Runnable Process Definition

A runnable process is a process which is in the TASK_RUNNING process state.

A process, also referred to as a task, is an instance of a program in execution. A process state is a field in the process descriptor. This field can accept any of five possible flags (i.e., values), one of which is TASK_RUNNING.

A process descriptor is a task_struct-type data structure whose fields contain all of the information regarding a single process. Its process state field describes what is currently happening to the process. A data structure is a way of storing data in a computer so that it can be used efficiently. A task_struct data structure is a data structure that is used to describe a process on the system.

The TASK_RUNNING state means that the process is runnable, and it is either currently running or on a runqueue waiting to run. This is the only possible state for a process executing in user space (i.e., that portion of system memory in which user processes run); it can also apply to a process in kernel space (i.e., that portion of memory in which the kernel executes and provides its services) that is actively running.

A runqueue is the basic data structure in the scheduler, and it contains the list of runnable processes for the CPU (central processing unit), or for one CPU on a multiprocessor system. The scheduler, also called the process scheduler, is a part of the kernel that allocates the scare CPU time among the various runnable processes on the system.

Created July 15, 2005.
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