Synchronized Methods vs. Blocks: When Should You Use Which?

When to Use Synchronized Methods and Blocks

Synchronized methods and blocks are two mechanisms used to ensure thread-safe access to shared resources. While both accomplish this goal, they differ in their applicability and potential advantages.

Advantage of Synchronized Methods

The only potential advantage of a synchronized method over a block is that it eliminates the need to explicitly specify the object reference. A synchronized method automatically locks the current instance, whereas a block requires the object reference to be explicitly specified using the this keyword.

Example:

Method:

public synchronized void method() {
    // code goes here
}

Block:

public void method() {
    synchronized(this) {
        // code goes here
    }
}

Advantages of Synchronized Blocks

• Flexibility: A synchronized block can use any object as the lock, whereas a synchronized method always locks the calling object. This allows for more precise control over synchronization.
• Modularity: Since synchronized blocks are a part of a regular method, they can be selectively used to protect specific sections of code, providing more granular concurrency control.

Comparison:

In terms of performance and effectiveness, there is no clear advantage between synchronized methods and blocks. However, synchronized blocks offer greater flexibility and control over synchronization, making them generally preferable when granular or conditional synchronization is required.

For example, if a method contains both input-related and output-related code, using specific locks with synchronized blocks allows for more efficient synchronization:

Object inputLock = new Object();
Object outputLock = new Object();

private void method() {
    synchronized(inputLock) { 
        // input-related code
    } 
    synchronized(outputLock) { 
        // output-related code
    }
}

In contrast, a synchronized method would unnecessarily lock the entire object for both input and output operations.

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