ReentrantReadWriteLock: what's the difference between ReadLock and WriteLock?

Question

What I know is:

• ReadLock and WriteLock affect each other somehow
• WriteLock is just like synchronized
• ReadLock

Answer 1

Consider a situation: In a case when data structures are read-mostly - they are mutable and are sometimes modified, but most accesses involve mostly reading, so in these case we can relax the locking mechanism in away that we can allow multiple readers to access the data structures instead of readers waiting while one reader has released the lock. As long as each thread is guaranteed an up to date view of the shared data and no thread modifies it while the readers are viewing it, there will no problems. This is what read write allows : a resource can be accessed by multiple readers or a single writer at a time, but not both.