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authorPaolo Bonzini <pbonzini@redhat.com>2017-02-13 19:12:43 +0100
committerStefan Hajnoczi <stefanha@redhat.com>2017-02-21 11:39:40 +0000
commit1ace7ceac507d90d50ecb2e13f7222beadb64d92 (patch)
tree0a457dc7da86284d408e13ceefc764b914b90b41 /util/qemu-coroutine-lock.c
parentf8c6e1cbc3d397207bedabdb2932fd6e1d7484df (diff)
coroutine-lock: add mutex argument to CoQueue APIs
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>
Diffstat (limited to 'util/qemu-coroutine-lock.c')
-rw-r--r--util/qemu-coroutine-lock.c24
1 files changed, 21 insertions, 3 deletions
diff --git a/util/qemu-coroutine-lock.c b/util/qemu-coroutine-lock.c
index 73fe77cc80..b0a554f40d 100644
--- a/util/qemu-coroutine-lock.c
+++ b/util/qemu-coroutine-lock.c
@@ -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++;