Process (computing)

program kodunu, atanan sistem kaynaklarını, fiziksel ve mantıksal erişim izinlerini ve yürütme etkinliğini başlatmak, denetlemek ve koordine etmek için veri yapılarını içeren bir işletim sistemi (OS) sürecine dayanan birçok farklı süreç modeli bulunmaktadır. İşletim Sistemi Bir bilgisayar programı tipik olarak diskteki bir dosyada saklanan pasif bir talimat koleksiyonu olsa da, bir işlem bu talimatların diskten belleğe yüklendikten sonra yürütülmesidir. Birkaç süreç aynı programla

Representatio

olduğu söylenircutable code, process-specific data (input and output), a call stack (to keep track of active subroutines and/or other events), and a heap to hold intermediate computation data generated during run time. İşlem sahibi ve işlemincu ve fiziksel bellek adresledressing. Bdevlet genellikle işlem yürütülürken bilgisayar kayıtlarında ve aksi takdirde bellekte saklanır.^[1]The operating system holds most of this information about active processes in data structures called process control blocks. Any subset of the resources, typically at least the processor state, may be associated with each of the process' threads in operating systems that support threads or child processes.İşletim sistemi, işlemlerini )

ir.ss management

A multitasking operating system may just switch between processes to give the appearance of many processes executing simultaneously (that is, in parallel), though in fact only one process can be executing at any one time on a single CPU (unless the CPU has multiple cores, then multithreading or other similar technologies can be used).^[a]

It is usual to associate a single process with a main program, and child processes with any spin-off, parallel processes, which behave like asynchronous subroutines. A process is said to own resources, of which an image of its program (in memory) is one such resource. However, in multiprocessing systems many processes may run off of, or share, the same reentrant program at the same location in memory, but each process is said to own its own image of the program.

Processes are often called "tasks" in embedded operating systems. The sense of "process" (or task) is "something that takes up time", as opposed to "memory", which is "something that takes up space".^[b]

The above description applies to both processes managed by an operating system, and processes as defined by process calculi.

If a process requests something for which it must wait, it will be blocked. When the process is in the blocked state, it is eligible for swapping to disk, but this is transparent in a virtual memory system, where regions of a process's memory may be really on disk and not in main memory at any time. Note that even portions of active processes/tasks (executing programs) are eligible for swapping to disk, if the portions have not been used recently. Not all parts of an executing program and its data have to be in physical memory for the associated process to be active.

Process states

An operating system kernel that allows multitasking needs processes to have certain states. Names for these states are not standardised, but they have similar functionality.^[1]

First, the process is "created" by being loaded from a secondary storage device (hard disk drive, CD-ROM, etc.) into main memory. After that the process scheduler assigns it the "waiting" state.
While the process is "waiting", it waits for the scheduler to do a so-called context switch. The context switch loads the process into the processor and changes the state to "running" while the previously "running" process is stored in a "waiting" state.
If a process in the "running" state needs to wait for a resource (wait for user input or file to open, for example), it is assigned the "blocked" state. The process state is changed back to "waiting" when the process no longer needs to wait (in a blocked state).
Once the process finishes execution, or is terminated by the operating system, it is no longer needed. The process is removed instantly or is moved to the "terminated" state. When removed, it just waits to be removed from main memory.^[1]^[2]

Inter-process communication

When processes need to communicate with each other they must share parts of their address spaces 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 protocols for distributed computing) are needed (e.g., the Message Passing Interface, often simply called MPI).

History

By the early 1960s, computer control software had evolved from monitor control software, for example IBSYS, to executive control software. Over time, computers got faster while computer time was still neither cheap nor fully utilized; such an environment made multiprogramming possible and necessary. Multiprogramming means that several programs run concurrently. At first, more than one program ran on a single processor, as a result of underlying uniprocessor computer architecture, and they shared scarce and limited hardware resources; consequently, the concurrency was of a serial nature. On later systems with multiple processors, multiple programs may run concurrently in parallel.

Programs consist of sequences of instructions for processors. A single processor can run only one instruction at a time: it is impossible to run more programs at the same time. A program might need some resource, such as an input device, which has a large delay, or a program might start some slow operation, such as sending output to a printer. This would lead to processor being "idle" (unused). To keep the processor busy at all times, the execution of such a program is halted and the operating system switches the processor to run another program. To the user, it will appear that the programs run at the same time (hence the term "parallel").

