A Thread Notifying Another Thread
Here is what I would like to accomplish. Before thread A terminates, I would like thread A to notify thread B that it is about to terminate. I would like to do this notification through a function, which need to be called regardless if the thread terminates gracefully.
Is there a way to define this function and have the JVM call it. I was told by someone that JVM calls a function when a thread exits and I can override the function so that thread A notifies thread B. If this function exists, please let me know how to accomplish this. If this function does not exist, what are my options, if any, to come up with a solution to this problem?
thanks,
Paul0al
If you want to handle abnormal termination due to an uncaught exception, (OutOfMemoryError, NullPointerException, etc.) you can put thread A into a subclass of ThreadGroup, which you subclass like this:
// Untested code! Coding on the fly...
class MyThreadGroup extends ThreadGroup {
public void uncaughtException(Thread t, Throwable e) {
// Notify your other thread here of the death of our thread
}So our thread group's uncaughtException() method is called when a thread in it dies. I believe this is the only useful feature of ThreadGroup, although I think inheriting ClassLoaders might be a feature only provided by ThreadGroup as well.
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Thx.It really depends on what you want to do with your exception. Is there some sort of global handler that will process the exceptions in some meaningful way? Unless you have that, there's not much point in throwing an exception in a thread, unless you simply want the stack trace generated.
Presuming that you have a global handler that can catch exceptions, nest your Exception subclass inside a RuntimeException:
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Shutting down a panel in one thread from another thread.
For various reasons, I have a program with two threads (actually more than two, but only two are concerned here). One is the main panel that runs at startup, another is a Virtual O'Scope panel with a real-time display. Everything works more or less well, until it's time to exit the program.
The main program starts by calling a routine to display the VO'scope; this routine calls CmtScheduleThreadPoolFunctionAdv to schedule the VOscope thread with the function VOscopePanelMain.
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When it comes time to close the window, closing the panel (the X box in the upper right corner) triggers the panel callback CB_VoscopePanel, which processes the EVENT_CLOSE: event by calling QuitUserInterface(0); which, in turn, causes RunUserInterface to return to VOscopePanelMain, which then shuts things down, closes the panel properly, and exits. So far so good.
int CVICALLBACK CB_VoscopePanel (int panel, int event, void *callbackData,
int eventData1, int eventData2)
int iPanelHeight, iPanelWidth, iV2ControlLeft, iV2ControlWidth, iWidth,
iT2ControlTop, iT2ControlHeight, iHeight, iLeft, iGap, iScreenTop, iScreenLeft,
iTop, iBoxWidth;
switch (event) {
break;
case EVENT_GOT_FOCUS: //happens when first displayed or refreshed
case EVENT_PANEL_SIZE: //size the controls on the panel
... do stuff here;
break;
case EVENT_CLOSE:
QuitUserInterface(0); //stop VOscopePanelMain, which in turn closes the panel and cleans stuff up.
break;
return 0;
However, I also want the panel to stop when I close the main program. The only way that I know how to do this cleanly is to have the main program (which has closed all of its panels and is in the process of shutting down) call VOSCOPE_Close_VOScope () which, in turn, calls CallPanelCallback (iHandle_VOscope, EVENT_CLOSE, 0, 0, 0); (which forces a call to CB_VoscopePanel above with the EVENT_CLOSE event), which should call QuitUserInterface, which should cause the RunUserInterface in VOscopePanelMain to return and let it continue to shut down. In addition, after calling CallPanelCallback, the shutdown routine calls CmtWaitForThreadPoolFunctionCompletion to wait for the VOscopePanelMain thread to actually quit and clean up before proceeding.
But, of course, it doesn't since, and it took me a while to realize this. The call to QuitUserInterface isn't coming from inside of the VOscopePanelMain thread, it's coming from the main panel's thread - which is already in the process of shutting down. So, the main panel thread is telling itself to quit, VOscopePanelMain never gets the QuitUserInterface message, and things stall.
So: how do I have one thread tell a panel in another thread to cleanly close? Or do I have to get complicated and either replace RunUserInterface in VOscopePanelMain with a loop that processes events manually and looks for a flag, or figure out something with a thread-safe queue? Any help appreciated.
