double-checked-locking

I'm new to PHP, so to get started I've decided to implement a singleton. While I am able to recreate the singleton pattern in php, but I am not sure how to implement double-checked locking. Is that even possible/needed in PHP. I have read somewhere that PHP is not multithreaded? Can someone confirm that? If it is multithreaded, can someone explain to me how lock() or synchronize() work in PHP? Thanks, Henry Alfred Share-nothing Architecture PHP has a Share-nothing Architecture : Like HTTP, each request is distinct Shared data is pushed down to the data-store layer Avoid front controllers This

I was reading this article about "Double-Checked locking" and out of the main topic of the article I was wondering why at some point of the article the author uses the next Idiom: Listing 7. Attempting to solve the out-of-order write problem public static Singleton getInstance() { if (instance == null) { synchronized(Singleton.class) { //1 Singleton inst = instance; //2 if (inst == null) { synchronized(Singleton.class) { //3 inst = new Singleton(); //4 } instance = inst; //5 } } } return instance; } And my question is: Is there any reason to synchronize twice some code with the same lock? Have

The fallowing clause is taken from jetbrains.net After reading this and some other articles on the web, I still don't understand how is it possible to return null, after the first thread go in to the lock. Some one that does understand it can please help me and explain it in more humanized way? "Consider the following piece of code: public class Foo { private static Foo instance; private static readonly object padlock = new object(); public static Foo Get() { if (instance == null) { lock (padlock) { if (instance == null) { instance = new Foo(); } } } return instance; } }; Given the above code,

I happened upon an article recently discussing the double checked locking pattern in Java and its pitfalls and now I'm wondering if a variant of that pattern that I've been using for years now is subject to any issues. I've looked at many posts and articles on the subject and understand the potential issues with getting a reference to a partially constructed object, and as far as I can tell, I don't think my implementation is subject to these issues. Are there any issues with the following pattern? And, if not, why don't people use it? I've never seen it recommended in any of the discussion I

I came across this article discussing why the double-check locking paradigm is broken in Java. Is the paradigm valid for .NET (in particular, C#), if variables are declared volatile ? Cameron MacFarland Implementing the Singleton Pattern in C# talks about this problem in the third version. It says: Making the instance variable volatile can make it work, as would explicit memory barrier calls, although in the latter case even experts can't agree exactly which barriers are required. I tend to try to avoid situations where experts don't agree what's right and what's wrong! The author seems to