rafa/src/core/Context.js

Rafa.js is a Javascript framework for building concurrent applications.

// # constructor(done: () => _): Context
// Each time a message is pushed through a stream tree, a context is created 
// to keep track of any pending tasks (i.e. a stream"s handler returns a 
// promise). Once all of the stream"s tasks have completes, the function
// stored in the `done` parameter is called.
function Context(done) {
  this.done = done || this.noop;
  this.pending = 0;
}

inherit(Context, Rafa, {

  // # finished()
  // Decrement the number of pending streams we're waiting for and call this
  // Context's done method if all streams have processed their message.
  end() {
    if (!--this.pending) this.done();
  },

  // # reset(done: () => _)
  // Reset this context so it can be used to push another message through
  // a stream.
  reset(done) {
    if (done) this.done = done;
    this.pending = 1;
  },

  wait() {
    this.pending++;
  },

  // # waitfor(Stream, Message)
  // Wait for the Promise inside a Message to finish, then call the finished
  // method of this context.
  waitfor(stream, message) {
    this.pending++;
    const push = m => { this.pending--; stream.push(this, m); };
    message.value.then(
      v => push(message.copy(v)),
      e => push(this.errorMessage(e))
    );
  }
});