[libmicrohttpd] a strange thing when send call returns -1 in send_cls()

[Taehwan Weon]

While testing our web-server (based on MHD 0.9.38), sometimes, I found
heavy cpu load.
It caused by infinite send_cls() calls because send call in send_cls()
returned -1 with errno of 0.

I read and read again send() manual page, but there is no mention about the
case that send() returns -1 with errno of 0.

My current environment is:
     OS Kernel :  2.6.32-358.11.5.el6.x86_64 (CentOS)
     MHD options:  MHD_USE_POLL_INTERNALLY | MHD_USE_THREAD_PER_CONNECTION|
MHD_USE_DEBUG;


Any help will be highly appreciated.

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weon