Method Scope variables controls Multi-Threading !
Hye there Experts !
First, let me thank you all for such a brain-stuff sharing around; feel nice to be a part here.
While browsing through the below article, found something confusing...kindly clarify.
http://www.javaworld.com/javaworld/jw-07-2004/jw-0712-threadsafe.html?page=1
Extract from the above discussion I understand :
when a variable is moved to method scope instead of instance scope, synchronization is achieved.
How is this true for servlets ???
Method scope variables are available only during method call I think...here, since this is a servlet, there will be only one instance and if many (lets say 10) requests hits this servlet object, all these threads will read same counter as all of them enter into this only one method of this object,
so...this should be still not thread safe I guess.
I didn't want to execute and see results of this code, but I am trying to understand the key at first.
Please guide me before brain blows... :-)
Would also appreciate any references that really says true things about
'synchronization for enterprize (handle huge requests) web apps - technques for servlets and any other stuff'
Thanks again guys, have a wonderful time.
feel nice to be a part here.Welcome to the mad-house ;-)
Method scope variables are available only during method callWARNING: I'm no guru, so this may be misleading or just plain wrong.. but as I understand it:
Yep a "local" variable exists only the context of the execution of it's containing method... so a local variable is implicitly bound to the thread that created it (by invoking the method in which the local is declared)... a local variable can't be accessed directly by another thread simply because the other thread has no access-path to the variable (you can't expose a local through getters & setters)... hence locals are thread safe.
The important bit is that it's the thread which "owns" the local variable... not the declaring method... if the method is executed concurrently by two threads, each thread will have its own private copy of all the local variables.
One other question though: are locals in static methods still thread safe? I'm not sure.
package forums;
class NonfinalLocalVariableInThreadTest
public static void main(String[] args) {
try {
new Thread(new Runnable() {
public void run() {
System.out.println(args[0]);
}).start();
} catch (Exception e) {
e.printStackTrace();
compiler error
C:\Java\home\src\forums>"C:\Program Files\Java\jdk1.6.0_07\bin\javac.exe" -Xlint -d c:\java\home\classes -cp c:\java\home\src;.;c:\java\home\classes c:\java\home\src\forums\NonfinalLocalVariableInThreadTest.java
C:\Java\home\src\forums\NonfinalLocalVariableInThreadTest.java:9: local variable args is accessed from within inner class; needs to be declared final
System.out.println(args[0]);
^
1 error
Output completed (0 sec consumed)
Similar Messages
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Static methods in multi-thread environment.
Sorry for this silly question, but I have no clue...
If you're using classes with static methods in a application server environment, would that imply all threads use that same 'one in the jvm' method and would there be a possibility for performance loss?
Is calling another static method from a static method a good idea in a multi-thread environment, with respect to performance? Somehow I seem to get this java.lang.NoClassDefFoundError. Any ideas? The classes are in the same package. I only get these kind of problems calling static methods from static methods in a multi-thread environmnent. The static methods are pure utility functions and of course do not use class state.
Thanks for your help.Sorry for this question, wasn't thinking straight. I have the answer, won't post question on multiple forums.
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Multi-thread application recompile object with make but runs with old value
Hi. I am working on a simulation in Java, and there is some behavior going on that I cannot understand. Granted, I'm a mechanical engineer, not a CS student (a fact that is probably made obvious by the code I'm posting below). The simulation comprises three parts: a controller, a robot, and a 3-d sensor. Here's the code for the "Simulation" application.
class Simulation {
void go() {
ThreeDSensor sensorRunner = new ThreeDSensor();
VSController controllerRunner = new VSController();
KukaKR15SL robotRunner = new KukaKR15SL();
Thread sensorThread = new Thread(sensorRunner);
Thread controllerThread = new Thread(controllerRunner);
Thread robotThread = new Thread(robotRunner);
sensorThread.start();
try {
Thread.sleep(1000); // Give sensorThread time to start in order to catch first triggers
} catch(InterruptedException ex) {
ex.printStackTrace();
controllerThread.start();
try {
Thread.sleep(1000); // Give controllerThread time to open the socket for communication with robotThread
} catch(InterruptedException ex) {
ex.printStackTrace();
robotThread.start();
public static void main(String[] args) {
Simulation sim = new Simulation();
sim.go();
}I guess the big reason I'm using multi-threading is that once this simulation is working I want to be able to just run VSController alone and have it interface with a robot controller and a PC performing image processing. So with multiple threads I'm sending TCP and UDP messages around just like the final system will.
I have made an object for my VSController that just stores values used by the simulation. That way I could have them all in one place instead of hunting through methods to change them. One example is "double noiseThreshold". Quickly, here is the code for "ControllerSettings.java".
class ControllerSettings {
final double cameraXOffset = 0; // If > 0 then the origin of the camera CS is not on the center line of the lens
final double cameraYOffset = 0; // If > 0 then the origin of the camera CS is not on the center line of the lens
final double cameraZOffset = 700; // The distance that must be kept between the camera and the target
// Error magnitude less than this is disregarded (in centimeters if roundingData else in millimeters)
final double noiseThreshold = 60;
final boolean estimatingEndPoints = false; // If the controller is using two images per cycle then true
final boolean roundingData = false;
final boolean using3DData = true; // How double[] sent from Matlab image processing is used
* If the robot controller uses the output of this controller to command
* motions in cartesian space then true. This is used in two places: 1) initial guess of Jacobian,
* and 2) "commandType" element sent to robot controller.
final boolean useRobotControllerModel = false;
final double thetaBumpValueForEstimationOfJacobian = .1; // Distance each joint is jogged in estimation process
final double bumpDistance = 50; // Distance robot moves each time (magnitude of translation in mm)
final double limitAngular = .5; // Max amout robot joint will be commanded to rotate (in degrees)
}And here is some pertinent code from "VSController.java".
class VSController implements Runnable{
ControllerSettings cSettings; // Stores all the preferences used by the controller
NGN controller; // This is the controller algorithm.
int dof; // The degrees of freedom of the robot being controlled
KukaSendData ksd; // This provides communication to the robot.
protected DatagramSocket socketForVisionSystem = null;
ImageFeaturesData ifd; // This parses and stores data from the image system.
double[] errorVector; // This is what's acted on by the algorithm
PrintWriter errorTrackerOut = null; // For analysis of error vector
public void run() {
VSController vsc = new VSController();
vsc.go();
public void go() {
initWriters();
cSettings = new ControllerSettings();
public boolean isNoise() {
boolean ret = false;
double magnitude = 0;
for (int i = 0; i < errorVector.length; i++) {
magnitude += errorVector[i] * errorVector;
magnitude = Math.sqrt(magnitude);
if (magnitude <= cSettings.noiseThreshold) {
System.out.println("VSController: magnitude (of errorVector) = " + magnitude +
", threshold = " + cSettings.noiseThreshold); // Debug
Now here's my issue: I change the value for "noiseThreshold" in "ControllerSettings.java" then run make from terminal (makefile code posted below) and rerun "Simulation". However, despite my changes to "ControllerSettings.java" the value for "noiseThreshold" is not changed, as evidenced by the output on the terminal screen:VSController: magnitude (of errorVector) = 6.085046125925263, threshold = 10.0 See, that value of 10.0 is what I used to have for noiseThreshold. I do not know why this value does not update even though I save the java file and execute make in between executions of Simulation. I would love it if someone could explain this problem to me.
