According to MSDN, SemaphoreSlim.WaitAsync may throw: ObjectDisposedException – If the semaphore has been disposed ArgumentOutOfRangeException – if you choose the overload which accepts an int and it is a negative number (excluding -1) In both cases, the SemaphoreSlim wont acquire the lock, which makes it unnessacery to release it in a finally block. One thing … Read more
Here, save and try this script (kill_ipcs.sh) on your shell: #!/bin/bash ME=`whoami` IPCS_S=`ipcs -s | egrep “0x[0-9a-f]+ [0-9]+” | grep $ME | cut -f2 -d” “` IPCS_M=`ipcs -m | egrep “0x[0-9a-f]+ [0-9]+” | grep $ME | cut -f2 -d” “` IPCS_Q=`ipcs -q | egrep “0x[0-9a-f]+ [0-9]+” | grep $ME | cut -f2 -d” “` for … Read more
If you access the AvailableWaitHandle property, then Yes, you must call Dispose() to cleanup unmanaged resources. If you do not access AvailableWaitHandle, then No, calling Dispose() won’t do anything important. SemaphoreSlim will create a ManualResetEvent on demand if you access the AvailableWaitHandle. This may be useful, for example if you need to wait on multiple … Read more
The typical use case for a mutex (allowing only one thread access to a resource at any time) is far more common than the typical uses if a semaphore. But a semaphore is actually the more general concept: A mutex is (almost) a special case of a semaphore. Typical applications would be: You don’t want … Read more
The BashFAQ noted by shellter has some good examples. The basic idea, which I’m moving here so the page is self-contained, is to use an operation that both tests and sets at the same time: mkdir mkdir will fail if the directory exists and will make it if it does not. It’s an atomic operation … Read more
It is working fine, its just that its printing too fast for you to see . Try putting a time.sleep() in both functions (a small amount) to sleep the thread for that much amount of time, to actually be able to see both 1 as well as 2. Example – import threading import time sem … Read more
A semaphore is suited cleanly to a producer-consumer model, although it has other uses. Your program logic is responsible for ensuring that the right number of posts are made for the number of waits. If you post a semaphore and nobody is waiting on it yet, then when they do wait they continue immediately. If … Read more
Turns out there isn’t a way to reliably recover the semaphore. Sure, anyone can post_sem() to the named semaphore to get the count to increase past zero again, but how to tell when such a recovery is needed? The API provided is too limited and doesn’t indicate in any way when this has happened. Beware … Read more
Conceptually, both of DispatchGroup and Semaphore serve the same purpose (unless I misunderstand something). The above is not exactly true. You can use a semaphore to do the same thing as a dispatch group but it is much more general. Dispatch groups are used when you have a load of things you want to do … Read more
Since you haven’t specified which OS or language/library you are talking about, let me answer in a generic way. Conceptually they are the same. But usually they are implemented slightly differently Monitor Usually, the implementation of monitors is faster/light-weight, since it is designed for multi-threaded synchronization within the same process. Also, usually, it is provided … Read more