mutex - w3toppers.com

Is it smart to replace boost::thread and boost::mutex with c++11 equivalents?

There are several differences between Boost.Thread and the C++11 standard thread library: Boost supports thread cancellation, C++11 threads do not C++11 supports std::async, but Boost does not Boost has a boost::shared_mutex for multiple-reader/single-writer locking. The analogous std::shared_timed_mutex is available only since C++14 (N3891), while std::shared_mutex is available only since C++17 (N4508). C++11 timeouts are different … Read more

Why is locking a std::mutex twice ‘Undefined Behaviour’?

Because it never happens in a correct program, and making a check for something that never happens is wasteful (and to make that check it needs to store the owning thread ID, which is also wasteful). Note that it being undefined allows debug implementations to throw an exception, for example, while still allowing release implementations … Read more

System-wide mutex in Python on Linux

The “traditional” Unix answer is to use file locks. You can use lockf(3) to lock sections of a file so that other processes can’t edit it; a very common abuse is to use this as a mutex between processes. The python equivalent is fcntl.lockf. Traditionally you write the PID of the locking process into the … Read more

If I am using channels properly should I need to use mutexes?

You don’t need mutex if you use channels correctly. In some cases a solution with mutex might be simpler though. Just make sure the variable(s) holding the channel values are properly initialized before multiple goroutines try to access the channel variables. Once this is done, accessing the channels (e.g. sending values to or receiving values … Read more

Using string as a lock to do thread synchronization

Strings like that (from the code) could be “interned“. This means all instances of “ABC” point to the same object. Even across AppDomains you can point to the same object (thx Steven for the tip). If you have a lot of string-mutexes, from different locations, but with the same text, they could all lock on … Read more

Check to see if a pthread mutex is locked or unlocked (After a thread has locked itself)

You can use pthread_mutex_trylock. If that succeeds, the mutex was unclaimed and you now own it (so you should release it and return “unheld”, in your case). Otherwise, someone is holding it. I have to stress though that “check to see if a mutex is unclaimed” is a very bad idea. There are inherent race … Read more

Why doesn’t Mutex get released when disposed?

The documentation explains (in the “Remarks” section) that there is a conceptual difference between instantiating a Mutex object (which does not, in fact, do anything special as far as synchronization goes) and acquiring a Mutex (using WaitOne). Note that: WaitOne returns a boolean, meaning that acquiring a Mutex can fail (timeout) and both cases must … Read more

How can I use something like std::vector?

vector requires that the values are movable, in order to maintain a contiguous array of values as it grows. You could create a vector containing mutexes, but you couldn’t do anything that might need to resize it. Other containers don’t have that requirement; either deque or [forward_]list should work, as long as you construct the … Read more

How to give priority to privileged thread in mutex locking?

I can think of three methods using only threading primitives: Triple mutex Three mutexes would work here: data mutex (‘M’) next-to-access mutex (‘N’), and low-priority access mutex (‘L’) Access patterns are: Low-priority threads: lock L, lock N, lock M, unlock N, { do stuff }, unlock M, unlock L High-priority thread: lock N, lock M, … Read more

What are the differences between various threading synchronization options in C#?

Great question. I maybe wrong.. Let me try.. Revision#2 of my orig answer.. with a little bit of more understanding. Thanks for making me read 🙂 lock(obj) is a CLR construct that for (intra-object?) thread synchronization. Ensures that only one thread can take ownership of the object’s lock & enter the locked block of code. … Read more