cluster: remove handles when disconnecting worker

Due to the race window between the master's "disconnect" message and the
worker's "handle received" message, connections sometimes got stuck in
the pending handles queue when calling `worker.disconnect()` in the
master process.

The observable effect from the client's perspective was a TCP or HTTP
connection that simply stalled.  This commit fixes that by closing open
handles in the master when the "disconnect" message is sent.

Fixes: https://github.com/nodejs/node/issues/3551
PR-URL: https://github.com/nodejs/node/pull/3677
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Fedor Indutny <fedor@indutny.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

diff --git a/lib/cluster.js b/lib/cluster.js
index bbb61889400bd49f5b37073691e197d7eb5db3c2..c4c2c0d9ac4c93c05ad65c028278b257e9736d82 100644 (file)
--- a/lib/cluster.js
+++ b/lib/cluster.js
@@ -217,7 +217,7 @@ function masterInit() {
   // Keyed on address:port:etc. When a worker dies, we walk over the handles
   // and remove() the worker from each one. remove() may do a linear scan
   // itself so we might end up with an O(n*m) operation. Ergo, FIXME.
-  var handles = {};
+  const handles = require('internal/cluster').handles;
 
   var initialized = false;
   cluster.setupMaster = function(options) {
@@ -308,6 +308,26 @@ function masterInit() {
 
   var ids = 0;
 
+  function removeWorker(worker) {
+    assert(worker);
+
+    delete cluster.workers[worker.id];
+
+    if (Object.keys(cluster.workers).length === 0) {
+      assert(Object.keys(handles).length === 0, 'Resource leak detected.');
+      intercom.emit('disconnect');
+    }
+  }
+
+  function removeHandlesForWorker(worker) {
+    assert(worker);
+
+    for (var key in handles) {
+      var handle = handles[key];
+      if (handle.remove(worker)) delete handles[key];
+    }
+  }
+
   cluster.fork = function(env) {
     cluster.setupMaster();
     const id = ++ids;
@@ -319,26 +339,6 @@ function masterInit() {
 
     worker.on('message', this.emit.bind(this, 'message'));
 
-    function removeWorker(worker) {
-      assert(worker);
-
-      delete cluster.workers[worker.id];
-
-      if (Object.keys(cluster.workers).length === 0) {
-        assert(Object.keys(handles).length === 0, 'Resource leak detected.');
-        intercom.emit('disconnect');
-      }
-    }
-
-    function removeHandlesForWorker(worker) {
-      assert(worker);
-
-      for (var key in handles) {
-        var handle = handles[key];
-        if (handle.remove(worker)) delete handles[key];
-      }
-    }
-
     worker.process.once('exit', function(exitCode, signalCode) {
       /*
        * Remove the worker from the workers list only
@@ -404,6 +404,8 @@ function masterInit() {
   Worker.prototype.disconnect = function() {
     this.suicide = true;
     send(this, { act: 'disconnect' });
+    removeHandlesForWorker(this);
+    removeWorker(this);
   };
 
   Worker.prototype.destroy = function(signo) {
@@ -490,11 +492,12 @@ function masterInit() {
     cluster.emit('listening', worker, info);
   }
 
-  // Server in worker is closing, remove from list.
+  // Server in worker is closing, remove from list.  The handle may have been
+  // removed by a prior call to removeHandlesForWorker() so guard against that.
   function close(worker, message) {
     var key = message.key;
     var handle = handles[key];
-    if (handle.remove(worker)) delete handles[key];
+    if (handle && handle.remove(worker)) delete handles[key];
   }
 
   function send(worker, message, handle, cb) {

diff --git a/lib/internal/cluster.js b/lib/internal/cluster.js
new file mode 100644 (file)
index 0000000..8380ea7
--- /dev/null
+++ b/lib/internal/cluster.js
@@ -0,0 +1,4 @@
+'use strict';
+
+// Used in tests.
+exports.handles = {};

diff --git a/node.gyp b/node.gyp
index 386074be796d8a1c42f942516813794f6af82055..a587edc926945e94c75d0e82e31538d3c99fdc0c 100644 (file)
--- a/node.gyp
+++ b/node.gyp
@@ -69,6 +69,7 @@
       'lib/vm.js',
       'lib/zlib.js',
       'lib/internal/child_process.js',
+      'lib/internal/cluster.js',
       'lib/internal/freelist.js',
       'lib/internal/module.js',
       'lib/internal/socket_list.js',

diff --git a/test/parallel/test-cluster-disconnect-handles.js b/test/parallel/test-cluster-disconnect-handles.js
new file mode 100644 (file)
index 0000000..5fa9884
--- /dev/null
+++ b/test/parallel/test-cluster-disconnect-handles.js
@@ -0,0 +1,65 @@
+/* eslint-disable no-debugger */
+// Flags: --expose_internals
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const cluster = require('cluster');
+const net = require('net');
+
+const Protocol = require('_debugger').Protocol;
+
+if (common.isWindows) {
+  console.log('1..0 # Skipped: SCHED_RR not reliable on Windows');
+  return;
+}
+
+cluster.schedulingPolicy = cluster.SCHED_RR;
+
+// Worker sends back a "I'm here" message, then immediately suspends
+// inside the debugger.  The master connects to the debug agent first,
+// connects to the TCP server second, then disconnects the worker and
+// unsuspends it again.  The ultimate goal of this tortured exercise
+// is to make sure the connection is still sitting in the master's
+// pending handle queue.
+if (cluster.isMaster) {
+  const handles = require('internal/cluster').handles;
+  // FIXME(bnoordhuis) lib/cluster.js scans the execArgv arguments for
+  // debugger flags and renumbers any port numbers it sees starting
+  // from the default port 5858.  Add a '.' that circumvents the
+  // scanner but is ignored by atoi(3).  Heinous hack.
+  cluster.setupMaster({ execArgv: [`--debug=${common.PORT}.`] });
+  const worker = cluster.fork();
+  worker.on('message', common.mustCall(message => {
+    assert.strictEqual(Array.isArray(message), true);
+    assert.strictEqual(message[0], 'listening');
+    const address = message[1];
+    const host = address.address;
+    const debugClient = net.connect({ host, port: common.PORT });
+    const protocol = new Protocol();
+    debugClient.setEncoding('utf8');
+    debugClient.on('data', data => protocol.execute(data));
+    debugClient.once('connect', common.mustCall(() => {
+      protocol.onResponse = common.mustCall(res => {
+        protocol.onResponse = () => {};
+        const conn = net.connect({ host, port: address.port });
+        conn.once('connect', common.mustCall(() => {
+          conn.destroy();
+          assert.notDeepStrictEqual(handles, {});
+          worker.disconnect();
+          assert.deepStrictEqual(handles, {});
+          const req = protocol.serialize({ command: 'continue' });
+          debugClient.write(req);
+        }));
+      });
+    }));
+  }));
+  process.on('exit', () => assert.deepStrictEqual(handles, {}));
+} else {
+  const server = net.createServer(socket => socket.pipe(socket));
+  server.listen(() => {
+    process.send(['listening', server.address()]);
+    debugger;
+  });
+  process.on('disconnect', process.exit);
+}