synchronization

问题 When I run the following code in from Python's multiprocessing module page: from multiprocessing import Process, Lock def f(l, i): l.acquire() print 'hello world', i l.release() if __name__ == '__main__': lock = Lock() for num in range(10): Process(target=f, args=(lock, num)).start() Sometimes I get unordered output such as: hello world 0 hello world 1 hello world 2 hello world 4 hello world 3 hello world 6 hello world 5 hello world 7 hello world 8 hello world 9 Note that 4 is printed before

问题 When I run the following code in from Python's multiprocessing module page: from multiprocessing import Process, Lock def f(l, i): l.acquire() print 'hello world', i l.release() if __name__ == '__main__': lock = Lock() for num in range(10): Process(target=f, args=(lock, num)).start() Sometimes I get unordered output such as: hello world 0 hello world 1 hello world 2 hello world 4 hello world 3 hello world 6 hello world 5 hello world 7 hello world 8 hello world 9 Note that 4 is printed before

问题 It is a follow up question of Shared_ptr and Memory Visibility in c++ and Create object in thread A, use in thread B. Mutex required?. This question is more about memory visibility rather than data race. In Java, I have: ExecutorService executor = Executors.newSingleThreadExecutor(); Integer i = new Integer(5); // no write to i afterwards executor.submit(() -> { System.out.println(i); }); I don't think this is thread-safe. Because there is no need to put value 5 in the main memory, it could

问题 Am I right in saying that a deadlock is supposed to happen in the following case: Object P calls a synch method of object A , that calls a synch method of object B , that calls a synch method of object A . Sorry if it looks stupid of me, most probably it is. But that's why I'm asking. Thanks! 回答1: By the information you give - no, a deadlock can't occur: First, you don't mention multiple threads. A single thread can't cause a deadlock. But let's assume you have multiple threads. So, if any

问题 I need to populate my map with annotations. Each annotation has corresponding Place resource that is being fetched from remote server. Each Place has associated Category - it is fetched from the server too as a separate resource. Let's assume that to populate a given region I need to fetch 100 places, each belonging to the one of 20 categories (actually there are much more of them). I use AFNetworking to fetch the both of resources. I try to cache both places and categories for offline use,

问题 If you heap allocate an object with shared_ptr on thread A , then copy the shared_ptr to another thread without any synchronization. Is the other thread guaranteed to see a fully constructed object? int main(){ auto sp = std::make_shared<int>(5); auto f=std::async(std::launch::async, [sp](){ std::cout<<*sp;}); } Is it guaranteed to print 5? 回答1: In your example, the shared_ptr object has been duplicated before std::async returns, hence it still exists in the new thread even if the original

问题 I'm in the initial phase of designing an application that will have a backend implemented in C# that will provide data for other platforms using WCF web services hosted on IIS. One of the platforms will the the iPhone. Since it's a personal project, I want to use it to learn MongoDB. I already know that there are community developed drivers for MongoDB and C#, so I could handle the persistence on the server side using MongoDB. Without even knowing the replications models offered by MongoDB, I

问题 I need somebody with high skills in threading and event raising. I have an abstract class A and two concrete classes C1 , C2 (e.g plugins). Since I need them to communicate between each other, like "plugin-application" "plugin-plugin" communication, I have a method ExecuteCommand in the abstract class which should accomplish this. This function raises an event to the application in order to process a certain command and return the result (e.g if one plugin needs data from the app it calls

问题 Process A forks say 4 child processes. exec() is used to replace the code of the children. The children initialize and have to wait for the parent to create all of the 4 of them. Then the parent sends a sigusr1 to each child process in order for them to start processing. The parent waits for all the children to complete procesing. When a child finishes its work it sends a sigusr2 to the parent. When the parent receives all the sigusr2 signals it continues with execution, merging the

问题 We have a website running .NET 2.0 and have started using the ASP.Net HttpRuntime.Cache to store the results of frequent data lookups to cut down our database access. Snippet: lock (locker) { if (HttpRuntime.Cache[cacheKey] == null) { HttpRuntime.Cache.Insert(cacheKey, GetSomeDataToCache(), null, DateTime.Today.AddDays(1), Cache.NoSlidingExpiration); } return ((SomeData)HttpRuntime.Cache[cacheKey]).Copy(); } We are pessimistically locking whenever we want to look at the cache. However, I've