Menu
I have used the synchronized keyword and re-entrant locks in Java, but I don't understand how they differ, or which is appropriate for a given situation.
How do I decide when should I use synchronized and when I should use re-entrant locks?
396
What Is a Reentrant Lock? A reentrant lock is a mutual exclusion mechanism that allows threads to reenter into a lock on a resource (multiple times) without a deadlock situation. A thread entering into the lock increases the hold count by one every time. Similarly, the hold count decreases when unlock is requested.
As stated earlier, the main difference between synchronized and ReentrantLock is the ability to trying to lock interruptibly, and with a timeout. The thread doesn't need to block infinitely, which was the case with synchronized.
In computer science, a lock or mutex (from mutual exclusion) is a synchronization primitive: a mechanism that enforces limits on access to a resource when there are many threads of execution.
Synchronized blocks in Java are reentrant. This means, that if a Java thread enters a synchronized block of code, and thereby take the lock on the monitor object the block is synchronized on, the thread can enter other Java code blocks synchronized on the same monitor object.
A ReentrantLock is:
A reentrant mutual exclusion Lock with the same basic behavior and semantics as the implicit monitor lock accessed using synchronized methods and statements, but with extended capabilities.
Extended capabilities include:
"[fair] locks favor granting access to the longest-waiting thread. Otherwise this lock does not guarantee any particular access order."
The disadvantages of reentrant locks are:
synchronized keyword can be put in method definitions which avoids the need for a block which reduces nesting.Summary
The synchronized keyword is syntactically nicer, but the Reentrant lock has more features.
146
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
