subprocesses

Subprocesses are processes created by a running process. A subprocess is typically a child of the creating process, and a parent can spawn multiple subprocesses. Subprocesses run in a separate execution context with their own memory space, system resources, and process identifier, but may inherit attributes from the parent such as the environment, working directory, or certain privileges.

Process hierarchy and lifecycle: Each subprocess has a parent; if the parent exits, the system may reassign the child to a different supervising process. Subprocesses go through creation, execution, waiting for completion, and termination. They yield an exit status or may be signaled to stop. The operating system reclaims their resources when they exit and ensures proper cleanup of system resources like file descriptors.

Communication and I/O: Subprocesses commonly communicate with the parent and with other processes via inter-process communication mechanisms such as pipes, sockets, shared memory, or file systems. The standard input, output, and error streams can be redirected to facilitate data exchange and control.

Creation mechanisms: Unix-like systems typically create subprocesses using fork and exec or newer primitives such as posix_spawn; Windows systems use CreateProcess. High-level programming languages provide libraries that wrap these primitives to simplify spawning, piping, and monitoring subprocesses.

Usage and considerations: Subprocesses enable running external programs, isolating tasks, or performing parallel work. Important considerations include proper handling of input and output, timeouts, resource limits, and clean termination to avoid zombie processes and security risks.

Subprocess vs. threads: Subprocesses are independent processes with separate memory spaces, which provides stronger isolation but higher overhead compared to threads, which share memory within a single process.