Benefiting From Multithreading

This section briefly describes the benefits of multithreading.

Multithreading your code can help in the following areas:

• Improving Application Responsiveness

• Using Multiprocessors Efficiently

• Improving Program Structure

• Using Fewer System Resources

Improving Application Responsiveness

Any program in which many activities are not dependent upon each other can be redesigned so that each independent activity is defined as a thread. For example, the user of a multithreaded GUI does not have to wait for one activity to complete before starting another activity.

Using Multiprocessors Efficiently

Typically, applications that express concurrency requirements with threads need not take into account the number of available processors. The performance of the application improves transparently with additional processors because the operating system takes care of scheduling threads for the number of processors that are available. When multicore processors and multithreaded processors are available, a multithreaded application's performance scales appropriately because the cores and threads are viewed by the OS as processors.

Numerical algorithms and numerical applications with a high degree of parallelism, such as matrix multiplications, can run much faster when implemented with threads on a multiprocessor.

In this manual, whenever multiprocessors are discussed, the context applies also to multicore and multithreaded processors unless noted otherwise.

Improving Program Structure

Many programs are more efficiently structured as multiple independent or semi-independent units of execution instead of as a single, monolithic thread. For example, a non-threaded program that performs many different tasks might need to devote much of its code just to coordinating the tasks. When the tasks are programmed as threads, the code can be simplified. Multithreaded programs, especially programs that provide service to multiple concurrent users, can be more adaptive to variations in user demands than single-threaded programs.

Using Fewer System Resources

Programs that use two or more processes that access common data through shared memory are applying more than one thread of control.

However, each process has a full address space and operating environment state. Cost of creating and maintaining this large amount of state information makes each process much more expensive than a thread in both time and space.

In addition, the inherent separation between processes can require a major effort by the programmer. This effort includes handling communication between the threads in different processes, or synchronizing their actions. When the threads are in the same process, communication and synchronization becomes much easier.

Combining Threads and RPC

By combining threads and a remote procedure call (RPC) package, you can exploit nonshared-memory multiprocessors, such as a collection of workstations. This combination distributes your application relatively easily and treats the collection of workstations as a multiprocessor.

For example, one thread might create additional threads. Each of these children could then place a remote procedure call, invoking a procedure on another workstation. Although the original thread has merely created threads that are now running in parallel, this parallelism involves other computers.

The Message Processing Interface (MPI) might be a more effective approach to achieve multithreading in applications that run across distributed systems. See http://www-unix.mcs.anl.gov/mpi/ for more information about MPI.

The Sun HPC ClusterTools^TM software includes Open MPI Message Passing Interface (OMPI), which is an open source implementation of MPI. See the Sun HPC ClusterTools product page for more information about ClusterTools.