Watchdog feature to remove unresponsive cluster nodes.

In some intstances (e.g. while resolving an error) it's possible for a
hung process to hang the entire cluster as they wait for its response.
The cluster can handle terminated processes but hung processes present
a problem.

If the watchdog plugin is loaded and --watchdog-interval is set then
the broker forks a child process that runs a very simple watchdog
program, and starts a timer in the broker process to signal the watchdog
every interval/2 seconds. The watchdog kills its parent if it does not
receive a signal for interval seconds. This allows a stuck broker to be 
removed from the cluster so other cluster members can continue.


git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk/qpid@802927 13f79535-47bb-0310-9956-ffa450edef68

2 files changed, 174 insertions, 0 deletions

diff --git a/cpp/src/qpid/cluster/WatchDogPlugin.cpp b/cpp/src/qpid/cluster/WatchDogPlugin.cpp
new file mode 100644
index 0000000000..1b813411f6
--- /dev/null
+++ b/cpp/src/qpid/cluster/WatchDogPlugin.cpp
@@ -0,0 +1,114 @@
+/*
+ *
+ * Copyright (c) 2006 The Apache Software Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include "qpid/Plugin.h"
+#include "qpid/Options.h"
+#include "qpid/log/Statement.h"
+#include "qpid/broker/Broker.h"
+#include "qpid/sys/Timer.h"
+#include "qpid/sys/Fork.h"
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <signal.h>
+
+namespace qpid {
+namespace cluster {
+
+using broker::Broker;
+
+struct Settings {
+    Settings() : interval(0) {}
+    int interval;
+};
+
+struct WatchDogOptions : public qpid::Options {
+    Settings& settings;
+
+    WatchDogOptions(Settings& s) : settings(s) {
+        addOptions()
+            ("watchdog-interval", optValue(settings.interval, "N"),
+             "broker is automatically killed if it is hung for more than \
+	      N seconds. 0 disables watchdog.");
+    }
+};
+
+struct WatchDogTask : public sys::TimerTask {
+    int pid;
+    sys::Timer& timer;
+    int interval;
+
+    WatchDogTask(int pid_, sys::Timer& t, int _interval)
+        : TimerTask(_interval*sys::TIME_SEC/2), pid(pid_), timer(t), interval(_interval) {}
+
+    void fire() {
+        timer.add (new WatchDogTask(pid, timer, interval));
+        QPID_LOG(debug, "Sending keepalive signal to watchdog");
+        ::kill(pid, SIGUSR1);
+    }
+};
+
+struct WatchDogPlugin : public qpid::Plugin, public qpid::sys::Fork {
+    Settings settings;
+    WatchDogOptions options;
+    Broker* broker;
+    int watchdogPid;
+
+    WatchDogPlugin() : options(settings), broker(0), watchdogPid(0) {}
+
+    ~WatchDogPlugin() {
+        if (watchdogPid) ::kill(watchdogPid, SIGTERM);
+        ::waitpid(watchdogPid, 0, 0);
+    }
+
+    Options* getOptions() { return &options; }
+
+    void earlyInitialize(qpid::Plugin::Target& target) {
+        broker = dynamic_cast<Broker*>(&target);
+        if (broker && settings.interval) {
+            QPID_LOG(notice, "Starting watchdog process with interval of " <<
+                     settings.interval << " seconds");
+            fork();
+        }
+    }
+
+    void initialize(Target&) {}
+
+  protected:
+
+    void child() {              // Child of fork
+        const char* watchdog = ::getenv("QPID_WATCHDOG_EXE"); // For use in tests
+        if (!watchdog) watchdog=QPID_EXEC_DIR "/qpidd_watchdog";
+        std::string interval = boost::lexical_cast<std::string>(settings.interval);
+        ::execl(watchdog, watchdog, interval.c_str(), NULL);
+        QPID_LOG(critical, "Failed to exec watchdog program " << watchdog );
+        ::kill(::getppid(), SIGKILL);
+        exit(1);
+    }
+
+    void parent(int pid) {          // Parent of fork
+        watchdogPid = pid;
+        broker->getTimer().add(
+            new WatchDogTask(watchdogPid, broker->getTimer(), settings.interval));
+        // TODO aconway 2009-08-10: to be extra safe, we could monitor
+        // the watchdog child and re-start it if it exits.
+    }
+};
+
+static WatchDogPlugin instance; // Static initialization.
+
+}} // namespace qpid::cluster
diff --git a/cpp/src/qpid/cluster/qpidd_watchdog.cpp b/cpp/src/qpid/cluster/qpidd_watchdog.cpp
new file mode 100644
index 0000000000..0e7f4f18fd
--- /dev/null
+++ b/cpp/src/qpid/cluster/qpidd_watchdog.cpp
@@ -0,0 +1,60 @@
+/*
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ *
+ */
+#include <sys/types.h>
+#include <sys/time.h>
+#include <signal.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <limits.h>
+
+long timeout;
+
+void killParent(int) {
+    ::kill(getppid(), SIGKILL);
+    ::fprintf(stderr, "Watchdog killed unresponsive broker, pid=%d\n", ::getppid());
+    ::exit(1);
+}
+
+void resetTimer(int) {
+    struct ::itimerval itval = { { 0, 0 }, { timeout, 0 } };
+    if (::setitimer(ITIMER_REAL, &itval, 0) !=0) {
+        ::perror("Watchdog failed to set timer");
+        killParent(0);
+        ::exit(1);
+    }
+}
+
+/** Simple watchdog program: kill parent process if timeout
+ * expires without a SIGUSR1.
+ * Will be killed with SIGHUP when parent shuts down.
+ * Args: timeout in seconds.
+ */
+int main(int argc, char** argv) {
+    if(argc != 2 || (timeout = atoi(argv[1])) == 0) {
+        ::fprintf(stderr, "Usage: %s <timeout_seconds>\n", argv[0]);
+        ::exit(1);
+    }
+    ::signal(SIGUSR1, resetTimer);
+    ::signal(SIGALRM, killParent);
+    resetTimer(0);
+    while (true) { sleep(INT_MAX); }
+}