recursivemutex

A recursive mutex, also known as a reentrant mutex, is a synchronization primitive that can be locked multiple times by the same thread. Unlike a standard mutex, which becomes locked indefinitely if the same thread attempts to lock it again, a recursive mutex keeps track of the number of times it has been acquired by the owner thread.

When a thread successfully locks a recursive mutex, a counter is incremented. If the same thread attempts to lock the mutex again, the counter is incremented further, and the thread is allowed to proceed without blocking. The mutex is only truly unlocked when the owner thread calls the unlock operation as many times as it previously called the lock operation.

This behavior is useful in scenarios where a thread might call functions that recursively call each other, and these functions all need to access a shared resource protected by the same mutex. Without a recursive mutex, such recursive calls could lead to a deadlock, as the thread would block indefinitely on a mutex it already holds.

However, recursive mutexes can sometimes mask design flaws. Over-reliance on them might indicate that the program's locking strategy could be simplified or that shared data is not being accessed in a well-structured manner. They can also introduce performance overhead compared to non-recursive mutexes due to the need to maintain the ownership count. Therefore, while they solve specific problems, they should be used judiciously.