| 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. This may have an impact on performance. For this reason, the POSIX standard calls for an alternative API called poll() . It does much the same thing as select() but uses arrays rather than bit vectors to represent sets of filehandles. Because only the filehandles of interest are placed in the arrays, the poll() call doesn't waste time scanning through a large data structure to determine which filehandles to watch. You might also want to use poll() if you prefer its API, which is more elegant in some ways than select() . poll() is available to Perl programmers only via its object-oriented interface, IO::Poll. It was introduced during the development of Perl version 5.6. Be sure to use IO::Poll version 0.04 and higher because earlier versions weren't completely functional. This version can be found in Perl versions 5.7 and higher.  |
