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POImplementing Wait and Notify
 

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    <p>I'm trying to write a program that checks on the health of a database. One of the elements of the elements of the program is supposed to be that the program queries a database and then waits 5 minutes using wait. If there is no response it notifies and sends out some emails. My connection to the database/sending out emails all works, but i'm having trouble implementing wait and notify. I read the api and its easy to understand in a simple program, but i'm really confused as to how to implement it in this case with all the additional complications because of errors where I can't call something dynamic from a static method.</p> <p>I've been reading through lots of threads with wait and notify, but haven't figured out how do to it correctly in my program. If anyone could give me a few tips it would be a huge help. Thanks!</p> <pre><code>import com.fmr.ipgt.email.*; import java.io.File; import java.io.IOException; import java.util.List; import org.jdom.Document; import org.jdom.Element; import org.jdom.JDOMException; import org.jdom.input.SAXBuilder; import javax.mail.MessagingException; class MyResource { synchronized void qQuery() throws Exception { String query = ".z.k"; // The query that is used to query q; this can be changed here. int version = 0; c qConn = null; qConn = new c(Main.host,Main.port); // Connect to the q database while (Main.healthy) { Object o = qConn.k(query); // Query q version = c.t(o); if(!(version==0)) { break; // End the process if the database responds } } } synchronized void start() throws Exception { Main.setHealth(false); Main.sendMessages(); } } class MyThread implements Runnable { MyResource myResource; MyThread(String name, MyResource so) { myResource = so; new Thread(this, name).start(); } public void run() { try { myResource.qQuery(); // Begin a method to query q. } catch (Exception e) { e.printStackTrace(); } } } public class Main { private static String[] recipients; private static String subject = "Database Failure"; private static String message = "The database has failed or is in a hung state"; private static String from; static String host; static int port; private static String emails; private static int minutes; static boolean healthy = true; public static void main(String args[]) throws Exception { // Import information from the configuration file SAXBuilder builder = new SAXBuilder(); File xmlFile = new File("/export/home/jflt/file.xml"); // Note: The directory for the configuration file may need to be changed try { Document document = (Document) builder.build(xmlFile); Element rootNode = document.getRootElement(); List list = rootNode.getChildren("parameters"); Element node = (Element) list.get(0); host = node.getChildText("host"); port = Integer.parseInt(node.getChildText("port")); emails = node.getChildText("emails"); String delims = "[ ]+"; recipients = emails.split(delims); // parse email list minutes = Integer.parseInt(node.getChildText("time")); from = node.getChildText("from"); } catch (IOException io) { System.out.println(io.getMessage()); } catch (JDOMException jdomex) { System.out.println(jdomex.getMessage()); } MyResource unhealthy = new MyResource(); new MyThread("MyThread", unhealthy); // Create new Thread new MyThread("WaitThread", unhealthy); while(healthy) { Thread.sleep(minutes*60000); // The wrong thread is sleeping here. The main method should probably be a different thread instead which will then need to wait and the second thread will notify. } unhealthy.start(); // The database has not responded for the given time. Report that it is unhealthy. } public static void setHealth(boolean health){ System.out.println("database unhealthy"); healthy = health; } public static void sendMessages() throws MessagingException { System.out.println("sending emails"); FCAPMailSender.postMail(recipients,subject,message,from); } } </code></pre>
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    1. COThis is too much code. Boil the problem down to the basics before posting. Make an SSCCE.
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    2. COhmm well i suppose i could delete the code because none of it is really relevant to what i'm asking. i'm just trying to figure out how to do wait and notify where thread 2 starts a query, thread 1 waits 5 minutes, if thread 2 returns a result it notifies, if not, thread 1 does a different task. The problem for me is that in all the wait and notify examples the threads use one run method and do the same thing
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