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[Qemu-devel] [PATCH 11/11] coroutine-lock: make CoRwlock thread-safe and
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 11/11] coroutine-lock: make CoRwlock thread-safe and fair |
Date: |
Fri, 15 Apr 2016 13:32:06 +0200 |
This adds a CoMutex around the existing CoQueue. Because the write-side
can just take CoMutex, the old "writer" field is not necessary anymore.
Instead of removing it altogether, count the number of pending writers
during a read-side critical section and forbid further readers from
entering.
Signed-off-by: Paolo Bonzini <address@hidden>
---
include/qemu/coroutine.h | 3 ++-
util/qemu-coroutine-lock.c | 29 +++++++++++++++++++++--------
2 files changed, 23 insertions(+), 9 deletions(-)
diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h
index 25e31a1..0dfb301 100644
--- a/include/qemu/coroutine.h
+++ b/include/qemu/coroutine.h
@@ -198,8 +198,9 @@ bool qemu_co_queue_empty(CoQueue *queue);
typedef struct CoRwlock {
- bool writer;
+ int pending_writer;
int reader;
+ CoMutex mutex;
CoQueue queue;
} CoRwlock;
diff --git a/util/qemu-coroutine-lock.c b/util/qemu-coroutine-lock.c
index 828d79a..db9cf01 100644
--- a/util/qemu-coroutine-lock.c
+++ b/util/qemu-coroutine-lock.c
@@ -322,36 +322,49 @@ void qemu_co_rwlock_init(CoRwlock *lock)
{
memset(lock, 0, sizeof(*lock));
qemu_co_queue_init(&lock->queue);
+ qemu_co_mutex_init(&lock->mutex);
}
void qemu_co_rwlock_rdlock(CoRwlock *lock)
{
- while (lock->writer) {
- qemu_co_queue_wait(&lock->queue, 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);
}
lock->reader++;
+ qemu_co_mutex_unlock(&lock->mutex);
+
+ /* The rest of the read-side critical section is run without the mutex. */
}
void qemu_co_rwlock_unlock(CoRwlock *lock)
{
assert(qemu_in_coroutine());
- if (lock->writer) {
- lock->writer = false;
+ if (!lock->reader) {
+ /* The critical section started in qemu_co_rwlock_wrlock. */
qemu_co_queue_restart_all(&lock->queue);
} else {
+ 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_mutex_unlock(&lock->mutex);
}
void qemu_co_rwlock_wrlock(CoRwlock *lock)
{
- while (lock->writer || lock->reader) {
- qemu_co_queue_wait(&lock->queue, NULL);
+ qemu_co_mutex_lock(&lock->mutex);
+ lock->pending_writer++;
+ while (lock->reader) {
+ qemu_co_queue_wait(&lock->queue, &lock->mutex);
}
- lock->writer = true;
+ lock->pending_writer--;
+
+ /* The rest of the write-side critical section is run with
+ * the mutex taken, so lock->reader remains zero.
+ */
}
--
2.5.5
- [Qemu-devel] [PATCH 05/11] coroutine-lock: reschedule coroutine on the AioContext it was running on, (continued)
- [Qemu-devel] [PATCH 05/11] coroutine-lock: reschedule coroutine on the AioContext it was running on, Paolo Bonzini, 2016/04/15
- [Qemu-devel] [PATCH 06/11] coroutine-lock: make CoMutex thread-safe, Paolo Bonzini, 2016/04/15
- [Qemu-devel] [PATCH 02/11] throttle-groups: restart throttled requests from coroutine context, Paolo Bonzini, 2016/04/15
- [Qemu-devel] [PATCH 04/11] aio: introduce aio_co_schedule, Paolo Bonzini, 2016/04/15
- [Qemu-devel] [PATCH 07/11] coroutine-lock: add limited spinning to CoMutex, Paolo Bonzini, 2016/04/15
- [Qemu-devel] [PATCH 10/11] coroutine-lock: add mutex argument to CoQueue APIs, Paolo Bonzini, 2016/04/15
- [Qemu-devel] [PATCH 08/11] test-aio-multithread: add performance comparison with thread-based mutexes, Paolo Bonzini, 2016/04/15
- [Qemu-devel] [PATCH 09/11] coroutine-lock: place CoMutex before CoQueue in header, Paolo Bonzini, 2016/04/15
- [Qemu-devel] [PATCH 11/11] coroutine-lock: make CoRwlock thread-safe and fair,
Paolo Bonzini <=
- Re: [Qemu-devel] [RFC PATCH resend 00/11] Make CoMutex/CoQueue/CoRwlock thread-safe, Stefan Hajnoczi, 2016/04/26