Detailed explanation of Java memory model: from principle to practice, building a robust concurrency system

1. Overview of Java memory model

The Java memory model is an indispensable and important link in development, and understanding its principles is crucial to building a robust concurrent system. PHP editor Yuzai will analyze the Java memory model in detail, guide you from theory to practice, help you better master the skills of concurrent programming, and improve system stability and performance.

2. Basic concepts of JMM

2.1 Main memory and working memory

JMM divides memory into two parts: main memory and working memory. Main memory is a memory area shared by all threads, while working memory is a memory area private to each thread. A thread can only access its own working memory, but can share main memory with other threads.

2.2 Atomicity

Atomicity means that an operation is either fully executed or not executed at all and will not be interrupted by other operations. In JMM, atomicity is achieved through the use of atomic instructions. Atomic instructions are a set of instructions that cannot be interrupted by other threads, ensuring the atomicity of operations.

2.3 Visibility

Visibility means that modifications to shared memory by one thread can be immediately seen by other threads. In JMM, visibility is achieved through the use of memory barriers. A memory barrier is a set of instructions that prohibits instruction reordering and ensures that modifications to shared memory are immediately visible to other threads. 3. Practical application of JMM

3.1 volatile keyword

volatile keyword can mark a variable as "volatile", which means that the value of the variable may be modified by other threads, so a memory barrier must be used to ensure visibility before accessing the variable.

3.2 synchronized keyword

synchronized keyword can mark a code block as "synchronized", which means that when the code block is executed, other threads cannot access the shared variables in the code block. This ensures atomicity of shared variables.

3.3 Lock interface

Lock interface can be used to create

lock

objects, which can be shared by multiple threads. When a thread acquires a lock object, other threads cannot access the shared variables protected by the lock object. This ensures atomicity of shared variables. 4. Build a robust

Concurrency

system 4.1 Avoid race conditions

A race condition refers to a situation where two or more threads access shared variables at the same time and lead to incorrect results. To avoid race conditions, synchronization mechanisms need to be used to ensure the atomicity of shared variables.

4.2 Correct use of memory barriers

Memory barriers ensure that modifications to shared memory can be immediately seen by other threads. When using shared variables, proper use of memory barriers is required to ensure visibility.

4.3 Use appropriate synchronization mechanisms

In a concurrent system, appropriate synchronization mechanisms need to be used to ensure the atomicity of shared variables. Synchronization can be achieved using the volatile keyword, synchronized keyword, or Lock interface.

5.

Summary

The Java Memory Model (JMM) is the foundation of the Java Virtual Machine (JVM) and defines how threads access and operate on shared memory. Understanding JMM helps understand memory visibility issues in concurrent systems and build robust concurrent systems.

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