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coroutine-lock: add mutex argument to CoQueue APIs

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All that CoQueue needs in order to become thread-safe is help
from an external mutex.  Add this to the API.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20170213181244.16297-6-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Paolo Bonzini 2017-02-13 19:12:43 +01:00 • committed by Stefan Hajnoczi
parent f8c6e1cbc3
commit 1ace7ceac5
9 changed files with 34 additions and 16 deletions
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24
util/qemu-coroutine-lock.c
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@ -40,12 +40,30 @@ void qemu_co_queue_init(CoQueue *queue)
QSIMPLEQ_INIT(&queue->entries);
}
void coroutine_fn qemu_co_queue_wait(CoQueue *queue)
void coroutine_fn qemu_co_queue_wait(CoQueue *queue, CoMutex *mutex)
{
Coroutine *self = qemu_coroutine_self();
QSIMPLEQ_INSERT_TAIL(&queue->entries, self, co_queue_next);
if (mutex) {
qemu_co_mutex_unlock(mutex);
}
/* There is no race condition here. Other threads will call
* aio_co_schedule on our AioContext, which can reenter this
* coroutine but only after this yield and after the main loop
* has gone through the next iteration.
*/
qemu_coroutine_yield();
assert(qemu_in_coroutine());
/* TODO: OSv implements wait morphing here, where the wakeup
* primitive automatically places the woken coroutine on the
* mutex's queue. This avoids the thundering herd effect.
*/
if (mutex) {
qemu_co_mutex_lock(mutex);
}
}
/**
@ -335,7 +353,7 @@ void qemu_co_rwlock_rdlock(CoRwlock *lock)
Coroutine *self = qemu_coroutine_self();
while (lock->writer) {
qemu_co_queue_wait(&lock->queue);
qemu_co_queue_wait(&lock->queue, NULL);
}
lock->reader++;
self->locks_held++;
@ -365,7 +383,7 @@ void qemu_co_rwlock_wrlock(CoRwlock *lock)
Coroutine *self = qemu_coroutine_self();
while (lock->writer || lock->reader) {
qemu_co_queue_wait(&lock->queue);
qemu_co_queue_wait(&lock->queue, NULL);
}
lock->writer = true;
self->locks_held++;