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As developers, we are used to applying the @Transactional annotation provided by the Spring framework and rely on the mechanisms implemented by the framework for transaction management. But is this enough?
Well, the answer is clear: No.
Multithreading chapters are the most difficult to understand and use in Java. Unfortunately, there are not that many sources where you can get all the answers. Meanwhile, concurrency knowledge is critically important. In this article, I explain the core aspects of multithreading that every Java developer has to know. In this part, we start with the Thread and Runnable subject.
Multithreading knowledge almost certainly is the subject of interviews for senior Java positions. Without a clear understanding of multithreading with and without hands-on experience, you most likely will fail.
Thread creation is a well-known process and there are two ways to create it:
Let's implement both options:
Every programmer comes across Multithreading and for some reason, it has been considered hard to understand. Well, it's not. In this blog, we will go through some basics of multithreading and in the process will try to understand why it is such an important topic in software development.
A program can have multiple processes and Multithreading allows us to run these multiple processing units concurrently. Our programs by default run on a Single thread also known as the main thread. Multithreading is useful because:
Thread synchronization is a great tool to overcome race conditions in multithreaded programs. But, it also has a dark side; deadlocks: nasty errors that are difficult to discover, reproduce, and fix. The only surefire way to prevent them is properly designing your code, which is the subject of this article. We will take a look at the origin of deadlocks, consider a method for discovering potential deadlocks in existing code, and present practical approaches to designing a deadlock-free synchronization. The concepts will be illustrated with a simple demo project.
It is assumed that the reader is already familiar with multithreaded programming and has a good understanding of thread synchronization primitives in Java. In the following sections, we will not distinguish between the synchronized statements and the lock API, using the term “lock” for reentrant locks of both types, preferring the former in the examples.
In the previous chapter, we learned about the following:
In the previous article, we faced a problem with a shared variable that shouldn't be shared or at least one that we have to define the order for updating this variable.
[Updates to the Article and Codebase / Code Snippets ~ 17/Feb/2021]
- Fixed Possible Con. Leaks in Network Connections
- Fixed Poor Code and Bad Programming Practices
- Improved Code Formatting, Practiced Clean Code*
- Mowglee v0.02a is Released (Previously, v0.01a')
This article provides the implementation of a web crawling system called Mowglee that uses geography as the main classifying criteria for crawling. Also, it runs in a multi-threaded mode that provides a default implementation of the robot's exclusion protocol, sitemap generation, data classifiers, data analyzers, and a general framework for application to be built of a web crawler. The implementation is in core Java. Mowglee is a multi-threaded geo web crawler in Java.
This is part II of my previous article Async Programming in Java: Part I. We have seen the various ways to create threads and run them. Java Executor framework helps us to create, run and manage the threads.
We will look deep at how the executor service works internally and various factory methods provided by the Executor framework.
By an interruptible method, we mean a blocking method that may throwInterruptedException, for example, Thread.sleep(), BlockingQueue.take(), BlockingQueue.poll(long timeout, TimeUnit unit), and so on. A blocking thread is usually in a BLOCKED, WAITING, or TIMED_WAITING state, and if it is interrupted, then the method tries to throw InterruptedException as soon as possible.
Since InterruptedException is a checked exception, we must catch it and/or throw it. In other words, if our method calls a method that throws InterruptedException, then we must be prepared to deal with this exception. If we can throw it (propagate the exception to the caller), then it is not our job anymore. The caller has to deal with it further. So, let's focus on the case when we must catch it. Such a case can occur when our code is run inside Runnable, which cannot throw an exception.
A long time ago, in a galaxy far, far away, ‘threads’ were a programming novelty rarely used and seldom trusted. In that environment, the first PostgreSQL developers decided forking a process for each connection to the database is the safest choice. It would be a shame if your database crashed, after all.
You may also like: PostgreSQL Connection Pooling With PgBouncer
Since then, a lot of water has flown under that bridge, but the PostgreSQL community has stuck by their original decision. It is difficult to fault their argument, as it’s absolutely true that:
Concurrency is a game-changer for building Java applications, referring to the ability to run several programs at the same time using multiple threads.
This post is the first in a series of posts about Java concurrency. All code shared in this article has been tested in Java 12.
If you are a Java developer and looking for some awesome resources, e.g. books and courses, to improve your multithreading and concurrency skills in Java, then you have come to the right place! In the past, I have shared books and tutorials on Java concurrency and multithreading, and in this article, I am going to talk about some of the best free and paid courses to learn multithreading and concurrency.
You can join these courses to improve your understanding of Java concurrency and multithreading. It's one of the most important skills for Java developers, as almost all the companies who interview Java developers pay particular attention to his knowledge and experience in this area.
The Tascalate Concurrent library provides an implementation of the CompletionStage interface and related classes. These are designed to support long-running blocking tasks (typically, I/O bound). This functionality augments the sole Java 8 built-in implementation, CompletableFuture, that primarily supports computational tasks. Also, the library helps with numerous asynchronous programming challenges like handling timeouts, retry/poll functionality, orchestrating results of multiple concurrent computations, and similar.
The library is shipped as a multi-release JAR and may be used both with Java 8 as a classpath library or with Java 9+ as a module.