debian man page for io_canwrite

io_canwrite(3)						     Library Functions Manual						    io_canwrite(3)

NAME
       io_canwrite - return a file descriptor that can be written to

SYNTAX
       #include <io.h>

       int64 io_canwrite();

DESCRIPTION
       io_canwrite  returns the next file descriptor that can be written to.  You have to have used io_wantwrite() on the file descriptor earlier,
       and you have to have called io_wait() or io_waituntil().

       These functions then keep an internal data structure on which descriptors were reported writable by the operating system.

       Please note that there is no guarantee that you can still write data without  blocking  to  that  descriptor,  just  that  you  could  when
       io_wait() or io_waituntil() were called.  Another process could have written something before you.  Look at the result from io_trywrite().

       If  there  are  no  more  descriptors  that  you  can  write to without blocking, io_canwrite will return -1.  In this case you should call
       io_wait() or io_waituntil() again.

       You should only use io_trywrite(3), io_sendfile(3) or iob_send(3) to write to the file, not plain write(2).  If you use	write(2)  and  get
       EAGAIN, call io_eagain(3).

SEE ALSO
       io_wait(3), io_canwrite(3)

																    io_canwrite(3)