Java tutorial
/** * 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. */ package org.apache.hadoop.util; import java.io.File; import java.io.IOException; import java.util.ArrayList; import java.util.Arrays; import java.util.Timer; import java.util.TimerTask; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.FileUtil; import org.apache.hadoop.service.AbstractService; import org.apache.hadoop.util.Shell.ExitCodeException; import org.apache.hadoop.util.Shell.ShellCommandExecutor; import org.apache.hadoop.util.Shell; import org.apache.hadoop.util.StringUtils; /** * * The class which provides functionality of checking the health of the node * using the configured node health script and reporting back to the service * for which the health checker has been asked to report. */ public class NodeHealthScriptRunner extends AbstractService { private static Log LOG = LogFactory.getLog(NodeHealthScriptRunner.class); /** Absolute path to the health script. */ private String nodeHealthScript; /** Delay after which node health script to be executed */ private long intervalTime; /** Time after which the script should be timedout */ private long scriptTimeout; /** Timer used to schedule node health monitoring script execution */ private Timer nodeHealthScriptScheduler; /** ShellCommandExecutor used to execute monitoring script */ ShellCommandExecutor shexec = null; /** Pattern used for searching in the output of the node health script */ static private final String ERROR_PATTERN = "ERROR"; /** Time out error message */ public static final String NODE_HEALTH_SCRIPT_TIMED_OUT_MSG = "Node health script timed out"; private boolean isHealthy; private String healthReport; private long lastReportedTime; private TimerTask timer; private enum HealthCheckerExitStatus { SUCCESS, TIMED_OUT, FAILED_WITH_EXIT_CODE, FAILED_WITH_EXCEPTION, FAILED } /** * Class which is used by the {@link Timer} class to periodically execute the * node health script. * */ private class NodeHealthMonitorExecutor extends TimerTask { String exceptionStackTrace = ""; public NodeHealthMonitorExecutor(String[] args) { ArrayList<String> execScript = new ArrayList<String>(); execScript.add(nodeHealthScript); if (args != null) { execScript.addAll(Arrays.asList(args)); } shexec = new ShellCommandExecutor(execScript.toArray(new String[execScript.size()]), null, null, scriptTimeout); } @Override public void run() { HealthCheckerExitStatus status = HealthCheckerExitStatus.SUCCESS; try { shexec.execute(); } catch (ExitCodeException e) { // ignore the exit code of the script status = HealthCheckerExitStatus.FAILED_WITH_EXIT_CODE; // On Windows, we will not hit the Stream closed IOException // thrown by stdout buffered reader for timeout event. if (Shell.WINDOWS && shexec.isTimedOut()) { status = HealthCheckerExitStatus.TIMED_OUT; } } catch (Exception e) { LOG.warn("Caught exception : " + e.getMessage()); if (!shexec.isTimedOut()) { status = HealthCheckerExitStatus.FAILED_WITH_EXCEPTION; } else { status = HealthCheckerExitStatus.TIMED_OUT; } exceptionStackTrace = StringUtils.stringifyException(e); } finally { if (status == HealthCheckerExitStatus.SUCCESS) { if (hasErrors(shexec.getOutput())) { status = HealthCheckerExitStatus.FAILED; } } reportHealthStatus(status); } } /** * Method which is used to parse output from the node health monitor and * send to the report address. * * The timed out script or script which causes IOException output is * ignored. * * The node is marked unhealthy if * <ol> * <li>The node health script times out</li> * <li>The node health scripts output has a line which begins with ERROR</li> * <li>An exception is thrown while executing the script</li> * </ol> * If the script throws {@link IOException} or {@link ExitCodeException} the * output is ignored and node is left remaining healthy, as script might * have syntax error. * * @param status */ void reportHealthStatus(HealthCheckerExitStatus status) { long now = System.currentTimeMillis(); switch (status) { case SUCCESS: setHealthStatus(true, "", now); break; case TIMED_OUT: setHealthStatus(false, NODE_HEALTH_SCRIPT_TIMED_OUT_MSG); break; case