EV_BUSY.
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* At that point it is safe to call WaitForSingleObject.
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*/
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ResetEvent(ev->event);
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/* Tell qemu_event_set that there are waiters. No need to retry
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* because there cannot be a concurent busy->free transition.
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* After the CAS, the event will be either set or busy.
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*/
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if (atomic_cmpxchg(&ev->value, EV_FREE, EV_BUSY) == EV_SET) {
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value = EV_SET;
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} else {
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value = EV_BUSY;
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}
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}
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if (value == EV_BUSY) {
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WaitForSingleObject(ev->event, INFINITE);
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}
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}
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}
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struct QemuThreadData {
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/* Passed to win32_start_routine. */
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void *(*start_routine)(void *);
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void *arg;
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short mode;
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NotifierList exit;
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/* Only used for joinable threads. */
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bool exited;
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void *ret;
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CRITICAL_SECTION cs;
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};
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static bool atexit_registered;
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static NotifierList main_thread_exit;
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static __thread QemuThreadData *qemu_thread_data;
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static void run_main_thread_exit(void)
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{
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notifier_list_notify(&main_thread_exit, NULL);
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}
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void qemu_thread_atexit_add(Notifier *notifier)
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{
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if (!qemu_thread_data) {
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if (!atexit_registered) {
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atexit_registered = true;
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atexit(run_main_thread_exit);
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}
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notifier_list_add(&main_thread_exit, notifier);
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} else {
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notifier_list_add(&qemu_thread_data->exit, notifier);
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}
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}
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void qemu_thread_atexit_remove(Notifier *notifier)
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{
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notifier_remove(notifier);
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}
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static unsigned __stdcall win32_start_routine(void *arg)
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{
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QemuThreadData *data = (QemuThreadData *) arg;
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void *(*start_routine)(void *) = data->start_routine;
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void *thread_arg = data->arg;
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qemu_thread_data = data;
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qemu_thread_exit(start_routine(thread_arg));
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abort();
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}
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void qemu_thread_exit(void *arg)
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{
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QemuThreadData *data = qemu_thread_data;
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notifier_list_notify(&data->exit, NULL);
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if (data->mode == QEMU_THREAD_JOINABLE) {
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data->ret = arg;
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EnterCriticalSection(&data->cs);
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data->exited = true;
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LeaveCriticalSection(&data->cs);
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} else {
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g_free(data);
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}
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_endthreadex(0);
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}
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void *qemu_thread_join(QemuThread *thread)
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{
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QemuThreadData *data;
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void *ret;
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HANDLE handle;
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data = thread->data;
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if (data->mode == QEMU_THREAD_DETACHED) {
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return NULL;
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}
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/*
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* Because multiple copies of the QemuThread can exist via
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* qemu_thread_get_self, we need to store a value that cannot
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* leak there. The simplest, non racy way is to store the TID,
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* discard the handle that _beginthreadex gives back, and
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* get another copy of the handle here.
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*/
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handle = qemu_thread_get_handle(thread);
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if (handle) {
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WaitForSingleObject(handle, INFINITE);
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CloseHandle(handle);
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}
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ret = data->ret;
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DeleteCriticalSection(&data->cs);
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g_free(data);
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return ret;
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}
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void qemu_thread_create(QemuThread *thread, const char *name,
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void *(*start_routine)(void *),
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void *arg, int mode)
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{
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HANDLE hThread;
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struct QemuThreadData *data;
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data = g_malloc(sizeof *data);
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data->start_routine = start_routine;
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data->arg = arg;
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data->mode = mode;
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data->exited = false;
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notifier_list_init(&data->exit);
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if (data->mode != QEMU_THREAD_DETACHED) {
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InitializeCriticalSection(&data->cs);
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}
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hThread = (HANDLE) _beginthreadex(NULL, 0, win32_start_routine,
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data, 0, &thread->tid);
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if (!hThread) {
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error_exit(GetLastError(), __func__);
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}
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CloseHandle(hThread);
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thread->data = data;
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}
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void qemu_thread_get_self(QemuThread *thread)
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{
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thread->data = qemu_thread_data;
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thread->tid = GetCurrentThreadId();
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}
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HANDLE qemu_thread_get_handle(QemuThread *thread)
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{
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QemuThreadData *data;
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HANDLE handle;
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data = thread->data;
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if (data->mode == QEMU_THREAD_DETACHED) {
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return NULL;
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}
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EnterCriticalSection(&data->cs);
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if (!data->exited) {
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handle = OpenThread(SYNCHRONIZE | THREAD_SUSPEND_RESUME, FALSE,
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thread->tid);
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} else {
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handle = NULL;
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}
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LeaveCriticalSection(&data->cs);
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return handle;
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}
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bool qemu_thread_is_self(QemuThread *thread)
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{
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return GetCurrentThreadId() == thread->tid;
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}
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