*/
#include "qemu/osdep.h"
-#include "qemu/coroutine.h"
#include "qemu/coroutine_int.h"
#include "qemu/processor.h"
#include "qemu/queue.h"
QSIMPLEQ_INIT(&queue->entries);
}
-void coroutine_fn qemu_co_queue_wait_impl(CoQueue *queue, QemuLockable *lock)
+void coroutine_fn qemu_co_queue_wait_impl(CoQueue *queue, QemuLockable *lock,
+ CoQueueWaitFlags flags)
{
Coroutine *self = qemu_coroutine_self();
- QSIMPLEQ_INSERT_TAIL(&queue->entries, self, co_queue_next);
+ if (flags & CO_QUEUE_WAIT_FRONT) {
+ QSIMPLEQ_INSERT_HEAD(&queue->entries, self, co_queue_next);
+ } else {
+ QSIMPLEQ_INSERT_TAIL(&queue->entries, self, co_queue_next);
+ }
if (lock) {
qemu_lockable_unlock(lock);
}
}
-static bool qemu_co_queue_do_restart(CoQueue *queue, bool single)
-{
- Coroutine *next;
-
- if (QSIMPLEQ_EMPTY(&queue->entries)) {
- return false;
- }
-
- while ((next = QSIMPLEQ_FIRST(&queue->entries)) != NULL) {
- QSIMPLEQ_REMOVE_HEAD(&queue->entries, co_queue_next);
- aio_co_wake(next);
- if (single) {
- break;
- }
- }
- return true;
-}
-
-bool coroutine_fn qemu_co_queue_next(CoQueue *queue)
-{
- assert(qemu_in_coroutine());
- return qemu_co_queue_do_restart(queue, true);
-}
-
-void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue)
-{
- assert(qemu_in_coroutine());
- qemu_co_queue_do_restart(queue, false);
-}
-
bool qemu_co_enter_next_impl(CoQueue *queue, QemuLockable *lock)
{
Coroutine *next;
return true;
}
+bool coroutine_fn qemu_co_queue_next(CoQueue *queue)
+{
+ /* No unlock/lock needed in coroutine context. */
+ return qemu_co_enter_next_impl(queue, NULL);
+}
+
+void qemu_co_enter_all_impl(CoQueue *queue, QemuLockable *lock)
+{
+ while (qemu_co_enter_next_impl(queue, lock)) {
+ /* just loop */
+ }
+}
+
+void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue)
+{
+ /* No unlock/lock needed in coroutine context. */
+ qemu_co_enter_all_impl(queue, NULL);
+}
+
bool qemu_co_queue_empty(CoQueue *queue)
{
return QSIMPLEQ_FIRST(&queue->entries) == NULL;
QSLIST_ENTRY(CoWaitRecord) next;
} CoWaitRecord;
-static void push_waiter(CoMutex *mutex, CoWaitRecord *w)
+static void coroutine_fn push_waiter(CoMutex *mutex, CoWaitRecord *w)
{
w->co = qemu_coroutine_self();
QSLIST_INSERT_HEAD_ATOMIC(&mutex->from_push, w, next);
unsigned old_handoff;
trace_qemu_co_mutex_lock_entry(mutex, self);
- w.co = self;
push_waiter(mutex, &w);
+ /*
+ * Add waiter before reading mutex->handoff. Pairs with qatomic_set_mb
+ * in qemu_co_mutex_unlock.
+ */
+ smp_mb__after_rmw();
+
/* This is the "Responsibility Hand-Off" protocol; a lock() picks from
* a concurrent unlock() the responsibility of waking somebody up.
