JOptionPane works once in synchronized method
Hi,
I'm having a bit of trouble using JOptionPane in a synchronised method. The GUI maintains a list of allowed and blocked sites.
Many threads access these lists to check if an access to a site should be allowed or not. If the new access does not match an entry in either list then a JOptionPane is displayed to ask the user for the action to take.
The lists need to be synchronised so the GUI class looks like this:
public class Console extends JFrame{
private JTextArea allowedHosts;
private JTextArea blockedHosts;
public Console()
{...creates and displays GUI... }
public synchronized boolean isRequestAllowed(Request request)
{ ...//code to check if the request is in allowed or blocked list
else
//Pop up a JDialog to ask the user for the next action to take
return promptForAction(request);
private boolean promptForAction(Request request)
...//creates options for JOptionPane
try
SwingUtilities.invokeAndWait( new Runnable() {
public void run()
actionCode[0] = JOptionPane.showOptionDialog(frame, message, "Access Attempt",
JOptionPane.DEFAULT_OPTION,
JOptionPane.QUESTION_MESSAGE,
null, options, options[0]);
catch (InterruptedException ignore){}
catch (InvocationTargetException ignore) {}
...//checks actionCode[0] to specify next action
The need for synchronisation is that I don't want one thread checking the allowed or blocked lists while the user is being prompted for input about a previous request.
The JOptionPane works fine for first request and will return. A second request is then attempted and the JOptionPane displays but will not respond to any inputs or clicks on buttons.
My experience of Java is very limited and I might be making alot of mistakes but I have read the tutorials on the java website and any other related sites.
Any help would be much appreciated,
Mark
Double post, duplicate of [5291829|http://forum.java.sun.com/thread.jspa?threadID=5291829]
db
Similar Messages
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Dont understand Synchronized method to complete program
I'm trying to finish theis program but i don't understand synchronized methods. I checked the java tutorial and i am still confused. Can someone help me approach finishing this program. Here is the spec and the first part of the program i have done.
===================================================================================
When the above is working, create a class called Food. The objective here is to demonstrate the behavior of threads that share data, and use synchronized methods.
Simulating an animal eating, simply means that the thread will sleep for some length of time.
There is one instance of the Food class that is shared by both of the animals. Pass it to the constructor of the Animal class.
There is a method in the Food class called eat(). This method is synchronized, i.e., only one Animal can be eating at a time.
The rabbit eats the food (the thread will sleep) for a longer time than the turtle, thus giving an advantage to the rabbit.
But, the turtle must wait until the rabbit is done eating until it can eat, so the advantage is reduced. Print out a message in the eat method when the animal begins to eat, and when it is done eating. Indicate which animal it is that starts to eat.
Try making the eat method not synchronized, and observe the different behavior if the eat method allows the rabbit to begin eating before the turtle is done eating
import java.util.Random;
public class Animal extends Thread implements Runnable{
private String name;
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if (position >= 100){
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rabbit.start();
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this.donkey = donkey;
this.time = time;
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for (int i = 0; i < 10; i++) {
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Donkeyphile jverd = new Donkeyphile(donkey, 500);
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synchronized void love(long time) {
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System.out.println(name + " hugs the donkey.");
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done=true;if you don't use threads, you don't need "synchronized" all it does is slowing down your code, without any other effects.
Either you go into threads completely (yes, it is a non-trivial topic that requires some work) or you better leave it. Simply calling methods "synchronized" has no effect on your single-threaded program. -
Nested synchronized method class
Hi. I have a situation where there are two synchronized methods: Method A and Method B. In the course of execution, Method A calls Method B. Method B calls wait(). This causes a classical deadlock as wait() releases the monitor for Method B, but no for Method A. What are my options to work around this problem?
Thanks in Advance,
Paul0alA and B cannot synchronize on the same object because if A acquires the monitor, then B cannot obtain the same monitor without A releasing the monitor. My problem is that A and B are synchronized on different objects. A calls B and B calls wait(). A deadlock occurs because A's monitor is not released.
Thanks,
Paul0al -
Optimizing synchronized method?
A couple of other threads got me to thinking about a bit of code I commonly use. Is a synchronized method really expensive enough to make this modification warranted?
Original method:
private static Manager theManager = null;
public static synchronized getManager() {
if (theManager != null) return theManager;
theManager = new Manager();
return theManager;
}Optimized version:
private static Manager theManager = null;
public static getManager() {
if (theManager != null) return theManager;
synchronized (theManager) {
if (theManager != null) return theManager;
theManager = new Manager();
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However, I am more interested in the solution presented by a link elsewhere in that article:
http://en.wikipedia.org/wiki/Initialization_on_demand_holder_idiom
That method solves the problem and no synchronized keyword is needed at all.That's true. However, follow the [double-checked locking|http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html] link in that article, to actually understand what's going on. And pay particular attention to the part that says For most applications, the cost of simply making the getHelper() method synchronized is not high. You should only consider this kind of detailed optimizations if you know that it is causing a substantial overhead for an application.
