Modern real-time systems are based on the complementary concepts of multitasking and intertask communications. A multitasking environment allows a real-time application to be constructed as a set of independent tasks, each with its own thread of execution and set of system resources. The intertask communication facilities allow these tasks to synchronize and communicate in order to coordinate their activity. In VxWorks, the intertask communication facilities range from fast semaphores to message queues and pipes to network-transparent sockets.

Another key facility in real-time systems is hardware interrupt handling, because interrupts are the usual mechanism to inform a system of external events. To get the fastest possible response to interrupts, interrupt service routines (ISRs) in VxWorks run in a special context of their own, outside of any task's context.

This chapter discusses the multitasking kernel, tasking facilities, intertask communication, and interrupt handling facilities, which are at the heart of the VxWorks run-time environment.