What is the role of the Java Memory Model in memory management when working with multithreading?

The Java Memory Model (JMM) defines the rules for how threads interact with memory, ensuring correct reading and writing of shared variables in a multithreaded environment. It describes how and when changes in one thread's memory become visible to other threads, preventing issues related to caching and instruction reordering.

The main role of the JMM is to guarantee data consistency and avoid race conditions by providing mechanisms such as:

• Visibility of changes: modifications made by one thread should be visible to others when proper synchronization is used.
• Atomicity of operations: certain operations must be executed entirely without interruption.
• Order of execution: the JMM specifies which optimizations and reorderings are permitted to prevent unpredictable behavior.

For example, using the volatile keyword guarantees that reading and writing a variable will be visible to all threads without caching, and synchronized blocks provide mutual exclusion and visibility of changes.

volatile boolean flag = false;

// Thread 1
flag = true; // change will be visible to other threads

// Thread 2
if (flag) {
    // will definitely see the updated value
}