atomicity

问题 I have a ConcurrentMap which I need to populate from multithread application. My map is shown below: private final ConcurrentMap<String, AtomicLongMap<String>> deviceErrorHolder = Maps.newConcurrentMap(); Below is my method which is called from multithreaded application at very fast rate so I need to make sure it is fast. public void addDeviceErrorStats(String deviceName, String errorName) { AtomicLongMap<String> errorMap = deviceErrorHolder.get(deviceName); if (errorMap == null) { errorMap =

问题 I've three models Question, Submission, UserResult. users submit an answer to a Question, this answer is scored by the system and stored in a Submission. The score of a user for one question is maximum amongst all of his/her submissions. This score is saved in a model called UserResult(it has three fields, a foreign key to Question, another to User and a score which is an integer) What I want to do is to make sure when a submission is saved the related UserResult is updated. Actually it's

问题 I'm wondering whether methods of PHPs SPLFileObject are atomic (e.g. thread-safe) or not? If they aren't, I'll implement my own class, which will use flock() , but is this enough? Is the flock function really thread-safe? What if the collision occurs after I fopen() the file, but before I flock() it? 回答1: I think you're misusing the term "thread-safe." Thread saftey is (mostly) about shared resources in threaded code. PHP doesn't have threading, and file handles aren't shared resources. Files

问题 I have an openmp parallel loop in C++ in which all the threads access a shared array of double. Each thread writes only in its own partition of the array. Two threads cannot write on the same array entry. Each thread read on partitions written by the other threads. It does not matter if the data has been updated by the thread who owns the partition or not, as soon as the double is either the old or the updated value (not an invalid value resulting from reading a half-written double). Do I

问题 Lets say I have an application that is writing to a boolean from one thread and reading from the same boolean from another thread. I don't care if my reading thread reads a stale value. Is this safe on all ARM cores and x86? I don't want to run into an issue were a partially written value is read by my reading thread. Follow up question: Which swift types have guaranteed atomic reads and writes on x86 and ARM? 来源： https://stackoverflow.com/questions/37932737/are-boolean-reads-and-writes

问题 OpenCL and CUDA have included atomic operations for several years now (although obviously not every CUDA or OpenCL device supports these). But - my question is about the possibility of "living with" races due to non-atomic writes. Suppose several threads in a grid all write to the same location in global memory. Are we guaranteed that, when kernel execution has concluded, the results of one of these writes will be present in that location, rather than some junk? Relevant parameters for this

问题 I have to synchronize access between threads to a shared object, whose state consists of several fields. Say: class Shared{ String a; Integer b; //constructor, getters and setters .... } I have possibly many threads reading this objects, doing //readers shared.getA(); shared.getB(); and only one thread that will write at a certain point: //writer shared.setA("state"); shared.setB(1); now my question is how to ensure that reading threads won't find the shared object in an inconsistent state. I

问题 As in the title, are read and write operations regarding uint8, atomic? Logically it must be a single cpu instruction obviously to read and write for a 8 bit variable. But in any case, two cores could simultaneously read and write from the memory, is it possible to create a stale data this way? 回答1: There's no guarantee that the access on native types are on any platform atomic. This is why there is sync/atomic. See also the advice in the memory model documentation. Example for generic way of

问题 I am trying to understand atomic and non atomic operations.With respect to Operating System and also with respect to C. As per the wikipedia page here Consider a simple counter which different processes can increment. Non-atomic The naive, non-atomic implementation: reads the value in the memory location; adds one to the value; writes the new value back into the memory location. Now, imagine two processes are running incrementing a single, shared memory location: the first process reads the

问题 In a Mysql database with every table based on InnoDB with Autocommit enabled, will queries with subqueries and/or joins be atomic? Examples: INSERT INTO users SELECT (x,y,z) FROM users, comments WHERE users.id = comments.user_id; (joins) UPDATE users, comments SET users.x = x1 WHERE users.age > 30; (joins) UPDATE users, comments SET users.x = x1, comments.y = y1 WHERE users.age > 30; (joins) UPDATE users, comments SET users.x = x1, comments.y = y1 WHERE users.id IN (SELECT id FROM users WHERE