thread-safety

问题 I'm seeing some strange behaviour when using stateless token-based authentication on a rest API written using Spring Boot. The client includes a JWT token with each request, and a custom filter I've written that extends GenericFilterBean adds an Authentication object based on the claims in the token to the security context using the following : SecurityContextHolder.getContext().setAuthentication(authentication); And clears the context after processing the request by doing :

问题 I'm working a lot with asynchronous workflows and agents in F#. While I was going a little bit deeper into events I noticed that the Event<_>() type is not thread-safe. Here I'm not talking about the common problem of raising an event. I'm actually talking about subscribing and removing/disposing from an event. For testing purposes, I have written this short program: let event = Event<int>() let sub = event.Publish [<EntryPoint>] let main argv = let subscribe sub x = async { let mutable

问题 I'm working on a huge system based on Asp.net MVC 3.0 and working on Mono-2.10.8 (Windows 7). Everything was fine until a moment couple of days ago. Inside my API I have several utility classes using dictionaries. For example, like this one: public static class KeyUtility { static KeyUtility() { Alphabet = new[] { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'R', 'S', 'T', 'U', 'V', 'X', 'Y', 'Z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' }; ReverseAlphabet =

问题 Apple says: Important: Instances of ABAddressBookRef can not be used by multiple threads. Each thread must make its own instance. But why? I know that some particular class or operations must be done in main thread. And I know some objects are not thread-safe (which means it would cause problem if these objects are accessed by two different threads concurrently). But, if you can make sure that the the thread-unsafe objects are accessed by only one thread at any moment, then there should be

问题 I am trying to make a producer/consumer thread situation more efficient by skipping expensive event operations if necessary with something like: //cas(variable, compare, set) is atomic compare and swap //queue is already lock free running = false // dd item to queue – producer thread(s) if(cas(running, false, true)) { // We effectively obtained a lock on signalling the event add_to_queue() signal_event() } else { // Most of the time if things are busy we should not be signalling the event add

问题 Is using the remove() method okay? I've read an article that synchronization hasn't been added to the remove method. How do I properly remove a specific item from a ConcurrentHashMap? Example Code: ConcurrentHashMap<String,Integer> storage = new ConcurrentHashMap<String,Integer>(); storage.put("First", 1); storage.put("Second", 2); storage.put("Third",3); //Is this the proper way of removing a specific item from a tread-safe collection? storage.remove("First"); for (Entry<String, Integer>

问题 I've got a relatively expensive data-fetching operation that I want to cache the results of. This operation is called from const methods, roughly like this: double AdjustData(double d, int key) const { double factor = LongRunningOperationToFetchFactor(key); return factor * d; } I'd like AdjustData to remain const , but I want to cache out the factor so I only fetch it the first time. At present I'm using a mutable map<int, double> to store the result (the map being from key to factor ), but I

问题 Suppose I have the following class: public class Foo { private List<Integer> list = Lists.newArrayList(1, 2, 3, 4, 5); private Iterator<Integer> iterator = Iterators.cycle(list); public void bar(){ Integer value = iterator.next(); doSomethingWithAnInteger(value); } } If an instance of Foo is acessed simultaneously by two threads, I need that each thread gets a different value from iterator.next() . Does the bar() method have to be made synchronized? Or is iterator.next() guaranteed to be

问题 Is there a race condition in the following code that could result in a NullReferenceException ? -- or -- Is it possible for the Callback variable to be set to null after the null coalescing operator checks for a null value but before the function is invoked? class MyClass { public Action Callback { get; set; } public void DoCallback() { (Callback ?? new Action(() => { }))(); } } EDIT This is a question that arose out of curiosity. I don't normally code this way. I'm not worried about the

问题 I have written a timer which will measure the performance of a particular code in any multithreaded application. In the below timer, it will also populate the map with how many calls took x milliseconds. I will use this map as part of my histogram to do further analysis, like what percentage of calls took this much milliseconds and etc. public static class StopWatch { public static ConcurrentHashMap<Long, Long> histogram = new ConcurrentHashMap<Long, Long>(); /** * Creates an instance of the