A generic synchronization term used inconsistently between threading systems. In some systems, a monitor is simply a lock; in others, a monitor is similar to the wait-and-notify mechanism.
Mutex
Another term for a lock. Mutexes do not nest like synchronization methods or blocks and generally can be used across processes at the operating system level.
Reader/writer locks
A lock that can be acquired by multiple threads simultaneously as long as the threads agree to only read from the shared data or that can be acquired by a single thread that wants to write to the shared data. J2SE 5.0 supplies a reader-writer lock class, and a similar class for previous versions of Java can be found in the Appendix A.
Semaphores
Semaphores are used inconsistently in computer systems. Many developers use semaphores to lock objects in the same way Java locks are used; this usage makes them equivalent to mutexes. A more sophisticated use of semaphores is to take advantage of a counter associated with them to nest acquisitions to the critical sections of code; Java locks are exactly equivalent to semaphores in this usage. Semaphores are also used to gain access to resources other than code. Semaphore classes that implement most of these features are available in J2SE 5.0.
Synchronization Classes Added in J2SE 5.0
You probably noticed a strong pattern while reading this list of terms: beginning with J2SE 5.0, almost all these things are included in the core Java libraries. We'll take a brief look into these J2SE 5.0 classes.
