SIGPIPE

TCPのsocket書き込み時等に，既に相手側が閉じていたら，SIGPIPEが投げられる．
SIGPIPEが飛んでくるとアプリケーションが終了してしまうので，SIGPIPEを捕捉しなければいけないっぽい．
writeやsendtoに失敗した場合，errnoにはEPIPEがセットされる．

WRITE(2)                    BSD System Calls Manual                   WRITE(2)

NAME
     write, writev, pwrite - write output

...

ERRORS
     Write(), writev(), and pwrite() will fail and the file pointer will
     remain unchanged if:
     [EPIPE]            An attempt is made to write to a pipe that is not open
                        for reading by any process.

     [EPIPE]            An attempt is made to write to a socket of type
                        SOCK_STREAM that is not connected to a peer socket.