What is the purpose of the Java Memory Model?

The Java Memory Model (JMM) defines the rules for interaction between threads and memory in Java programs. It describes how and when changes made by one thread become visible to other threads, and also guarantees the correct operation of multithreaded applications.

Main tasks of the JMM:

• Defines how read and write operations to memory are ordered and visible to other threads.
• Ensures correctness of synchronization through keywords like synchronized, volatile, and atomic operations.
• Helps avoid issues with caching and reordering of instructions by the processor and compiler.

Example: without proper synchronization, one thread may not see the updated value of a variable written by another thread. The JMM guarantees that when using volatile or synchronized, changes will be visible.

volatile boolean flag = false;

// Thread 1
flag = true;

// Thread 2
if (flag) {
    // will definitely see the update to flag
}