What is the difference between ReentrantLock and synchronized mechanisms in thread management?

Main differences between ReentrantLock and synchronized:

• Flexibility: ReentrantLock offers more features, such as the ability to interrupt lock waiting (lockInterruptibly), attempt to acquire the lock with a timeout (tryLock), which synchronized does not provide.

• Reentrancy: Both mechanisms support reentrancy, meaning a thread that already holds the lock can acquire it again without blocking.

• Lock management: synchronized is a block or method where the JVM automatically manages acquiring and releasing the lock. ReentrantLock requires explicit calls to lock() and unlock(), providing more control but requiring careful handling.

• Performance: In some cases, ReentrantLock can be more efficient, especially under high thread contention, but this depends on the JVM implementation.

Example of using ReentrantLock:

ReentrantLock lock = new ReentrantLock();

lock.lock();
try {
    // critical section
} finally {
    lock.unlock();
}