synchronization

I get following error when trying to do invoke notifyAll() inside a synchronized statement: Invoked Object.notify() outside synchronized context. Example: final List list = new ArrayList(); synchronized(list) {..... invoked notifyAll() here}; You can only call wait() , notify() , and notifyAll() on the object that is being synchronized on: synchronized (list) { //... list.notifyAll(); } In other words, the calling thread must own the object's monitor. If, inside synchronized (list) , you call notifyAll() , you are actually calling notifyAll() on this rather than list . My guess is that you are

When a synchronized method is completed, will it push only the data modified by it to main memory, or all the member variables, similarly when a synchronized method executes, will it read only the data it needs from main memory or will it clear all the member variables in the cache and read their values from main memory ? For example public class SharedData { int a; int b; int c; int d; public SharedData() { a = b = c = d = 10; } public synchronized void compute() { a = b * 20; b = a + 10; } public synchronized int getResult() { return b*c; } } In the above code assume compute is executed by

I'm trying to use a shared string variable between my Python processes, but it seems that I'm doing something wrong since I'm getting coredumps and invalid memory values. I use multiprocessing.Value to create a ctypes.c_char_p value and use the value attribute to access it. In my understanding of the Python docs the value attribute should be synchronized, as long it is an instance of Value (contrary of an instance of RawValue ). Is that correct so far? I've created a short example to demonstrate my use of Value and to show the inconsistency while executing: from multiprocessing import Process,

I have a native method method defined like this: public static native int doSomething(); However, this method is not thread-safe. So, I put a synchronized keyword on it, so it looks like this now: public static synchronized native int doSomething(); This appears to fix the problem, but I'm not sure if it actually does. Is this valid? Does it actually properly lock access to the method? After reading the relevant JLS section , there is nothing in the JLS which prohibits static and native from being in the method definition. According to the relevant JVM spec: Method-level synchronization is

I attended an interview and I was asked to design a class for the following requirement. Assume I have a class A and it can have any number of children, i.e., subclasses. The class A has a method called doSomething() which is synchronized. The requirements are : It is mandatory that all subclasses of A override the doSomething() method. All subclasses' overriden doSomething() method must be Thread safe in nature. All subclasses' must have the provision to implement their own logic for their doSomething() method implementations. Class A's constructor is upto me (the designer) to decide how to

I recently learned "Spurious wakeups" Any people say that this problem possible only for some types of Linux PC. I use windows. I wrote test for Spurious wakeups. I got result that it is possible. But I want to show this test for you. Maybe I made mistake somewhere. my initial variant: import java.util.Random; import java.util.concurrent.*; import java.util.concurrent.atomic.AtomicInteger; public class TestSpuriousWakeups { static final int MAX_THREADS = 600; static final Object mutex = new Object(); static final CountDownLatch allThreadsStarted = new CountDownLatch(MAX_THREADS); static final

I recently encountered a class on our code base that extends HashMap and synchronizes the put method. Aside from it being less efficient than using ConcurrentHashMap, what sort of problems may arise with extending HashMap and synchronizing only put(K,V)? Assume that we don't care whether get(K) returns the latest value or not(e.g. we are fine with threads overwriting each other and we don't care about the possible race conditions that may arise if the values of the map are used as locks themselves). Example: public class MyMap<K,V> extends HashMap<K,V> { //... public synchronized void put(K