*/
- old_handoff = qatomic_mb_read(&mutex->handoff);
+ old_handoff = qatomic_read(&mutex->handoff);
if (old_handoff &&
has_waiters(mutex) &&
qatomic_cmpxchg(&mutex->handoff, old_handoff, 0) == old_handoff) {
}
our_handoff = mutex->sequence;
- qatomic_mb_set(&mutex->handoff, our_handoff);
+ /* Set handoff before checking for waiters. */
+ qatomic_set_mb(&mutex->handoff, our_handoff);
if (!has_waiters(mutex)) {
/* The concurrent lock has not added itself yet, so it
* will be able to pick our handoff.
trace_qemu_co_mutex_unlock_return(mutex, self);
}
+struct CoRwTicket {
+ bool read;
+ Coroutine *co;
+ QSIMPLEQ_ENTRY(CoRwTicket) next;
+};
+
void qemu_co_rwlock_init(CoRwlock *lock)
{
- memset(lock, 0, sizeof(*lock));
- qemu_co_queue_init(&lock->queue);
qemu_co_mutex_init(&lock->mutex);
+ lock->owners = 0;
+ QSIMPLEQ_INIT(&lock->tickets);
}
-void qemu_co_rwlock_rdlock(CoRwlock *lock)
+/* Releases the internal CoMutex. */
+static void coroutine_fn qemu_co_rwlock_maybe_wake_one(CoRwlock *lock)
{
- Coroutine *self = qemu_coroutine_self();
+ CoRwTicket *tkt = QSIMPLEQ_FIRST(&lock->tickets);
+ Coroutine *co = NULL;
- qemu_co_mutex_lock(&lock->mutex);
- /* For fairness, wait if a writer is in line. */
- while (lock->pending_writer) {
- qemu_co_queue_wait(&lock->queue, &lock->mutex);
+ /*
+ * Setting lock->owners here prevents rdlock and wrlock from
+ * sneaking in between unlock and wake.
+ */
+
+ if (tkt) {
+ if (tkt->read) {
+ if (lock->owners >= 0) {
+ lock->owners++;
+ co = tkt->co;
+ }
+ } else {
+ if (lock->owners == 0) {
+ lock->owners = -1;
+ co = tkt->co;
+ }
+ }
}
- lock->reader++;
- qemu_co_mutex_unlock(&lock->mutex);
- /* The rest of the read-side critical section is run without the mutex. */
- self->locks_held++;
+ if (co) {
+ QSIMPLEQ_REMOVE_HEAD(&lock->tickets, next);
+ qemu_co_mutex_unlock(&lock->mutex);
+ aio_co_wake(co);
+ } else {
+ qemu_co_mutex_unlock(&lock->mutex);
+ }
}
-void qemu_co_rwlock_unlock(CoRwlock *lock)
+void coroutine_fn qemu_co_rwlock_rdlock(CoRwlock *lock)
{
Coroutine *self = qemu_coroutine_self();
- assert(qemu_in_coroutine());
- if (!lock->reader) {
- /* The critical section started in qemu_co_rwlock_wrlock. */
- qemu_co_queue_restart_all(&lock->queue);
+ qemu_co_mutex_lock(&lock->mutex);
+ /* For fairness, wait if a writer is in line. */
+ if (lock->owners == 0 || (lock->owners > 0 && QSIMPLEQ_EMPTY(&lock->tickets))) {
+ lock->owners++;
+ qemu_co_mutex_unlock(&lock->mutex);
} else {
- self->locks_held--;
+ CoRwTicket my_ticket = { true, self };
+ QSIMPLEQ_INSERT_TAIL(&lock->tickets, &my_ticket, next);
+ qemu_co_mutex_unlock(&lock->mutex);
+ qemu_coroutine_yield();
+ assert(lock->owners >= 1);
+
+ /* Possibly wake another reader, which will wake the next in line. */
qemu_co_mutex_lock(&lock->mutex);
- lock->reader--;
- assert(lock->reader >= 0);
- /* Wakeup only one waiting writer */
- if (!lock->reader) {
- qemu_co_queue_next(&lock->queue);
- }
+ qemu_co_rwlock_maybe_wake_one(lock);
}
- qemu_co_mutex_unlock(&lock->mutex);
+
+ self->locks_held++;
}
-void qemu_co_rwlock_downgrade(CoRwlock *lock)
+void coroutine_fn qemu_co_rwlock_unlock(CoRwlock *lock)
{
Coroutine *self = qemu_coroutine_self();
- /* lock->mutex critical section started in qemu_co_rwlock_wrlock or
- * qemu_co_rwlock_upgrade.
