Spawn (computing)

Spawn in computing refers to a function that loads and executes a new child process. The current process may wait for the child to terminate or may continue to execute asynchronously. Creating a new subprocess requires enough memory in which both the child process and the current program can execute.

There is a family of spawn functions in DOS, inherited by Microsoft Windows.

There is also a different family of spawn functions in an optional extension of the POSIX standards .

The DOS/Windows spawn functions are inspired by Unix functions fork and exec; however, as these operating systems do not support fork, the spawn function was supplied as a replacement for the fork-exec combination. However, the spawn function, although it deals adequately with the most common use cases, lacks the full power of fork-exec, since after fork any process settings which will survive an exec may be changed. However, in most cases, this deficiency can be made up for by using the more low-level CreateProcess API.

In the spawnl, spawnlp, spawnv, and spawnvp calls, the child process inherits the environment of the parent. Files that are open when a spawn call is made remain open in the child process.

The base name of each function is spawn, followed by one or more letters:

The mode argument determines the way the child is run. Values for mode are:

The path argument specifies the filename of the program to execute. For spawnlp and spawnvp only, if the filename does not have a path and is not in the current directory, the PATH environment variable determines which directories to search for the file. The string pointed to by argv[0] is the name of the program to run.

The command line passed to the spawned program is made up of the character strings, arg0 through argn, in the spawn call. The accepted maximum combined length of these strings differs between compilers, ranging from 128 characters on Digital Mars to 1024 on Microsoft Visual C++ or as much as memory permits, on DJGPP. The last argument after argn has to be a NULL pointer.

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