It's a bit inefficient. If you need to synchronize on the x.y Class object, and you know the name at compile time, a better way is synchronized (x.y.class) { // whatever } The .class notation incidates a class literal. I'd usually only use Class.forName() if the name is a variable, not known at compile time. The other part of the question ... |
Ellen, are you sure this code will deadlock? Assuming this is the only method that synchronizes on monitor, A, and B, I don't think it will deadlock. This is the kind of nested synchronization that will definitely deadlock: method 1: lock A lock B method 2: lock B lock A Only where the order of nested lock acquisition is different do ... |
I have discussed this problem with people but they all seem quite confused about it. Can any one help me? // position a synchronized void A() { <-- method // position b B(); } synchronized void B() { <-- method // position c C(); } synchronized void C() { } <-- method synchronized void D() { <-- method C(); } There ... |
Hi Would someone confirm that this block of code doesn't really serve any purpose? public MyConnection getConnection() throws IOException { int attempts=0; MyConnection c = null; Object sync = new Object(); while (c == null && _maxConnectionRetries > attempts) { c = doGetConnection(); if (c == null) { synchronized(sync) { try { sync.wait(100); } catch (InterruptedException e) { // Ignore. } ... |
HI, I got question about the synchronized method. class A { synchronized void m1() { } synchronized void m2() { } } supposing two threads t1 and t2 have the same instance of A (a). t1 is calling a.m1() and t2 is calling a.m2(). My question is what would the behavior of t2 like when it calls m2 method and can't ... |
Let's say I've the following code segments: [a] public boolean synchronized update1(Object any) { // perform update of any and return success or failure if(condition is true) return true else return false } [b] public boolean synchronized update2(Object any) { //do something synchronized(privateObj) { return SomeMethod(); } //do the rest } In case of [a] what will happen if some thread ... |
Hi everybody, Acually I have a problem with threads .Im using a jsp page and a part of my code uses static variables.So this jsp page is used by many and its locking the page.So I used a synchronized block in this context. synchronized(this){static variables shared by many users }.Is this solution ok.Or do I need to used synchronized variables.Please let ... |
|
Originally posted by Ashish Agrawal: As much as i know we can only synchronize method (instance methods and static methods). I think you are looking for a synchronized block: public class SomeClass{ public void someMethod(){ // . . . synchronized(this){ // critical section } // . . . } } If you synchronize a number of critical sections on the "this" ... |
That probably depends on what class modifyBalance() is in. If it's in a Teller class, then synchronizing on the Teller won't help you much - because two different Tellers will still be able to acto concurrently, and that's the problem in this case - you don't want them accessing the Balance simultaneously. But if modifyBalance() is in the Balance class, then ... |
Hi, I have a delete method that has to be executed first , before I call the method that inserts. The delete method (deletes in batches of 2000)and waits. The problem was that when I run the program, my delete method was not executed fully and when I called the batch inserts method I had a problem, because the delete did ... |
Hi. assume that I have one database server, and many swing desktop clients connected to that server (I don't want to use a server btw the database and the swing apps). now, these swing apps may add values or update some values (when the user click on a jbutton). the question is, where to put the synchronize keyword in my application ... |
|
Originally posted by Rstem e Zal: EX1 [...] HERE, i think BOTH Methods must be synchronized. Yes; alternatively, you could declare the field x "volatile". Characters are read and written atomically. another [...]BUT Here, I think only the setter method should be synchronized [...] Am I right? No. The second code snippet is a good example of a class that cannot ... |
I have some problem in getting digest value. printDigest() below is called in my servlet (doGet). it works perfectly by printing correct digest value. but there is some broblem when I fired 30 requests using Jmeter to access doGet concurrently. some results I got is not correct value. but when I did synchronized printDigest method it returns correct result. I wonder ... |
Hi, Lemme explain with the following scenario, for proof I'll also attach code with it. Let objA be an object with two methods: 1. public void call(String callerThreadName) 2. public synchronized void callSync(String callerThreadName) Let C1 & C2 be two threads that have access to objA. If C1 accesses objA via the synchronized method, C2 can still call the unsynchronized method ... |
