DistributedLock's implementation of distributed semaphore have an API similar to the framework's non-distributed SemaphoreSlim class.
The semaphore acts like a lock that can be acquired by a fixed number of processes/threads simultaneously instead of a single process/thread. This capability is frequently used to "throttle" access to some resource such as a database or email server, generally with the goal of preventing it from becoming overloaded. In such cases, a distributed mutex lock is inappropriate because we do want to allow concurrent access and simply want to cap the level of concurrency. For example:
// uses the Redis implementation; others are available
var semaphore = new RedisDistributedSemaphore("ComputeDatabase", maxCount: 5, database: database);
using (semaphore.Acquire())
{
// only 5 callers can be inside this block concurrently
UseComputeDatabase();
}Whenever a distributed semaphore is created, you must specify the max count value as well as the name. Specifying the same name with different max count values on different instances of a semaphore has undefined and unpredictable results, so make sure to use the same max count value for each instance of a particular semaphore.