Synchronized Is Blocking
May 12, 2014
I'm just starting up with Java Mulithreading.Below is the repo I set up, and I am having trouble with this test I am doing playing around with Executor threadpools. I am trying to setup a managed system where I first add some lines to be printed, then add the work to the work pool, and then finally launch n number of threads to handle the work (or in this case, print out the strings I added to WorkManager instance fields). I watched this series of videos starting with this one: URL...., and I planned on playing with the concept of multithreading, but it doesn't seem to work and gets stuck at Thread1:27. I thought that by synchronizing access to the ListIterator return, that it would not block. URL....
View Replies
Feb 22, 2014
How to check if a web page is synchronized on a local server in JSP ? I have tried to make database updation synchronized in jsp but how can i check it on local web server (tomcat) ? I have used Oracle database.
More Info:
Class.forName("oracle.jdbc.driver.OracleDriver");
Connection con=DriverManager.getConnection("jdbcracle:thin:@localhost:1521:xe","username","password");
balance=balance-1500;
String query1= "update bank set bal=? where card_no='"+cnumber+"'";
PreparedStatement st1 = con.prepareStatement(query1);
st1.setString(1,String.valueOf(balance));
int qresult1 = st1.executeUpdate();
This is some of the code in which I have not applied any synchronization. In simple words, I want to know how to test if synchronization part is really working or not ?
My main motive is... I am trying to make an admission form and I want a limited number of seats but I want after every registration process my database updates the seat numbers accordingly and show the right information about how many seats are left to the user. (though in the given code i am just changing the balance)
Like in this example
<%!
PreparedStatement pst = con.prepareStatement("query");
%>
synchronization
<%
synchronized(pst) {
pst.setXXX(...);
pst.setXXX(...);
pst.executeXXX(...);
}
%>
View Replies
View Related
Jun 30, 2014
I have a multithreaded application. I have a Logger class with static methods that I use across threads. Would it behoove me to add the synchronized keyword to the static methods of the Logger class since I use this class statically in different threads?
View Replies
View Related
Apr 6, 2014
I use JDK 1.7.
My java application is blocking from time to time. I have added some log lines and now I know exactly where is blocking, but I have no solution to fix it.
This code runs in a parallel thread, distinct from the main application thread and updates a big JTextArea swing:
try {
....
JTextArea element = (JTextArea)add_containers[objColIndex];
System.out.println("setEditValue start seting text ");
element.setText(VAL);
System.out.println("setEditValue text is set ");
[Code] ....
The code reaches "setEditValue start seting tex" but never reaches "setEditValue text is set". No exception is triggered. The whole application is blocked - main thread and this paralel thread. This section of code is called many times, but in rare cases is blocking without any apparent reason. Sometimes I run the exact same instructions and is blocking and sometimes is working.
View Replies
View Related
Jan 21, 2014
Question : What would you do block a user if he fails to login in 3 consecutive attempts ?
My Answer : I will make use of Session object, so that server could identify that all 3 requests came from the same system.
Dont know if i am right .
View Replies
View Related
Jul 24, 2014
I set the limit to 2 so the producer blocks after two insertions until an item is consumed. Because we are dealing with a basic counter that increments, we do not lose any data. Since after queue is freed up we simply increment by 1, so we are able to store all numbers. However, in real world situation, you might be storing data coming from redis server into the queue. And redis server may be publishing a plethora of data. So when the queue blocks, and new data comes in, what happens? Is the currently blocked data lost forever and the new data that came in is now blocked, or is the new data that came in ignored and the old data remains being blocked until queue is freed up?
Java Code:
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
public class BlockingQueueBlocking {
private BlockingQueue<Integer> sQueue = new ArrayBlockingQueue<Integer>(2);
int counter=0;
private void test() throws InterruptedException{
[code]...
View Replies
View Related
Feb 3, 2014
Me and my brother decided to make a relatively simple client/server program where clients get into a simple chat lobby and can invite others to play small games(like pong). The basic server code has been written, and we have made a special client that is used for debugging.
We use a self-defined protocol of Strings where a message looks like "4-|user,pass". The number before the delimiter "-|" is the operation code, that tells the server what kind of message this client sends. Based on that number, the server dispatches the message to the appropriate handler method. 4 is authentication for example, and the handler looks the user and pass up in a file and if found, returns true, otherwise, false. Then the server responds to the clinet with 2-|"any message" where the client will recognize opcode 2 as a "authentication accepted" and proceed with the next part of client code. In a similar way, we plan to write all message types(both in the game, in the lobby and in a game setup room).
While testing we ran into a problem where the BufferedReader .readLine() does not seem to be a blocking call like it should be, so the client keeps spamming 'null' in the output field that we made to see the server response to the message we send. When we try to debug the server code and set breakpoints at the suspicious locations, it strangely skips both while(true) loops without activating either breakpoint and executes the finally{} code, even though the client did not close the connection and the second while loop was never entered. The first while loop IS entered though, because the test client gets a "0" on its output, which is the server message indicating "please authenticate yourself".
We decided to use messages in a string format and decode it at both sides as it seemed easier than transmitting java objects and making sure they are of the same type, also for reducing overhead as much of possible.URL....
package Chatroom;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.HashSet;
[code]....
View Replies
View Related