|
I do believe that when you lock an object using the sychronized(objname) syntax , it just prevents other threads from locking on it. Threads do not have to lock on to an object to alter it and this may cause trouble. For the first one, why don't you try it. Make a sychrnoized method that keeps printing out "sych" and an ... |
I'm not sure that you will. If you call a method that happens to be synchronized your thread will block - sit there doing nothing but waiting - until it can get the lock. Your calling method might observe that the call is taking a long time but I think that's about it. Do you have a requirement to know more ... |
Originally posted by David Ulicny: Does the synchronized keyword any impact on performance? Yes... we actually spend a whole chapter on performance. And a large part of it is on synchronization. Basically, there are two impacts on performance due to synchronization. First, is the cost to execute the synchronization primatives. And second, the blocking of the thread because of the synchronization. ... |
I have a threadded server application. Once my server accepts a connection, a thread is started to work on the client data, while the server returns to accept futher connections. This is working pretty well... until yesterday, that is. I needed to modify my "worker" thread. It now has included a class that is not threaded and needs to invoke one ... |
|
Hello everyone, Suppose I have a method which is a synchronized method (for example, method Foo in the following code block), and in this synchronized method another method which is not synchronized is invoked (for example, method Goo in the following code block). I am wondering when executing in Goo from Foo, whether we still have the synchronized feature (i.e. obtain ... |
|
i had study the theme about Thread class some weeks with the book Oreilly Java Threads 2nd Edition Scott Oaks & Henry Wong hence very good, i worked the chapther 3 about syncronization techniques, all good, but exists a doubt that not able sleep. Exactly in the keyword synchronized, the book says that exists syncronization in methods and in a block ... |
Hi there I ask myself if method of an abstract base class is unique when called from different instances. Let me explain: I have abstract base class that has a method (not a static one, a simple instance method). Now I have a implementation class of this abstract base class that has a lot of instances. Now these instances all call ... |
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - ... |
|
Hi all, I am having a multithreaded application which involves access of one static method which would generate unique id against a particular variable. This id is selected from database table and an incremented id is stored in table for next thread. Not the problem is, when two threads are simultaneously accessing this mehthod this gives out same code for both ... |
The synchronized keyword simply acquires the monitor for some object. For example: synchronized (anObject) { } will acquire the monitor for anObject. If another thread already has the monitor it will have to wait for that thread to finish before it can acquire it and proceed. Any piece of code that synchronizes on a common object will not be able to ... |
Hi all, Java.util.Vector is a synchronized class. I checked the syntax of all methods in Vector class, but no method signature include synchronized keyword. My question is how can we create a synchronized class? In synchronized class wheather class is synchronized or both class and all methods are synchronized? Thanks in advance. Subbarao |
Not quite sure what you mean. If you mean that you do not want to declare the whole method as synchronised, then there are alternatives. You can use a synchronised block within the method. The advantage of that approach is that you can choose whatever object you like for the monitor, whereas a synchronised method always uses "this". If you mean ... |
class Buffer2 { private int value; private boolean isEmpty = true; synchronized void put(int i) { while (!isEmpty) { try { this.wait(); } catch(InterruptedException e) { System.out.println(e.getMessage()); } } value = i; isEmpty = false; notify(); } synchronized int get() { while (isEmpty) { try { this.wait(); } catch(InterruptedException e) { System.out.println(e.getMessage()); } } isEmpty = true; notify(); return value; } ... |
i have created one application in which i have created 10 classes(from Class1,Class2........Class10)...in one class i have used Synchronized block Class1 class1 = new Class1( ); synchronized(class1){ //Statements ..} this block will acquire lock for Class1 class. i.e, no body can call Class1 class methods or update instance variables until Synchronized block finishes its job.. This is *not* true. Acquiring a ... |
|
|
