wait

A thread can use Object.wait() to block until another thread calls notify() or notifyAll() on that object. But what if a thread wants to wait until one of multiple objects is signaled? For example, my thread must wait until either a) bytes become available to read from an InputStream or b) an item is added to an ArrayList . How can the thread wait for either of these events to occur? EDIT This question deals with waiting for multiple threads to complete -- my case involves a thread waiting for one of many objects to be singnaled. sgokhales A thread cannot wait on more than one object at a time

I am trying to scrape a few dynamic websites using Splash for Scrapy in python. However, I see that Splash fails to wait for the complete page to load in certain cases. A brute force way to tackle this problem was to add a large wait time (eg. 5 seconds in the below snippet). However, this is extremely inefficient and still fails to load certain data (sometimes it take longer than 5 seconds to load the content). Is there some sort of a wait-for-element condition that can be put through these requests? yield SplashRequest( url, self.parse, args={'wait': 5}, 'User-Agent':"Mozilla/5.0 (X11; Linux

I have a program that uses fork() to create a child process. I have seen various examples that use wait() to wait for the child process to end before closing, but I am wondering what I can do to simply check if the file process is still running. I basically have an infinite loop and I want to do something like: if(child process has ended) break; How could I go about doing this? Use waitpid() with the WNOHANG option. int status; pid_t result = waitpid(ChildPID, &status, WNOHANG); if (result == 0) { // Child still alive } else if (result == -1) { // Error } else { // Child exited } EDIT: If you

During the start of my windows application, I have to make a call to a web service to retrieve some default data to load onto my application. During the load of the form, I run a backgroundworker to retrieve this data. I want to display the wait cursor until this data is retrieved. How would I do this? I've tried setting the wait cursor before calling the backgroundworker to run. When I report a progress of 100 then I set it back to the default cursor. The wait cursor comes up but when I move the mouse it disappears. Environment: Windows 7 Pro 64-bit VS2010 C# .NET 4.0 Windows Forms EDIT: I am

简单的说，notify()只唤醒一个正在等待的线程，当该线程执行完以后施放该对象的锁，而没有再次执行notify()方法，则其它正在等待的线程 则一直处于等待状态，不会被唤醒而进入该对象的锁的竞争池，就会发生死锁。 JVM多个线程间的通信是通过 线程的锁、条件语句、以及wait（）、notify()/notifyAll组成。 下面来实现一个启用多个线程来循环的输出两个不同的语句: package com.tyxh.block; class OutTurn { private boolean isSub = true; private int count = 0; public synchronized void sub() { try { while (!isSub ) { this.wait(); } System. out .println("sub ---- " + count); isSub = false ; this.notify(); } catch (Exception e) { e.printStackTrace(); } count++; } public synchronized void main() { try { while (isSub ) { this.wait(); } System. out .println("main ((((((((((((

Every Java Object has the methods wait() and notify() (and additional variants). I have never used these and I suspect many others haven't. Why are these so fundamental that every object has to have them and is there a performance hit in having them (presumably some state is stored in them)? EDIT to emphasize the question. If I have a List<Double> with 100,000 elements then every Double has these methods as it is extended from Object . But it seems unlikely that all of these have to know about the threads that manage the List . EDIT excellent and useful answers. @Jon has a very good blog post