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A "ready" or "waiting" process has been loaded into main memory and is awaiting execution on a CPU (to be context switched onto the CPU by the dispatcher, or short-term scheduler). There may be many "ready" processes at any one point of the system's execution—for example, in a one-processor system, only one process can be executing at any one ...
Ready (ready to be executed); Blocked (waiting for an event, I/O for example). Most tasks are blocked or ready most of the time because generally only one task can run at a time per CPU core. The number of items in the ready queue can vary greatly, depending on the number of tasks the system needs to perform and the type of scheduler that the ...
When the operating system creates a new process, that process is initially labeled as NOT RUNNING, and is placed into a queue in the system in the NOT RUNNING state. The process (or some portion of it) then exists in main memory , and it waits in the queue for an opportunity to be executed.
When a process is created (initialized or installed), the operating system creates a corresponding process control block, which specifies and tracks the process state (i.e. new, ready, running, waiting or terminated). Since it is used to track process information, the PCB plays a key role in context switching. [1]
In computer operating systems, a process (or task) may wait for another process to complete its execution. In most systems, a parent process can create an independently executing child process . The parent process may then issue a wait system call , which suspends the execution of the parent process while the child executes.
The waiting primitive can be a busy-wait loop or an OS-provided primitive that prevents the thread from being scheduled until it is ready to proceed. Here is an example pseudocode implementation of parts of a threading system and mutexes and Mesa-style condition variables, using test-and-set and a first-come, first-served policy:
Then the operating system calls the switch() routine to first save the general-purpose user registers of A onto A's kernel stack, then it saves A's current kernel register values into the PCB of A, restores kernel registers from the PCB of process B, and switches context, that is, changes kernel stack pointer to point to the kernel stack of ...
CFS is the first implementation of a fair queuing process scheduler widely used in a general-purpose operating system. [5] The Linux kernel received a patch for CFS in November 2010 for the 2.6.38 kernel that has made the scheduler "fairer" for use on desktops and workstations.