Processes

Process

Windows Task Manager provides information about computer performance and details of the programs and processes running on the computer.

A process is one execution of a program with a particular function operating on a data set. It is the basic unit of resource allocation; in systems with threads, a thread is the basic unit of scheduling. A process entity contains three parts:

1. Program
2. Data
3. Process control block (PCB)

A program is static, whereas a process is dynamic. A process is created when the system loads a program and establishes its execution state and resources. A process can be considered a program in execution and needs resources such as CPU time, memory, files, and I/O devices. These resources can be allocated at creation or during execution. A program can be started by clicking in a graphical user interface (GUI) or entering its name in a command-line interface (CLI).

Memory Organization

Memory normally includes a stack, heap, data region, and code region:

• Stack: normally allocated and released automatically; stores function parameters and local variables.
• Heap: normally allocated and released by the programmer or runtime; reclaimed by the OS when the program ends.
• Data: stores global and static variables; released by the system when the program ends.
• Code: stores the binary code of function bodies.

Process State Models

The two-state model divides processes into running and not running.

Not every nonrunning process is ready. Some must wait for I/O completion, so the nonrunning state can be divided into ready and blocked.

Every process has a lifecycle from creation to destruction and passes through these stages:

1. New: the system is allocating the PCB and execution context; the process cannot yet be scheduled.
2. Ready: the process is eligible to execute and awaits CPU scheduling.
3. Running: the process has obtained CPU resources and is executing.
4. Blocked: the process must wait for I/O completion or another event before continuing. An expired time slice instead returns it to ready.
5. Terminated: the process has ended naturally or has been forcibly stopped and will no longer execute.

Multiple Processes

Python's multiprocessing module provides a Process class for creating multiple processes. A Python program begins in the main process; processes created through Process are child processes.

Creating Multiple Processes

import multiprocessing

def worker():
	process = multiprocessing.current_process()
	print(process.pid, process.name)

def main():
	workers = [multiprocessing.Process(target=worker, name=f"Worker-{index}")
			   for index in range(3)]
	for process in workers:
		process.start()
	for process in workers:
		process.join()

if __name__ == "__main__":
	main()

psutil is a third-party process-management module supporting platforms such as Linux, UNIX, macOS, and Windows. It simplifies process-management operations across systems.

Inspecting All Processes

import psutil

for process in psutil.process_iter(attrs=["pid", "name", "create_time"]):
	try:
		print(process.info)
	except (psutil.NoSuchProcess, psutil.AccessDenied):
		continue