Network Programming with Perl

Chapter 16. IO::Poll

We've used select() and IO::Select extensively to multiplex among multiple I/O streams. However, the select() system call has some design limitations related to its use of a bit vector to represent the filehandles to be monitored. On an ordinary host, such as a desktop machine, the maximum number of files is usually a small number, such as 256, and the bit vectors will therefore be no longer than 32 bytes. However, on a host that is tuned for network applications, such as a Web server, this limit may be in the thousands. The bit vectors necessary to describe every possible filehandle then become quite large, forcing the operating system to scan through a large, sparsely populated bit vector each time select() is called. ...