Thank you all for you effort, I finally solved it.
The problem was that the linked library expected some environment variable to be set; and I forgot to set them :-(
Now after having these variables set everything works fine and it had nothing to do with the shared memory segments.

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In reply to Re^2: Apache, mod_perl, C++, XS and Shared Memory by Anonymous Monk
in thread Apache, mod_perl, C++, XS and Shared Memory by oseeliger

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