Synchronization

The Java programming language provides multiple mechanisms for communicating between threads. The most basic of these methods is synchronization, which is implemented using monitors. Each object in Java is associated with a monitor, which a thread can lock or unlock. Only one thread at a time may hold a lock on a monitor. Any other threads attempting to lock that monitor are blocked until they can obtain a lock on that monitor. A thread may lock a particular monitor multiple times; each unlock reverses the effect of one lock operation.

Other mechanisms, such as reads and writes of volatile variables and the use of classes in the java.util.concurrent package, provide alternative ways of synchronization.