Java Concurrency - Synchronization (Thread Safety)

About

Concurrency - Synchronization in java.

Java offers two basic synchronization idioms:

synchronized methods
synchronized statements

final fields, which cannot be modified after the object is constructed, can be safely read through non-synchronized methods, once the object is constructed.
Atomic Access does not require synchronization

The Java programming language neither prevents nor requires detection of deadlock conditions.

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Idioms

To create synchronized code (ie which gives consistent values) between threads, you use the synchronized word..

Method

Java Concurrency - Synchronized method: If an object is visible to more than one thread, all reads or writes to that object's variables must be done through synchronized methods.

Statement

Java Concurrency - Synchronized Statement

Implementation

Synchronization is implemented by an internal entity known as the monitor (intrinsic lock or monitor lock).

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.

Documentation / Reference