Reader/writer lock with reduced cache contention

• Main Author: Detlefs, David L
• Format: Patent
• Language: English
• Published: 27.03.2012

A scalable locking system is described herein that allows processors to access shared data with reduced cache contention to increase parallelism and scalability. The system provides a reader/writer lock implementation that uses randomization and spends extra space to spread possible contention over multiple cache lines. The system avoids updates to a single shared location in acquiring/releasing a read lock by spreading the lock count over multiple sub-counts in multiple cache lines, and hashing thread identifiers to those cache lines. Carefully crafted invariants allow the use of partially lock-free code in the common path of acquisition and release of a read lock. A careful protocol allows the system to reuse space allocated for a read lock for subsequent locking to avoid frequent reallocating of read lock data structures. The system also provides fairness for write-locking threads and uses object pooling techniques to make reduce costs associated with the lock data structures.