I use volatile fields when said field is ONLY UPDATED by its owner thread and the value is only read by other threads, you can think of it as a publish/subscribe scenario where there are many observers but only one publisher. However if those observers must perform some logic based on the value of the … Read more
When multiple threads need to check and change the boolean. For example: if (!initialized) { initialize(); initialized = true; } This is not thread-safe. You can fix it by using AtomicBoolean: if (atomicInitialized.compareAndSet(false, true)) { initialize(); }
Concurrent and parallel are effectively the same principle as you correctly surmise, both are related to tasks being executed simultaneously although I would say that parallel tasks should be truly multitasking, executed “at the same time” whereas concurrent could mean that the tasks are sharing the execution thread while still appearing to be executing in … Read more
What is the potential damage if it was possible to invoke wait() outside a synchronized block, retaining it’s semantics – suspending the caller thread? Let’s illustrate what issues we would run into if wait() could be called outside of a synchronized block with a concrete example. Suppose we were to implement a blocking queue (I … Read more
Updated with Jörg’s Sept 2011 comment You seem to be confusing two very different things here: the Ruby Programming Language and the specific threading model of one specific implementation of the Ruby Programming Language. There are currently around 11 different implementations of the Ruby Programming Language, with very different and unique threading models. (Unfortunately, only … Read more
While my perspective may be biased, my current intention for updating the book would be almost strictly additive, covering fork-join, parallel decomposition, and the new parallel bulk data operations coming in Java SE 8. EDIT 2020: … and Project Loom. EDIT 2021: … and Project Loom 🙂 EDIT 2022: … and Project Loom !
ConcurrentLinkedQueue If you don’t care about having index-based access and just want the insertion-order-preserving characteristics of a List, you could consider a java.util.concurrent.ConcurrentLinkedQueue. Since it implements Iterable, once you’ve finished adding all the items, you can loop over the contents using the enhanced for syntax: Queue<String> globalQueue = new ConcurrentLinkedQueue<String>(); //Multiple threads can safely call … Read more
(I’m not completely happy with the answers so far, so here is my attempt…) I think that Kevin Wright’s comment You can make a Promise and it’s up to you to keep it. When someone else makes you a promise you must wait to see if they honour it in the Future summarizes it pretty … Read more
Ok now I’ve done my research, here is the deal: In TDS protocol, SET NOCOUNT ON only saves 9-bytes per query while the text “SET NOCOUNT ON” itself is a whopping 14 bytes. I used to think that 123 row(s) affected was returned from server in plain text in a separate network packet but that’s … Read more
Twistedless solution: from urlparse import urlparse from threading import Thread import httplib, sys from Queue import Queue concurrent = 200 def doWork(): while True: url = q.get() status, url = getStatus(url) doSomethingWithResult(status, url) q.task_done() def getStatus(ourl): try: url = urlparse(ourl) conn = httplib.HTTPConnection(url.netloc) conn.request(“HEAD”, url.path) res = conn.getresponse() return res.status, ourl except: return “error”, ourl … Read more