How to handle pre-req flow using Jake.exec

gistfile1.js

var spawn = require('child_process').spawn;

desc('Do thing 1');
task('thing1', [], function () {
  var cmds = ['node -e "console.log(\'--> Thing 1... Executing\')"'];

  console.log('--> Thing 1... Starting');

  jake.exec(cmds, function () {
    var echo = spawn('echo',
        ["--> Thing 1... I'm doing a spawned process in thing 1"])
    , data = '';
    echo.stdout.on('data', function (d) {
      data += d;
    });
    echo.stdout.on('end', function () {
      console.log(data);
    });
    echo.on('exit', function () {
      console.log('--> Thing 1... Done');
      complete();
    });
  }, {stdout: true});

}, {async: true});

desc('Do thing 2');
task('thing2', [], function () {
  console.log('--> Thing 2... Starting');
  var cmds = ['node -e "console.log(\'--> Thing 2... Executing\')"'];

  jake.exec(cmds, function () {
    console.log('--> Thing 2... Done');
    complete();
  }, {stdout: true});
}, {async: true});

desc('Do thing 3');
task('thing3', [], function () {
  console.log('--> Thing 3... Starting');
  var cmds = ['node -e "console.log(\'--> Thing 3... Executing\')"'];

  jake.exec(cmds, function () {
    console.log('--> Thing 3... Done');
    complete();
  }, {stdout: true});
}, {async: true});

desc('Do all the things');
task('default', ['thing1', 'thing2'], function () {
  console.log('* Default... Starting');
  var cmds = ['node -e "console.log(\'* Default... Executing\')"' ];

  jake.exec(cmds, function () {
    var thing = jake.Task.thing3;
    thing.addListener('complete', function () {
      console.log('* Default... Done');
      complete();
    });
    thing.invoke();
  }, {stdout: true});
}, {async: true});




/*

jake
--> Thing 1... Starting
--> Thing 1... Executing
--> Thing 1... I'm doing a spawned process in thing 1

--> Thing 1... Done
--> Thing 2... Starting
--> Thing 2... Executing
--> Thing 2... Done
* Default... Starting
* Default... Executing
--> Thing 3... Starting
--> Thing 3... Executing
--> Thing 3... Done
* Default... Done

*/

Yes, I should have been clearer that the code above is a working version of what you seemed to be wanting here, including how to use spawn (even though you shouldn't really need it) and how to use invoke.

Yes, the entire reason for having an "async:true" flag for tasks is so you can break things down into smaller units of code for reusability, and still ensure prereqs execute sequentially. You should always flag a task that does asynchronous work as async and use complete, even if it's initially a standalone task.