Shortly thereafter, the notion of a "program" was expanded to the notion of an "executing program and its context". The concept of a process was born, which also became necessary with the invention of re-entrant code. Threads came somewhat later. However, with the advent of concepts such as time-sharing, computer networks, and multiple-CPU shared memory computers, the old "multiprogramming" gave way to true multitasking, multiprocessing and, later, multithreading.

Notes

^ Some modern CPUs combine two or more independent processors in a multi-core configuration and can execute several processes simultaneously. Another technique called simultaneous multithreading (used in Intel's Hyper-threading technology) can simulate simultaneous execution of multiple processes or threads.
^ Tasks and processes refer essentially to the same entity. And, although they have somewhat different terminological histories, they have come to be used as synonyms. Today, the term process is generally preferred over task, except when referring to "multitasking", since the alternative term, "multiprocessing", is too easy to confuse with multiprocessor (which is a computer with two or more CPUs).

References

^ ^a ^b ^c Silberschatz, Abraham; Cagne, Greg; Galvin, Peter Baer (2004). "Chapter 4. Processes". Operating system concepts with Java (Sixth ed.). John Wiley & Sons. ISBN 0-471-48905-0.
^ Stallings, William (2005). Operating Systems: internals and design principles (5th ed.). Prentice Hall. ISBN 0-13-127837-1. (particularly chapter 3, section 3.2, "process states", including figure 3.9 "process state transition with suspend states")

External links

Media related to Process (computing) at Wikimedia Commons
Online Resources For Process Information
Computer Process Information Database and Forum
Process Models with Process Creation & Termination Methods Archived 2021-02-06 at the Wayback Machine

[2] Some modern CPUs combine two or more independent processors in a multi-core configuration and can execute several processes simultaneously. Another technique called simultaneous multithreading (used in Intel's Hyper-threading technology) can simulate simultaneous execution of multiple processes or threads.

[3] Tasks and processes refer essentially to the same entity. And, although they have somewhat different terminological histories, they have come to be used as synonyms. Today, the term process is generally preferred over task, except when referring to "multitasking", since the alternative term, "multiprocessing", is too easy to confuse with multiprocessor (which is a computer with two or more CPUs).

[OSC_Chap4-1] Silberschatz, Abraham; Cagne, Greg; Galvin, Peter Baer (2004). "Chapter 4. Processes". Operating system concepts with Java (Sixth ed.). John Wiley & Sons. ISBN 0-471-48905-0.

[Stallings-4] Stallings, William (2005). Operating Systems: internals and design principles (5th ed.). Prentice Hall. ISBN 0-13-127837-1. (particularly chapter 3, section 3.2, "process states", including figure 3.9 "process state transition with suspend states")

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v t e Parallel computing
General	Distributed computing Parallel computing Parallel algorithm Massively parallel Cloud computing High-performance computing Multiprocessing Manycore processor GPGPU Computer network Systolic array
Levels	Bit Instruction Thread Task Data Memory Loop Pipeline
Multithreading	Temporal Simultaneous (SMT) Simultaneous and heterogenous Speculative (SpMT) Preemptive Cooperative Clustered multi-thread (CMT) Hardware scout
Theory	PRAM model PEM model Analysis of parallel algorithms Amdahl's law Gustafson's law Cost efficiency Karp–Flatt metric Slowdown Speedup
Elements	Process Thread Fiber Instruction window Array
Coordination	Multiprocessing Memory coherence Cache coherence Cache invalidation Barrier Synchronization Application checkpointing
Programming	Stream processing Dataflow programming Models Implicit parallelism Explicit parallelism Concurrency Non-blocking algorithm
Hardware	Flynn's taxonomy SISD SIMD Array processing (SIMT) Pipelined processing Associative processing MISD MIMD Dataflow architecture Pipelined processor Superscalar processor Vector processor Multiprocessor symmetric asymmetric Memory shared distributed distributed shared UMA NUMA COMA Massively parallel computer Computer cluster Beowulf cluster Grid computer Hardware acceleration
APIs	Ateji PX Boost Chapel HPX Charm++ Cilk Coarray Fortran CUDA Dryad C++ AMP Global Arrays GPUOpen MPI OpenMP OpenCL OpenHMPP OpenACC Parallel Extensions PVM pthreads RaftLib ROCm UPC TBB ZPL
Problems	Automatic parallelization Deadlock Deterministic algorithm Embarrassingly parallel Parallel slowdown Race condition Software lockout Scalability Starvation
Category: Parallel computing