How safe is using a common CMapStringToPtr declared globally in a thread which is called simulataniously more than 500 times?

how many times is your map written? just once? or many times?

CMap objects are not thread-safe, according to MS documentation. So, multithreading writing is absolutely risky.
In theory, multithreading reading should work, since internal MFC implementation doesn't seem to have static members, but I wouldn't take the risk in a critical application. So, better you use a CMutex object to protect access.

Hi
Many times. Since thread, there is a possibility of "SetAt" called same time (same object).
I have no practical issues when I do that even on 100 threads, but, I want to be very sure on this.
Thanks
Eugene

No, sometime you will have a simultaneous write and your collection will corrupt. I have experienced that many times.

What is the solution?
Regards
Eugene

Derive your own Map:

class CMyMap : protected CMapStringToPtr
{
protected:
        CMutex m_Mutex;

public:
        void SetAt(LPCTSTR key, void *value)
        {
                 CSingleLock lock(&m_Mutex);
                 lock.Lock();
                 CMapStringToPtr::SetAt(key, value);
                 lock.Unlock();
        }
        void *GetAt(LPCTSTR key)
        {
                 void *ret;

                 CSingleLock lock(&m_Mutex);
                 lock.Lock();
                 ret = CMapStringToPtr::GetAt(key);
                 lock.Unlock();

                return ret;
        }
}

Seems to be more professional. My application is similer to IIS (In Async) running more than 1000 connections and many critical operations in thread.
Will this make any performance issue? Because, all other threads have to wait till one lock process is busy.
Thanks
Eugene

depends on service load, indeed it will be a bit slower than not using mutex, but it will be slower where collisions are produced. Just look at your performance window.

I am not beginer, but, I have not worked on the "performance window", which I belive must one of the very useful area.
Could you please guide me on how and where do I check the "performance window"?
Thanks
Eugene

just press ctrl-alt-del to see the Task Manager, press the "Performance" tab.

I normally look at only "Processes" and the CPU time here.
Now looking at the "Performance" tab. Could you please tell me the approximate ideal values here?
CPU Usage and PF Usage.
When do we get alert?
What are the worst condition?
Thanks
Eugene

In your previous sample, you have the line...

ret = CMapStringToPtr::GetAt(key);

I think it should be Lookup with two parameters.

Could you please rewrite the codings?
Thanks
Eugene

I did as below
Is it ok?
Eugene

    BOOL Lookup(LPCTSTR key,void*& rValue)
    {
		
		CSingleLock lock(&m_Mutex);
		lock.Lock();
		BOOL ret = CMapStringToPtr::Lookup(key,rValue);
		lock.Unlock();
		return ret;
    }

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you can use as:

       void *GetAt(LPCTSTR key)
        {
                 void *ret;

                 CSingleLock lock(&m_Mutex);
                 lock.Lock();
                 if (!Lookup(key, ret))
                      ret = NULL;
                 lock.Unlock();

                return ret;
        }

if there is not key present, it will return NULL

After looking at your code, even I like yours.
Thanks for the help. Its all clear.
Eugene