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 … Read more
I have the following class. class Test{ public HashSet<string> Data = new HashSet<string>(); } I need to change the field “Data” from different threads, so I would like some opinions on my current thread-safe implementation. class Test{ public HashSet<string> Data = new HashSet<string>(); public void Add(string Val){ lock(Data) Data.Add(Val); } public void Remove(string Val){ lock(Data) … Read more
POSIX allows mutexes to be recursive. That means the same thread can lock the same mutex twice and won’t deadlock. Of course it also needs to unlock it twice, otherwise no other thread can obtain the mutex. Not all systems supporting pthreads also support recursive mutexes, but if they want to be POSIX conform, they … Read more
I guess the real question is: If I don’t care about dirty reads, will adding the with (NOLOCK) hint to a SELECT statement affect the performance of: the current SELECT statement other transactions against the given table Example: Select * from aTable with (NOLOCK) 5 Answers 5
Seeing various locking related question and (almost) always finding the ‘loop because of spurious wakeups’ terms1 I wonder, has anyone experienced such kind of a wakeup (assuming a decent hardware/software environment for example)? I know the term ‘spurious’ means no apparent reason but what can be the reasons for such kind of an event? (1 … Read more
If I have 2 synchronized methods in the same class, but each accessing different variables, can 2 threads access those 2 methods at the same time? Does the lock occur on the object, or does it get as specific as the variables inside the synchronized method? Example: class X { private int a; private int … Read more
C++17 introduced a new lock class called std::scoped_lock. Judging from the documentation it looks similar to the already existing std::lock_guard class. What’s the difference and when should I use it? 4 Answers 4
Can any one tell me the advantage of synchronized method over synchronized block with an example? 23 Answers 23
The MSDN documentation says that public class SomeObject { public void SomeOperation() { lock(this) { //Access instance variables } } } is “a problem if the instance can be accessed publicly”. I’m wondering why? Is it because the lock will be held longer than necessary? Or is there some more insidious reason? 17 s 17 … Read more
I’ve heard these words related to concurrent programming, but what’s the difference between lock, mutex and semaphore? 10 s 10 A lock allows only one thread to enter the part that’s locked and the lock is not shared with any other processes. A mutex is the same as a lock but it can be system … Read more