And finally: you do realize that singleton is almost never necessary, introduces tight coupling into your program, and makes it difficult to test. Right? -
I've read many times that synchronized methods have a severe performance penalty; anywhere from 4-100 times slower than unsynchronized. So, I wrote a test that called 2 methods 100,000 times in separate tight loops. One method was synchronized, the other was not. All the methods did was print something to stdout. The synch. method was .23 milliseconds slower than the unsynch. method. In my opinion this is nothing to worry about; am I missing something that would lead to such poor performance in synch. methods?
I was using whatever JVM comes with J2SE 1.4
ThanksThere are two costs due to synchronizing a method :
1. Overhead in executing the primitives that lock and
unlock a monitor required to make a call synchronized.
I've a hard time believing they would be
insignificant. That would affect the response time
per request.There are two different costs here, too.
If a single thread attempts to gain a monitor lock, it will be successful and the cost is minimal, almost free. We're talking a couple of CPU cycles.
If there is contention to gain a monitor lock... that is, more than one thread is simultaneously trying to gain the lock, the cost increases dramatically, and you could quite realistically expect the lock acquisition to generate a large load.
I imagine
2. Delays due to other threads not being able to run
while a specific thread is executing the synchronized
code. This would affect the throughput of the
application, i.e. the number of requests your
application can handle in a unit of time.Synchronization certainly enforces serial execution, even in parallel threads. That's why it's useful :-)
If one thread currently holds the lock and another thread requests it, the second thread will quickly notice that the lock is held and enter the lock's wait queue. Once the first thread releases the lock, the second thread will be awoken and immediately get the lock - this situation involves no contention and would be rather efficient. In a two-thread situation, true (expensive) contention will only occur if both threads attempt to gain the lock at the same time.
If more than one thread is waiting on the lock when it is released, there will be guaranteed contention as both threads are woken up simultaneously.
ie- synchronization can cause significant overhead in an application if thread patterns aren't examined and an appropriate synchronization framework used. -
Which object's monitor does a synchronized method acquire?
from the Java Tutorial for concurrency programming:
" When a thread invokes a synchronized method, it automatically acquires the intrinsic lock _for that method's object_ and releases it when the method returns. The lock release occurs even if the return was caused by an uncaught exception. "
what exactly does this mean?
do synchronized methods acquire the monitors for objects of type: java.lang.reflection.Method
please consider this code:
public class Foo {
private int counter = 0;
public synchronized void incriment() { counter++; }
public synchronized void decriment() { counter--; }
Foo f = new Foo();
Class[] sig = new Class[0];
Method m = f.getClass().getMethod("incriment", sig);
// ok. so "m" is the relevant method object.
f.incriment(); // <-- is the monitor for "m" ,
// or the monitor for "f", acquired?
.......my reading of the Concurrency Tutorial is that synchronized methods use the monitors of java.lang.reflection.Method objects?
and thus, Foo is not thread safe, right?
however, this simple change makes Foo thread-safe?
public class Foo {
private volatile int counter = 0; // "volatile"
public void incriment() { counter++; }
public void decriment() { counter--; }
}thanks.
Edited by: kogose on Feb 23, 2009 7:13 PMtensorfield wrote:
jverd wrote:
tensorfield wrote:
kogose wrote:
what exactly does this mean?It means you're complicating things.
If a method is synchronized, it is. You don't need to go beyond that. The method is synchronized.Not true. You have to know what it means for a method to be synchronized. Often people come in with the erroneous impression that it somehow prevents you from using or accessing the object in any other thread.It's very simple. If a synchronized method is called at the same time from many threads only one call will be executed at a time. The calls will be lined up and performed one after the other in sequence.
AND because synchronization is on a per object basis, when one synchronized method is being called from one thread, all synchronized methods of that same object are blocked for calling from other threads.
Simple as that.No, it's not that simple, and as stated, that is not correct. In particular, you didn't mention that for an instance method, all the various threads have to be trying to call instance methods on the same object in order for execution to be sequential.
You really can't understand Java's syncing without understanding how it relates to locks, and what it means for a method to be synchronized in terms of which lock it acquires.
Edited by: jverd on Feb 25, 2009 2:47 PM -
# Question
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Calling static synchronized method in the constructor
Is it ok to do so ?
(calling a static synchronized method from the constructor of the same class)
Please advise vis-a-vis pros and cons.
regards,
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a method should be bound to the class (made static) if the method operates on the class's static variables (modifies the class's state). an instance object should not directly modify the state of the class.
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although it is permitted, i do not access the static methods through an instance object. i only access static methods through the class object for clarity.