Here's the contents of makefile.
JFLAGS = -cp ../Jama\-1\.0\.2.jar:../utils/:/usr/share/java/vecmath\-1\.5\.2.jar:.
JC = javac
.SUFFIXES: .java .class
.java.class:
$(JC) $(JFLAGS) $*.java
CLASSES = \
ControllerSettings.java \
ImageFeaturesData.java \
KukaKR15SL.java \
../utils/KukaSendData.java \
NGN.java \
Puma560.java \
Robot.java \
RobotSettings.java \
Simulation.java \
SimulationSettings.java \
SixRRobot.java \
Targets.java \
TargetsSettings.java \
ThreeDData.java \
ThreeDSensor.java \
VSController.java
default: classes
classes: $(CLASSES:.java=.class)
clean:
$(RM) *.classEdited by: raequin on Apr 5, 2010 1:43 PMI saw this explanation about what's causing my problem.
"When the Java compiler sees a reference to a final static primitive or String, it inserts the actual value of that constant into the class that uses it. If you then change the constant value in the defining class but don't recompile the using class, it will continue to use the old value."
I verified that the value updates if I also change something in VSController.java, forcing it to recompile. I think I will solve this problem by just making the variables in ControllerSettings no longer final (and then recompile VSController to make sure it takes effect!). Is there another solution? I saw intern(), but that seems to only apply to Strings.
Thanks. -
SSRS - Is there a multi thread safe way of displaying information from a DataSet in a Report Header?
In order to dynamically display data in the Report Header based in the current record of the Dataset, we started using Shared Variables, we initially used ReportItems!SomeTextbox.Value, but we noticed that when SomeTextbox was not rendered in the body
(usually because a comment section grow to occupy most of the page if not more than one page), then the ReportItem printed a blank/null value.
So, a method was defined in the Code section of the report that would set the value to the shared variable:
public shared Params as String
public shared Function SetValues(Param as String ) as String
Params = Param
Return Params
End Function
Which would be called in the detail section of the tablix, then in the header a textbox would hold the following expression:
=Code.Params
This worked beautifully since, it now didn't mattered that the body section didn't had the SetValues call, the variable persited and the Header displayed the correct value. Our problem now is that when the report is being called in different threads with
different data, the variable being shared/static gets modified by all the reports being run at the same time.
So far I've tried several things:
- The variables need to be shared, otherwise the value set in the Body can't be seen by the header.
- Using Hashtables behaves exactly like the ReportItem option.
- Using a C# DLL with non static variables to take care of this, didn't work because apparently when the DLL is being called by the Body generates a different instance of the DLL than when it's called from the header.
So is there a way to deal with this issue in a multi thread safe way?
Thanks in advance!
Hi Angel,
Per my understanding that you want to dynamic display the group data in the report header, you have set page break based on the group, so when click to the next page, the report hearder will change according to the value in the group, when you are using
the shared variables you got the multiple thread safe problem, right?
I have tested on my local environment and can reproduce the issue, according to the multiple safe problem the better way is to use the harshtable behaves in the custom code, you have mentioned that you have tryied touse the harshtable but finally got
the same result as using the ReportItem!TextBox.Value, the problem can be cuased by the logic of the code that not works fine.
Please reference to the custom code below which works fine and can get all the expect value display on every page:
Shared ht As System.Collections.Hashtable = New System.Collections.Hashtable
Public Function SetGroupHeader( ByVal group As Object _
,ByRef groupName As String _
,ByRef userID As String) As String
Dim key As String = groupName & userID
If Not group Is Nothing Then
Dim g As String = CType(group, String)
If Not (ht.ContainsKey(key)) Then
' must be the first pass so set the current group to group
ht.Add(key, g)
Else
If Not (ht(key).Equals(g)) Then
ht(key) = g
End If
End If
End If
Return ht(key)
End Function
Using this exprssion in the textbox of the reportheader:
=Code.SetGroupHeader(ReportItems!Language.Value,"GroupName", User!UserID)
Links belowe about the hashtable and the mutiple threads safe problem for your reference:
http://stackoverflow.com/questions/2067537/ssrs-code-shared-variables-and-simultaneous-report-execution
http://sqlserverbiblog.wordpress.com/2011/10/10/using-custom-code-functions-in-reporting-services-reports/
If you still have any problem, please feel free to ask.
Regards
Vicky Liu -
Multi-Thread application and common data
I try to make a multi-Thread application. All the Threads will update some common data.
How could I access the variable �VALUE� with the Thread in the following code:
public class Demo {
private static long VALUE;
public Demo(long SvId) {
VALUE = 0;
public static class makeThread extends Thread {
public void run() {
VALUE++;
public static long getVALUE() {
return VALUE;
The goal is to get the �VALUE� updated by the Thread with �getVALUE()�
Thanks for your reply
BenoitThat code is so wrong in so many ways......
I know you're just experimenting here, learning what can and can't be done with Threads, but bad habits start early, and get harder to kick as time goes on. I am going to give a little explanation here about what's wrong, and what's right.. If you're going to do anything serious though, please, read some books, and don't pick up bad habits.
Alright, The "answer" code. You don't use Thread.sleep() to wait for Threads to finish. That's just silly, use the join() method. It blocks until the threads execution is done. So if you have a whole bunch of threads in an array, and you want to start them up, and then do something once they finish. Do this.
for(int k=0; k<threads.length; k++) {
threads[k].start();
for(int k=0; k<threads.length; k++) {
threads[k].join();
System.out.println("All Threads Done");Now that's the simple problem. No tears there.
On to the java memory model. Here where the eye water starts flowing. The program you have written is not guarenteed to do what you expect it to do, that is, increment VALUE some amount of time and then print it out. The program is not "Thread Safe".
Problem 1) - Atomic Operations and Synchronization
Incrementing a 'long' is not an atomic operation via the JVM spec, icrementing an int is, so if you change the type of VALUE to an int you don't have to worry about corruption here. If a long is required, or any method with more then one operation that must complete without another thread entering. Then you must learn how to use the synchronized keyword.
Problem 2) - Visiblity
To get at this problem you have to understand low level computing terms. The variable VALUE will NOT be written out to main memory every time you increment it. It will be stored in the CPUs cache. If you have more then one CPU, and different CPUs get those threads you are starting up, one CPU won't know what the other is doing. You get memory overwrites, and nothing you expect. If you solve problem 1 by using a synchronized block, you also solve problem 2, because updating a variable under a lock will cause full visiblity of the change. However, there is another keyword in java.. "volatile".. A field modified with this keyword will always have it's changes visible.
This is a very short explaination, barely scratching the surface. I won't even go into performance issues here. If you want to know more. Here's the resources.
Doug Lea's book
http://java.sun.com/docs/books/cp/
Doug Lea's Site
http://g.cs.oswego.edu
-Spinoza -
How to make a global scope component to be thread safe?
One of my global component preserves states in its member variables, I am afraid that it's might messed up in multi-threading conditions, so how to make a nucleus global component to be thread safe?