Hi, I'm just starting with threads, using Head First Java. I tried to code the Ryan and Monica example (Ryan and Monica both withdraw $10 at a time from their joint bank account...) and everything went swimmingly until I tried to put in a synchronized block to avoid overdrafts. If this works correctly, the total amount withdrawn should always be $100 ... |
A question for the real profis. When a thread enters a synchronized method (or block) and locks the object, what happens when a non-synchronized method is called within this synchronized block? Does the thread give ups its lock? Or does it wait until leaving the synchronized method (or block)? In other words, are non-synchronized methods only non-synchronized when called directly, but ... |
Hi all, I would like to know whether a class can be synchronized or not !!! plz provide some info as this was asked in an interview..plz provide me some examples.. Waiting for ur coments,and suggestions... [EFH: One question mark in the subject is plenty, thanks. ] [ July 19, 2006: Message edited by: Ernest Friedman-Hill ] |
Originally posted by Shrawan Bhageria: Hi all, Please clear this. If 2 different threads hit 2 different synchronized methods in an object at the same time will they both continue? Thanks in advance. Regards, Shrawan Synchronization is based on Objects -- they acquire locks specific to the object. If neither method is static and they both call methods on the same ... |
Hi All, Please go through the code block given below. Can somebody expalin the difference between these code blocks. Thanks in advace Anupam ********************************************************************* public void waitForStop() { Object monitor = new Object(); while (true) { synchronized (monitor) { try { monitor.wait(); } catch (InterruptedException e) { break; } } } } class pqr extends Thread { public void run () ... |
|
Is it absolutely necessary to synchronize methods that return (read) primitive values, e.g. ints, longs, etc? I used to not think so but then I re-read the Java Tutorial on Synchronized Methods this morning and it seems to indicate that you should. I had always thought that, if I declared my setter methods synchronized thereby locking the object, I could avoid ... |
I have a problem with my code. I have a class Counter with count variable and the class includes 2 method * add() method to implement count = count+2; * sub() method to implement count = count -1; and.... public class Counter implements Runnable { private static int count = 100; private boolean isAdd = false; private String name; public Counter(boolean ... |
|
Frnds, I have a small confusion on Thread synchronization. When you have synchronized method, basically it acquires the lock for the object and releases it when it is done. Today I ran a sample test program for threads. I have a class named Test with two methods(one synchronized and one non-synchronized method). In my program I am creating two threads and ... |
Sridhar, Synchronization is to manage access to data from multiple threads. Some classic example is web hit counter, where you have 1 object that keep track of the number of visits but you have multiple threads of request/servlet which tries to increment the same instance of the counter object. The example that you have is not working because each test has ... |
Hi, I'm trying to loop and print the twice however the output for the following code, is printed thrice, as: Output: run-single: 0 1 Thread[Thread-0,5,main] A B C Thread[Thread-1,5,main] A B C A B C BUILD SUCCESSFUL (total time: 0 seconds) Code: public class Test126 { /** Creates a new instance of Test126 */ public Test126() { } private List names ... |
Can a thread call a non-synchronized instance method of an Object when a synchronized method is being executed ? I am having difficulty understanding this synchronization stuff. Assume if a Class has two methods - method1 is synchronized instance method - method2 is a regualr instance method So in this scenario, can there be two threads calling these two methods in ... |
Your query is prone to ambiguous interpretation . What exactly do you mean by 'class synchronization'? If you mean synchronizing on the class object of some class,then yes. As for the need,well it could be for preventing race conditions arising out of multiple threads concurrently trying to access the static variables of a class. |
|
I have a question concerning the use of a synchronized method by two different objects. I have tried searching the forums for a similar question, but I wasn't able to find anything. If this question has already been answered, then a simple link to that thread would be great. Thanks in advance for any help. The code examples come from the ... |