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I have been having trouble getting my email on my iPad2.
It started when I brought it to the US on vacation (I live in London and my email provider is Virgin Media). It worked once since I returned, but that is it.
I can send emails, but can't get them.
Any ideas, people?Hi Kharels
Just posted this reply to 2 others with same sort of question:
I have the same issue as i have my own email address and only want to use.
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The other is to set up your iCloud email as normal, then create a new one altogether. Choose 'Other' when creating this new account. Then put for the incoming server mail.me.com, along with your user name and password. For the outgoing server put the server you want to use - ie your own domain one. This is therefore a hybrid account and does work.
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Providing you have directed your own domain email address to your me.com one, you will find the iPhone should behave itself and you can use the folders etc and these will synch with your Mac ok.
Hope this work for you - let us know.
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Synchronized method in a java class used by many interfaces
My interface (idoc to file) is using a java class, which has one method that reads a table from a central database and after doing some calculations updates it.
(The interface instantiate the class inside a user-defined function and calls the method there.)
The problem is that if somebody sends 100 idocs at the same time, there can be a dirty read, I mean, a read just before other interface updates the table.
We want the following:
Interface 1:
- Read counter from the table (counter = 5 )
- Increment counter (counter = 6)
- Update table with that counter (table with counter = 6)
Interface 2:
- Read counter from the table (counter = 6 )
- Increment counter (counter = 7)
- Update table with that counter (table with counter = 7)
RESULT: The table has the counter = 7
But what is happening is the following:
- Interface 1 reads (counter = 5)
- Interface 2 reads (counter = 5)
- Interface 1 increments counter (counter = 6)
- Interface 2 increments counter (counter = 6)
- Interface 1 updates table (table with counter = 6)
- Interface 2 updates table (table with counter = 6)
RESULT: The table has the counter = 6 (WRONG)
I made the method synchronized. What I was expecting was that only one interface (i1) could enter the method (read the table and update it) while other interfaces running at the same time would have to wait until i1 finished that method.
My first test indicates that's not happening. Can anybody help me to find a solution?Hi Bhavesh,
If the QOS is EOIO this means that the integration engine manage the call to the mapping program (and all the other blocks) inside an "internal" synchronized method.
So this means that in this case you do not need to manage the queued access (synchronization) inside your custom java code because it is already enveloped in a queued block by XI.
The problem that Jorge had can be easily reproduced using the sample code that follows:
<b>class Synch Object</b>
import java.util.Date;
public class SynchObject {
String strName;
public SynchObject(String strName){
this.strName = strName;
public synchronized void syncWrite(String strCaller) throws InterruptedException{
Date now;
now = new Date();
System.out.println("-- " + now.toLocaleString() + " " + strCaller + " entering syncWrite of " + strName);
System.out.flush();
Thread.sleep(1000);
now = new Date();
System.out.println("-- " + now.toLocaleString() + " syncWrite of " + strName + " called by " + strCaller );
System.out.flush();
Thread.sleep(1000);
now = new Date();
System.out.println("-- " + now.toLocaleString() + " " + strCaller + " leaving syncWrite of " + strName);
System.out.println("");
System.out.flush();
<b>class Caller</b>
public class Caller implements Runnable {
String strName;
SynchObject target;
int intMax;
public Caller(String strName, SynchObject target, int intMax) {
this.strName = strName;
this.target = target;
this.intMax = intMax;
public void run() {
for(int i=0; i<intMax;i++)
try {
target.syncWrite(strName);
} catch (InterruptedException e) {
e.printStackTrace();
<b>class Workbench</b>
public class Workbench {
public static void main(String[] args) {
// TODO Auto-generated method stub
SynchObject sObj1 = new SynchObject("syncObj1");
SynchObject sObj2 = new SynchObject("syncObj2");
Caller c1 = new Caller("caller1",sObj1,2);
Caller c2 = new Caller("caller2",sObj1,2); '[*CHANGE*]
Thread ct1 = new Thread(c1);
Thread ct2 = new Thread(c2);
ct1.start();
ct2.start();
Run the workbench class to see what happen when setting QOS EOIO (the synch object is the same).
To see instead what happen now (missing synchronization) you have to change in Workbench class the statement
Caller c2 = new Caller("caller2",sObj1,2); '[*CHANGE*]
with
Caller c2 = new Caller("caller2",sObj2,2); '[*CHANGE*]
The reason is that every instance of the mapping program declare a new instance of the "Synchronized object" so the calls are synchronized inside the same mapping program but not between several mapping program.
Hope this give you a better idea on this problems with java synchronization, but if you have further doubts (I know it's a little bit tricky ) feel free to ask.
Kind Regards,
Sergio -
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I have a link to an intranet address that will not work once the PowerPoint presentation has been published via Presenter 7.0.7. The cursor does not change to a pointer and nothing launches when the link is clicked. I have verified the Flash Player security settings as well as ensured no formatting of the text link except for the color change that happens when the link is inserted.
