Deadlock Java Example: Java Explained

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Deadlock is a critical topic for anyone who develops software and applications with the Java programming language. Deadlocks occur when two different threads of an application are waiting for the same resource to become available, leading to an inability to continue processing. In this article, we’ll explain what a deadlock is, discuss the benefits of using Java deadlock, and give an example of a Java deadlock that you can use as a template.

What is a Deadlock?

A deadlock occurs when two or more threads of execution in a computer program are all waiting on one another, forming a circular dependency. This circulatory wait prevents the program from progressing any further. Therefore, the threads are stuck forever, which is why it’s called a deadlock. This can be particularly troublesome if the application being developed is a multithreaded application, such as an online database application, that requires multiple threads to access the same resources.

In order for a situation to be identified as a deadlock, four conditions must hold true. First, a circular wait must exist between multiple threads. Secondly, the resources bounded by each of those threads must be mutually exclusive and not shareable. Thirdly, each thread must hold a resource already owned by another thread. Finally, no other thread can preempt or release any of the resources held.

Deadlocks can be avoided by using techniques such as lock ordering, lock splitting, and lock timeouts. Lock ordering is a technique that ensures that all threads acquire locks in the same order, thus avoiding the possibility of a deadlock. Lock splitting is a technique that splits a single lock into multiple locks, thus reducing the chances of a deadlock. Finally, lock timeouts are a technique that sets a timeout for each lock, so that if a thread is waiting for a lock for too long, it will be released and the thread can continue execution.

Understanding Java Deadlock

Since Java is a powerful language with built-in support for multithreading, Java is particularly susceptible to deadlock issues. In Java, deadlocks typically occur when multiple threads are attempting to access different objects simultaneously. The problem arises when they are blocked while attempting to acquire the locks of the other threads involved. As the name implies, Java deadlocks occur when threads are “locked” out of access to certain resources.

To help prevent deadlocks in Java applications, it’s important to understand how multithreading works and how locks can prevent access to shared resources. Furthermore, it’s important to consider the order in which locks are acquired as both a cause and a solution for deadlocks. Design errors can lead to deadlock, so it’s important to take the time to understand potential cause-and-effect relationships between your application logic and thread locking.

It is also important to ensure that locks are released as soon as possible, as this can help to reduce the chances of deadlock occurring. Additionally, it is important to use synchronization techniques such as wait/notify and volatile variables to ensure that threads are properly synchronized and that shared resources are accessed in a safe manner.

Benefits of Using Java Deadlocks

The most obvious benefit of using the deadlock feature in Java is that it helps enforce concurrency within an application. When you lock an object in Java, you’re essentially providing exclusive access to that object and its resources. This prevents other threads from accessing them while keeping track of any threads waiting on the lock.

Another benefit of using Java deadlocks is that they help you isolate critical sections of code within your program to prevent any code that could cause harm or damage from running. In a multi-threaded environment, all threads must be controlled very carefully or unexpected behavior could occur. Locking in Java helps ensure that only one thread at a time has control over a certain set of resources, thereby eliminating any potential side effects.

Deadlocks also help to improve the performance of an application by reducing the amount of time spent waiting for locks to be released. By using locks, threads can be released from waiting for resources and can instead focus on executing their tasks. This can help to reduce the overall time taken to complete a task, as well as reduce the amount of resources used.

Avoiding Deadlocks in Java

The key to avoiding deadlock issues in Java is to design your code in such a way as to reduce or eliminate the possibility of contention between threads for a given resource. Here are some ways you can do this:

  • Be aware of shared resources and ensure that all threads have access to them.
  • Avoid thread starvation by ensuring that no thread has to wait too long for a lock.
  • Acquire all locks in the same order across all threads.
  • Use safe programming practices, such as try/catch blocks.

Additionally, you should consider using synchronization techniques such as semaphores or monitors to ensure that only one thread can access a given resource at a time. This will help to prevent deadlocks from occurring in the first place.

How to Implement Java Deadlocks

When implementing Java deadlocks in your code, you should always follow the same basic principles:

  • Always acquire multiple locks consecutively in the same order.
  • Make sure no other thread has access to a resource before attempting to acquire that resource’s lock.
  • Let go of any locks that aren’t necessary.
  • Ensure that any locking mechanisms used are robust and well tested.

It’s also important to remember that the most important aspect of preventing deadlocks is understanding how your code works and which locks might be necessary to ensure consistent behavior.

In addition, it is important to consider the potential for deadlocks when designing your code. If you can identify potential deadlock scenarios, you can take steps to avoid them. This may include using different locking mechanisms, or restructuring your code to ensure that locks are acquired in a consistent order.

Troubleshooting Deadlock Issues in Java

If you’re having trouble understanding why your Java application is experiencing deadlock issues, there are several techniques that can help you identify the problem:

  • Use a thread dump tool to analyze what your application was doing at the time of the deadlock.
  • Check your application logs for suspicious entries that could point to potential contention points.
  • Examine your code and look for any potential locks that are getting acquired out of order.
  • Check for potential cause-and-effect relationships between your different objects.

It’s also useful to have an experienced programmer on hand who can review your code and help identify potential deadlock conditions.

In addition, you can use a profiler to monitor the performance of your application and identify any areas where contention is occurring. This can help you pinpoint the exact source of the deadlock and take steps to resolve it.


As you can see, understanding and preventing deadlocks in Java is an important part of developing reliable and robust applications. By following best practices and understanding how locks work in Java, you can ensure that your code runs as expected without any unexpected behavior. Additionally, understanding how to troubleshoot deadlock issues makes it much easier to diagnose and resolve any issues that do arise.

It is also important to remember that deadlocks can be avoided by using proper synchronization techniques and avoiding the use of shared resources. By following these best practices, you can ensure that your code runs smoothly and efficiently without any unexpected behavior.

Anand Das

Anand Das

Anand is Co-founder and CTO of Bito. He leads technical strategy and engineering, and is our biggest user! Formerly, Anand was CTO of Eyeota, a data company acquired by Dun & Bradstreet. He is co-founder of PubMatic, where he led the building of an ad exchange system that handles over 1 Trillion bids per day.

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