Why Synchronization Is Needed in Multi-Threading Applications?

This section describes why synchronization is needed in multi-threading applications.

The biggest problem of allowing multiple threads sharing the same data set is that one operation in one thread could collide with another operation in another threads on the same data. When this happens, the result is un-desirable.

Let's use a bank application program as an example. Assuming that the program has multiple threads running, with each thread connecting one ATM system, and you have a saving account in the bank with $100.00, now you and your friend are going to two different ATMs at about the same time, and trying to withdraw $50.00 from your account, what do you think it will happen?

If the threads are running independently, the following could happen:

Time     01:01      02:01     03:01     04:01
Thread 1            Get       Set
Action   You        Account   Account   You
         Withdraw   Balance   Balance   Receive
         $50.00     $100.00   $50.00    $50.00
Time      01:02      02:02     03:02     04:02
Thread 2             Get       Set
Action    Friend     Account   Account   Friend
          Withdraw   Balance   Balance   Receive
          $50.00     $100.00   $50.00    $50.00
Time     01:01      02:01     03:01     04:01
Account  $100.00    $100.00   $50.00    $50.00

Both you and your friend will receive $50.00 each, and your account will still have $50.00. The bank could lose $50.00.

The solution to this problem is synchronization.

Last update: 2014.

Table of Contents

 About This Book

 Installing JDK 1.8 on Windows

 Execution Process, Entry Point, Input and Output

 Primitive Data Types and Literals

 Bits, Bytes, Bitwise and Shift Operations

 Managing Bit Strings in Byte Arrays

 Reference Data Types and Variables

 StringBuffer - The String Buffer Class

 System Properties and Runtime Object Methods

 Generic Classes and Parameterized Types

 Generic Methods and Type Inference

 Lambda Expressions and Method References

 Execution Threads and Multi-Threading Java Programs

 ThreadGroup Class and "system" ThreadGroup Tree

Synchronization Technique and Synchronized Code Blocks

Why Synchronization Is Needed in Multi-Threading Applications?

 Synchronization Technique - Lock and Synchronized Code

 "synchronized" - How Java Supports Synchronization

 BankingThread.java - Synchronization Sample Program

 BankingThread.java - Synchronization Sample Program Output

 Deadlock Condition Example Programs

 Garbage Collection and the gc() Method

 Outdated Tutorials


 PDF Printing Version