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@Locked

Pop it and lock it! ReentrantLock, now with less hassle.

@Locked was introduced in lombok v1.18.32.

Overview

@Locked wraps all code in a method into a block that acquires a java.util.concurrent.locks.ReentrantLock first, and unlocks it when exiting the method. It is a lot like @Synchronized.

You can optionally name a field, which must be a ReentrantLock; in that case, lombok locks on that field. Otherwise, the annotation defaults to a field named $LOCK (on static methods) / $lock (on instance methods), which lombok will generate if the field does not exist yet.

Additionally, there are the @Locked.Read and @Locked.Write annotations. These use a java.util.concurrent.locks.ReadWriteLock (specifically, ReentrantReadWriteLock). Methods annotated with @Locked.Write will lock on the write lock and methods annotated with @Locked.Read will lock on the read lock. When required, a java.util.concurrent.locks.ReentrantReadWriteLock is generated.

When using Virtual threads (introduced in Java 20), these locks are recommended compared to what @Synchronized does.

With Lombok

import lombok.Locked;

public class LockedExample {
  private int value = 0;
  
  @Locked.Read
  public int getValue() {
    return value;
  }
  
  @Locked.Write
  public void setValue(int newValue) {
    value = newValue;
  }
  
  @Locked("baseLock")
  public void foo() {
    System.out.println("bar");
  }
}

Vanilla Java

public class LockedExample {
  private final ReadWriteLock lock = new ReentrantReadWriteLock();
  private final Lock baseLock = new ReentrantLock();
  private int value = 0;
  
  public int getValue() {
    this.lock.readLock().lock();
    try {
      return value;
    } finally {
      this.lock.readLock().unlock();
    }
  }
  
  public void setValue(int newValue) {
    this.lock.writeLock().lock();
    try {
      value = newValue;
    } finally {
      this.lock.writeLock().unlock();
    }
  }
  
  public void foo() {
    this.baseLock.lock();
    try {
      System.out.println("bar");
    } finally {
      this.baseLock.unlock();
    }
  }
}

Supported configuration keys:

lombok.locked.flagUsage = [warning | error] (default: not set)
Lombok will flag any usage of @Locked as a warning or error if configured.

Small print

Because @Locked.Read and @Locked.Write use a different type of lock than @Locked, these annotations cannot be used on the same lock object without explicitly specifying the name of the field containing the lock object.
The name of the default field of the @Locked, @Locked.Read, and @Locked.Write annotations is the same, so it is not possible to mix the basic @Locked annotation with the other two using the default name.