locking

问题 What is the opposite of Object.freeze or Object.seal ? Is there a function that has a name such as detach? 回答1: There is no way to do this, once an object has been frozen there is no way to unfreeze it. Source Freezing an object is the ultimate form of lock-down. Once an object has been frozen it cannot be unfrozen – nor can it be tampered in any manner. This is the best way to make sure that your objects will stay exactly as you left them, indefinitely 回答2: I think you can do, using some

问题 I have a function in C# that can be called multiple times from multiple threads and I want it to be done only once so I thought about this: class MyClass { bool done = false; public void DoSomething() { lock(this) if(!done) { done = true; _DoSomething(); } } } The problem is _DoSomething takes a long time and I don't want many threads to wait on it when they can just see that done is true. Something like this can be a workaround: class MyClass { bool done = false; public void DoSomething() {

问题 In my project I need an application lock (same as windows lock). If the application is idle for a time period the application should be locked i.e, the login window for the application will appear. How can I do it in a WPF C# application? 回答1: You can use these functions LockWorkStation GetLastInputInfo see this code, you must add a timer to your form, and set this.timer1.Enabled = true; using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using

问题 What I know is: ReadLock and WriteLock affect each other somehow WriteLock is just like synchronized ReadLock seems cannot work alone 回答1: readLock.lock(); This means that if any other thread is writing (i.e. holds a write lock) then stop here until no other thread is writing. Once the lock is granted no other thread will be allowed to write (i.e. take a write lock) until the lock is released. writeLock.lock(); This means that if any other thread is reading or writing , stop here and wait

问题 What I know is: ReadLock and WriteLock affect each other somehow WriteLock is just like synchronized ReadLock seems cannot work alone 回答1: readLock.lock(); This means that if any other thread is writing (i.e. holds a write lock) then stop here until no other thread is writing. Once the lock is granted no other thread will be allowed to write (i.e. take a write lock) until the lock is released. writeLock.lock(); This means that if any other thread is reading or writing , stop here and wait

问题 Is there a way to detect locked tables in MySQL? I mean tables locked by the LOCK TABLE table WRITE/READ command. (Note that readers interested in detecting named locks acquired with GET_LOCK should read Show all current locks from get_lock instead.) 回答1: SHOW OPEN TABLES to show each table status and its lock. For named locks look Show all current locks from get_lock 回答2: Use SHOW OPEN TABLES : http://dev.mysql.com/doc/refman/5.1/en/show-open-tables.html You can do something like this SHOW

问题 Is it true that the x86 ASM "LOCK" command prefix causes all cores to freeze while the instruction following "LOCK" is being executed? I read this in a blog post and it doesn't make sense. I can't find anything that indicates if this is true or not. 回答1: It's about locking the memory bus for that address. The Intel 64 and IA-32 Architectures Software Developer's Manual - Volume 3A: System Programming Guide, Part 1 tells us: 7.1.4 Effects of a LOCK Operation on Internal Processor Caches. For

问题 In a low level language (C, C++ or whatever): I have the choice in between either having a bunch of mutexes (like what pthread gives me or whatever the native system library provides) or a single one for an object. How efficient is it to lock a mutex? I.e. how many assembler instructions are there likely and how much time do they take (in the case that the mutex is unlocked)? How much does a mutex cost? Is it a problem to have really a lot of mutexes? Or can I just throw as much mutex

问题 In C++ is a return value guaranteed to be created before automatic variables in the function are destroyed? Notice Basket::get: class Basket { public: // Gift is a struct containing safely copyable things like int or string Gift gift; // Used to protect access and changes to gift Mutex mutex; // Copy gift into present, while locked to be thread safe void put (const Gift & gift) { Lock lock(mutex); // Constructor locks, destructor unlocks mutex this->gift = gift; // Gift assignment operator }

问题 I have a problem with automating a deployment, after I stop the service there is still a lock on the file and I am unable to delete it. I really do not want to start hacking about with sleeps to make something that 'usually works'. Is there a good way to properly resolve the problem of locked files, perhaps some kind of 'wait until file is removable': Get-ChildItem : Access to the path 'D:\MyDirectory\' is denied. 'Test-Path' is not sufficient in this case as the folder both exists and I have