Network Programming with Perl

Creating Nonblocking I/O Handles

You can make a Perl filehandle nonblocking when you first open it, or change its nonblocking status at any time thereafter. As implied by the name, a filehandle that is nonblocking never blocks on read or write operations, but instead generates an error message. Nonblocking filehandles can be safely operated only on using the sysread() and syswrite() functions. Because of the buffering issues, combining nonblocking handles with the stdio routines used by the higher-level functions is guaranteed to lead to tears of frustration.

A nonblocking handle always returns immediately from sysread() or syswrite(). If the call can be satisfied without blocking, it returns the number of bytes read or written. If the call ...