Edited by: user13344577 on Jul 14, 2011 9:45 AMHi,
Just to help integrate Shaik's and my own seemingly contradictory replies:
If the member variables in your global component actually need to be globally available, so that multiple threads/sessions need to seem the same data, then you need to use synchronization or some scheme to make this data thread-safe when updating it. If the member variables are non-global data and are simply for convenience of having data available for multiple method calls or something like that, then you should do as I said (don't use synchronization) and use one of my suggestions to avoid this.
I have seen customers frequently do what I replied about and store non-global data in a global component, and Shaik simply interpreted what "user13344577" is trying to do differently. Clarification is needed to know which of our answers better applies.
Thanks.
Nick Glover
Oracle Support for ATG Products -
Suggestion: JavaScript scope variables and event listeners
Invoking Java from JavaScript in ADF Mobile is surprisingly efficient although it is still relatively expensive compared to plain HTML5/JavaScript/CSS stuff in the native UIWebView. But whenever you want to do something "dynamic" you have to revert to invoking Java, even for simple use cases. As far as I can see it as soon as you use listeners on components, managed beans or data controls you're in the Java world.
Why not add similar concepts that are pure JavaScript implementations for performance. As an example I want to have a SelectOneButton component and depending on its state I want to enable/disable an InputText component. As far as I can see it I would need Java to make this happen. First, I would need a Java managed bean to keep the enabled/disabled state. Then I would set the value property of the SelectOneButton with an EL expression to this managed bean property, or for other scenarios use a Java based ActionListener to change the state. Then the InputText component could use an EL expression in its Disabled property.
For this simple use case this would still perform fast, but real applications grow more complex.
Why not have the option of creating JavaScript based managed "beans"? The could live on javaScriptPageFlowScope or javaScriptViewScope. Then the AMX components could reference this from EL and it would be even better if we can create pure javascript ActionListeners (or other listeners). This would make it similar to the choice with ADF Faces application between doing a server roundtrip with partial-page-rendering and using pure clientListeners and clientAttributes for optimal performance.
For situations where we do need to power of Java, it would be great if we can access these javascript scope variables from Java.This is a good suggestion, Wilfred. We haven't gotten to this level of optimization in the framework yet. At some point it's likely we'll have an option for the developer to specify the layer to handle the method.
Thanks -
Some general questions about multi-threading
Hey Everybody,
I have a dilemma with a multi-threaded program that I have written.
Well to be truthful I actually wrote the program with no consideration whatsoever for multithreading.
As a result of this complete lack of concern I get a completely hung user interface.
My program performs a lot of network communications over URL��s and also writes information from URL��s to disk. The combination of networking and I/O in my program and the fact that I have not built multi-threading into the program has lead to complete failure of the user interface. When I say complete failure I mean complete failure. If it were only button��s not responding then I wouldn��t be all that worried, however the entire drawing area of my programs ��Frame�� completely freezes. It��s cool if nothing is maximized or minimized over the frame but as soon as this happens my programs drawing area has a ��serious hang over!��.
I have begun learning about threads, in principle they sound wicked however in practice they have proven to be a brain tease (oops �K.. honesty).
The difficulty of threads should not be all that daunting to me, however I have a couple of very simple questions that I would love to have answered�K..anybody out there!!!!!!!!!
This is the normal basic method of running a thread that I have been attempting to incorporate into my program:
1). Extend the thread class,
2). Override the run() method in the subclass (created from step 1),
3). Create an instance of the subclass,
4). Call the start() method on the instance (from step 3).
I have read that every statement the thread will execute is contained within it��s run() method.
Question 1). This being the case is it possible to have member variables or methods inside a class that extends thread? Please explain!
Question 2). Can a class that extends thread contain a constructor? Please explain!
Question 3). If a subclass of thread cannot contain a constructor as I assume to be the case then how can code executing within the newly spawned thread reference information from the object that spawned it?
If anybody out there on the great net can answer even half of one of these questions I will be more than grateful. Thanks for your time, and rock on Java!
DavidThread t = new Thread(MyRunnableDerivedClass);
t.start();I hope it is understood that MyRunnableDerivedClass is actually an object of the MyRunnableDerivedClass. sorry for the confusion.
so here's a thread that reads from a file using constructors, member variables, other funcs. It's not optimal but shows use of all of the above. I just typed this in so there are probably syntax errors, but you should get the point.
public class ThreadedFileReader implements Runnable
private File m_File;
byte[] contents = new byte[0];
public ThreadedFileReader( File f )
m_File = f;
public void run()
BufferedInputStream bis = null;
try
bis = new BufferedInputStream( new FileInputStream( m_File ));
int avail = bis.available();
while (avail > 0)
int oldLen = contents.length();
contents = expand( contents, avail );
bis.read( contents, oldLen, avail );
avail = bis.available();
catch (Exception e)
{ //do something witty
finally
try{ if (bis != null) bis.close(); } catch (Exception e){}
private byte[] expand( byte[] oldBuf, int addedLen )
byte[] newBuf = new char[oldBuf.length + addedLen];
System.arrayCopy( newBuf, 0, oldBuf, 0, oldBuf.length );
return newBuf;
public byte[] getContents()
return contents;
//here's where we use it
File f = new File( "c:\myfile" );
ThreadedFileReader tfr = new ThreadedFileReader( f );
Thread t = new Thread( tfr );
t.start();
t.join();
// At this point the thread has died, but the thread object still exists
byte [] data = tfr.getContents(); -
Multi-threaded performance server using 2 ports to two-way communication
Hi, I'm new in the forums so welcome everyone. I'm developing now an online computer game based on orginal Polish board-game, but it doesn't mean. Important is that I need to develope a high-performance multi-threaded server, which can serve... let's say few hundres of games, and a thousend of players simulateously. My server works on two ports/sockets.
First one is represented by "ServerSocketChannel clientConSsc" in my code. The main thread in my server class which invokes the method "run()" (which You can see below), registers clientConSsc with Selector and then repeatingly accepts incoming connections from clients on this socket. When connection(channel) is estabilished and clients wants to write some request to this channel, the main thread on server creates a new instance of class "RequestHandler" which extends Thread and handles this request (reads the request from channel, makes some changes on server, spreads some new messages to other clients in the same game and so on... everything on the same socket/port/channel). Then the channel/connection is closed by the server - I call such connections: "a short connections". In the same time the main thread continues the loop and is still able to accept connections from another players. That's the idea of multi-threaded server, right? :) And to this point, everything works fine, but... what if the server wants to trigger some new command, write new information to client?
Server could have tried to open a SocketChannel to client's IP address, but then the client programme would have to create and ServerSocketChannel object, bind it to some InetAddress and then... and then client becomes a server! - that breaks the idea of client-server cooperation and demands on players of my game to have routed some port on their machines. To resolve this problem I made some sort of "system" which, when some player/client is logging into my server, accepts second (this time constant, not "short") connection on the second port I mentoined on the beginning. This connection is held in variable "SocketChannel serverCon" of class "Player" - which reflects a player logged onto server. Server maintains every such connection till the client logs off. After the connection is accepted, the player whom connection it was is added to collection called "playersToRegisterToWrite". After the Selector.selectNow() is invoked (as You can see in the code below), each and every player's connection is registered in selector (with selection key - OP_WRITE and attachment pointing on owning player). In the same time client's code is trying to read some bytes from this connection and blocks on it until some bytes are written to this connection. When server wants to "tell" something to client, deliver some message/command, it creates a new instance of class which extends an abstract class called "ServerAction" (another new thread) and adds it to collection "actionsToDo". In ServerAction's method "run()" there are whole code to interact with client (e.g. send an update of players' list, an update of games' list, a chat message). Finnaly when Selector informs the server that some connection is writable (some client is waiting for commands), then server checks if there's any "actionToDo" involving this client/player. If there is, it unregisters the connection from Selector (so no other ServerAction (thread) can write on this connection) and starts the action. At the end of every "run()" method of subclass of ServerAction there's a code, which again adds the player to collection "playersToRegisterToWrite", so the player's connection can again be registered in Selector and the player can again receive informations from server - after it consumed THIS "ServerAction".
