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author | Paolo Bonzini <pbonzini@redhat.com> | 2017-06-29 15:27:40 +0200 |
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committer | Fam Zheng <famz@redhat.com> | 2017-07-17 11:28:15 +0800 |
commit | 667221c10d05a22573dae1928880bca525f8cd20 (patch) | |
tree | bb15947cc81b0073b1f4903b76036a2bf1306d9f /include/qemu | |
parent | a8c57408cd5443186c5b1c7a393702b316d4722b (diff) | |
download | qemu-667221c10d05a22573dae1928880bca525f8cd20.zip qemu-667221c10d05a22573dae1928880bca525f8cd20.tar.gz qemu-667221c10d05a22573dae1928880bca525f8cd20.tar.bz2 |
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 <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20170629132749.997-3-pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Diffstat (limited to 'include/qemu')
-rw-r--r-- | include/qemu/coroutine.h | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h index a4509bd..9aff9a73 100644 --- a/include/qemu/coroutine.h +++ b/include/qemu/coroutine.h @@ -229,6 +229,24 @@ 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 * coroutine. |