Attachments:
Voscope.c 76 KBSorry for delay in answering, it took me a while to find time to build up a working example.
The attached program spawns a thread in a new thread pool and permit you to choose whether to close it from the main thread or the spawned thread itself.
It appears that in such a minimal configuration the process works as expected. There may be some different configuration in your actual program that prevents this.
Proud to use LW/CVI from 3.1 on.
My contributions to the Developer Zone Community
If I have helped you, why not giving me a kudos?
Attachments:
ThreadPoolWithGUI.zip 7 KB -
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public class ServerThread extends Thread{
private skt;
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InputObjectStream ios = null;
try{
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//here i want to refresh the JTable,how to write??
catch(){}
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}Use the "code" formatting tags when posting code.
Read this article on [url http://www.physci.org/codes/sscce.jsp]Creating a Simple Demo Program before posting any more code.
Here is an example that updates a table from another thread:
http://forum.java.sun.com/thread.jspa?forumID=57&threadID=435487 -
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I have a SocketServer that creates new threads to handle incoming clients. If one of the threads throw a SQLException is it possible to catch that exception in the SocketServer that created that thread.
I tried implementing this code and I cannot get the server to catch an exception thrown in the thread. Are my assumptions correct?
I was reading something about Thread Groups and implementing an uncoughtException() method, but this looked like overkill.
Thanks for your time!
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try
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To follow up on another thread, I checked out the keymappings and found most of what I was looking for.
Only a couple of things I miss:
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For 2) Is it the same as
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If yes, then you can change the key mapping in Tools-->Preferences --> Accelerators to the keyboard combination you are most familiar with (look for "find").
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How to use ImageControl on another thread out main
Hi All,
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Here my code
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tony -
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.*;
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clientSocket = connectingSocket;
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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)
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currentGroup.enumerate(listOfThreads);
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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:
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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();
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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. -
Are you suppose to access UIView from another thread?
A lot of UI events in my apps take place in another thread. So in my uivewcontroller, it catches a button click for example, it launches a NSThread with some parameter. The reason I decided to use a thread is because if the duration takes long the UI completely locks up. The thread then fetches for some result and access a pointer to a UIView (a UILabel for example) and update it's content.
Now, is this model correct? I'm running in cases where setting the UILabel.text from the thread sometimes work, sometimes doesnt. I'm not sure how to debug. If I change the thread call to a standard method call (which blocks until results are ready) the text is updated correctly.
Any hints?http://developer.apple.com/documentation/Cocoa/Conceptual/Multithreading/ThreadS afetySummary/chapter950_section2.html
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How do I move my thread to another forum
somebody has suggested I move my thread to another forum - how do I do that?
the thread I want to move is
[Reports based on Linked Universes in BOXI 3.0 do not work|Reports based on Linked Universes in BOXI 3.0 do not work]thanks, could you please move it to the BusinessObjects Enterprise Administration forum BI Platform
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Can i catch an exception from another thread?
hi,guys,i have some code like this:
public static void main(String[] args) {
TimeoutThread time = new TimeoutThread(100,new TimeOutException("超时"));
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i asked this question in concurrent forums,somebody told me that i can't.so ,i think if i can do this from aspect of jvm.
thank you for your help
Edited by: Darryl Burke -- Double post of how to catching exceptions from another thread lockinguser5449747 wrote:
so ,i think if i can do this from aspect of jvm. What does that mean? You think you'll get a different answer in a different forum?
You can't catch exceptions from another thread. It's that easy. You could somehow ensure that exceptions from that other thread are always caught and somehow passed to your thread, but that would be a different thing (you would still be catching the exception on the thread it is originating from, as is the only way).
For example you can use setUncaughtExceptionHandler() on your thread to provide an object that handles an uncaught exceptions (and you could pass that uncaught exception to your other thread in some way). -
The FAQ says that you can create a link to both a thread and a message using tags. I just right clicked on a thread title, clicked “Copy Link Location”, pasted and saw a url with a messageID. But if I wanted to use the {thread} tag, what id do I use?
Where are you right clicking when you do that.
If go to the forum page for this forum and right click on the title of this thread and "copy link location" I get...
Link to another thread.
which is clearly the thread ID.
If however I do the same on your name under the "Last Post" column, I get...
Re: Link to another thread.
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