(PECL sync >= 1.0.0) Waits for a read lock
(PECL sync >= 1.0.0) Waits for an exclusive write lock
(PECL sync >= 1.0.0) Constructs a new SyncReaderWriter object
(PECL sync >= 1.0.0) Releases a read lock
(PECL sync >= 1.0.0) Releases a write lock