concurrency

问题 I have got a concurrent queue with dispatch barrier from Raywenderlich post Example private let concurrentPhotoQueue = DispatchQueue(label: "com.raywenderlich.GooglyPuff.photoQueue", attributes: .concurrent) Where write operations is done in func addPhoto(_ photo: Photo) { concurrentPhotoQueue.async(flags: .barrier) { [weak self] in // 1 guard let self = self else { return } // 2 self.unsafePhotos.append(photo) // 3 DispatchQueue.main.async { [weak self] in self?.postContentAddedNotification(

问题 The task I have in hand is to read the lines of large file, process them, and return ordered results. My algorithm is: start with master process that will evaluate the workload (written in the first line of the file) spawn worker processes: each worker will read part of the file using pread/3, process this part, and send results to master master receives all sub-results, sort, and return so basically no communication needed between workers. My questions: How to find the optimal balance

问题 I have built a Ecommerce Backend in Nodejs(Express), Lets say there a product and only 1 quantity is left and two users are trying to buy that product at the same time both are getting that product leaving minus value in the quantity section of my Mysql Db How to get rid of this , Suggestions will be helpful Thank you 回答1: Database Transaction Isolation Levels This can be accomplished in your database by leveraging guarantees from your specific DB (mysql). The default isolation level for

问题 I have built a Ecommerce Backend in Nodejs(Express), Lets say there a product and only 1 quantity is left and two users are trying to buy that product at the same time both are getting that product leaving minus value in the quantity section of my Mysql Db How to get rid of this , Suggestions will be helpful Thank you 回答1: Database Transaction Isolation Levels This can be accomplished in your database by leveraging guarantees from your specific DB (mysql). The default isolation level for

问题 I have built a Ecommerce Backend in Nodejs(Express), Lets say there a product and only 1 quantity is left and two users are trying to buy that product at the same time both are getting that product leaving minus value in the quantity section of my Mysql Db How to get rid of this , Suggestions will be helpful Thank you 回答1: Database Transaction Isolation Levels This can be accomplished in your database by leveraging guarantees from your specific DB (mysql). The default isolation level for

问题 For some reason I am confused over the following: Assume that I have Thread A that absolutely needs to execute after Thread B has completed its processing. A way to do this would be by Thread A joining Thread B . Trivial example: public class MainThread { public static void main(String[] args){ Thread b = new Thread (new SomeRunnable(args[0])); b.start(); try { b.join(); } catch(InteruptedException e) { } // Go on with processing } } My question is the following: What is the proper way to

问题 Does the following variable, x, need to be volatile? Or does the manipulation within a utils.concurrent lock perform the same function as a synchronized block (ensuring it's written to memory, and not stored in cpu cache)? myMethod(){ myLock.lock(); x++; myLock.unlock(); } 回答1: Such variables only need to be volatile if they're accessed elsewhere without a lock. For example, as a fast read-only access to a size variable. The lock methods do serve the same purpose as a synchronized block. See

问题 I am trying to design a class as a Code Kata for myself that has a value property that can be set, and the class can issue ValueListener instances. The idea is that there is one instance of ValueHolder with many client threads accessing it concurrently. Each client thread has requested a ValueWatcher and has called waitForValue(). What I am really struggling with is what condition I should use on the while loop around the wait() to avoid spurious notifications (i.e. value hasn't changed). I

问题 I have a situation where I am making several (say four) ajax calls (using AngularJS http get, if that matters) and I want each call to callback and increment a counter, so I can know when all (four) of the threads have completed. My concern is that since JavaScript does not have anything comparable to Java's "synchronized" or "volatile" keywords, that it would be possible for multiple concurrent threads to collide while incrementing a counter, thereby missing some increments. In other words,

问题 Can someone provide real-life example of std::this_thread::yield() usage in c++ application? 回答1: I used yield in the implementation of std::lock, found here: http://llvm.org/svn/llvm-project/libcxx/trunk/include/mutex It turns out that when locking multiple locks/mutexes at a time, when you fail to get one, you can make the application faster by using yield prior to trying the locks/mutexes in a different order. In this source code I'm actually calling sched_yield() . But that is only for