Is there a technical explanation as to why Throwable.initCause is synchronized when Throwable.getCause and the constructor Throwable.Throwable(Throwable cause) aren't? I am considering the memory model for java 1.4. I mean, what use is it that initCause is synchronized when getCause isn't? Even though one thread calls initCause, and the cause field is flushed to shared memory because of synchronization, there is ... |
|
|
|
I have a class: pulic class TestSynchronization { public void method1() { } public synchronized method2() { } } Now if multiple request at the same time tries to request method2() at the same time. Now as the method is synchronized one one thread would be allowed and others had to wait. In the mean same time if another request comes ... |
I have written this interface, public interface MandateSync { public synchronized void doXXX(); } On compiling it we get the following error, MandateSync.java:3: modifier synchronized not allowed here public synchronized void doXXX(); Why is synchronized not allowed there? Also is there any other way to get around tht? So tht the implementor of this interface always write a synchronized API. Thanks, ... |
The synchronized part is in reference to iterating through the collection. If while iterating the Vector has an entry added or removed, the iterator will through a ConcurrentModificationException. You can have multiple threads call get or add on the Vector without issue as long as you are not iterating through it. From the API: The Iterators returned by Vector's iterator and ... |
|
Note that a method declared in an interface must not be declared strictfp or native or synchronized, or a compile-time error occurs, because those keywords describe implementation properties rather than interface properties. However, a method declared in an interface may be implemented by a method that is declared strictfp or native or synchronized in a class that implements the interface. |
|
Hi Shubha....what are trying to accomplish with this? If you want all actions of the class to be locked in a single thread, then just modify all public methods of the class with synchronized. If you want a single instance of the class to be shared accross all other objects in your system, then declare the constructor protected and use static ... |
I have code that includes a line which runs a shell script (a .bat file on AIX). The output from this .bat file is incorrect unless the code is delayed before the line that runs the shell script. For example, the 'sleep' method or a statement that writes to a log needs to be applied first to slow down the code ... |
Can two threads call two different synchronized instance methods of an Object? I am still not sure on this, If I have two different methods in a object and two different threads are calling them.....is it possible? Not sure if I understood the question right.... but looks like really fundamental question. Please provide your suggestions and pointers... |
|
Synchronized is not a return type, it is a modifier saying that a Thread calling this method obtains a lock, causing all other Threads trying to access that object's synchronized methods to wait until the current thread is done. Do a search on "synchronized" for more information, or read any Java book you have available to you. Jason |
|
If it reads fields that might get changed in other threads, you need to synchronize the method, too. That is because threads are allowed to make copies of the variables they use, so you are only guaranteed to work with the current data if the access is synchronized (or the field is volatile and access atomic). |
You can use synchronized methods in both server-side and fat client applications. The main purpose of synchronized methods is to prevent multiple threads from modifying an objects state simultaneously. Synchronizing your methods does add some extra overhead (time needed to obtain and release object locks). Therefore you should usually synchronize only those critical code blocks. For example: Instead of doing public ... |
Hi Taha, Welcome to JavaRanch. Java is a multi-threaded language, which means that in a single application you can have many threads of execution running at the same time. Let's say you have a class which has a reference to some object which can be changed when certain methods are called. What do you think would happen to that object if ... |
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - ... |
Please help me with the following quizz. ---------------------------------- A Java Program uses four threads. The first three threads each read a text file and count the number of times that a given word is used in the text file. The words which are to be counted are provided on a command line as shown when the execution of the program is ... |
Q. Here we have a CallMe class which have a call method,another class Caller implementing Runnable interface , it has a String variable.In main class three Threads have been created & initialised to different strings, now the run method creates objects of CallMe class & call method -> call which is synchronized but it is not working in a synchronized way.As ... |
