Explicit Lock vs Implicit Lock

Explicit locks, such as those provided by the java.util.concurrent.locks package (e.g., ReentrantLock, ReadWriteLock), offer several advantages over using intrinsic locks provided by synchronized blocks or methods. Some of the key benefits of using explicit locks are:

1. Flexibility: Explicit locks offer more flexibility in terms of lock acquisition and release. You can lock and unlock the lock object at different scopes and in separate blocks of code, which is not possible with synchronized blocks or methods.

2. Fairness: ReentrantLock allows you to specify fairness when creating the lock object. When a lock is fair, it grants access to the longest-waiting thread. Intrinsic locks provided by synchronized blocks or methods do not have a fairness option and may lead to thread starvation in some scenarios.

java
Lock lock = new ReentrantLock(true); // Create a fair lock

3. Try to acquire lock: Explicit locks provide the tryLock() method, which allows a thread to attempt to acquire the lock without waiting indefinitely. This can help avoid deadlocks and improve performance in some cases.

java
if (lock.tryLock()) {
    try {
        // Perform the operation
    } finally {
        lock.unlock();
    }
} else {
    // Handle the lock not being acquired
}

4. Interruptible lock acquisition: With explicit locks, you can use the lockInterruptibly() method, which allows a thread to be interrupted while waiting to acquire the lock. Intrinsic locks do not support this functionality.

java
try {
    lock.lockInterruptibly();
    try {
        // Perform the operation
    } finally {
        lock.unlock();
    }
} catch (InterruptedException e) {
    // Handle the interruption
}

5. Separate read and write locks: The ReadWriteLock interface provides separate locks for read and write operations, allowing multiple threads to read shared data simultaneously while still providing exclusive access for write operations. This can lead to better performance in scenarios with more reads than writes.

java
ReadWriteLock rwLock = new ReentrantReadWriteLock();
Lock readLock = rwLock.readLock();
Lock writeLock = rwLock.writeLock();

While explicit locks offer several advantages, they also require more careful handling and can be more error-prone due to the need for manual lock management. When choosing between explicit locks and intrinsic locks, consider the specific use case, the complexity of the code, and the required functionality.