Merge pull request brianc#15 from slickmb/bug/close_race

Avoid race when stream closed while fetching

Author: brianc

index.js

@@ -32,10 +32,11 @@ for(var key in Cursor.prototype) {
   }
 }
 
-QueryStream.prototype.close = function() {
+QueryStream.prototype.close = function(cb) {
   this._closing = true
   var self = this
   Cursor.prototype.close.call(this, function(err) {
+    if (cb) { cb(err); }
     if(err) return self.emit('error', err)
     process.nextTick(function() {
       self.push(null)
@@ -51,6 +52,9 @@ QueryStream.prototype._read = function(n) {
     if(err) {
       return self.emit('error', err)
     }
+
+    if (self._closing) { return; }
+
     if(!rows.length) {
       process.nextTick(function() {
         self.push(null)

test/close.js

@@ -33,3 +33,68 @@ helper('early close', function(client) {
     })
   })
 })
+
+helper('should not throw errors after early close', function(client) {
+  it('can be closed early without error', function(done) {
+    var stream = new QueryStream('SELECT * FROM generate_series(0, 2000) num');
+    var query = client.query(stream);
+    var fetchCount = 0;
+    var errorCount = 0;
+
+
+    function waitForErrors() {
+
+      setTimeout(function () {
+        assert(errorCount === 0, 'should not throw a ton of errors');
+        done();
+      }, 10);
+    }
+
+    // hack internal _fetch function to force query.close immediately after _fetch is called (simulating the race condition)
+    // race condition: if close is called immediately after _fetch is called, but before results are returned, errors are thrown
+    // when the fetch results are pushed to the readable stream after its already closed.
+    query._fetch = (function (_fetch) {
+      return function () {
+
+        // wait for the second fetch.  closing immediately after the first fetch throws an entirely different error :(
+        if (fetchCount++ === 0) {
+          return _fetch.apply(this, arguments);
+        }
+
+        var results = _fetch.apply(this, arguments);
+
+        query.close();
+        waitForErrors();
+
+        query._fetch = _fetch; // we're done with our hack, so restore the original _fetch function.
+
+        return results;
+      }
+    }(query._fetch));
+
+    query.on('error', function () { errorCount++; });
+
+    query.on('readable', function () {
+      query.read();
+    });
+  });
+});
+
+helper('close callback', function (client) {
+  it('notifies an optional callback when the conneciton is closed', function (done) {
+    var stream = new QueryStream('SELECT * FROM generate_series(0, $1) num', [10], {batchSize: 2, highWaterMark: 2});
+    var query = client.query(stream);
+    query.once('readable', function() { // only reading once
+      query.read();
+    });
+    query.once('readable', function() {
+      query.close(function () {
+        // nothing to assert.  This test will time out if the callback does not work.
+        done();
+      });
+    });
+    query.on('close', function () {
+      assert(false, "close event should not fire"); // no close event because we did not read to the end of the stream.
+    });
+  });
+});