Nodejs - 承诺，未处理的终止和内存泄漏

Question

seeking help from nodejs gurus out there on usage of promises. I have the following test program, in which I invoke an async "q" function that simply throws an exception. This program leaks memory pretty consistently; but the leak goes away if uncomment the .done() call.

Why does the leak happen when the promise is unterminated (ie no done() call)? I tried to follow the documentation , but have trouble understanding the explanation of the done() method. Thanks in advance for your help!

Here's my code:

(function() {
  var MAX_ITER_COUNT, Q, iterCount, maxMem, noop, qDoit, test;

  Q = require("q");

  iterCount = 0;

  MAX_ITER_COUNT = 10 * 1000;

  maxMem = 0;

  noop = function() {};

  qDoit = function() {
    var currentMem;
    currentMem = Math.round(process.memoryUsage().heapUsed / 1024 / 1024);
    if (currentMem > maxMem) {
      maxMem = currentMem;
    }
    console.log("" + iterCount + " - memory is: " + currentMem + "/" + maxMem + " MB");
    return Q(10).then(function() {
      throw new Error("X");
    });
  };

  test = function() {
    if (iterCount++ > MAX_ITER_COUNT) {
      console.log("DONE");
      return;
    }

    // ----  If I uncomment the done() call below the leak goes away ----
    return qDoit()["finally"](function() {
      return setImmediate(test);
    })
    //.done(noop, noop, noop);


  };

  Q.onerror = function() {};

  test();

}).call(this);

Answer 1

Answering my own question, hopefully it will help someone.

On digging a bit into the q library code, it looks like all unhandled exceptions are put in an array called unhandledRejections , by default. Not sure why it was implemented like this, but presumably to help developers track down un-handled exceptions. This behavior can be changed by calling Q.stopUnhandledRejectionTracking() . When I did this, the memory leak went away, even without the .done() call.