- */
- assert(lock->reader == 0);
- lock->reader++;
- qemu_co_mutex_unlock(&lock->mutex);
+ assert(qemu_in_coroutine());
+ self->locks_held--;
- /* The rest of the read-side critical section is run without the mutex. */
- self->locks_held++;
+ qemu_co_mutex_lock(&lock->mutex);
+ if (lock->owners > 0) {
+ lock->owners--;
+ } else {
+ assert(lock->owners == -1);
+ lock->owners = 0;
+ }
+
+ qemu_co_rwlock_maybe_wake_one(lock);
}
-void qemu_co_rwlock_wrlock(CoRwlock *lock)
+void coroutine_fn qemu_co_rwlock_downgrade(CoRwlock *lock)
{
qemu_co_mutex_lock(&lock->mutex);
- lock->pending_writer++;
- while (lock->reader) {
- qemu_co_queue_wait(&lock->queue, &lock->mutex);
- }
- lock->pending_writer--;
+ assert(lock->owners == -1);
+ lock->owners = 1;
- /* The rest of the write-side critical section is run with
- * the mutex taken, so that lock->reader remains zero.
- * There is no need to update self->locks_held.
- */
+ /* Possibly wake another reader, which will wake the next in line. */
+ qemu_co_rwlock_maybe_wake_one(lock);
}
-void qemu_co_rwlock_upgrade(CoRwlock *lock)
+void coroutine_fn qemu_co_rwlock_wrlock(CoRwlock *lock)
{
Coroutine *self = qemu_coroutine_self();
qemu_co_mutex_lock(&lock->mutex);
- assert(lock->reader > 0);
- lock->reader--;
- lock->pending_writer++;
- while (lock->reader) {
- qemu_co_queue_wait(&lock->queue, &lock->mutex);
+ if (lock->owners == 0) {
+ lock->owners = -1;
+ qemu_co_mutex_unlock(&lock->mutex);
+ } else {
+ CoRwTicket my_ticket = { false, qemu_coroutine_self() };
+
+ QSIMPLEQ_INSERT_TAIL(&lock->tickets, &my_ticket, next);
+ qemu_co_mutex_unlock(&lock->mutex);
+ qemu_coroutine_yield();
+ assert(lock->owners == -1);
}
- lock->pending_writer--;
- /* The rest of the write-side critical section is run with
- * the mutex taken, similar to qemu_co_rwlock_wrlock. Do
- * not account for the lock twice in self->locks_held.
- */
- self->locks_held--;
+ self->locks_held++;
+}
+
+void coroutine_fn qemu_co_rwlock_upgrade(CoRwlock *lock)
+{
+ qemu_co_mutex_lock(&lock->mutex);
+ assert(lock->owners > 0);
+ /* For fairness, wait if a writer is in line. */
+ if (lock->owners == 1 && QSIMPLEQ_EMPTY(&lock->tickets)) {
+ lock->owners = -1;
+ qemu_co_mutex_unlock(&lock->mutex);
+ } else {
+ CoRwTicket my_ticket = { false, qemu_coroutine_self() };
+
+ lock->owners--;
+ QSIMPLEQ_INSERT_TAIL(&lock->tickets, &my_ticket, next);
+ qemu_co_rwlock_maybe_wake_one(lock);
+ qemu_coroutine_yield();
+ assert(lock->owners == -1);
+ }
}
projects / mirror_qemu.git / blobdiff