Should You Avoid `synchronized(this)` in Java?

Should Synchronized(this) in Java Be Avoided?

Some developers advocate against using synchronized(this), claiming that a lock on a private reference is preferable. Reasons cited include potential lock theft, reduced throughput, and excessive information exposure.

Lock Theft

While lock theft is a potential concern, it's more likely to occur unintentionally due to accidental access to the lock. When synchronized(this) is used, the lock becomes part of the class's exposed interface and should be documented accordingly. In certain scenarios, other code may intentionally access the lock, such as when using Collections.synchronizedMap.

Reduced Throughput

The claim that synchronized(this) reduces throughput is overly simplistic. Eliminating synchronized(this) alone will not improve performance. Proper synchronization requires careful design to optimize throughput.

Excessive Information Exposure

Synchronized(this) shares the lock across all synchronized methods within a class. If fine-grained locking is required, then synchronized(this) is not applicable and should be replaced with a private lock.

When to Use Synchronized(this)

Despite the concerns raised, synchronized(this) remains a valid synchronization idiom with several advantages:

• It is a widely-used idiom, facilitating code readability and understanding.
• It is safe and well-tested, providing reliable synchronization.
• If applicable, it offers a straightforward solution for synchronizing an entire class.

Conclusion

The choice between synchronized(this) and a private lock depends on the specific requirements of the application. While synchronized(this) should not be avoided outright, developers should carefully consider its implications and use a private lock when necessary, such as when granularity or information hiding is a priority.

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