Why we use a ReentrantReadWriteLock.WriteLock instead of ReentrantLock in DeltaSession?

[xueliang liu]

Hi,

I'm curious the implementation of Tomcat's Cluster, so i'm taking a look at
this part codes. (tomcat 7.0.68)

In DeltaSession, we are using a diffLock to protect the concurrent access,
and diffLock is instantiated as ReentrantReadWriteLock.WriteLock().

Since ReentrantReadWriteLock.WriteLock() is also a Reentrant and exclusive
lock and here we don't use the read lock, why we don't just use the
ReentrantLock instead?

Thanks.
/Nicola