POE::Driver(3) User Contributed Perl Documentation POE::Driver(3)

POE::Driver - an abstract interface for buffered, non-blocking I/O

This is a contrived example of how POE::Filter and POE::Driver objects may be used in a stand-alone application.

my $driver = POE::Driver::SysRW->new();
my $filter = POE::Filter::Line->new();
my $list_of_octet_chunks = $filter->put("A line of text.");
$driver->put( $list_of_octet_chunks );
my $octets_remaining_in_buffer = $driver->flush($filehandle);
die "couldn't flush everything" if $octets_remaining_in_buffer;
while (1) {
  my $octets_list = $driver->get($filehandle);
  die $! unless defined $octets_list;
  while (my $line = $filter->get_one()) {
    print "Input: $line\n";

Most programs will use POE::Filter and POE::Driver objects as parameters to POE::Wheel constructors. See the synopses for particular classes for details.

POE::Driver is a common API for I/O drivers that can read from and write to various files, sockets, pipes, and other devices.

POE "drivers" implement the specifics of reading and writing to devices. Drivers plug into POE::Wheel objects so that wheels may support a large number of device types without implementing a separate subclass for each.

As mentioned in the SYNOPSIS, POE::Driver objects may be used in stand-alone applications.

These methods are the generic Driver interface, and every driver must implement them. Specific drivers may have additional methods related to their particular tasks.


new() creates, initializes, and returns a new driver. Specific drivers may have different constructor parameters. The default constructor parameters should configure the driver for the most common use case.


get() immediately tries to read information from a FILEHANDLE. It returns an array reference on success---even if nothing was read from the FILEHANDLE. get() returns undef on error, and $! will be set to the reason why get() failed.

The returned arrayref will be empty if nothing was read from the FILEHANDLE.

In an EOF condition, get() returns undef with the numeric value of $! set to zero.

The arrayref returned by get() is suitable for passing to any POE::Filter's get() or get_one_start() method. Wheels do exactly this internally.

put() accepts an ARRAYREF of raw octet chunks. These octets are added to the driver's internal output queue or buffer. put() returns the number of octets pending output after the new octets are buffered.

Some drivers may flush data immediately from their put() methods.

flush() attempts to write a driver's buffered data to a given FILEHANDLE. The driver should flush as much data as possible in a single flush() call.

flush() returns the number of octets remaining in the driver's output queue or buffer after the maximum amount of data has been written.

flush() denotes success or failure by the value of $! after it returns. $! will always numerically equal zero on success. On failure, $! will contain the usual Errno value. In either case, flush() will return the number of octets in the driver's output queue.

get_out_messages_buffered() returns the number of messages enqueued in the driver's output queue, rounded up to the nearest whole message. Some applications require the message count rather than the octet count.

Messages are raw octet chunks enqueued by put(). The following put() call enqueues two messages for a total of six octets:

$filter->put( [ "one", "two" ] );

It is possible for a flush() call to write part of a message. A partial message still counts as one message.

The SEE ALSO section in POE contains a table of contents covering the entire POE distribution.

POE::Wheel - A base class for POE::Session mix-ins.

POE::Filter - A base class for data parsers and serializers.

POE::Driver::SysRW - A driver that encapsulates sysread() and buffered syswrite().

There is no POE::Driver::SendRecv, but nobody has needed one so far. sysread() and syswrite() manage to do almost everything people need.

In theory, drivers should be pretty much interchangeable. In practice, there seems to be an impermeable barrier between the different SOCK_* types.

Please see POE for more information about authors and contributors.

2024-07-13 perl v5.38.2