Multi-threaded programs may often come to a situation where multiple threads try to access the same resources and finally produce erroneous and unforeseen results. So it needs to be made sure by some synchronization method that only one thread can access the resource at a given point in time.
What is Synchronization in java?
Synchronization in java is the capability to control the access of multiple threads to any shared resource. In the Multithreading concept, multiple threads try to access the shared resources at a time to produce inconsistent results. Synchronization is necessary for reliable communication between threads.
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Why do we use Synchronization?
- Synchronization helps in preventing thread interference.
- Synchronization helps to prevent concurrency problems.
Types of Synchronization
Synchronization is classified into two types
- Process Synchronization
- Thread Synchronization
Process Synchronization:
Process Synchronization is the term used to define sharing the resources between two or more processes and meanwhile ensuring the inconsistency of data. In a programming language, the piece of code that is being shared by different processes is called the Critical Section.
There are many solutions to avoid critical section problems like Peterson’s Solution, the most popular way to deal with this is Semaphores. The process is nothing but a program under execution. It runs independently isolated from another process. The resources like memory and CPU time, etc. are allocated to the process by the operation System.
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Thread Synchronization:
The concurrent execution of the critical resource by two or more Threads is termed Thread Synchronization. Thread is the subroutine that can execute independently within a single process.
A single process can contain multiple threads and the process can schedule all the threads for a critical resource. In fact, a single thread also contains multiple threads.
Thread synchronization is two types, they are:
1. Mutual Exclusive:
A Mutex or Mutual Exclusive helps only one thread to access the shared resources. It won’t allow the accessing of shared resources at a time. It can be achieved in the following ways.
- Synchronized Method
- Synchronized block
- Static Synchronization
2. Cooperation (Inter Thread Communication in java)
Example of Synchronization in Java
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Synchronized Instance methods
When we use a synchronized block with the instance methods, then each object has its synchronized method. There can be only one thread for each object, that can execute inside a method. If there is more than one object, then only a single thread can execute inside the block for each object.
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Synchronized Static Methods
We can mark the Static methods as synchronized just like we mark the instance methods using the synchronized keyword. Below is an example of a Java synchronized static method:
Example:
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The synchronized block inside Instance Methods
If you do not want to synchronize the whole method, you can just make a particular block inside the method synchronized.
Example:
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The synchronized block inside Static Methods
We can also use the Synchronized blocks inside the static methods. Below is an example of using a synchronized block inside the static method:
Java Synchronized Method
If we use the Synchronized keywords in any method then that method is Synchronized Method.
- It is used to lock an object for any shared resources.
- The object gets the lock when the synchronized method is called.
- The lock won’t be released until the thread completes its function.
Syntax:
Acess_modifiers synchronized return_type method_name (Method_Parameters) {
// Code of the Method.
}
Need for synchronization in Java
We use the Java synchronized keyword that helps in performing various activities related to concurrent programming. Some of the essential features of the synchronized keyword are:
- The synchronized keyword in Java provides the facility of locking, which ensures that no race condition occurs among threads.
- The synchronized keyword also prevents the reordering of the program statements.
- The synchronized keyword provides locking and unlocking. The thread needs to get the lock before getting inside the synchronized block. After getting the lock, it reads data from the main memory.
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