(* Unix -- SML Basis Library *)
type signal = Signal.signal
val executeInEnv : string * string list * string list -> proc
val execute : string * string list -> proc
val streamsOf : proc -> TextIO.instream * TextIO.outstream
val kill : proc * signal -> unit
val reap : proc -> Process.status
This structure allows Moscow ML programs to start other processes
and to communicate with them.
Child processes are not automatically terminated when the parent
(ML) process terminates. To forcibly terminate a child process pr,
use Unix.kill(pr, Signal.term). Then, to remove the terminated
process from the operating system tables, call Unix.reap(pr).
The protocol for communication between the ML program and its child
process must be designed with some care, typically using
non-blocking input for reading from the child process.
[proc] is the type of processes started by the ML program.
[signal] is the type of Unix-style signals, which can be sent to
another process. Signal values must be obtained from the Signal
[execute (cmd, args)] asks the operating system to execute the
command cmd with the argument list args, as a separate process.
Two pipes connected to the standard input and standard output of
the new process are created; these may be obtained using streamsOf.
A proc value representing the new process is returned. The new
process executes using the same environment as the calling process.
Raises Fail in case of failure, e.g. if the process or the pipes
cannot be created.
Typically, the cmd argument will be the full pathname of an
executable. On Unix systems, simple command searching as done by
the shell, allowing cmd to be a relative pathname, can be achieved
execute("/bin/sh", "-c" :: concat (cmd :: " " :: args))
[executeInEnv (cmd, args, env)] asks the operating system to
execute the command cmd with the argument list args in the
environment env, as a separate process. Returns a proc value
representing the new process. Typically, a string in the env list
has the form "NAME=VALUE". See also Process.getEnv.
[streamsOf pr] returns a pair (ins, outs) of input and output
streams associated with process pr. The standard output of pr is
the source for the input stream ins, and the standard input of pr
is the sink for the output stream outs.
[reap pr] closes the input and output streams associated with pr,
and then suspends the current (ML) process until the process
corresponding to pr terminates. Returns the exit status given by
pr when it terminated. Raises Fail in case of failure, e.g. if pr
has already been reaped.
Under Unix, information about a terminated process remains in the
system tables until the process is reaped. Thus, an ML program
using execute or executeInEnv must make sure to reap any process it
has created, or else the system tables will fill up.
[kill (pr, s)] sends the signal s to the process pr. Raises Fail
in case of failure, e.g. if pr has already been killed.