Avoid synchronized(this) in Java?

java

concurrency-control

synchronization-strategy

lock-contention

byAnton Shumikhin·Jan 28, 2025

Leverage a private final lock rather than synchronized(this) to retain optimal control over your lock, and to encapsulate synchronization within a confined context:

// Our trusty lock object!
private final Object lock = new Object();

public void myMethod() {
    synchronized(lock) {
        // Do all the thread-safe stuff here! No fear of hijacking!
    }
}

Doing so counters the hijacking of a this lock, which often leads to concurrency dilemmas.

Maximising throughput with an effective synchronization strategy

Locking on this enlarges the granularity of the lock, sheltering the entire object, which consequently restricts your concurrency control. Subtle, but impactful!

Unlock finer control with private locks

Skip the this reference lock and introduce private final Object instances as locks:

// Two locks, they're like fraternal twins – similar, but not identical!
private final Object readLock = new Object();
private final Object writeLock = new Object();

Now you have distinct locks for diverse operations. Picture readLock for read operations and writeLock for write operations. This paves a neat path towards improved concurrency by permitting multiple threads to read data concurrently, while maintaining exclusive access for writes. Performance levels? Over 9000 🚀.

Concurrency in check: Keeping deadlocks and race conditions at bay

While multiple locks can unleash your concurrency potential, they are also notorious for inviting complexity and bugs. Tread carefully!

Locks as your defensive arsenal

Defensive programming is all about foreseeing others' code misuse and fortifying against it. Using a private lock object means client code cannot acquire your lock, shutting the door on potential invasions and security breaches.

Battle-tested practices for synchronization

Synchronized(this) can be a sensible choice in some contexts. However, it calls for cautious planning and adequate documentation to guide users when they engage in a shared locking protocol.

Choosing the right synchronization approach for the right context

In a high-security environment, balance the potential risks against concurrency benefits. If your object serves as a vital resource, opting for private locking might spare you from unanticipated vulnerability exploitation.

Throughput face-off: Rethinking your synchronization strategy

Occasionally, removing synchronized(this) doesn't resolve throughput issues due to lock contention. In such instances, reimagining your concurrency strategy could involve exploring non-blocking algorithms and hardware-based transactional memory techniques.