Java Threads

Java Threads

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  Threads In JAVA -M Vishnuvardhan, Dept.of Computer Science, SSBN Degree College, ATP
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  SSBN Degree College,ATP M Vishnuvardhan Introduction The ability of an Operating Systems to perform multiple jobs concurrently is called as Multi-Tasking. Similarly in programming, we divide the program in to multiple units and execute them concurrently is called as Multi-Threading. Multi- Threading improves the performance of the Program and makes the programs to execute in a faster way Java Supports Multi-Threading.
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  SSBN Degree College,ATP M Vishnuvardhan Thread – Defined A Thread is a piece of control which performs a job. A thread is considered as light weight process since it doesn't put burden on the CPU by demanding new resources when a new thread is created instead it shares the resources of its parent thread. But a process always burden on the CPU by demanding new resources when a new Process is created. In order to deal with the threads java defined Thread class in java.lang package
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  SSBN Degree College,ATP M Vishnuvardhan Creation of Threads In java Threads can be created in two ways  By extending Thread class  By implementing Runnable interface class NumThread extends Thread { ==== } class NumThread implements Runnable { ==== }
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  SSBN Degree College,ATP M Vishnuvardhan Creation of Threads Steps for creating thread by extending Thread class 1.Create a class by extending Thread class 2.Override run() method defined in Thread class. The run() is considered as heart of the Thread since it holds the job of the Thread 3.Create an object for the newly created thread 4.Start the thread using start() method present in the Thread class class NumThread extends Thread { public void run() { //job of the thread } } NumThread T1=new NumThread(); T1.start();
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  SSBN Degree College,ATP M Vishnuvardhan Creation of Threads Steps for creating thread by implementing Runnable interface 1.Create a class by implementing Runnable interface 2.Override run() method declared in Runnable interface. 3.Create an object for the newly created class 4.Create a Thread class object by passing the reference of new created object 5.Now start the thread using start() method class NumThread implements Runnable { public void run() { //job of the thread } } NumThread T1=new NumThread(); T1.start(); // gives error Thread T2=new Thread(T1); T2.start();
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  SSBN Degree College,ATP M Vishnuvardhan Life Cycle of the Thread start() suspend() sleep() wait() resume() notify() RunnableRunning New Born Blocked Dead yeild() stop() stop() stop()
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  SSBN Degree College,ATP M Vishnuvardhan Thread Methods  void start(): used to start a Thread  void stop(): used to stop a Thread  void run() : used to specify the job of the Thread  void sleep( int milliseconds): used to suspend the Thread for a definite time  void suspend(): used to suspend a Thread for a indefinite time until the Thread uses resume() method  void resume(): used to resume a suspended thread  void wait(): used to suspend a thread until other Thread notifies it using notify()  void notify(): used to notify a waiting Thread.
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  SSBN Degree College,ATP M Vishnuvardhan Thread Exceptions  IllegalThreadStateException: Occurs when a Thread is moved to invalid state of thread.  InterruptedException: Occurs when a Thread is interrupted. Generally sleep() generates this exception
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  SSBN Degree College,ATP M Vishnuvardhan Thread Priority Priority is an integer number which is associated with each thread. Which specifies the priority of the Threads. In general threads contains three priorities. These are defined as constants in Thread class. MIN_PRIRORITY --- 1 NORM_PRIRORITY --- 5 MAX_PRIRORITY --- 10 Priority for threads can given using following methods int getPriority(): gets the priority of the thread void setPriority(int priority): sets the priority for the thread Eg: T1.setPriority(Thread.MAX_PRIORITY);
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  SSBN Degree College,ATP M Vishnuvardhan Need of Synchronization Account accountNo Name Balance getBalance() Deposit() withDraw() Thread A Thread B deposit(5000) withDraw(3000)
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  SSBN Degree College,ATP M Vishnuvardhan Synchronization It is common that two or more threads do the same job. This doesn't cause any problem as long as the job doesn’t contain critical section. A section is said to be critical section when the statements share common data. When multiple threads work on critical section some times they result in Data Integrity failure. Synchronization is a technique of allowing only one thread in to critical section at a time. It can be applied in two levels Method level Synchronization Block level Synchronization
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  SSBN Degree College,ATP M Vishnuvardhan Method level Synchronization If all the statements inside a method are critical section then we apply synchronization at method level. i.e, only one thread is allowed in that method until that thread completes its job no other thread is allowed to enter in to the method. Syntax: synchronized returnType methodName ( <<parms>>) { ====== } Eg: synchronized double getBalance() { return balance; }
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  SSBN Degree College,ATP M Vishnuvardhan Block level Synchronization If only few statements inside a method are critical section but not all the statements then we apply synchronization at block level. i.e, only one thread is allowed in that block until that thread completes its job no other thread is allowed to enter in to that block. Syntax: returnType methodName ( <<parms>>) { ===== synchronized(this) { //critical section ===== } ====== } Eg: double getBalance() { == ==== synchronized(this) { return balance; } }
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  SSBN Degree College,ATP M Vishnuvardhan Questions