It looks to me like it should be working fine, but it's not. When I test my server and clients on the same machine (no ping/latency) everything seems to be working fine. But when it comes to play my game with somebody even on LAN or through the Internet there comes the problems. My first socket I describe (and first type of connections - short connections) works perfectly fine, so the requests triggered by client are delivered and handled properly. But the second socket is cirppling. For example: the server triggers a command refering to an update of clients logged to server' list. It is triggered by Selector so the client should be ready to read data from server, so the server sends data! And the client never receives it... Why?
It experimented a whole lot of time on SocketChannel's method "configureBlocking(boolean)", but it never helps. I think the client should always block it's listening thread on connection, contratry to server which is ment to be fast, so it should send the data through non-blocking channels. Am I right? Are there any rules refering blocking configuration of SocketChannels?
I will be grateful for every answer. To help You out I attach also drafts from run()'s methods of my classes.
Server's main method - main thread :
public void run() {
try {
selector = Selector.open();
clientConSsc.configureBlocking(false);
clientConSsc.register(selector , SelectionKey.OP_ACCEPT);
while(serverRunning) {
try {
selector.selectNow();
Iterator it;
synchronized(playersToRegisterToWrite) {
it = playersToRegisterToWrite.iterator();
while(it.hasNext()) {
Player player = (Player)it.next();
it.remove();
player.serverCon.configureBlocking(false);
player.serverCon.register(selector , SelectionKey.OP_WRITE , player);
Set keys = selector.selectedKeys() {
it = keys.iterator();
while(it.hasNext()) {
SelectionKey key = (SelectionKey)it.next();
if(key.isAcceptable()) {
it.remove();
clientCon = clientConSsc.accept();
clientCon.configureBlocking(false);
clientCon.register(selector , SelectionKey.OP_READ);
continue;
if(key.isReadable()) {
it.remove();
key.cancel();
new RequestHandler(this , (SocketChannel)key.channel()).start();
continue;
if(key.isWritable()) {
if(key.attachment() != null ) {
ServerAction action = null;
synchronized(actionsToDo) {
Iterator aIt = actionsToDo.iterator();
while(aIt.hasNext()) {
ServerAction temp = (ServerAction)aIt.next();
if(temp.getPlayer().equals((Player)key.attachment())) {
action = temp;
aIt.remove();
break;
if(action != null) {
key.channel().configureBlocking(false);
it.remove();
key.cancel();
action.start();
continue;
} catch(Exception e) {
statusArea.append(e.toString() + "\n");
e.printStackTrace();
continue;
} catch(ClosedChannelException e) {
statusArea.append(e.toString() + "\n");
} catch(IOException e) {
statusArea.append(e.toString() + "\n");
A part of server's RequestHandler's class' method run() - the method which handles requests triggered by client on first port:
public void run() {
boolean served = false;
try {
channel.configureBlocking(true);
retryCount++;
retry = false;
String command = ns.readText(channel).trim();
ns.statusArea.append("ktos przesyla komende: " + command + "\n");
if(command != null && !command.equals("ERROR")) {
String[] cmd = command.split("�");
ns.statusArea.append("komenda: " + cmd[0] + "\n");
if(cmd[0].equals("CHAT")) {
if(cmd.length != 5) {
retry();
} else {
if(cmd[2].equals("NOGAME")) { // jezeli nie ma okreslonej gry czyli rozsylamy do wszystkich
for(int i = 0 ; i < ns.loggedPlayersListItems.size() ; i++) {
Player current = (Player)ns.loggedPlayersListItems.get(i);
if(current.state == Player.CHOOSING && !current.equals(new Player(Integer.parseInt(cmd[1])))) // jezeli gracz jest w okienku wybierania gry to wysylamy mu broadcast
ns.actionsToDo.add(new SendMsg(ns , current , "CHAT�" + cmd[1] + "�" + cmd[3] + "�" + cmd[4]));
} else {
Game game = (Game)ns.gamesListItems.get(ns.gamesListItems.indexOf(new Game(Integer.parseInt(cmd[2]))));
for(int i = 0 ; i < game.players.size() ; i++) {
Player current = (Player)game.players.get(i);
if(!current.equals(new Player(Integer.parseInt(cmd[1]))))
ns.actionsToDo.add(new SendMsg(ns , current , "CHAT�" + cmd[1] + "�" + cmd[3] + "�" + cmd[4]));
served = true;
} else if(cmd[0].equals("GETGAMEINFO")) {
if(cmd.length != 3)
retry();
else {
int gameID = Integer.parseInt(cmd[2]);
ns.statusArea.append("poproszono o informacje o grze nr: " + gameID + "\n");
Game checkedGame = new Game(gameID);
if(ns.gamesListItems.contains(checkedGame)) {
Game game = (Game)ns.gamesListItems.get(ns.gamesListItems.indexOf(checkedGame));
channel.configureBlocking(true);
ObjectOutputStream oos = new ObjectOutputStream(channel.socket().getOutputStream());
oos.writeObject(game);
oos.writeObject(game.players);
oos.flush();
ns.statusArea.append("wyslano informacje o grze nr: " + gameID + "\n");
} else {
ns.statusArea.append("brak gry o nr: " + gameID + "\n");
served = true;
} catch(IOException e) {
e.printStackTrace();
if(!served) {
ns.findAndDisconnectPlayer(channel);
try {
channel.close();
} catch(IOException e) {
e.printStackTrace();
}An example of ServerAction's subclass - the class which triggers server commands to client on second port:
class UpdateLoggedPlayersList extends ServerAction {
public UpdateLoggedPlayersList(NeuroServer ns , Player player) {
super(ns , player);
public void run() {
try {
serverCon.configureBlocking(true);
ns.sendText("UPDATELOGGEDPLAYERSLIST" , serverCon);
if(ns.readText(serverCon).equals("OK")) {
ObjectOutputStream oos = new ObjectOutputStream(serverCon.socket().getOutputStream());
oos.writeObject(ns.loggedPlayersListItems);
oos.flush();
synchronized(ns.playersToRegisterToWrite) {
ns.playersToRegisterToWrite.add(player);
} catch(IOException e) {
e.printStackTrace();
}A part of client's CmdHandler's class' method run() - the method which handles commands triggered by server:
public void run() {
try {
while(works) {
String command = nc.readText(nc.serverCon);
System.out.println("Server przesyla komende: " + command + "\n");
String[] cmd = command.split("�");
if(cmd[0] != null && !cmd[0].equals("ERROR")) {
if(cmd[0].equals("CHAT")) {
if(nc.chooseGameDialog != null && nc.chooseGameDialog.isVisible()) { // jezeli na wybieraniu gry
newChatEntry(cmd[2] , null , cmd[3] , nc.chooseGameDialog.chatPane);
} else if(nc.readyDialog != null && nc.readyDialog.isVisible()) { // jesli na przygotowywaniu
Player sender = (Player)nc.actGame.players.get(nc.actGame.players.indexOf(new Player(Integer.parseInt(cmd[1]))));
newChatEntry(cmd[2] , sender.fraction , cmd[3] , nc.readyDialog.chatPane);
} else if(nc.ng != null) { // jesli w grze
Player sender = (Player)nc.actGame.players.get(nc.actGame.players.indexOf(new Player(Integer.parseInt(cmd[1]))));
newChatEntry(cmd[2] , sender.fraction , cmd[3] , nc.ng.inGameChatPane);
} else if(cmd[0].equals("UPDATELOGGEDPLAYERSLIST")) {
nc.sendText("OK" , nc.serverCon , false);
nc.serverCon.configureBlocking(true);
ObjectInputStream ois = new ObjectInputStream(nc.serverCon.socket().getInputStream());
DefaultListModel players = (DefaultListModel)ois.readObject();
nc.chooseGameDialog.updateLoggedPlayersList(players);
} catch(IndexOutOfBoundsException e) {
System.out.println(e);
} catch(IOException e) {
System.out.println(e);
} catch(ClassNotFoundException e) {
System.out.println(e);
}And two methods I used in codes above: sendText(String text , SocketChannel sc) and readText(SocketChannel sc) - they are my "utility" methods, which I use to send and receive Strings through specified SocketChannels.
