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authorPaolo Bonzini <pbonzini@redhat.com>2017-06-29 15:27:40 +0200
committerFam Zheng <famz@redhat.com>2017-07-17 11:28:15 +0800
commit667221c10d05a22573dae1928880bca525f8cd20 (patch)
treebb15947cc81b0073b1f4903b76036a2bf1306d9f /include/qemu
parenta8c57408cd5443186c5b1c7a393702b316d4722b (diff)
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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.h18
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.