thread-safety

问题 My Rails 3.1 app uses an engine and I want to know if access to this engine is threadsafe. I have /lib/mymodule.rb in the engine and it looks something like this: module MyModule def self.my_method() begin data = WebResource.find(:all) # Where WebResource < ActiveResource::Base rescue data = nil end return data end end Then in my views/controllers, I call this method like this: MyModule::WebResource.headers[:some_id] = cookies[:some_id] MyModule::my_method() In my main app, I have the

问题 I have written a method which should only be called on a particular thread. Is there a standard annotation or note which should be added to the method's javadoc to denote this? 回答1: Don't know of any such standard annotations. Java Concurrency in Practice deals with the question in its section 4.5: Documenting Synchronization Policies . A few hints which hopefully help you make your documentation clear and useful: At the very least, document the thread safety guarantees made by a class. Is it

问题 In the following code (copied from Java Concurrency in Practice Chapter 2, section 2.5, Listing 2.8): @ThreadSafe public class CachedFactorizer implements Servlet { @GuardedBy("this") private BigInteger lastNumber; @GuardedBy("this") private BigInteger[] lastFactors; @GuardedBy("this") private long hits; @GuardedBy("this") private long cacheHits; public synchronized long getHits() { return hits; } public synchronized double getCacheHitRatio() { return (double) cacheHits / (double) hits; }

问题 In the following code (copied from Java Concurrency in Practice Chapter 2, section 2.5, Listing 2.8): @ThreadSafe public class CachedFactorizer implements Servlet { @GuardedBy("this") private BigInteger lastNumber; @GuardedBy("this") private BigInteger[] lastFactors; @GuardedBy("this") private long hits; @GuardedBy("this") private long cacheHits; public synchronized long getHits() { return hits; } public synchronized double getCacheHitRatio() { return (double) cacheHits / (double) hits; }

问题 I was going through the source code of java.util.concurrent.atomic.AtomicInteger to find out how atomicity is achieved by the atomic operations provided by the class. For instance AtomicInteger.getAndIncrement() method source is as follows public final int getAndIncrement() { for (;;) { int current = get(); int next = current + 1; if (compareAndSet(current, next)) return current; } } I am not able to understand the purpose of writing the sequence of operations inside a infinite for loop. Does

问题 In a single-threaded application I use code like this: Interface function GetNextUID : integer; Implementation function GetNextUID : integer; const cUID : integer = 0; begin inc( cUID ); result := cUID; end; This could of course be implemented as a singleton object, etc. - I'm just giving the simplest possible example. Q: How can I modify this function (or design a class) to achieve the same result safely from concurrent threads? 回答1: You can use the Interlocked* functions: function

问题 I have an application that I need to have wait a specific amount of time, but I also need to be able to cancel the current operation if needed. I have the following code: private void waitTimer(int days) { TimeSpan waitTime = TimeSpan.FromDays(days); System.Timers.Timer timer = new System.Timers.Timer(waitTime.TotalMilliseconds); // Wait for some number of milliseconds timer.Enabled = true; timer.Start(); timer.Elapsed += new ElapsedEventHandler(OnTimedEvent); // Subscribe to event handler

问题 I'm writing a Tomcat application which need to maintain some internal states across different requests, so I need share something between different threads created by Tomcat. My question is, if I write code like this, will Map (which is static to the class) be shared between threads created by Tomcat. public class sessionManager extends HttpServlet { private static HashMap<Integer, String> Map; protected void doPost(HttpServletRequest request, HttpServletResponse response) throws

问题 I understood that calling boost::asio::ip::tcp::socket::async_receive (or boost::asio::ip::tcp::socket::async_send ) two times may result in a bad behavior.. Is it OK if i call boost::asio::ip::tcp::socket::async_recive and boost::asio::ip::tcp::socket::async_send at the same time? I am going to have 2 or more threads running the boost::asio::run so you need to take that into account.. Thanks 回答1: This has to be OK. How else would you perform full duplex async communications on a single

问题 I recently wrote up a simple Twitter app for Android to learn the ropes of the Twitter API and OAuth. The app's main activity simply asks for a username to follow. It then calls another activity which handles the OAuth & Twitter API calls. It redirects the user to an authorization page, which then returns to the app after the user finishes. It used to work just fine, but now for some reason when I call webview.loadUrl(authorizationURL), NOTHING happens. I never changed anything that would