FAILED_WITH_EXCEPTION: setHealthStatus(false, exceptionStackTrace); break; case FAILED_WITH_EXIT_CODE: setHealthStatus(true, "", now); break; case FAILED: setHealthStatus(false, shexec.getOutput()); break; } } /** * Method to check if the output string has line which begins with ERROR. * * @param output * string * @return true if output string has error pattern in it. */ private boolean hasErrors(String output) { String[] splits = output.split("\n"); for (String split : splits) { if (split.startsWith(ERROR_PATTERN)) { return true; } } return false; } } public NodeHealthScriptRunner(String scriptName, long chkInterval, long timeout, String[] scriptArgs) { super(NodeHealthScriptRunner.class.getName()); this.lastReportedTime = System.currentTimeMillis(); this.isHealthy = true; this.healthReport = ""; this.nodeHealthScript = scriptName; this.intervalTime = chkInterval; this.scriptTimeout = timeout; this.timer = new NodeHealthMonitorExecutor(scriptArgs); } /* * Method which initializes the values for the script path and interval time. */ @Override protected void serviceInit(Configuration conf) throws Exception { super.serviceInit(conf); } /** * Method used to start the Node health monitoring. * */ @Override protected void serviceStart() throws Exception { nodeHealthScriptScheduler = new Timer("NodeHealthMonitor-Timer", true); // Start the timer task immediately and // then periodically at interval time. nodeHealthScriptScheduler.scheduleAtFixedRate(timer, 0, intervalTime); super.serviceStart(); } /** * Method used to terminate the node health monitoring service. * */ @Override protected void serviceStop() { if (nodeHealthScriptScheduler != null) { nodeHealthScriptScheduler.cancel(); } if (shexec != null) { Process p = shexec.getProcess(); if (p != null) { p.destroy(); } } } /** * Gets the if the node is healthy or not * * @return true if node is healthy */ public boolean isHealthy() { return isHealthy; } /** * Sets if the node is healhty or not considering disks' health also. * * @param isHealthy * if or not node is healthy */ private synchronized void setHealthy(boolean isHealthy) { this.isHealthy = isHealthy; } /** * Returns output from health script. if node is healthy then an empty string * is returned. * * @return output from health script */ public String getHealthReport() { return healthReport; } /** * Sets the health report from the node health script. Also set the disks' * health info obtained from DiskHealthCheckerService. * * @param healthReport */ private synchronized void setHealthReport(String healthReport) { this.healthReport = healthReport; } /** * Returns time stamp when node health script was last run. * * @return timestamp when node health script was last run */ public long getLastReportedTime() { return lastReportedTime; } /** * Sets the last run time of the node health script. * * @param lastReportedTime */ private synchronized void setLastReportedTime(long lastReportedTime) { this.lastReportedTime = lastReportedTime; } /** * Method used to determine if or not node health monitoring service should be * started or not. Returns true if following conditions are met: * * <ol> * <li>Path to Node health check script is not empty</li> * <li>Node health check script file exists</li> * </ol> * * @return true if node health monitoring service can be started. */ public static boolean shouldRun(String healthScript) { if (healthScript == null || healthScript.trim().isEmpty()) { return false; } File f = new File(healthScript); return f.exists() && FileUtil.canExecute(f); } private synchronized void setHealthStatus(boolean isHealthy, String output) { LOG.info("health status being set as " + output); this.setHealthy(isHealthy); this.setHealthReport(output); } private synchronized void setHealthStatus(boolean isHealthy, String output, long time) { LOG.info("health status being set as " + output); this.setHealthStatus(isHealthy, output); this.setLastReportedTime(time); } /** * Used only by tests to access the timer task directly * @return the timer task */ public TimerTask getTimerTask() { return timer; } }