{"id":9099,"date":"2019-06-04T07:15:55","date_gmt":"2019-06-04T11:15:55","guid":{"rendered":"https:\/\/www.eginnovations.com\/blog\/?p=9099"},"modified":"2024-05-28T13:18:26","modified_gmt":"2024-05-28T17:18:26","slug":"java-synchronized-blocks","status":"publish","type":"post","link":"https:\/\/www.eginnovations.com\/blog\/java-synchronized-blocks\/","title":{"rendered":"Java Synchronization Issues
and How to Solve Them"},"content":{"rendered":"

<\/span>What is Synchronization in Java?<\/span><\/h2>\n

Java applications deployed in production must be multi-threaded to ensure scalability (i.e., that they can handle a large number of requests in parallel). Java threads<\/a> are used for process requests in parallel. Depending on the tasks that each thread executes, it is often necessary to synchronize between different threads. Synchronization is the capability to control the access of multiple Java threads to a common resource or object. For example, in an eCommerce application<\/a>, different Java threads may be used to fulfil different orders, but to get an accurate count of the number of orders processed, synchronization is necessary when incrementing the count of orders processed.\u00a0 Without synchronization, different threads could be updating a common variable in parallel and this could lead in errors when reporting the total numbers of orders. In this example, synchronization coordinates accesses across multiple Java threads as they write to a common location (e.g., a memory variable where the count of orders is maintained).<\/p>\n

Troubleshoot the Top 10 Java Performance Problems in Minutes. Learn how \u00bb<\/a><\/div>\n
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<\/span>Thread Synchronization is Very Easy in Java<\/span><\/h2>\n

While synchronization in many other programming languages was difficult to implement, the Java programming language makes it extremely simple to synchronize between threads. You can define any method as being synchronized just by adding the “synchronized” keyword in the method definition. When a method is synchronized, the code inside that method will be executed by only one thread at a time.<\/p>\n

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class MyPrinter {\r\n\tpublic synchronized<\/strong> void print10(int value) {\r\n\t\tfor(int i = 10; i < 10; i++) {\r\n\t\t\tSystem.out.print(value);\r\n\t\t}\r\n\tSystem.out.println(\"\"); \/\/ newline after 10 numbers\r\n\t}\r\n}<\/pre>\n<\/div>\n
Synchronized method<\/em><\/center><\/div>\n
You can even synchronize Java code blocks (instead of entire methods) on a common object. The common object may be an instance of a class or it could be a static instance of a class. In the former case, synchronization is limited to all accesses to that instance, whereas in the latter case, all accesses to all instances of the class will be synchronized.<\/p>\n
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public void add(int value) {\r\n\tStudent s = new Student();\r\n\t\tsynchronized(s) {\r\n\t\tthis.count += value;\r\n\t}\r\n}<\/pre>\n<\/div>\n
Synchronized block<\/em><\/center><\/div>\n
You can also synchronize between web requests by having Java servlets that implement a single threaded model<\/a>. In this case, requests to the servlet will wait while the executing request is being processed.<\/p>\n
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import java.io.*;\r\nimport javax.servlet.*;\r\nimport javax.servler.http.*;\r\n\r\npublic class MyServlet extends HttpServlet  \r\n\timplements SingleThreadModel {\r\n\tservlet methods...\r\n}<\/pre>\n<\/div>\n
Single threaded servlet<\/em><\/center><\/div>\n
In the above cases, the developer has explicitly chosen to synchronize between the executions of different threads. Many a time, you may even be using synchronization without explicitly knowing. Access to Java collection classes such as Vector and Hashtable are synchronized, even though you may not explicitly be accessing them from within synchronized blocks.<\/p>\n
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<\/span>How Synchronization Impacts Java Application Performance<\/span><\/h2>\n
Many Java developers and programmers use synchronization constructs without thinking about their performance implications. There are two types of overheads associated with synchronization:<\/p>\n