Process Class

Overview

The Process class provides functionality for interacting with a system process.

Methods

Process.getPid

Returns the process id associated with a process.

Process.getStandardError

Retrieves the stderr stream of the process

Process.getStandardOutput

Retrieves the stdout stream of the process

Process.isRunning

Determines whether the process is running

Process.kill

Stops a system process

Process.setRedirect

Puts process object in redirect mode

Process.waitForExit

Waits for the process to terminate

Example

// Process runs an external program and can capture its output.
//
//   setRedirect(true)  must come before start(), or
//                      getStandardOutput()/getStandardError() give null
//   start()            returns at once, reports completion through the
//                      finished event, and so needs Application.run()
//   startAndWait()     blocks until the program exits
//
// Output is buffered while the program runs, so by the time finished
// fires the whole of it is there to read.

const process = new Process();

// capture the output; must be set before starting
process.setRedirect(true);

process.finished.connect(function(sender, event_args) {
    let output = `still running: ${sender.isRunning()}\n\n`;

    // getStandardOutput() returns a ProcessOutputStream; read it a line
    // at a time until eof().  getStandardError() is the same for stderr.
    const stream = sender.getStandardOutput();
    let count = 0;

    while (!stream.eof()) {
        const line = stream.readLine();
        if (line === null) {
            break;
        }

        count++;
        if (count <= 8) {
            output += `${line}\n`;
        }
    }

    alert(`${output}\n${count} line(s) of output`);

    Application.exit();
});

// on macOS or Linux this would be "/bin/sh -c env"
process.start("cmd /c set");

// getPid() is 0 if the program could not be launched -- in which case
// no finished event is coming.  kill() stops one that is still running.
if (process.getPid() === 0) {
    alert("could not start the process");
} else {
    // start() is asynchronous, so the event loop must run for finished
    // to arrive.  The blocking alternative is
    //
    //     process.startAndWait("cmd /c set");
    //
    // which returns only once the program has exited, letting the output
    // be read on the next line instead of from a handler.
    Application.run();
}