Multitasking Considerations

The recommended guideline is to use as few threads as possible, thereby minimizing the use of system resources. This improves performance. Multitasking has resource requirements and potential conflicts to be considered when designing your application. The resource requirements are as follows:

• The system consumes memory for the context information required by both processes and threads. Therefore, the number of processes and threads that can be created is limited by available memory.
• Keeping track of a large number of threads consumes significant processor time. If there are too many threads, most of them will not be able to make significant progress. If most of the current threads are in one process, threads in other processes are scheduled less frequently.

Providing shared access to resources can create conflicts. To avoid them, you must synchronize access to shared resources. This is true for system resources (such as communications ports), resources shared by multiple processes (such as file handles), or the resources of a single process (such as global variables) accessed by multiple threads. Failure to synchronize access properly (in the same or in different processes) can lead to problems such as deadlock and race conditions. The Win32 API provides a set of synchronization objects and functions you can use to coordinate resource sharing among multiple threads. For more information about synchronization, see Synchronizing Execution of Multiple Threads. Reducing the number of threads makes it easier and more effective to synchronize resources.

A good design for a multithreaded application is the pipeline server. In this design, you create one thread per processor and build queues of requests for which the application maintains the context information. A thread would process all requests in a queue before processing requests in the next queue.