boolean sendText(String text , SocketChannel sc) {
ByteBuffer bbuf = ByteBuffer.allocate(BSIZE);
boolean sendRetry;
boolean sent = false;
do {
sendRetry = false;
try {
StringBuffer cmd = new StringBuffer();
cmd.setLength(0);
if(text.length()+4 < 100)
cmd.append("0");
if(text.length()+4 < 10)
cmd.append("0");
cmd.append(Integer.toString(text.length()+4) + "�");
cmd.append(text);
cmd.append("\n");
bbuf = charset.encode(CharBuffer.wrap(cmd));
sc.write(bbuf);
bbuf.clear();
int n = sc.read(bbuf);
if(n == 1) {
bbuf.flip();
Byte re = bbuf.get();
if(re == 1) {
sendRetry = true;
} else {
sent = true;
} catch(Exception e) {
findAndDisconnectPlayer(sc);
try {
sc.close();
} catch(IOException f) {
f.printStackTrace();
return false;
} while(!sent && sendRetry);
return true;
String readText(SocketChannel sc) {
ByteBuffer bbuf = ByteBuffer.allocate(BSIZE);
int readRetryCount = -1;
boolean readRetry;
do {
readRetry = false;
readRetryCount++;
StringBuffer cmd = new StringBuffer();
cmd.setLength(0);
bbuf.clear();
try {
readLoop:
while(true) {
int n = sc.read(bbuf);
if(n > 0) {
bbuf.flip();
CharBuffer cbuf = charset.decode(bbuf);
while(cbuf.hasRemaining()) {
char c = cbuf.get();
if(c == '\r' || c == '\n') break readLoop;
cmd.append(c);
} else break;
statusArea.append(Thread.currentThread().getId() + " readText() odczytuje: " + cmd.toString() + "\n");
if(cmd.length() < 3 || Integer.parseInt(cmd.substring(0 , 3)) != cmd.length()) {
sc.write(ByteBuffer.wrap(new byte[] {1}));
readRetry = true;
} else {
sc.write(ByteBuffer.wrap(new byte[] {0})); // length OK
return cmd.toString().substring(4 , cmd.toString().length());
} catch(Exception e) {
findAndDisconnectPlayer(sc);
try {
sc.close();
} catch(IOException f) {
f.printStackTrace();
return "ERROR";
} while(readRetry && readRetryCount < 3);
findAndDisconnectPlayer(sc);
try {
sc.close();
} catch(IOException e) {
e.printStackTrace();
return "ERROR";
}Edited by: Kakalec on Jul 23, 2008 11:04 AMYou seem to be using a horrendous mixture of PrintWriters, BufferedReaders, ObjectOutputStreams, and no doubt ObjectInputStreams. You can't do that.
Some rules about this:
(a) Whenever you use a stream or reader or writer on a socket, you must allocate it once for the life of the socket, not every time you want to do an I/O.
There are many reasons for this including losing buffered data in the old stream and auto-closure of the socket on garbage-collection of the old stream.
(b) You can't mix stream types on the same socket. (i) If you're writing objects, use an ObjectOutputStream, you must read with an ObjectInputStream, and you can't read or write anything that isn't supported by the API of ObjectOutputStream. (ii) If you're writing lines, use a BufferedWriter and a BufferedReader at the other end. If you're writing characters, use a Writer and a Reader. (iii) If you're writing primitive data or UTF strings, use a DataOutputStream and a DataInputStream. (iv) If you're writing bytes, use DataOutputStream and a DataInputStream or an OutputStream and an InputStream. You can't mix (i), (ii), (iii), and (iv).
(c) Don't use PrintWriter or PrintStream over the network. They swallow exceptions that you need to know about. They are for writing to the console, or log files, where you don't really care about exceptions.
(d) Call flush() before reading.
(e) Always close the 'outermost' output stream or writer of a socket, never the input stream or the socket itself. Closing any of these closes the socket and therefore makes the other stream unusable, but only closing the output stream/writer will flush it. -
How to use Multi Thread to make a animation
Hello
Currently i am writing a router simulator using Java SE 1.4.2. I am facing a problem that is I cannot use multithread to update my Jframe animation.
Here i give my approach.
My idea is I used a JPanel in JFrame and I used Graphics g draw all background in Jpanel and add it into Jframe. It works since there is no animation invovled. I want to do some animation based on this background which i draw. But all animation should be controled by other threads due to i want other threads can control all animation. But i hit a error which is nullpointexception. The reason looks like which i used another to do animation, it cannot find the reference which is point to the Jpanel and Jframe. May u teach me a correct way to do multi threads animation in Jframe? thanks.
all the best and regards!A simple annimation moving a circle round a screen. This uses a model that defines the dynamics of the annimation, a view to display a visual representation of the model and an event system (observer/observable) to notify the view that the model has changed.
