debian man page for io_getcookie

io_getcookie(3) 					     Library Functions Manual						   io_getcookie(3)

NAME
       io_getcookie - retrieve cookie

SYNTAX
       #include <io.h>

       void* io_getcookie(int64 fd);

DESCRIPTION
       io_getcookie retrieves a cookie (pointer to some anonymous data structure you associated with this descriptor).

       Use io_setcookie(3) to associate a cookie with a descriptor.

       If you did not associate a cookie with this descriptor, io_getcookie returns NULL.

       The  idea  is  that you put the state associated with a TCP connection you serve in a common struct.  Then you do not need to have your own
       data structure to retrieve the state for a connection, you can just use the data structure io_wait already maintains.  The lookup works	in
       constant time and should not cause any cache misses.

SEE ALSO
       io_wait(3), io_setcookie(3)

																   io_getcookie(3)