Multitasking, Multithreading, and Multiprocessing

Multitasking refers to the ability of the operating system to quickly switch between tasks, giving the appearance of simultaneous execution of those tasks. For example, on Windows 3.1, a task is generally an entire application, such as Microsoft Word, Microsoft Excel, or LabVIEW. Each application runs for a small time slice before yielding to the next application. Windows 3.1 uses a technique known as cooperative multitasking, where the operating system relies on running applications to yield control of the processor to the operating system at regular intervals. Windows relies on preemptive multitasking, where the operating system can take control of the processor at any instant, regardless of the state of the application currently running. Preemptive multitasking guarantees better response to the user and higher data throughput.

Multithreading extends the idea of multitasking into applications, so that specific operations within a single application can be subdivided into individual threads, each of which can theoretically run in parallel. Then, the operating system can divide processing time not only among different applications, but also among each thread within an application. For example, in a LabVIEW multithreaded program, the application might be divided into three threads � a user interface thread, a data acquisition thread, and an instrument control thread � each of which can be assigned a priority and operate independently. Thus, multithreaded applications can have multiple tasks progressing in parallel along with other applications.

Multiprocessing, or multi-core programming, refers to two or more processors in one computer, each of which can simultaneously run a separate thread. Thus, a single-threaded application can run on only one processor at a time. A multithreaded application can have multiple separate threads executing simultaneously on multiple processors. In the LabVIEW multithreaded example, the data acquisition thread could run on one processor while the user interface thread runs on another processor. Single-threaded applications can have a serious effect on system performance.

Note��You can use the LabVIEW Desktop Execution Trace Toolkit to monitor thread usage, memory leaks, and other aspects of LabVIEW programming.