Editing Pipeline (software) (section)

==Implementation==
Pipelines are often implemented in a [[computer multitasking|multitasking]] [[operating system|OS]], by launching all elements at the same time as processes, and automatically servicing the data read requests by each process with the data written by the upstream process. This can be called a ''multiprocessed pipeline.'' In this way, the [[Scheduling (computing)|scheduler]] will naturally switch the CPU among the processes so as to minimize its idle time. In other common models, elements are implemented as lightweight threads or as coroutines to reduce the OS overhead often involved with processes. Depending on the OS, threads may be scheduled directly by the OS or by a thread manager. Coroutines are always scheduled by a coroutine manager of some form.

Read and write requests are usually blocking operations. This means that the execution of the source process, upon writing, is suspended until all data can be written to the destination process. Likewise, the execution of the destination process, upon reading, is suspended until at least some of the requested data can be obtained from the source process. This cannot lead to a [[Deadlock (computer science)|deadlock]], where both processes would wait indefinitely for each other to respond, since at least one of the processes will soon have its request serviced by the operating system, and continue to run.

For performance, most operating systems implementing pipes use pipe [[Buffer (computer science)|buffers]], which allow the source process to provide more data than the destination process is currently able or willing to receive. Under most Unixes and Unix-like operating systems, a special command is also available, typically called "buffer", that implements a pipe buffer of potentially much larger and configurable size. This command can be useful if the destination process is significantly slower than the source process, but it is desired that the source process complete its task as soon as possible. E.g., if the source process consists of a command which reads an audio track from a [[CD]] and the destination process consists of a command which compresses the [[waveform]] audio data to a format like [[MP3]]. In this case, buffering the entire track in a pipe buffer would allow the CD drive to spin down more quickly, and enable the user to remove the CD from the drive before the encoding process has finished.

Such a buffer command can be implemented using [[system call]]s for reading and writing data. Wasteful [[busy waiting]] can be avoided by using facilities such as [[poll (Unix)|poll]] or [[select (Unix)|select]] or [[Thread (computer science)|multithreading]].

Some notable examples of pipeline software systems include:
* [[RaftLib]] – C/C++ Apache 2.0 License