I hope this helps.
import java.awt.*;
import javax.swing.*;
import java.util.*;
public class Test20041023 extends JFrame
public Test20041023()
super("Simple Annimation Demo");
AnnimationModel annimationModel = new AnnimationModel();
AnimationView animationView = new AnimationView(annimationModel);
setContentPane(animationView);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
pack();
private static class AnimationView extends JPanel
private static final int PREFERRED_WIDTH = 512;
private static final int PREFERRED_HEIGHT = 256;
AnimationView(AnnimationModel annimationModel)
// Save a reference to the model for use
// when the view is updated
annimationModel_ = annimationModel;
// Listen for the events indicating that the model has changed
annimationModel_.addObserver(new Observer()
public void update(Observable o, Object arg)
// All we need to do is to get the view to repaint
AnimationView.this.repaint();
public void paintComponent(Graphics g)
super.paintComponent(g);
// Update the view based on the information in the model.
g.setColor(Color.red);
// Convert the model positions to view positions
// in this case by scaling to the actual width and height.
int xScreenPosition = scaleValue(annimationModel_.getX(), getWidth() - 20 ) + 5;
int yScreenPosition = scaleValue(annimationModel_.getY(), getHeight() - 20 ) + 5;
// Display the position of the point
g.fillOval(xScreenPosition, yScreenPosition, 10, 10);
private int scaleValue(double v, double size)
return (int)((v+1.0)*0.5 * size + 0.5);
public Dimension getPreferredSize()
return new Dimension(PREFERRED_WIDTH, PREFERRED_HEIGHT);
// The saved reference to the model
private AnnimationModel annimationModel_;
private static class AnnimationModel extends Observable
AnnimationModel()
Thread annimationThread = new Thread()
public void run()
// Loop forever updating the model
// and notifying the observers.
while(true)
// Wait 0.05 seconds until the next frame update point
try
sleep(50L);
catch (InterruptedException e)
// Nothing to do
// Update the model - in this case it is very simple
theta_ += 0.1;
// Notify the observers
setChanged();
notifyObservers();
annimationThread.start();
// Model access methods
public double getX()
return Math.cos(theta_);
public double getY()
return Math.sin(theta_);
// The angular position of the point
private double theta_;
// Simple test main
static public void main(String[] args)
new Test20041023().setVisible(true);
} -
How to write a multi threaded Cache Event Listener
I have a distributed data cache called tokenCache for my application. I have also added a mapListener to this cache to listen to a particular kind of events.
tokenCache.addMapListener((MapListener) new TokenCacheListenerBean(), new MapEventFilter(tokenFilter), false);
So bascially everytime a token (The domain object of this cache) is updated the entryUpdated() method in my EJB TokenCacheListenerBean is invoked.
The issue I have though is that, from what I observe on running my code is that the Cache Listener is single threaded. So if two Token Objects on my tokenCache are updated,
lets say Token Object A and Token Object B one after the other, the entryUpdated() method in my EJB is invoked for Token Object A and once the invocation is complete
then the entryUpdated() method is invoked again for Token Object B(). At a given point of time there is only one instance of TokenCacheListenerBean EJB. Is there a way to
make this happen in multi-threaded manner ?
Is there a configuration setting somewhere which allows multiple CacheListeners to be instantiated at a given point of time ?
TokenCacheListenerBean EJB_
package oracle.communications.activation.asap.ace;
import java.util.Iterator;
import java.util.Set;
import java.util.logging.Logger;
import javax.ejb.Stateless;
import com.tangosol.net.NamedCache;
import com.tangosol.util.MapEvent;
import com.tangosol.util.MapListener;
import com.tangosol.util.ValueUpdater;
import com.tangosol.util.extractor.PofExtractor;
import com.tangosol.util.extractor.PofUpdater;
import com.tangosol.util.filter.EqualsFilter;
import com.tangosol.util.filter.LikeFilter;
import com.tangosol.util.filter.LimitFilter;
import com.tangosol.util.processor.UpdaterProcessor;
* Session Bean implementation class TokenCacheListenerBean
@Stateless
public class TokenCacheListenerBean implements TokenCacheListenerBeanRemote, TokenCacheListenerBeanLocal, MapListener {
NamedCache asdlCache;
NamedCache tokenCache;
private final int PAGE_SIZE = 1;
private static Logger logger = Logger.getLogger(ConnectionManager.class.getName());;
* An instance of the JCAModeler EJB, represents the JCA-JNEP
JCAModeler jcaBean;
* Default constructor.
public TokenCacheListenerBean() {
// TODO Auto-generated constructor stub
public void entryDeleted(MapEvent Event) {
public void entryInserted(MapEvent Event) {
public void entryUpdated(MapEvent Event) {
Token newToken = (Token) Event.getNewValue();
Token oldToken = (Token) Event.getOldValue();
if ((oldToken.getState() == Token.TOKEN_RESERVED)
&& (newToken.getState()== Token.TOKEN_AVAILABLE)) {
String networkID = newToken.getNeID();
asdlCache = AceCacheFactory.getCache("asdlCache");
tokenCache = AceCacheFactory.getCache("tokenCache");
EqualsFilter filterNE = new EqualsFilter(new PofExtractor(String.class,Asdl.NETWORKID), networkID);
LimitFilter limitFilter = new LimitFilter(filterNE, PAGE_SIZE);
Set removeASDL = asdlCache.keySet(limitFilter);
Iterator asdlIterator = removeASDL.iterator();
if (asdlIterator.hasNext()) {
logger.info(printASDLCache());
ValueUpdater updater = new PofUpdater(Token.STATE);
System.out.println("Token ID:" + newToken.getTokenID());
UpdaterProcessor updaterProcessor = new UpdaterProcessor(updater, Integer.toString(Token.TOKEN_RESERVED));
tokenCache.invoke(newToken.getTokenID(), updaterProcessor);
jcaBean = new JCAModeler(tokenCache);
Object asdlID = asdlIterator.next();
Asdl provisionAsdl = (Asdl) asdlCache.get(asdlID);
asdlCache.remove(asdlID);
jcaBean.provision(provisionAsdl, newToken.getTokenID());
logger.info(ConnectionManager.printTokenCache());
logger.info(printASDLCache());
}Here is what I am asking!
I have added 2 listeners (Listener A and Listener B) which each listen on for changes made to 2 different token Cache Objects (Token A and Token B).
for (i = 0; i < 2 ; i++) {
Token tokenAdded = new Token(UUID.randomUUID().toString(),TOKEN_AVAILABLE, networkID);
tokenCache.put(tokenAdded.getTokenID(), tokenAdded);
tokenCache.addMapListener((MapListener) new TokenCacheListener(), tokenAdded.getTokenID(), false);
Now assume that updates are made to Token A and Token B simuntaneosly.
Why do i observe in my diagnostic messages that only one Listener is invoked at a given point of time.
Which means I see Listener A getting invoked and then once invocation of Listener A is complete I see Listener B bieng invoked.
Ideally I would want both listeners to be invoked simultaneously rather than in a one off fashion.
