Why does the php-php fread two connections when waiting?

Php

PHP, I used pfsockopen and the server to establish a connection, and then use fwrite to send the connection, and finally with fread waiting for the data returned by the server.
But if there is no data return on the server side, Fread is blocked there, the middle process of the server over the print display will be again accept to a connection (the server will only have this one device to its connection).
Do you have the great God to guide this why, ask for answers, confused for many days?

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