locking

问题 For fun I am replacing the mysqli extension in my app with PDO. Once in awhile I need to use transactions + table locking. In these situations, according to the mysql manual, the syntax needs to be a bit different. Instead of calling START TRANSACTION, you do it like so... SET autocommit=0; LOCK TABLES t1 WRITE, t2 READ, ...; ... do something with tables t1 and t2 here ... COMMIT; UNLOCK TABLES; (http://dev.mysql.com/doc/refman/5.0/en/lock-tables-and-transactions.html) My question is, how

问题 Making every object lockable looks like a design mistake: You add extra cost for every object created, even though you'll actually use it only in a tiny fraction of the objects. Lock usage become implicit, having lockMap.get(key).lock() is more readable than synchronization on arbitrary objects, eg, synchronize (key) {...} . Synchronized methods can cause subtle error of users locking the object with the synchronized methods You can be sure that when passing an object to a 3rd parting API, it

问题 I'm an experienced .NET programmer and stretching my legs with iOS. One of my favorite multi-threading constructs in .NET is the ReaderWriterLock. It allows for multiple readers or a single writer. The one feature that I am really missing in iOS is that the locks are re-entrant. That is, reader threads can acquire the read lock multiple times as long as they release it the same number of times. Likewise, the single writer thread can acquire the lock multiple times as long as it releases the

问题 Take this code: public class MyClass { private final Object _lock = new Object(); private final MyMutableClass _mutableObject = new MyMutableClass() public void myMethod() { synchronized(_lock) { // we are synchronizing on instance variable _lock // do something with mutableVar //(i.e. call a "set" method on _mutableObject) } } } now, imagine delegating the code inside myMethod() to some helper class where you pass the lock public class HelperClass { public helperMethod(Object lockVar,

问题 First of all, I know that lock{} is synthetic sugar for Monitor class. (oh, syntactic sugar) I was playing with simple multithreading problems and discovered that cannot totally understand how lockng some arbitrary WORD of memory secures whole other memory from being cached is registers/CPU cache etc. It's easier to use code samples to explain what I'm saying about: for (int i = 0; i < 100 * 1000 * 1000; ++i) { ms_Sum += 1; } In the end ms_Sum will contain 100000000 which is, of course,

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Re-entrant locks in C# If I write some code like this: class Program { static void Main(string[] args) { Foo(); Console.ReadLine(); } static void Foo() { lock(_lock) { Console.WriteLine("Foo"); Bar(); } } static void Bar() { lock(_lock) { Console.WriteLine("Bar"); } } private static readonly object _lock = new object(); } I get as output: Foo Bar I expected this to deadlock, because Foo acquires a lock, and then

问题 On the redis documentation, I found a primitive lock can be implemented via SETNX: http://redis.io/commands/setnx C4 sends SETNX lock.foo in order to acquire the lock The crashed client C3 still holds it, so Redis will reply with 0 to C4. C4 sends GET lock.foo to check if the lock expired. If it is not, it will sleep for some time and retry from the start. Instead, if the lock is expired because the Unix time at lock.foo is older than the current Unix time, C4 tries to perform: GETSET lock

问题 I am just wondering if there is any locking policy in C++11 which would prevent threads from starvation. I have a bunch of threads which are competing for one mutex. Now, my problem is that the thread which is leaving a critical section starts immediately compete for the same mutex and most of the time wins. Therefore other threads waiting on the mutex are starving. I do not want to let the thread, leaving a critical section, sleep for some minimal amount of time to give other threads a

问题 How can I detect if the phone is locked by a password, pin or pattern? thank you! 回答1: Two methods Check programatically - API 16+ https://gist.github.com/doridori/54c32c66ef4f4e34300f Note that you dont need to check for face unlock as that requires that a pin/pass fallback is set. Device Admin Policies Can also look into the Device Admin Policies which allow restrictions on how the app is setup regarding security including pin/pass set restrictions Device Administration Enhancing Security

问题 Why may this happen? The thing is that monitor object is not null for sure, but still we get this exception quite often: java.lang.IllegalMonitorStateException: (m=null) Failed to get monitor for (tIdx=60) at java.lang.Object.wait(Object.java:474) at ... The code that provokes this is a simple pool solution: public Object takeObject() { Object obj = internalTakeObject(); while (obj == null) { try { available.wait(); } catch (InterruptedException e) { throw new RuntimeException(e); } obj =