synchronization | 易学教程

What is the best way to sync 2 sqlite tables over http and json?

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问题 I have a fairly simple sync problem. I have a table with about 10 columns that I want to keep in sync between a sqlite file on 3 different clients: an Iphone client, a browser client, and a Ruby on Rails client. So I need a simple sycing solution that will work for all 3, i.e. I can easily implement it in Javascript, Objective C, and Ruby and it works with JSON over HTTP. I have looked at various components of other syncing solutions like the one in git, some of the tutorials that have come

Java RMI and synchronized methods

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问题 I'm studying the book "Distributed Systems" (by Tanenbaum & Van Steen) and they say something that seems to conflict to what seems to be instead thought by many on Java RMI and synchronized methods. What I thought is that using a synchronized method on a Remote Object implementation (so the real implementation running at the server) concurrent execution of that method is prevented even when the calls to that method are from different clients machines (calling the method via a Proxy... aka a

What is the use of Collections.synchronizedList() method? It doesn't seem to synchronize the list

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问题 I am trying to add String values to an ArrayList using two threads. What I want is that while one thread is adding the values the other thread should not interfere so I have used the Collections.synchronizedList method. But it appears that if I don't explicitly synchronize on an object the adding is done in an unsynchronized way. Without explicit synchronized block: public class SynTest { public static void main(String []args){ final List<String> list=new ArrayList<String>(); final List

How can I ensure that an overridden method is synchronized

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问题 I have a class of common code that is thread safe. One of the methods in that class is abstract and needs to be overridden for different implementations. I need to ensure or at least flag to other developers that all implementations of this method need to be thread-safe. What is the best way to do this? Is there a keyword or annotation to this effect? I have already tried abstract synchronized but that combination of keywords is not allowed. 回答1: You can't do it directly. One thing you can do

Replace critical section with SRW lock

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If the application is targeted on Windows Vista or later, could we replace all critical sections with SRW locks ? Since critical section is mutually exclusive, for usage it is equivalent to SRW locks in exclusive mode, right? According to MSDN, SRW is optimized both for speed and space. Is there any drawback for doing this? I'm not sure how CS and SRW are implemented internally by Microsoft. Thanks! Mark oskin See Joe Duffy's book "Concurrent Programming on Windows", pg 289. The short answer to your question is "almost". There are semantics with recursively acquired CRITICAL_SECTION's that are

Java's equivalent to .Net's AutoResetEvent?

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问题 What should I use to get semantics equivalent to AutoResetEvent in Java? (See this question for ManualResetEvent). 回答1: @user249654's answer looked promising. I added some unit tests to verify it, and indeed it works as expected. I also added an overload of waitOne that takes a timeout. The code is here in case anyone else finds it useful: Unit Test import org.junit.Assert; import org.junit.Test; import static java.lang.System.currentTimeMillis; /** * @author Drew Noakes http://drewnoakes.com

What is the reason for “locks are an expensive operation” to be uttered so often?

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I have read a lot of material on threading, and all the synchronization mechanisms involved. I also understand the dangers of not doing it properly. I just watched this PDC 2009 video about Parallelism and Concurrency, and here is yet again this mention that "locks are an expensive operation". I've now come across a phrase like this in various texts, books, and I've heard experts in the field say it too. I was wondering, what exactly is so expensive about obtaining a lock (mutex or semaphore)? Is it the fact that it causes a LOCK# instruction to be emitted at Assembler level? Is it the fact

How are mutex and lock structures implemented?

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问题 I understand the concept of locks, mutex and other synchronization structures, but how are they implemented? Are they provided by the OS, or are these structures dependent on special CPU instructions for the CPUs MMU? 回答1: You may want to look at these links, but the main one is the Test-and-set on Wikipedia: http://en.wikipedia.org/wiki/Test-and-set How are mutexes implemented? You can also look at this patent: http://www.faqs.org/patents/app/20080222331 回答2: Most mutual exclusion and

Java synchronization between different JVMs

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The project I am working on would trigger various asynchronous jobs to do some work. As I look into it more these asynchronous jobs are actually being run as separate JVMs (separate java processes). Does it mean I would not be able to use any of the following if I need to synchronize between these processes: synchronized methods/blocks any lock that implements java.util.concurrent.locks Because it seems to me they are all thread-level? Does Java provide support for IPC like semaphores between processes? That's right. You can not use any standard synchronization mechanisms because they are

Why do we pass self in @synchronized block?

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I guess @synchronized blocks are not object dependent but thread dependent...right? In that case why do we pass self? @synchronized is a construct provided by the language to create synchronized scopes. As it would be highly inefficient to use a simple global shared mutex, and thus serializing every single @synchronized scope in the application, the language allows us to specify a synchronization point. Then it's up to the developer(s) to decide which synchronization points are appropriate for the task. On an instance method, using self is common: the instance is the synchronization point. The