The SMART interface provides two kinds of support for multimedia applications. One is to support the developers of multimedia applications that are faced with writing applications that have dynamic and adaptive real-time requirements. The other is to support the end users of multimedia applications, each of whom may have different preferences for how a given mix of applications should run. For the application developer, SMART provides time constraints and notifications for supporting applications with real-time computations. For the user of applications, SMART provides priorities and shares for predictable control over the allocation of resources. An overview of the interface is presented here. A more detailed description can be found in Nieh and Lam .
Application Developer Support
Multimedia application developers are faced with the problem of writing applications with real-time requirements. They know the time constraints that should be met in these applications and know how to allow them to adapt and degrade gracefully when not all time constraints can be met. The problem is that current operating system practice, as typified by UNIX, does not
provide an adequate amount of functionality for supporting these applications. For example, in dealing with time in UNIX time-sharing, an application can obtain simple timing information such as elapsed wall clock time and accumulated execution time during its computations. An application can also tell the scheduler to delay the start of a computation by “sleeping” for a duration of time. But it is not possible for an application to ask the scheduler to complete
a computation within certain time constraints, nor can it obtain feedback from the scheduler on whether or not it is possible for a computation to complete within the desired time constraints. The application ends up finding out only after the fact that its efforts were wasted on results that could not be delivered on time. The lack of system support exacerbates the difficulty of writing
applications with real-time requirements and results in poor application performance.
