![]() When you use the synchronized keyword with a method, the object reference is implicit. Only one thread can execute a method or block of code protected by the same object reference. All the synchronized sentences (used on methods or blocks of code) use an object reference. In this recipe, you will learn how to use one of the most basic methods of synchronization in Java, that is, the use of the synchronized keyword to control concurrent access to a method or a block of code. So let’s get started: Synchronizing a method In this article, we explore the use of synchronized keyword method to perform synchronization mechanism in Java. The Lock interface and its implementations.Java language offers two basic synchronization mechanisms: When more than one thread is waiting for a thread to finish the execution of a critical section, JVM chooses one of them and the rest wait for their turn. If yes, the thread is suspended by the synchronization mechanism until the thread that is currently executing the critical section ends it. If not, the thread enters the critical section. When a thread wants access to a critical section, it uses one of these synchronization mechanisms to find out whether there is any other thread executing the critical section. To help programmers implement critical sections, Java (and almost all programming languages) offers synchronization mechanisms. ![]() A critical section is a block of code that accesses a shared resource and can’t be executed by more than one thread at the same time. The solution to these problems lies in the concept of a critical section. We present to you a java multithreading tutorial taken from the book, Java 9 Concurrency Cookbook – Second Edition, written by Javier Fernández González. So if a thread changes the value of a shared variable, the changes would only be written in the local cache of that thread other threads will not have access to the change (they will only be able to see the old value). You can also have problems with change visibility. Therefore, the final result depends on the order of the execution of threads, and most of the time, it is incorrect. These situations are called race conditions and they occur when different threads have access to the same shared resource at the same time. These shared resources can provoke error situations or data inconsistency, and we have to implement some mechanism to avoid these errors. In a concurrent application, it is normal for multiple threads to read or write the same data structure or have access to the same file or database connection. One of the most common situations in concurrent programming occurs when more than one execution thread shares a resource.
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