synchronization | 易学教程

How to sync only the changed files from the remote directory using pysftp?

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问题 I am using pysftp library's get_r function (https://pysftp.readthedocs.io/en/release_0.2.9/pysftp.html#pysftp.Connection.get_r) to get a local copy of a directory structure from sftp server. Is that the correct approach for a situation when the contents of the remote directory have changed and I would like to get only the files that changed since the last time the script was run? The script should be able to sync the remote directory recursively and mirror the state of the remote directory -

Why does notifyAll() raise IllegalMonitorStateException when synchronized on Integer?

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Why does this test program result in a java.lang.IllegalMonitorStateException ? public class test { static Integer foo = new Integer(1); public static void main(String[] args) { synchronized(foo) { foo++; foo.notifyAll(); } System.err.println("Success"); } } Result: Exception in thread "main" java.lang.IllegalMonitorStateException at java.lang.Object.notifyAll(Native Method) at test.main(test.java:6) You have noted correctly that notifyAll must be called from a synchronized block. However, in your case, because of auto-boxing, the object you synchronized on is not the same instance that you

Couchdb sync access with userid and password

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问题 I have a couchdb running on a virtual linux machine. This db has cors enabled and setup. I have added an admin user and password to the db. I also have require_valid_user set to true. I am trying to sync a pouchdb in a web page with the couchdb online with the code below. If I just pass the address for the db (1 below), I get a dialog box asking for a user and password. The sync works in this example. If I try to pass the user name and password in the URL (as in 2 below), I get a sync error

Creating a Cross-Process EventWaitHandle

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I have two windows application, one is a windows service which create EventWaitHandle and wait for it. Second application is a windows gui which open it by calling EventWaitHandle.OpenExisting() and try to Set the event. But I am getting an exception in OpenExisting. The Exception is "Access to the path is denied". windows Service code EventWaitHandle wh = new EventWaitHandle(false, EventResetMode.AutoReset, "MyEventName"); wh.WaitOne(); Windows GUI code try { EventWaitHandle wh = EventWaitHandle.OpenExisting("MyEventName"); wh.Set(); } catch (Exception ex) { MessageBox.Show(ex.Message); } I

Java Thread synchronization - Thread.sleep() Method Not Working as desired

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问题 i heard, sleep() will lock the current sync method/block But here, when i call sleep() on thread 1, thread 2 is able to access the same block? Can anyone Explain? Main.java public class Main { public static void main(String args[]) { Thread1 t1 = new Thread1(); Thread2 t2 = new Thread2(); System.out.println("going to start t1"); t1.start(); System.out.println("going to start t2"); t2.start(); } } ===================================================================== Thread1.java public class

iCloud + CoreData - how to avoid pre-filled data duplication?

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I have a problem with an iCloud shoebox application and hope some-one can help me (I've spent many hours fighting it in vain). The App: - A simple library style application - containing set of categories (Cat1 .. CatN) each containing items (Item1...ItemM). I used Apple's iPhoneCoreDataRecipes to set up iCloud CoreData stack. Everything works almost perfect with iCloud except - there should be a number of pre-filled empty categories the user can start using once he has opened the app for the first time (he can also be offline at that time). And here's the devil. Here's what I do - Once my

Thread Safe Singletons in Java

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The wikipedia article on Singletons mentions a few thread safe ways to implement the structure in Java. For my questions, let's consider Singletons that have lengthy initialization procedures and are acccessed by many threads at once. Firstly, is this unmentioned method thread-safe, and if so, what does it synchronize on? public class Singleton { private Singleton instance; private Singleton() { //lots of initialization code } public static synchronized Singleton getInstance() { if(instance == null) { instance = new Singleton(); } return instance; } } Secondly, why is the following

Synchronizing a Timers.Timer elapsed method when stopping

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问题 With reference to this quote from MSDN about the System.Timers.Timer: The Timer.Elapsed event is raised on a ThreadPool thread, so the event-handling method might run on one thread at the same time that a call to the Timer.Stop method runs on another thread. This might result in the Elapsed event being raised after the Stop method is called. This race condition cannot be prevented simply by comparing the SignalTime property with the time when the Stop method is called, because the event

How is thread synchronization implemented, at the assembly language level?

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While I'm familiar with concurrent programming concepts such as mutexes and semaphores, I have never understood how they are implemented at the assembly language level. I imagine there being a set of memory "flags" saying: lock A is held by thread 1 lock B is held by thread 3 lock C is not held by any thread etc But how is access to these flags synchronized between threads? Something like this naive example would only create a race condition: mov edx, [myThreadId] wait: cmp [lock], 0 jne wait mov [lock], edx ; I wanted an exclusive lock but the above ; three instructions are not an atomic

Why use private lock over intrinsic lock?

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问题 While reading about synchronization, I came across "monitor pattern" to encapsulate mutable states. The following is the sample code public class MonitorLock { private final Object myLock = new Object(); Widget widget; void someMethod() { synchronized(myLock) { // Access or modify the state of widget } } } Is it better in any way to have a private lock instead of the intrinsic lock? 回答1: Yes - it means you can see all the code which could possibly acquire that lock (leaving aside the