multithreading - How does the recursive(reentrant) mutex works? -

i read 2 articles @ http://preshing.com/20120305/implementing-a-recursive-mutex http://en.wikipedia.org/wiki/reentrant_mutex on recursive(reentrant) mutex, neither article made sense.

could explain how recursive(reentrant) mutex works ?

(i found little material explaining how recursive mutex works. if has link explanation, close question.)

thanks !

one simple way pair standard mutex following auxiliary information:

• a pointer thread owns mutex (or null if it's not acquired), and
• a counter, 0.

you can acquire mutex in following way:

• if current mutex owner, increment counter , return immediately.
• if not, acquire mutex , set counter 0.

in other words, if own mutex already, increment counter indicating own more. if not, acquire mutex usual.

you can release mutex in following way:

• if counter nonzero, decrement counter , return immediately.
• otherwise, release mutex.

in order work, need able read counter , mutex owner in thread-safe way. can either having secondary mutex guard it, or marking counter / owner volatile.

hope helps!