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Thread & MultiThread

Thread (computing)

In computer science, a thread of execution is the smallest sequence of programmed instructions that can be managed independently by an operating system scheduler. The scheduler itself is a light-weight process. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process. In particular, the threads of a process share the latter’s instructions (its code) and its context (the values that its variables reference at any given moment).

To arrive at a solution, software architects began writing operating systems that supported running pieces of programs, called threads. Threads are small tasks that can run independently. Each thread gets its own time slice, so each thread represents one basic unit of processor utilization. Threads are organized into processes, which are composed of one or more threads. All threads in a process share access to the process resources.

Another Way, In Programming Language

public class Thread
extends Object
implements Runnable

A thread is a thread of execution in a program. The Java Virtual Machine allows an application to have multiple threads of execution running concurrently.

Every thread has a priority. Threads with higher priority are executed in preference to threads with lower priority. Each thread may or may not also be marked as a daemon. When code running in some thread creates a new Thread object, the new thread has its priority initially set equal to the priority of the creating thread, and is a daemon thread if and only if the creating thread is a daemon.

When a Java Virtual Machine starts up, there is usually a single non-daemon thread (which typically calls the method named  main of some designated class). The Java Virtual Machine continues to execute threads until either of the following occurs:

  • The exit method of class Runtime has been  called and the security manager has permitted the exit operation to take place.
  • All threads that are not daemon threads have died, either by  returning from the call to the run method or by  throwing an exception that propagates beyond the run  method.

There are two ways to create a new thread of execution. One is to declare a class to be a subclass of Thread. This subclass should override the run method of class  Thread. An instance of the subclass can then be allocated and started. For example, a thread that computes primes larger than a stated value could be written as follows:


     class PrimeThread extends Thread {
         long minPrime;
         PrimeThread(long minPrime) {
             this.minPrime = minPrime;
         }

         public void run() {
             // compute primes larger than minPrime
              . . .
         }
     }

The following code would then create a thread and start it running:

     PrimeThread p = new PrimeThread(143);
     p.start();

Multiple threads can exist within the same process and share resources such as memory, while different processes do not share these resources.

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