Thread

1. Thread A thread represents an independent module of an application that can be concurrently execution With other modules of the application. MULTITHREADING multithreading represents concurrent execution of multiple thread. Multiple thread is a light weight version of multiprocessing is the way that less overhead incurred by the o/s in the management to thread as compared to processes .

2. Difference between multiprocessing and multithreading • 1) in multiprocessing each process represents an independent application where as in multithreading each thread represents an independent module of an application . • 2) in multithreading each process has its own address space where as in multithreading all the threads share common address space . • Note: java.lang.Thread class provides functionality of defining a thread , starting a thread , suspending a thread , managing a thread . For each thread an object of thread class is created this object is used to manage the thread or to find out change the state of a thread.

3. Note: thread class object & thread are different. • A thread class provides various methods most of these methods are final.1) getName():- return a name of the thread. • Syntax: public String getName(); • 2) setName():- it gives name to thread. • Syntax:public void setName(String name); • 3)getpriority():- • Syntax:publicintgetPriority(); • 4) setpriority():- • Syntax:public void setpriority();

4. MAX _PRIORITY 10 • MIN_PRIORITY 1 • DEFAULT PRIORITY OF A USER THREAD 5 • Sleep():- it is used to suspend current thread for the specified type. • Syntax: public static void sleep(Long milliseconds )throws Interrupted exception. • isAlive():- returns a Boolean value that is true if thread represented by the thread object is in the memory otherwise returns false • Syntax: public booleanisAlive();

5. run():- represents a thread that is instruction and run method are executed by the JVM as a thread. (it is non final method) Syntax:public void run(); Start():- it is responsible for starting the execution of a thread. Syntax: public void start(); STATES OF THREADS

6. Scheduling algo works here. Start (); Runnable /ready to run nweInstance() Swaped states over Control is taken back from the thread by the scheduler Processor is alloted suspended Thread is suspended running

7. CurrentThread():- return the reference of the thread object for the currenrt thread. • Syntax:public static thread currentThread(); Pgm1 Defining user thread: A user thread is represented by the run method , run method can be defined in the following two ways: • Define a sub class of thread and override run method. • Define a class that implements java.lang.Runnable interface & define its only method run(). Public interface Runnable { Void run(); } Note: thread class provides default implementation of runnable interface . pgm 2

8. Join():- join method of thread class is used to suspend the current thread till invoking thread terminates or current thread times out. • Syntax: • public void join() throws Interruptedexception; • Public void join (long miliseconds)throws interruptedexception;

9. Execution of threads in java is asynchronous (can’t determine at which thread will executed at what time). • Synchronization is desirable in multithreading to share a common resources b/w multithreads in a mutually exclusive manner. • Synchronization is achieved with the help of monitor. • A monitor represents an exclusive lock that is obtained on an object by thread before the synchronization method or synchronized block is executed.

10. In java implicit locking method is used . • Synchronized keywords is provided to indicate that object must be locked exclusively before invoking a method or block of statement. • A synchronization keyword can be used with method signature as well as can be used within a method to specifying locking for some statement. • Syntax: synchronized acceessmodifier returntype mathodName(types arguments) • With the help of synchronized keyword only mutual exclusivity of a shared resource can be determine. • Sometimes order of usage of an object has to be determine. • i.e. for example in a reader & writer problem apart from a mutual exclusivity of the common buffer. • Order of usage by reader and writer threads has to be in a predetermine manner.

11. Inter thread communication • Inter thread communication is used to gain exact control over the execution of threads .inter thread communication is facilitates with help of following methods • 1) wait(); • 2) notify(); • notifyAll(); • Wait():- a wait method is used to instruct the current thread to release all the locks held by it &to get suspended until some other thread invokes noytify() or notifyAll() methods by taking the lock on the same object. • Syntax: public void wait()throws interrupted exception;

12. Notify():- it is used to invoke a thread that is suspended by invoking a wait method on itself . • Syntax: public void notify(); • notifyAll():- it is used to invoke all the threads that are suspended by wait method. Note: these methods are defined in object class.

13. Sleeping for the specified time 1.1 Runnable 1.0 Block for I/O 2.0 3.2 3.1 1 Switch Waiting for joined thread for complete or time out. 2 Running 3 Waiting for lock 4 4.1 4.2 Wating for notification Synchronized Method or some blockesexceuted

14. 1. call sleep() method. • 2. I/O is performed. • 3. join() method call. • 4. wait() method. • 1.0 thread is interrupted. • 1.1 specified time is over. • 2.0 I/O operation is completed. • 3.1 joined thread completed . • 3.2 thread is interrupted. • 4.1 thread is interrupted. • 4.2 notification is received.

15. All thread have a Boolean variable name interrupted that is used by an application programmer to interrupt a thread . • Value of interrupt flag is continuously check while a thread is an suspended state . If it set to true thread comes out the suspended pool & through interrupted exception. • Following methods are used to set or obtain value of interrupted flag of a thread • Interrupt():- sets the values of interrupted flag • Public void interrupt();

16. isInterrupted():-it is used to obtain the value of interrupted flag • Public Boolean isInterrupted(); • Interrupted():- returns the current value of interrupted flag & reset it. • Public static boolean interrupted(); • Thread Group • Java.lang.ThreadGroup class provides method to manage logically related threads –Commonly used methods of this class are:- • interrupt():- interrupts all the active threads of the group. • Public void interrupt();

17. activeCount():- returns number of active threads in the group. • Public intactiveCount(); • activeThreads():-returns the reference of all the active threads of the group. • Public Thread[] active thread(); • Note: to make a thread a part of a group ,Thread class provides following connstructor • Public Thread(ThreadGroup group, String name) • Public threadGroup(String name );

18. Daemon Threads • It is a thread are special threads that does not compact for resources with normal threads i.e. a daemon threads is executed only if there is no normal thread in the runnable and running state. Daemon threads are used to provide services to normal threads . • Garbage collection in java is an example of daemon thread. • If at any point of time only daemon threads remaining as active thread then JVM aborts them & terminates i.e. a daemon thread can’t executed its own .it needs normal thread.

19. setDaemon():- it is used to make a thread daemon thread. • Public void setDaemon(boolean flag); • Note: setDaemon() method must be invoke before starting a thread. • Yield():- it is used to voluntary release the control from a thread. • Public void yield();