Synchronous invocation in JavaScript, part 2: execution dissected

Let’s review the process definition and process constructor from part 1:

     1  function proc(processDef) {
     2      var process = processDef();
     3
     4      function driver() {
     5          var pseudoBlockingCall = process.next();
     6
     7          pseudoBlockingCall(driver);
     8      }
     9
    10      return driver;
    11  }

    12  var driver = proc(function() {
    13      dump("Going to bed...\n");
    14      var pseudoBlockingCall = function(driver) {
    15          window.setTimeout(driver, 3000);
    16      });
    17      yield(pseudoBlockingCall);
    18      dump("Sigh, I only slept three seconds.\n")
    19  });

    20  driver();

The conversation among the three actors (process definition, process driver and process costructor) goes like this. Notice the many control transfers, and remember that executing the process definition to get the process (at line 2) returns a generator—that’s why process can be entered and exited many times at intermediate stages.

Not bad for less than twenty lines of code…

In the next part, we’ll see how to make conversation more lively by allowing pseudo-blocking functions to compute and return values.

Articles in this series:

1. Part 1: Problem and basic solution
2. Part 2: Execution dissected
3. Part 3: Returning values
4. Part 4: Error handling