A private mutex (or private lock object) is often used to gain fine-grained control over synchronization without exposing the locking mechanism to the outside world.
Here are the key reasons you might want to use a private mutex instead of synchronized(this) or synchronized(SomeClass.class):
🔐 1. Encapsulation & Safety
- If you use
synchronized(this)or synchronize on a public object, external code can accidentally or intentionally acquire the same lock — leading to deadlocks or performance issues. - Using a
private final Object lock = new Object();ensures that only your class controls the synchronization.
💡 2. Avoid Lock Contention with Other Code
- Suppose you’re writing a library, and someone else also synchronizes on your object:
synchronized (myLibraryObject) { ... } // external code
This could block or interfere with your internal synchronization logic.
A private mutex avoids this by ensuring no one else can lock on it.
🧩 3. Multiple Independent Locks
- Sometimes you need to separate concerns. For example:
private final Object readLock = new Object();
private final Object writeLock = new Object();
This lets you synchronize different operations separately for better performance (e.g., readers and writers don’t block each other unnecessarily).
✅ 4. More Granular Synchronization
- You may want to lock only part of an object’s state:
private final Object stateLock = new Object();
public void updateState() {
synchronized (stateLock) {
// Only protects state, not other fields
}
}
🧠 Summary
| Reason | Benefit |
|---|---|
| Encapsulation | Lock can’t be accessed outside the class |
| Avoid external interference | Prevents external code from hijacking locks |
| Fine-grained locking | Better performance, less contention |
| Separate concerns | Organize locking by function/state |