synchronization | 易学教程

How to synchronize two Subversion repositories?

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问题 My company has a subsidiary with a slow Internet connection. Our developers there suffer to interact with our central Subversion server. Is it possible to configure a slave/mirror for them? They would interact locally with the server and all the commits would be automatically synchronized to the master server. This should work as transparently as possible for the developers. Usability is a must. Please, no suggestions to change our version control system. 回答1: Subversion 1.5 introduced proxy

Concurrent threads adding to ArrayList at same time - what happens?

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问题 We have multiple threads calling add(obj) on an ArrayList . My theory is that when add is called concurrently by two threads, that only one of the two objects being added is really added to the ArrayList . Is this plausable? If so, how do you get around this? Use a synchronized collection like Vector ? 回答1: There is no guaranteed behavior for what happens when add is called concurrently by two threads on ArrayList. However, it has been my experience that both objects have been added fine.

Sync JS time between multiple devices

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问题 I\'m using the wonderful reveal.js library to create a HTML slideshow. My only problem is that I need it to synchronise across multiple devices. At the moment I am making a AJAX request to the the time from the server and keep an internal clock for the page. function syncTime() { // Set up our time object, synced by the HTTP DATE header // Fetch the page over JS to get just the headers console.log(\"syncing time\") var r = new XMLHttpRequest(); r.open(\'HEAD\', document.location, false); r

How to use the CancellationToken property?

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问题 Compared to the preceding code for class RulyCanceler, I wanted to run code using CancellationTokenSource . How do I use it as mentioned in Cancellation Tokens, i.e. without throwing/catching an exception? Can I use the IsCancellationRequested property? I attempted to use it like this: cancelToken.ThrowIfCancellationRequested(); and try { new Thread(() => Work(cancelSource.Token)).Start(); } catch (OperationCanceledException) { Console.WriteLine(\"Canceled!\"); } but this gave a run-time

Java synchronized block vs. Collections.synchronizedMap

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问题 Is the following code set up to correctly synchronize the calls on synchronizedMap ? public class MyClass { private static Map<String, List<String>> synchronizedMap = Collections.synchronizedMap(new HashMap<String, List<String>>()); public void doWork(String key) { List<String> values = null; while ((values = synchronizedMap.remove(key)) != null) { //do something with values } } public static void addToMap(String key, String value) { synchronized (synchronizedMap) { if (synchronizedMap

Are Java static initializers thread safe?

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I'm using a static code block to initialize some controllers in a registry I have. My question is therefore, can I guarantee that this static code block will only absolutely be called once when the class is first loaded? I understand I cannot guarantee when this code block will be called, I'm guessing its when the Classloader first loads it. I realize I could synchronize on the class in the static code block, but my guess is this is actually what happens anyway? Simple code example would be; class FooRegistry { static { //this code must only ever be called once addController(new

How pthread_mutex_lock is implemented

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问题 I am just curious to know how functions related to synchronization between threads are implemented inside Unix. For example, what happens when I call pthread_mutex_lock ? Are there any pointers in use? A reference to the source code would really help. 回答1: It is both complicated and differs from Unix to Unix variant. In Linux, for example, a system called Futex (Short for Fast Userspace Mutex) is used. In this system an atomic increment and test operation is performed on the mutex variable in

C# version of java's synchronized keyword?

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Does c# have its own version of the java "synchronized" keyword? I.e. in java it can be specified either to a function, an object or a block of code, like so: public synchronized void doImportantStuff() { // dangerous code goes here. } or public void doImportantStuff() { // trivial stuff synchronized(someLock) { // dangerous code goes here. } } First - most classes will never need to be thread-safe. Use YAGNI : only apply thread-safety when you know you actually are going to use it (and test it). For the method-level stuff, there is [MethodImpl] : [MethodImpl(MethodImplOptions.Synchronized)]

When is a condition variable needed, isn't a mutex enough?

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问题 I\'m sure mutex isn\'t enough that\'s the reason the concept of condition variables exist; but it beats me and I\'m not able to convince myself with a concrete scenario when a condition variable is essential. Differences between Conditional variables, Mutexes and Locks question\'s accepted answer says that a condition variable is a lock with a \"signaling\" mechanism. It is used when threads need to wait for a resource to become available. A thread can \"wait\" on a CV and then the resource

How to synchronize or lock upon variables in Java?

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问题 Let me use this small and simple sample: class Sample { private String msg = null; public void newmsg(String x){ msg = x; } public String getmsg(){ String temp = msg; msg = null; return temp; } } Let\'s assume the function newmsg() is called by other threads that I don\'t have access to. I want to use the synchonize method to guarantee that the string msg is only used by one function per time. In other words, function newmsg() cannot run at the same time as getmsg() . 回答1: That's pretty easy: