In this post, we'll take a quick look at how to use locks in Java, so you can start using them in your code. We'll cover the Lock interface, an excellent synchronization mechanism that will help you make your code more reliable. Plus, we'll explore what happens if you try to acquire a lock you already own, so you can avoid some common pitfalls. Let's get started!
Lock in Java
Using a lock in Java is very straightforward. To implement a lock, you usually need to perform these steps:
- Create a Lock
- Give each thread access to the same lock
- Acquire the lock
- Release the lock when done
In the following example, we implement the first two steps. At Line 5, we create a lock that the Car class uses to synchronize the threads. Each thread must use the same lock because you can only synchronize threads that have a reference to the same Lock object. Because both threads use the same car object, they also use the same lock.
The last two steps are to acquire the lock using the lock reference and to release it when we are done. Acquiring and releasing the lock is done inside the lockedMethod.
As you can see, the lock is acquired inside a try-finally.
We use the try-finally because if an exception happens while we have acquired the lock, it will always be released.
So, for example, if your code throws an exception on line 12, the
finally will make sure that the lock is released again so
other threads can acquire the lock.
Acquiring the same Lock multiple times
One thing to keep in mind when using a lock is that you need to release it as many times as you have acquired it. In the following example, we acquire the lock three times, but we also release it three times. If you only release the lock twice, another thread won't be able to acquire the lock.
Locks are an essential tool for Java programmers who want to ensure the smooth and efficient execution of their code. By using the Lock interface, you can synchronize threads and prevent conflicts that could cause bugs or other issues. In this post, we looked at implementing a lock using Java in four steps. We also saw what happens when you acquire a lock multiple times.
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