there are two synchronized methods,s1 and s2 in the same class and two threads t1 and t2 in the same class.now t1 is inside method s1 and t2 wants to execute s2.Will it be able to able to execute s2. One more thing,is there one lock per class or one lock per method for our case? |
Hello All, Good Day... I have a question to ask regarding the following class that I am reading. class ThreadMonitor extends Thread { public ThreadMonitor (String strName) { super(strName); } synchronized public void run() { //Question here try { /*more code here */ } } catch (Exception e) { } } } From what I have understand the run method of ... |
|
|
|
Hi Friends, Need to know if a class (say class A) has two 'synchronized' methods, then is it possible to access each of these 'synchronized' methods by two separate object(say instance of class B and class C) ? As per theory in java: Every Class has a Lock. Every Instance has a Lock. Every Object has a Lock. (am not sure ... |
|
|
|
I am using a method from a class, which has been written by someone else Part of the method is synchronized. However, the part within the synchronized portion does the actual job for which the method has been called. The block has been synchronized on this. However, as many times I call the method, the executing thread fails to acquire lock ... |
|
Hi all, I have a chunk of code that I'm synchronizing, however it throws a NPE once in a while. private final ConcurrentHashMap queues; queues = new ConcurrentHashMap(); //more code List list = queues.remove(session.getSessionId()); synchronized (list) { if (logger.isDebugEnabled()) { logger.debug("Waking up threads waiting for notifications to be queued"); } list.notifyAll(); } I could easily avoid the NPE by ... |
Hi, I can't understand the output of the following code: class MyThread implements Runnable { String currth; public void run() { currth = Thread.currentThread().getName(); System.out.println(currth + ": in run"); meth(); } synchronized void meth() { System.out.println(currth + ": about to sleep"); try { Thread.sleep(5000); } catch (InterruptedException ie) {} System.out.println(currth + ": dying"); } } class A { public static void ... |
|
public class TestArrayListSync extends Thread { ArrayList a = new ArrayList(); public static void main(String[] args) { TestArrayListSync a1 = new TestArrayListSync(); Thread t = new Thread(a1); t.start(); Thread t1 = new Thread(a1); t1.start(); } public void run() { synchronized (a) { adding(); removing(); for (Object o : a) { System.out.println(o); } } } public void adding() { System.out.println("Adding Executed by ... |
I could nt understand the following clearly.so i ask you another example Let's use a bank application program as an example. Assuming that the program has multiple threads running, with each thread connecting one ATM system, and you have a saving account in the bank with $100.00, now you and your friend are going to two different ATMs at about the ... |
|
public class deduct { /** Creates a new instance of deduct */ public void deductaccount (int amount) { if (account.total >= amount) { account.total -= amount; if (account.total<0){ /* try{ wait(); } catch (InterruptedException e){ } notifyAll(); System.out.println("success" + account.total); } //System.out.println("success" + total); } else {*/ System.out.println("ERROR"); System.exit(0); } } } } public class account implements Runnable { public static ... |
|
|
Hi , I ran the following code from the java tutorial on Concurrency. This code's objective is to implement 'deadlock'. public class Deadlock { static int status; static class Friend { private final String name; public Friend(String name) { this.name = name; } public String getName() { return this.name; } public synchronized void bow(Friend bower) { status = status + 1; ... |
|
From what I've just read, Transient is used for variable you wish to not be persisted in the sense of being serialized (where the variable is converted to a stream of bytes and stored to a file). The synchronized keyword protects code from being executed by more than one thread at a time. Protected is (I believe) used as a keyword ... |
Hello All, I'm trying to revise what I learned about Threads and trying with an example. I do not see my threads operating as expected ( dangerous word with respect to thread execution). I wanted to know, if my design is correct or wrong. Briefly, one thread is setting age of a person and another thread reading it. I do want ... |
Here are some things to try: Is this line the very first line in the stack trace you see? Is it possible that you're running from .class files that are older than the corresponding .java files? You can get weird results like this if you don't fully recompile your files after editing them. li hao wrote:I am quite sure Semphore object ... |
|
|