Question

The result is populated in the exec function, but it never gets back to the main thread… what am I doing wrong?

  var Fiber, exec, execSync;

  exec = require("child_process").exec;

  Fiber = require('fibers');

  execSync = function(cmd) {
    var cmdExec, final;
    cmdExec = function(cmd) {
      var fiber,
        _this = this;
      fiber = Fiber.current;
      exec(cmd, function(se, so, e) {
        var result;
        fiber.run();
        result = se + so + e;
        return result;
      });
      return Fiber["yield"]();
    };
    final = '';
    Fiber(function() {
      return cmdExec(cmd);
    }).run();
    return final;
  };

  console.log(execSync('ls ..'));

Answer 1

there’s a few problems in that code.. Here’s some code that does what you want:

var Fiber, exec, execSync;

exec = require("child_process").exec;

Fiber = require('fibers');

execSync = function(cmd) {
  var fiber = Fiber.current;
  exec(cmd, function(err, so, se) { 
    if (err) fiber.throwInto(err);
    fiber.run(se + so);
  });
  return Fiber.yield();
};

Fiber(function() {
  console.log(execSync('ls ..'));
}).run();

The big problem is that you seem to be mixing up the role of run and yield. Basically yield suspends a Fiber and run will resume (or start it for the first time). What you should be doing is running any code that needs to call execSync inside a Fiber, and then execSync will grab a reference to the current fiber and then call Fiber.yield(). When the exec call returns the fiber is resumed with fiber.run().

The other smaller issue is some confused parameters to the callback for exec. The parameters are err, stdout, stderr.