From 667221c10d05a22573dae1928880bca525f8cd20 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 29 Jun 2017 15:27:40 +0200 Subject: coroutine-lock: add qemu_co_rwlock_downgrade and qemu_co_rwlock_upgrade These functions are more efficient in the presence of contention. qemu_co_rwlock_downgrade also guarantees not to block, which may be useful in some algorithms too. Reviewed-by: Eric Blake Reviewed-by: Stefan Hajnoczi Reviewed-by: Fam Zheng Signed-off-by: Paolo Bonzini Message-Id: <20170629132749.997-3-pbonzini@redhat.com> Signed-off-by: Fam Zheng --- include/qemu/coroutine.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'include/qemu/coroutine.h') diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h index a4509bd977..9aff9a735e 100644 --- a/include/qemu/coroutine.h +++ b/include/qemu/coroutine.h @@ -228,6 +228,24 @@ void qemu_co_rwlock_init(CoRwlock *lock); */ void qemu_co_rwlock_rdlock(CoRwlock *lock); +/** + * Write Locks the CoRwlock from a reader. This is a bit more efficient than + * @qemu_co_rwlock_unlock followed by a separate @qemu_co_rwlock_wrlock. + * However, if the lock cannot be upgraded immediately, control is transferred + * to the caller of the current coroutine. Also, @qemu_co_rwlock_upgrade + * only overrides CoRwlock fairness if there are no concurrent readers, so + * another writer might run while @qemu_co_rwlock_upgrade blocks. + */ +void qemu_co_rwlock_upgrade(CoRwlock *lock); + +/** + * Downgrades a write-side critical section to a reader. Downgrading with + * @qemu_co_rwlock_downgrade never blocks, unlike @qemu_co_rwlock_unlock + * followed by @qemu_co_rwlock_rdlock. This makes it more efficient, but + * may also sometimes be necessary for correctness. + */ +void qemu_co_rwlock_downgrade(CoRwlock *lock); + /** * Write Locks the mutex. If the lock cannot be taken immediately because * of a parallel reader, control is transferred to the caller of the current -- cgit 1.4.1