cluster: don't always kill the master on uncaughtException

uncaughtException handlers installed by the user override the default one that
the cluster module installs, the one that kills off the master process.

Fixes nodejs#2556.

Author: bnoordhuis

lib/cluster.js

@@ -78,6 +78,9 @@ function startMaster() {
   workerArgs = process.argv.slice(2);
 
   process.on('uncaughtException', function(e) {
+    // Did the user install a listener? If so, it overrides this one.
+    if (process.listeners('uncaughtException').length > 1) return;
+
     // Quickly try to kill all the workers.
     // TODO: be session leader - will cause auto SIGHUP to the children.
     eachWorker(function(worker) {

test/simple/test-cluster-uncaught-exception.js

@@ -0,0 +1,59 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+// Installing a custom uncaughtException handler should override the default
+// one that the cluster module installs.
+// https://github.com/joyent/node/issues/2556
+
+var common = require('../common');
+var assert = require('assert');
+var cluster = require('cluster');
+var fork = require('child_process').fork;
+
+var MAGIC_EXIT_CODE = 42;
+
+var isTestRunner = process.argv[2] != 'child';
+
+if (isTestRunner) {
+  var exitCode = -1;
+
+  process.on('exit', function() {
+    assert.equal(exitCode, MAGIC_EXIT_CODE);
+  });
+
+  var master = fork(__filename, ['child']);
+  master.on('exit', function(code) {
+    exitCode = code;
+  });
+}
+else if (cluster.isMaster) {
+  process.on('uncaughtException', function() {
+    process.nextTick(function() {
+      process.exit(MAGIC_EXIT_CODE);
+    });
+  });
+
+  cluster.fork();
+  throw new Error('kill master');
+}
+else { // worker
+  process.exit();
+}