Here is the code for my token cache Listener
package oracle.communications.activation.asap.ace;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.logging.Level;
import java.util.logging.Logger;
import com.tangosol.net.CacheFactory;
import com.tangosol.net.NamedCache;
import com.tangosol.util.AbstractMapListener;
import com.tangosol.util.Filter;
import com.tangosol.util.MapEvent;
import com.tangosol.util.MapListener;
import com.tangosol.util.ObservableMap;
import com.tangosol.util.ValueUpdater;
import com.tangosol.util.extractor.PofExtractor;
import com.tangosol.util.extractor.PofUpdater;
import com.tangosol.util.filter.AndFilter;
import com.tangosol.util.filter.EqualsFilter;
import com.tangosol.util.filter.LikeFilter;
import com.tangosol.util.filter.LimitFilter;
import com.tangosol.util.processor.UpdaterProcessor;
public class TokenCacheListener extends AbstractMapListener {
NamedCache asdlCache;
NamedCache tokenCache;
AceCacheFactory cacheFactoryBean = new AceCacheFactory();
private final int PAGE_SIZE = 1;
private static Logger logger = Logger.getLogger(ConnectionManager.class
.getName());;
* An instance of the JCAModeler EJB, represents the JCA-JNEP
JCAModeler jcaBean;
* This is a utility method and prints the tokens cache.
public String printTokenCache() {
NamedCache tokenCache = cacheFactoryBean.getCache("tokenCache");
LikeFilter tokenList = new LikeFilter(new PofExtractor(String.class,
Token.STATE), "%", (char) 0, false);
Set keySet = tokenCache.keySet(tokenList);
StringBuffer cachedTokenList = new StringBuffer("\n################################## Token(s) Cache ##################################");
int counter = 1;
for (Object tokenInCache: keySet) {
Token tokenObject = (Token) tokenCache.get(tokenInCache.toString());
cachedTokenList.append("\nS.NO:" + (counter++)
+ "\t ID:" + tokenInCache.toString()
+ "\t State:" + Token.tokenToString(tokenObject.getState()));
cachedTokenList.append("\n####################################################################################");
return cachedTokenList.toString();
* This method is a utility method and it prints all the ASDL(s) currently present on the
* asdlCache.
private String printASDLCache() {
NamedCache asdlCache = cacheFactoryBean.getCache("asdlCache");
LikeFilter asdlList = new LikeFilter(new PofExtractor(String.class,
Asdl.NETWORKID), "%", (char) 0, false);
Set keySet = asdlCache.keySet(asdlList);
StringBuffer cachedASDLList = new StringBuffer("\n################ ASDL Cache ######## ########");
int counter = 1;
for (Object asdlInCache: keySet) {
cachedASDLList.append("\nS.NO:" + (counter++) + "\t ID:" + asdlInCache.toString());
cachedASDLList.append("\n################ ASDL Cache ######## ########\n");
return cachedASDLList.toString();
public TokenCacheListener() {
public void checkASDLCache(MapEvent Event) {
// Not currently used
public void entryUpdated(MapEvent Event) {
Token newToken = (Token) Event.getNewValue();
Token oldToken = (Token) Event.getOldValue();
logger.info("\n=============================================================================================="
+ "\nTOKEN CACHE LISTENER"
+ "\n=============================================================================================="
+ printTokenCache()
+ "\n==============================================================================================");
if ((oldToken.getState() == Token.TOKEN_RESERVED)
&& (newToken.getState()== Token.TOKEN_AVAILABLE)) {
String networkID = newToken.getNeID();
asdlCache = cacheFactoryBean.getCache("asdlCache");
tokenCache = cacheFactoryBean.getCache("tokenCache");
EqualsFilter filterNE = new EqualsFilter(new PofExtractor(String.class,Asdl.NETWORKID), networkID);
LimitFilter limitFilter = new LimitFilter(filterNE, PAGE_SIZE);
Set removeASDL = asdlCache.keySet(limitFilter);
Iterator asdlIterator = removeASDL.iterator();
if (asdlIterator.hasNext()) {
logger.info(printASDLCache());
ValueUpdater updater = new PofUpdater(Token.STATE);
System.out.println("Token ID:" + newToken.getTokenID());
UpdaterProcessor updaterProcessor = new UpdaterProcessor(updater, Integer.toString(Token.TOKEN_RESERVED));
tokenCache.invoke(newToken.getTokenID(), updaterProcessor);
jcaBean = new JCAModeler(tokenCache);
Object asdlID = asdlIterator.next();
Asdl provisionAsdl = (Asdl) asdlCache.get(asdlID);
asdlCache.remove(asdlID);
jcaBean.provision(provisionAsdl, newToken.getTokenID());
logger.info(printTokenCache());
logger.info(printASDLCache());
I only see one instance of this listener alive at any given point of time.
Edited by: 807103 on Nov 3, 2011 1:00 PM
Edited by: 807103 on Nov 3, 2011 1:12 PM -
Passing a variable from one thread to another
Hi. I'm trying to produce a chat program in Java but need to pass a variable between two threads. I have included a snipet of the code.
import java.io.*;
import java.net.*;
class IndividualConnection extends Thread
public Socket clientSocket;
String userName = "";
public IndividualConnection(Socket connectingSocket)
clientSocket = connectingSocket;
public login(String name)
userName = name;
public void messageUser(Socket socket, String msg)
try
Socket newSocket = new Socket("192.168.0.162",5163);
DataOutputStream outToServer = new DataOutputStream(socket.getOutputStream());
outToServer.writeBytes(msg + '\n');
catch(Exception e)
System.out.println("The connection with the client has been closed.");
this.stop();
public void run()
Socket global = clientSocket;
// etc etc
A number of threads are created based on code similar to the above. Each thread communicates to a different client on the chat program. However, I want to be able to send messages between the clients.
Each thread has a method called messageUser(Socket socket, String msg). I should (hopefully) be able to send a message to anyone using the prog if I can access their socket. The problem is that the socket objects for each client is held in the clients own thread. I have tried writing some code to find the Socket object in another thread but to no success. The code I am trying is shown below.
public Socket findContact(String name)
ThreadGroup currentGroup = Thread.currentThread().getThreadGroup();
int numThreads = currentGroup.activeCount();
Thread[] listOfThreads = new Thread[numThreads];
currentGroup.enumerate(listOfThreads);
for (int i = 0; i < numThreads; i++)
String threadName = listOfThreads.getName();
if (threadName.compareTo(name) == 0)
// Socket tempSocket = threadName[i].getClass().getField(clientSocket);
return tempSocket;
The line I have commented out does not work. Please could someone tell me how to carry out this task. I have spent many hours trying to solve this but am not able to. The chat server is nearly complete now. I just need to find a way of obtaining another threads socket.
I hope the problem is comprehensible. I have found it difficult to explain clearly. Many thanks.Really simple, inelegant solution:
class MyThread extends Thread {
Socket socket;
MyThread( Socket s ) { socket = s; }
public Socket getSocket() { return socket; }
}Better: create a master object that includes an array
of sockets. Each time you create a Thread, update the
master object's list of sockets with a reference to
each Thread's socket. Under the current memory model, the socket field should be declared volatile. The proposed new memory model will guarantee that this will work if the socket field is declared final.
Sylvia. -
Copy variable from one thread to another
My program requires user to input a java file which contains the run() method.
In the input file, user can declare variables and use those variables inside the run method. User also need to enter the number of threads to be spawned.
The problem is how can I construct some method like "copy" which can copy the variable from one thread to another in my program? I can't do that since I don't know the name of the variables that the user inputted.
I've tried this:
class helloworld extends thread{
void run(){
String a="hello";
String b="world";
copy(0,1,a,b)
class myProgram {
Class c = Class.forName(fileName); // file name of user's file
Thread t[] = new Thread[p]; // p is number of threads
for (int i=0; i<p; i++){ // create threads
t[i] = (Thread) c.newInstance();
t.start();
public void copy(int sourThread, int destThread, String s1, String s2){
t[sourThread].s1=t[destThread].s2
But it doesn't work. It said "cannot resolve symbol s1 and s2".
please help. urgent. Thanks a lot in advance.You need to seriously reconsider what you're allowing the user to do. The short answer to your problem is to use a shared, synchronized associative array.
