Process (computing): Difference between revisions

Revision as of 06:40, 23 February 2022

Revision as of 15:36, 23 February 2022

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[[Computer multitasking|Multitasking]] is a method to allow multiple processes to share [[Central processing unit|processors]] (CPUs) and other system resources. Each CPU (core) executes a single [[Task (computing)|task]] at a time. However, multitasking allows each processor to [[context switch|switch]] between tasks that are being executed without having to wait for each task to finish ([[Preemption (computing)|preemption]]). Depending on the operating system implementation, switches could be performed when tasks initiate and wait for completion of [[input/output]] operations, when a task voluntarily yields the CPU, on hardware [[interrupt]]s, and when the operating system scheduler decides that a process has expired its fair share of CPU time (e.g, by the [[Completely Fair Scheduler]] of the [[Linux kernel]]).

A common form of multitasking is provided by CPU's [[time-sharing]] that is a method for interleaving the execution of users' processes and threads, and even of independent kernel tasks -– although the latter feature is feasible only in preemptive [[Kernel (operating system)|kernels]] such as [[Linux kernel|Linux]]. Preemption has an important side effect for interactive processes that are given higher priority with respect to CPU bound processes, therefore users are immediately assigned computing resources at the simple pressing of a key or when moving a mouse. Furthermore, applications like video and music reproduction are given some kind of real-time priority, preempting any other lower priority process. In time-sharing systems, [[context switch]]es are performed rapidly, which makes it seem like multiple processes are being executed simultaneously on the same processor. This simultaneous execution of multiple processes is called [[Concurrency (computer science)|concurrency]].

For security and reliability, most modern [[operating system]]s prevent direct [[inter-process communication|communication]] between independent processes, providing strictly mediated and controlled inter-process communication functionality.

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When processes need to communicate with each other they must share parts of their [[address space]]s or use other forms of inter-process communication (IPC).

For instance in a shell pipeline, the output of the first process need to pass to the second one, and so on; another example is a task that can be decomposed into cooperating but partially independent processes which can run at once (i.e., using concurrency, or true parallelism -– the latter model is a particular case of concurrent execution and is feasible whenever enough CPU cores are available for all the processes that are ready to run).

It is even possible for two or more processes to be running on different machines that may run different operating system (OS), therefore some mechanisms for communication and synchronization (called [[communications protocol]]s for distributed computing) are needed (e.g., the Message Passing Interface, often simply called [[Message Passing Interface|MPI]]).