CSingleLock same-thread double-access problem.

"Ricardo Vazquez" <rvazquez@dummy.com>
Mon, 24 Sep 2007 11:56:24 +0200
I'm afraid that something went wrong with my post! It lost most of its
So I post it again, and I hope this time it's readable!

This is my scenario:

My application has one instance of:
   class CMapDevices : public CMap <long, long&, CDevice*, CDevice*&>

Several threads can access this CMap; but they must not access it at the
same time.
So I added these member variables to CMapDevices:
   CSemaphore* m_sem;
   CSingleLock* m_lock;
   CMapDevices ::CMapDevices ()
    CString sSemaphoreName;
    m_sem = new CSemaphore (1, 1, sSemaphoreName);
    m_lock = new CSingleLock(m_sem);
So that wherever my code accesses the map I call
before the access, and then
after the access.

My problem is this:

Under certain circumstances, within the same thread, this is the code flow

[within the same thread]
-Access to map (lock)
|--2nd. access to map (lock -again- for the same thread)
|--2nd. access finishes (unlock)
-1st. access finishes (the map was already unlocked... but it shouldn't!)

As you can see, when the 2nd. access finishes the map is unlocked for
thisthread, so that any other thread could access it: but the map should be
keptlocked until the first access finishes!

So my question is:

What synchronization objects and access-control mechanisms should I use to
manage this possible situation and how should I use them?
Any other hints or clues?
Any helpful code I could find over the Internet?

Thank you!

Ricardo V?zquez.
Madrid, Spain.

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