Description:
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When forking php process with exec, if a mysqli connection is already established, the child process will retain this connection in a CLOSE_WAIT state, even if the parent destroys it afterwards.
It will retains one more CLOSE_WAIT connection per fork, leading to a "Unable to fork" error, when the maximum nproc in ulimit is reached.

The linked script reproduces the problem.
It's possible to avoid the problem by calling $this->disconnect(); before forking.

I can understand that the child shares resources with its parent, but is it normal that the parent cannot close the connection properly after the fork ?

Test script:
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http://pastebin.com/5RmQutkk

Expected result:
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Parent process should be able to close the mysqli connection.

Actual result:
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Parent process close the mysqli connection without error, but a connection in CLOSE_WAIT state is still present (lsof shows it).