locks

问题 I need to design distributed application using zookeeper. This is the first time I am using Zookeeper so I am little confused with its usage. I have read that Zab protocol ensures serializability when it comes to multiple updates but I am unable to understand, if that is the case than it will automatically allow lock free implementation. So why locks are needed in first place? It will be great if some one can help here. Thanks 回答1: Zab protocol is a critical PART of zookeeper.It ensures

问题 This question already has answers here : Threading Best Practices (11 answers) Closed 6 years ago . i have a question regards python locks and threading, i realise locks are used to prevent variables from being overwritten by another thread, is it normal to use locks to get around this issue as it then means you can only run a single thread concurrently, it also means creating acquire/release locks for every variable that maybe overwritten, which for my project runs into quite a few! how are

问题 I've been asked the following question and I'm not sure what the correct answer is to it: If monitors are implemented by replacing condition variables with semaphores (counters set to 0) with down() and up() as wait and signal, respectively, would the monitors work correctly? I'd be tempted to say it is a correct implementation because semaphores and condition variables can replace each other, correct? Is there a better explanation? 回答1: You are asking about a semaphore initialized to 1,

问题 I am aware of locking concepts with synchronization of static and non static methods to lock classes and instances respectively. What I am not able to understand is, how is class level lock achieved? I mean, class is a template only, with no physical significance. So, when we say that class level locking is achieved with synchronizing static methods what happens then? Do all the objects of that class get locked or some other process? With what I could find out with my search is that there are

问题 I am always very hesitant to bring my locks in the open, to make them public. I always try to keep the locks restricted to my implementation. Not doing that, is a recipe for deadlocks, I believe. I have the following class: class SomeClass { protected ArrayList<Listener> mListeners = new ArrayList<Listener>(); protected void addListener(Listener listener) { synchronized (mListeners) { mListeners.add(listener); } } protected void removeListener(Listener listener) { synchronized (mListeners) {

问题 I'm new to concurrent programming. I'd like to execute three tasks repeatedly. The first two should run all the time, the third should run every hour or so. The first two tasks can run in parallel, but I always want to pause them while the third task is running. Here's the skeleton of what I've tried: import threading import time flock = threading.Lock() glock = threading.Lock() def f(): while True: with flock: print 'f' time.sleep(1) def g(): while True: with glock: print 'g' time.sleep(1)

问题 So I want an array with 10 volatile booleans, not a volatile array with 10 booleans. It probably does not even make sense to have a volatile array reference, correct me if I am wrong. 回答1: If it's only 10 and is always 10, you could simply write: private volatile boolean b1, b2, ..., b10; A possibly cleaner way would be to use an AtomicIntegerArray(10) and map between integers and booleans (0=false, 1=true). You should clarify the reason why you need 10 volatile booleans: there may be a

问题 When i run 'Select * from table' on an INNODB table, does the table get locked implicity? Does it mean that during the time MySQL takes to return the result set, i cannot issue an update statement on the table? From what i have understood, the whole table would be locked in shared mode until the result set is returned from the server. Only then could the update command be executed. 回答1: InnoDB uses a feature called Multi-version concurrency control. Locking in shared mode is not required,

问题 >>> import multiprocessing >>> print multiprocessing.Manager().Lock() <thread.lock object at 0x7f64f7736290> >>> type(multiprocessing.Lock()) <class 'multiprocessing.synchronize.Lock'> Why the produced object is a thread.lock and not a multiprocessing.synchronize.Lock as it would be expected from a multiprocessing object? 回答1: Managed objects are always proxies; the goal of the manager is to make non-multiprocessing-aware objects into multiprocessing aware. There is no point in doing this for

问题 i have two programs working on the same file i want the first program to check regularly on the file, and if any changes are made operate on the file and empty it. the other program writes to the file. the problem occurs when the second program tries to write on the file because it's used from the first one is there an (if there's any implemented C# program would be even better) algorithm to handle this? 回答1: To check if file has changed you might first of all check its timestamp. In pseudo