Ananda

• Feb 3rd, 2006

 

Through the methods Wait(),notify() and notifyall() threads are communicate each others.

Kailas

• Sep 7th, 2015

 

In contrast, all the threads within a program share the same address space. The only information that is not shared, and differentiates one thread from another, is the thread's identity and its execution stack (along with certain system information such as the signal mask, the state of locks and conditions, etc.) From this viewpoint, threads resemble co-routines. The threads within a given program are all treated in the same fashion, except for the initial thread that was created when the program started. When this thread terminates, so do all the other threads and therefore the program as a whole. (Whenever we speak of multiple threads, we will implicitly mean threads within a given program.)

But unlike co-routines, which pass control explicitly from one to another and cannot execute in parallel, threads can execute in parallel and can be scheduled preemptively by the system. From this viewpoint, threads resemble processes.

The common address space permits threads to communicate directly among themselves using shared memory. The fact that threads can execute in parallel means that they must synchronize their access to shared data, so that one finishes writing before the other begins reading. Although not necessary in principle, in practice this requires going through the operating system. Synchronization is often a difficult part of programming with threads. It can be done with locks and conditions, or in a higher-level fashion with events.

The advantages of threads over processes are the lower cost of creation and the ability to exchange large data structures simply by passing pointers rather than copying.