Process¶

Category: Units of execution · Status: stub · Lessons: chapter 08, Processes (planned)

One line: A running program with its own address space, open files and at least one thread; two processes share nothing unless they arrange to.

Also called: OS process.

How it connects¶

flowchart LR
  n_subprocess["Child process"]
  n_ipc["Inter-process communication"]
  n_mpi["MPI"]
  n_multiprocessing["Multiprocessing"]
  n_process["Process"]
  n_thread["Thread"]
  n_ipc -->|uses| n_process
  n_mpi -->|uses| n_process
  n_multiprocessing -->|uses| n_process
  n_process ---|vs| n_thread
  n_subprocess -->|is a| n_process
  classDef center stroke-width:3px
  class n_process center
  classDef outside stroke-dasharray: 4 3
  class n_subprocess,n_ipc,n_mpi,n_multiprocessing,n_thread outside

Kinds: Child process
Is used by: Inter-process communication, MPI, Multiprocessing
Often confused with: Thread
See also: Context switch, Inter-process communication, Multiprocessing

In each language¶


Rust	`std::process::Command` ↗ spawns a child process and returns a `Child` ↗
Go	`os/exec` ↗ runs an external command
C	`fork` ↗ copies the calling process but only the thread that called it; `posix_spawn` ↗ starts a new program
Java	`ProcessBuilder` ↗ starts a `Process` ↗; `ProcessHandle` ↗ (Java 9) inspects any process
Python	`subprocess` ↗ runs programs; `multiprocessing` ↗ runs Python functions in child processes
C#	`Process.Start` ↗
Erlang and Elixir	An external program is reached through a port ↗, and runs in another OS process
The operating system	`fork(2)` ↗ and `execve(2)` ↗; on Linux `clone(2)` ↗ creates processes and threads alike

Where to read more¶

In this library: Who waits when main returns?
In a sibling library: Linux: head closes the pipe early ↗
In the books: The Little Elixir & OTP Guidebook, Benjamin Tan Wei Hao — ch. 3, 'Processes 101'
In the books: Learn Concurrent Programming with Go, James Cutajar — ch. 2, 'Dealing with threads' → 'Abstracting concurrency with processes and threads'
In the books: Async Rust, Maxwell Flitton, Caroline Morton — ch. 1, 'Introduction to Async' → 'Introduction to Processes'
In the books: Mastering C++ Multithreading, Maya Posch — ch. 2, 'Multithreading Implementation on the Processor and OS' → 'Defining processes and threads'
In the books: Learning Concurrent Programming in Scala, Aleksandar Prokopec — ch. 2, 'Concurrency on the JVM and the Java Memory Model' → 'Processes and threads'
In the books: Python Concurrency with asyncio, Matthew Fowler — ch. 1, 'Getting to know asyncio' → 'Understanding processes, threads, multithreading, and multiprocessing'
Notes: processes and the operating system ↗
Notes: process - rust ↗
Notes: exit - function - rust - std::process::exit ↗
Notes: how the CPU interacts with processes and threads ↗
Reference: Wikipedia: Process (computing) ↗