AutoLock

A wrapper library that wraps Lock and allows you to use locks inside Try-with-resources scopes to automatically unlock locks when it exits the try scope.

The wrapper library also have methods that allows you to use lambda functions with locks instead of using Try-with-resources.

By Tom Ansill

Motivation

I have been using Lock a lot for a while now, and I'm getting tired of writing like this:

Lock lock = new ReentrantLock();

try{  
  lock.lock();
    
  // Do stuff
  
}finally{
  lock.unlock();
}

Where I will need to remember to write finally block. If I forget, then my locks won't work properly. Also, coding with try with finally is pretty ugly and takes a lot of lines.

I liked how Java 8's Try-with-resources works, and I thought that it could be applied to Locks too. So I created this library and made the locking process much easier like this:

Lock lock = new ReentrantLock();

try(LockedAutoLock ignored = AutoLock.doLock(lock)){
  
  // Do stuff
  
}

Then I added methods that allows us to use locks with Java 8 lambda functions to make it even easier to use.

Lock lock = new ReentrantLock();

AutoLock.lockAndRun(lock, () -> {
  
  // Do stuff
  
});

Also, supplier functions are available to use to simplify variable initialization while using locks like this:

Lock lock = new ReentrantLock();

int value = AutoLock.lockAndGet(lock, () -> {
  
  // Do stuff
  
  // Return value
  return 100;
});

Prerequisites

• Java 8 or better

Download and Install

Package Repository

The library is available for download on Sonatype public Maven repository (https://oss.sonatype.org/#nexus-search;quick~com.ansill.lock).

<dependency>
  <groupId>com.ansill.lock</groupId>
  <artifactId>AutoLock</artifactId>
  <version>0.5.0</version>
</dependency>

Build and Install

Maven (or other similar build tools) is needed to build and install JavaUtility

$ git clone https://github.com/tomansill/autolock
$ cd autolock
$ mvn install

Usage

Let's start with the basics. AutoLock is a wrapper class that you wrap your Lock in then you can invoke AutoLock commands and use it in Try-with-resources scopes.

To create AutoLock object, you need an original Lock and create AutoLock with it using AutoLock.create(Lock) like this:

// Create lock
Lock lock = new ReentrantLock();

// Wraps the original lock in AutoLock
AutoLock autoLock = AutoLock.create(lock);

Then you can lock the lock in Try-with-resources scope with AutoLock class like this:

try(LockedAutoLock lockedAutoLock = autoLock.doLock()){
    
  // Do stuff here

} // Lock will be automatically be unlocked at this line

LockedAutoLock is an AutoCloseable reference to AutoLock's lock operation. Its close() operation will call Lock::unlock method. So, when try-with-resources exits, it will guarantee that the lock will unlock before continuing regardless of successful execution or failure due to exceptions being thrown.

Class Methods

AutoLock has several locking methods:

• doLock() - Acquires a lock. Same as Lock.lock(). Returns LockedAutoLock.
• doLockInterruptibly() - Acquires a lock unless the current thread is interrupted. Same as Lock::lockInterruptibly(). Returns LockedAutoLock.
• doTryLock() - Acquires the lock only if it is free at the time of invocation. Same as Lock.tryLock(). Returns LockedAutoLock.
• doTryLock(long,TimeUnit) - Acquires the lock if it is free within the given waiting time and the current thread has not been interrupted. Same as Lock.tryLock(long,TimeUnit). Returns LockedAutoLock.
• doTryLock(Duration) - Same as doTryLock(long,TimeUnit) but Duration is used instead of long and TimeUnit combination. Returns LockedAutoLock.

Static Methods

Creating AutoLock objects is not necessary to take advantage of Try-with-resources. AutoLock has static methods that you can use to directly lock your Locks without creating any objects.

LockedAutoLock methods

Using Lock, you can just create LockedAutoLock directly like this:

Lock lock = new ReentrantLock();

try(LockedAutoLock lockedAutoLock = AutoLock.doLock(lock)){
    
  // Do stuff here

}

If you have Java 11 or above, you can just use var like this:

Lock lock = new ReentrantLock();

try(var locked = AutoLock.doLock(lock)){
    
  // Do stuff here

}

AutoLock has several static locking methods:

• doLock(Lock)
• doLockInterruptibly(Lock)
• doTryLock()
• doTryLock(long,TimeUnit)
• doTryLock(Duration)

Lambda methods

Try-with-resources can be avoided entirely and still get the same benefits by using lambda functions in AutoLock.lockAndRun(Lock,ThrowableRunnable<T>) function like this:

Lock lock = new ReentrantLock();

// Will lock, run, then unlock when this method exits
AutoLock.lockAndRun(lock, () -> {

  // Do stuff here

});

AutoLock.lockAndRun(Lock,ThrowableRunnable<T>) will first attempt to lock your Lock, then runs the supplied runnable, then it will automatically unlock your Lock regardless of success or failure of your runnable function.

If you have something you want to return after the lock completes, Use AutoLock.lockAndGet(Lock,ThrowableSupplier<R,T>) instead like this.

Lock lock = new ReentrantLock();

// Will lock, retrieve, unlock, then return (if no exception) when this method exits
int value = AutoLock.lockAndGet(lock, () -> {

  // Do stuff here

  // Return value
  return 100;

});

Note: ThrowableRunner<T> and ThrowableSupplier<R,T> throws <T> generic that extends Throwable so you can use checked exceptions inside of lambdas and the locking methods will throw the checked exception. There's something to note that if there's multiple checked Exceptions in either lambdas, the function cannot throw both of those checked Exceptions, it can only throw their "least common" super-class of Exception which is usually Exception or Throwable.

AutoLock has several static lambda locking methods:

• lockAndRun(Lock,Runnable)
• lockAndGet(Lock,Supplier<T>)
• lockInterruptiblyAndRun(Lock,Runnable)
• lockInterruptiblyAndGet(Lock,Supplier<T>)
• tryLockAndRun(Lock,Runnable)
• tryLockAndGet(Lock,Supplier<T>)
• tryLockAndRun(Lock,long,TimeUnit,Runnable)
• tryLockAndGet(Lock,long,TimeUnit,Supplier<T>)
• tryLockAndRun(Lock,Duration,Runnable)
• tryLockAndGet(Lock,Duration,Supplier<T>)