RCU stands for "Read-Copy-Update". It is a synchronization mechanism used in computer programming to ensure safe concurrent access to shared data structures, particularly in multithreaded environments. RCU is primarily employed when there are multiple readers but fewer writers accessing the same data simultaneously.
In RCU, readers do not need to acquire locks or wait for exclusive access before accessing shared data. Instead, they obtain a 'read' lock, allowing concurrent access to shared data until a writer wants to perform an update. During this time, readers are not blocked, and they continue to access the data without any interruption.
When a writer wants to modify the shared data, it does not immediately apply the changes to the original data. Instead, it creates a new copy of the data structure, updates it, and then replaces the old data structure pointer with the updated version. This ensures that existing readers can continue accessing the original data structure without any disruption, while new readers can access the updated version.
RCU guarantees consistency of data for readers, while minimizing overhead and contention among concurrent readers. However, it places the burden of ensuring correctness on the writers to properly manage the update process.
Overall, RCU is a synchronization technique that allows for efficient concurrent access to shared data by readers while minimizing locks and ensuring data consistency. It is commonly used in operating systems, databases, and other systems where concurrent access and efficiency are critical.
