process

This library provides a portable abstraction over process handling predicates found in some backend Prolog systems. Currently supports ECLiPSe, GNU Prolog, SICStus Prolog, SWI-Prolog, Trealla Prolog, and XVM.

API documentation

Open the ../../docs/library_index.html#process link in a web browser.

Loading

To load all entities in this library, load the loader.lgt file:

| ?- logtalk_load(process(loader)).

Testing

To test this library predicates, load the tester.lgt file:

| ?- logtalk_load(process(tester)).

Usage

The process object provides the following predicates for portable process handling:

  • create(Executable, Arguments, Options) - Creates a new process

  • wait(Process, Status) - Waits for a process to terminate

  • kill(Process, Signal) - Terminates a process with a specific signal

  • kill(Process) - Terminates a process using the default signal (SIGKILL)

Exit status depends on the backend. For a successfully terminated process, Status is either 0 or exit(0). For unsuccessful processes, Status cannot be sensibly abstracted. Consult the backens documentation for the details.

The create/3 predicate supports the following options:

  • process(Pid) - Unifies Pid with the process identifier (an opaque ground term)

  • stdin(Stream) - Binds Stream to the process standard input

  • stdout(Stream) - Binds Stream to the process standard output

  • stderr(Stream) - Binds Stream to the process standard error

  • type(Type) - Sets the type (binary or text) of the stdin/1 and stdout/1 streams

Process identifiers (PIDs) should be treated as opaque ground terms. Their internal representation varies between backend Prolog systems.

The type/1 option is ignored on ECLiPSe, GNU Prolog, and XVM as these systems don’t provide the necessary support to set the streams type at process creation.

Example:

| ?- process::create('/bin/echo', ['hello.'], [stdout(Out), process(PID)]),
     read_term(Out, Term, []),
     close(Out).
Out = ..., PID = ..., Term = hello.