However, since the user can specify any number of threads, you will have to resolve deadlocks, and the fact that you're asking this question suggests you will have problems doing so until you have read up on threads and shared variables in more detail. (I don't mean to be dismissive. Deadlocks and shared variables have to be customized to the application, i.e., you have to figure out just when each thread will need access to the variable, what kind of access, and when.)
In the meantime, take a step back and take a look at the big picture.
From what you've said, I would guess a common example of your application is that I want to be able to read file "foo.dat", uppercase each letter in the file, and write it out to "fooXXX.dat" where XXX reflects the thread number. And specify any number of threads I want.
Threads would not be the best way to accomplish this. Do this serially.
Alternatively, I could interpret your problem as in you need to create a main() function that's capable of reading someone else's dot-class file, clone the object and start it. In which case, why do you want to share variables? If the user did his job correctly, then his file will already contain shared variables (or copy them as appropriate). All you have to do is clone the object via the new keyword, then call start() in it.
You cannot share something when you don't know what you're sharing.
The third option is that you're doing this as an academic exercise (i.e., homework). Granted, yes, your professor may ask you to do things illogically just to prove they can be done. Unfortunately, we're not supposed to help you in that case. People who read this forum generally try to find logical and efficient ways of doing things. -
Multi-Threaded server using ThreadPool
Dear friends,
I am writing a client-server program in which the client and server communicate using SUN-RPC. The client reads a file containing some numbers and then spawns threads which it uses to request the server for a service. These threads are executed using a thread pool. Till this time, it's working fine. But when it comes to the server, the real trouble begins because it too needs to be made a multi-threaded one using thread pooling. The server has to capture the call information for each request for the service and then pass this information to a thread/runnable object in whose run() method the code for execution of the service would be present. Since the tasks(requests for the service) are not present already, i am unable to execute the server side threads in a loop using a thread pool. How to solve this problem? Kindly help.
Thanks,
SubhashThe server has to capture the call information for each request for the serviceWhy?
and then pass this information to a thread/runnable object in whose run() method the code for execution of the service would be present.Why can't the run() method get the call information when it starts? That's what's normally done. The server's accept loop mustn't do any other I/O: otherwise a rogue client can block the server complete.y -
InfoPath: the multi-threading challenge
Or to be more specific: calling a DataSource from a different thread.
A project I'm working on includes an InfoPath form in which some heavy duty tasks are executed. These tasks can take over 10+ seconds to execute. To avoid the GUI to get stuck during execution, multi-threading is implemented. The problem lies in providing
feedback to the user. Several methods have been used, but all end in the exceptions shown below.
Unlike WinForms and such, InfoPath does not seem to provide a way to invoke the GUI. What we are trying to do is change field values to reflect the status of the process. This is done through the MainDataSource. I've tried several methods to call
this datasource through another thread, like invoking a provided delegate, or execution context. However all these methods have similar results.
When calling a method or property on the datasource the following exception is thrown:
System.InvalidOperationException was unhandled
Message="Operation is not valid due to the current state of the object."
Source="Microsoft.Office.InfoPath.Client.Internal.Host"
StackTrace:
at Microsoft.Office.Interop.InfoPath.SemiTrust.ICLRExtensionsWrapper.IncrementSqmPoint(Int32 idDataPt)
at Microsoft.Office.InfoPath.Internal.DataSourceHost.CreateNavigator()
at Form1.FormCode.ContextCallbackMethod(Object obj) in E:\Projects\InfoPath Multithreading\Source\Form1\FormCode.cs:line 74
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at Form1.FormCode.ThreadMethod(Object myParamsObj) in E:\Projects\InfoPath Multithreading\Source\Form1\FormCode.cs:line 68
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart(Object obj)
This seems to indicate the DataSource is locked for some reason. Even the ReadOnly property can not be read.
When calling the SetValue method on an XPathNavigator provided by a datasource and passed through another thread, the following exception is thrown:
System.AccessViolationException was unhandled
Message="Attempted to read or write protected memory. This is often an indication that other memory is corrupt."
Source="Microsoft.Office.InfoPath.Client.Internal.Host.Interop"
StackTrace:
at Microsoft.MsoOffice.InfoPath.MsxmlInterop.NativeHelpers.SetText(IXMLDOMNode* , Char* )
at Microsoft.MsoOffice.InfoPath.MsxmlInterop.MsxmlNodeImpl.set_Text(String strText)
at Microsoft.Office.InfoPath.MsxmlNavigator.SetValue(String value)
at Form1.FormCode.DelegateMethod(XPathNavigator nav) in E:\Projects\InfoPath Multithreading\Source\Form1\FormCode.cs:line 81
at Form1.FormCode.ThreadMethod(Object myParamsObj) in E:\Projects\InfoPath Multithreading\Source\Form1\FormCode.cs:line 70
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart(Object obj)
I have searched through the internet but am unable to find any useful information about this subject. There are only a few weeks remaining before the deadline. A work-around has been implemented, but since it requires additional active user interaction
it is far from ideal. I hope you can help me in finding a solution.For anyone who is still interested all this time later....
I wouldn't use a Dispatcher in InfoPath simply because InfoPath requires .Net 2.0 only and Dispatcher was not added until .Net 3.0 which means you would have to enforce installation of .Net 3.0 yourself.
There is an easy alternative which is SynchronizationContext (more specifically a WindowsFormsSynchronizationContext).
Also I suggest you do not use ThreadStart but rather use one of the more modern and well known threading paradigms. A good alternative is a BackgroundWorker.
e.g.
private BackgroundWorker _Worker;
public void InternalStartup()
InitializeWorker();
((ButtonEvent)EventManager.ControlEvents["Button"]).Clicked += new ClickedEventHandler(ButtonClick);
public void InitializeWorker()
_Worker = new BackgroundWorker();
_Worker.WorkerReportsProgress = true;
_Rorker.WorkerSupportsCancellation = true;
_Worker.DoWork += new DoWorkEventHandler(_Worker_DoWork);
_Worker.ProgressChanged += new ProgressChangedEventHandler(_Worker_ProgressChanged);
_Worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(_Worker_RunWorkerCompleted);
public void ButtonClick(object sender, ClickedEventArgs e)
if (_Worker.IsBusy)
_Worker.CancelAsync();
else
// Very important to include this line!
AsyncOperationManager.SynchronizationContext = new WindowsFormsSynchronizationContext();
_Worker.RunWorkerAsync();
void _Worker_DoWork(object sender, DoWorkEventArgs e)
// Do stuff in another thread and report back to the UI thread.
object state;
int percentage = 0;
_Worker.ReportProgress(percentage, state).
public void _Worker_ProgressChanged(object sender, ProgressChangedEventArgs e)
// This is called on the thread that started the worker.
// In this case the UI thread which means it is safe to use the MainDataSource.
CreateNavigator().SelectSingleNode("my:Main/my:Progress", NamespaceManager).SetValue(e.ProgressPercentage);
void _Worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
// Do anything you want to do on completion here.
One thing of note is that the SynchronizationContext in InfoPath for some reason or other always seems to be Null. The result is that when you call RunWorkerAsync() it captures the current synchronization context (null) which means the default is used and
a ProgressChanged is called on a new thread each time. To prevent this we need to manually set the context before calling RunWorkerAsync() which is done using the AsyncOperationManager.
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