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

Avoid synchronized(this) in Java?

The question of whether to avoid synchronized(this) in Java has been debated within the Java community, with proponents advocating for private lock references instead. This article aims to provide real-world examples where avoiding synchronized(this) is preferable when it would otherwise also suffice.

Reasons to Avoid synchronized(this)

Those who advocate against using synchronized(this) argue that it:

• Exposes a lock that external code could potentially steal or use maliciously.
• Can reduce throughput by causing all synchronized methods within the same class to lock on the same lock.
• Reveals unnecessary implementation details.

Arguments for synchronized(this)

Others argue that synchronized(this):

• Is a commonly used idiom that is well-understood and safe.
• Should not be avoided simply because it is part of a bug in the code or due to misunderstandings about multithreaded programming.

Real-World Examples

• Secure Access to Sensitive Data: If a class contains sensitive data that should only be accessed by authorized code, using a private lock limits who can access it, preventing malicious code from stealing the reference.
• Differential Locking: Sometimes, different parts of the class need to be locked independently to enhance concurrency. Using a private lock allows for more granular locking, preventing unnecessary synchronization on unrelated operations.
• Separation of Concerns: In some cases, it may be desirable to encapsulate the synchronization mechanism within a helper class, separating the synchronization details from the business logic.

Conclusion

While avoiding synchronized(this) may be preferable in certain situations, it should not be considered a blanket rule. If the benefits of synchronized(this) outweigh the potential drawbacks, it should be used to ensure thread safety and code correctness. The best approach is to carefully consider the specific requirements of the code and choose the appropriate synchronization mechanism accordingly.

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