Re: WaitForSingleObject() will not deadlock

File system drivers also use Executive Resources, a multi-reader single-writer lock
mechanism.
joe

On Sun, 1 Jul 2007 21:37:36 -0700, "Alexander Grigoriev" <alegr@xxxxxxxxxxxxx> wrote:

My guess that recursive mutexes may be handy to work on some tree-like
structures. File system drivers may be using them heavily.

"Doug Harrison [MVP]" <dsh@xxxxxxxx> wrote in message
news:66hg83t2evoskiqgf9pcb7clf6frr1rk8k@xxxxxxxxxx
On Sun, 1 Jul 2007 17:01:07 -0700, "Alexander Grigoriev"
<alegr@xxxxxxxxxxxxx> wrote:

Anybody tell me, why any other variants besides a recursive
one were invented?

If I may turn the question around, here are some arguments against
recursion:

1. Recursion makes it easy to hold a mutex across function calls and may
even encourage it, which is at odds with the goal of holding a mutex for
as
short a time as possible.

2. People who routinely take advantage of recursive mutexes tend to
develop
lax locking protocols and may end up writing code that has subtler races
than they'd get had they been limited to non-recursive mutexes.

3. The possibility of recursion makes it harder to implement algorithms
that requiring releasing the mutex. For example, a thread that holds a
mutex and needs to release it can't just unlock it, but must instead
unlock
it the correct number of times, which in Windows means keeping track of
the
lock count itself, since you can't query this property. (I wouldn't feel
comfortable calling ReleaseMutex until it fails, and LeaveCriticalSection
returns void.)

4. This is a relatively minor concern, but supporting recursion is more
expensive than not supporting it.

--
Doug Harrison
Visual C++ MVP

Joseph M. Newcomer [MVP]
email: newcomer@xxxxxxxxxxxx
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm
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