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Use of 'static' keyword in synchronized methods. Does it ease concurrency?
Friends,
I have a query regarding the use of 'synchronized' keyword in a programme. This is mainly to check if there's any difference in the use of 'static' keyword for synchronized methods. By default we cannot call two synchronized methods from a programme at the same time. For example, in 'Program1', I am calling two methods, 'display()' and 'update()' both of them are synchronized and the flow is first, 'display()' is called and only when display method exits, it calls the 'update()' method.
But, things seem different, when I added 'static' keyword for 'update()' method as can be seen from 'Program2'. Here, instead of waiting for 'display()' method to finish, 'update()' method is called during the execution of 'display()' method. You can check the output to see the difference.
Does it mean, 'static' keyword has anything to do with synchronizaton?
Appreciate your valuable comments.
1. Program1
public class SynchTest {
public synchronized void display() {
try {
System.out.println("start display:");
Thread.sleep(7000);
System.out.println("end display:");
} catch (InterruptedException e) {
e.printStackTrace();
public synchronized void update() {
try {
System.out.println("start update:");
Thread.sleep(2000);
System.out.println("end update:");
} catch (InterruptedException e) {
e.printStackTrace();
public static void main(String[] args) {
System.out.println("Synchronized methods test:");
final SynchTest synchtest = new SynchTest();
new Thread(new Runnable() {
public void run() {
synchtest.display();
}).start();
new Thread(new Runnable() {
public void run() {
synchtest.update();
}).start();
Output:
Synchronized methods test:
start display:
end display:
start update:
end update:
2. Program2
package camel.java.thread;
public class SynchTest {
public synchronized void display() {
try {
System.out.println("start display:");
Thread.sleep(7000);
System.out.println("end display:");
} catch (InterruptedException e) {
e.printStackTrace();
public static synchronized void update() {
try {
System.out.println("start update:");
Thread.sleep(2000);
System.out.println("end update:");
} catch (InterruptedException e) {
e.printStackTrace();
public static void main(String[] args) {
System.out.println("Synchronized methods test:");
final SynchTest synchtest = new SynchTest();
new Thread(new Runnable() {
public void run() {
synchtest.display();
}).start();
new Thread(new Runnable() {
public void run() {
synchtest.update();
}).start();
Output:
Synchronized methods test:
start display:
start update:end update:
end display:the synchronized method obtain the lock from the current instance while static synchronized method obtain the lock from the class
Below is some code for u to have better understanding
package facado.collab;
public class TestSync {
public synchronized void add() {
System.out.println("TestSync.add()");
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
System.out.println("TestSync.add() - end");
public synchronized void update() {
System.out.println("TestSync.update()");
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
System.out.println("TestSync.update() - end");
public static synchronized void staticAdd() {
System.out.println("TestSync.staticAdd()");
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
System.out.println("TestSync.staticAdd() - end");
public static synchronized void staticUpdate() {
System.out.println("TestSync.staticUpdate()");
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
System.out.println("TestSync.staticUpdate() - end");
public static void main(String[] args) {
final TestSync sync1 = new TestSync();
final TestSync sync2 = new TestSync();
new Thread(new Runnable(){
public void run() {
sync1.add();
}).start();
new Thread(new Runnable(){
public void run() {
sync2.update();
}).start();
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
new Thread(new Runnable(){
public void run() {
sync1.staticAdd();
}).start();
new Thread(new Runnable(){
public void run() {
sync2.staticUpdate();
}).start();
} -
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Inside my run method I'm calling a synchronized method which in turn calls other synchronized methods of the same and another class.
Now if the top level method is synchronized, does the need to make other methods synchronized still remain ?
Won't the other threads wait till the thread using the top level synchronized method returns.
VikWell, if you can be sure that the second method is not going to be called some other way except within that first synchronized method, then no it's not needed.
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Is it possible to add bookmarks to a PDF file with Adobe Reader for iOS?
In the App Store write-up on this app, it said that one could "Use bookmarks to jump directly to a section in your PDF file." But I don't see how one can add such bookmarks. Do they only mean that you can use bookmarks that were already in the docu
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To change the Purchase order header and line item text
Hi everybody, I need to upload the PO Header and item text for the combinaion of PO and a material. Please help???
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How to restore session item values
Hi, We have a request form which has more than 50 fields and some hidden items which are calculated depending on other items. We have to implement SAVE request feature so that the user can save their partially filled request. We are storing these fie
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Best practices for defining Environment Variables/User Accounts in Linux
Hello, After reading throught the Quick Install guide for 10gR2 on x86_64 Linux, I see that it is not recommended to define ANY variables in .bash_profile. I'm hoping to get a Best practices approach for defining environment variables - right now we