POE::Wheel::ReadWrite - buffered non-blocking I/O
$wheel = POE::Wheel::ReadWrite->new(
# To read and write from the same handle, such as a socket, use
# the Handle parameter:
Handle => $file_or_socket_handle, # Handle to read/write
# To read and write from different handles, such as a dual pipe to
# a child process, or a console, use InputHandle and OutputHandle:
InputHandle => $readable_filehandle, # Handle to read
OutputHandle => $writable_filehandle, # Handle to write
Driver => POE::Driver::Something->new(), # How to read/write it
# To read and write using the same line discipline, such as
# Filter::Line, use the Filter parameter:
Filter => POE::Filter::Something->new(), # How to parse in and out
# To read and write using different line disciplines, such as
# stream out and line in:
InputFilter => POE::Filter::Something->new(), # Read data one way
OutputFilter => POE::Filter::SomethingElse->new(), # Write data another
InputEvent => $input_event_name, # Input received event
FlushedEvent => $flush_event_name, # Output flushed event
ErrorEvent => $error_event_name, # Error occurred event
# To enable callbacks for high and low water events (using any one
# of these options requires the rest):
HighMark => $high_mark_octets, # Outgoing high-water mark
HighEvent => $high_mark_event, # Event to emit when high-water reached
LowMark => $low_mark_octets, # Outgoing low-water mark
LowEvent => $low_mark_event, # Event to emit when low-water reached
# Experimental: If true, flush output synchronously during put()
AutoFlush => $boolean,
);
$wheel->put( $something );
$wheel->event( ... );
# To set both the input and output filters at once:
$wheel->set_filter( POE::Filter::Something->new() );
# To set an input filter or an output filter:
$wheel->set_input_filter( POE::Filter::Something->new() );
$wheel->set_output_filter( POE::Filter::Something->new() );
# To alter the high or low water marks:
$wheel->set_high_mark( $new_high_mark_octets );
$wheel->set_low_mark( $new_low_mark_octets );
# To fetch driver statistics:
$pending_octets = $wheel->get_driver_out_octets();
$pending_messages = $wheel->get_driver_out_messages();
# To retrieve the wheel's ID:
print $wheel->ID;
# To pause and resume a wheel's input events.
$wheel->pause_input();
$wheel->resume_input();
# To shutdown a wheel's socket(s).
$wheel->shutdown_input();
$wheel->shutdown_output();
# Experimental: Flush a wheel's output on command.
$wheel->flush();
ReadWrite performs buffered, select-based I/O on filehandles. It generates events for common file conditions, such as when data has been read or flushed.
put() queues one or more RECORDS for transmission. Each record is of a form dictated by POE::Wheel::ReadWrite's current output filter. ReadWrite uses its output filter to translate the records into a form suitable for writing to a stream. It uses the currently configured driver to buffer and send them.
put() accepts a list of records. If a high water mark has been set, it returns a Boolean value indicating whether the driver's output buffer has reached that level. It always returns false if a high water mark has not been set.
This example will quickly fill a wheel's output queue if it has a high water mark set. Otherwise it will loop infinitely, eventually exhausting memory and crashing.
1 while $wheel->put( get_next_thing_to_send() );
set_input_filter() changes the filter a wheel uses for reading. set_output_filter() changes a wheel's output filter. set_filter() changes them both at once.
These methods let programs change a wheel's underlying protocol while it runs. It retrieves the existing filter's unprocessed input using its get_pending() method and passes that to the new filter.
Switching filters can be tricky. Please see the discussion of get_pending() in POE::Filter.
The HTTPD filter does not support get_pending(), and it will complain if a program tries to switch away from one.
Return the wheel's input or output filter. In many cases, they both may be the same. This is used to access custom methods on the filter itself; for example, Filter::Stackable has methods to push and pop filters on its stack.
$wheel->get_input_filter()->pop();
ReadWrite wheels will continually generate input events for as long as they have data to read. Sometimes it's necessary to control the flow of data coming from a wheel or the input filehandle it manages.
pause_input() instructs the wheel to temporarily stop checking its input filehandle for data. This can keep a session (or a corresponding output buffer) from being overwhelmed.
resume_input() instructs the wheel to resume checking its input filehandle for data.
Though the watermarks affect how often a wheel is flushed, in some cases you might want to manually flush a smaller output, such as before shutdown_output.
This method is experimental. Its behavior may change or it may disappear outright. Please let us know whether it's useful.
Driver is a POE::Driver subclass that is used to read from and write to ReadWrite's filehandle(s). It encapsulates the low-level I/O operations so in theory ReadWrite never needs to know about them.
Driver defaults to <POE::Driver::SysRW-new()>>.
Filter is a POE::Filter subclass that's used to parse incoming data and create streamable outgoing data. It encapsulates the lowest level of a protocol so in theory ReadWrite never needs to know about them.
Filter defaults to <POE::Filter::Line-new()>>.
InputEvent contains the event that the wheel emits for every complete
record read. Every InputEvent is accompanied by two parameters.
ARG0 contains the record which was read. ARG1 contains the
wheel's unique ID.
The wheel will not attempt to read from its Handle or InputHandle if InputEvent is omitted.
A sample InputEvent handler:
sub input_state {
my ($heap, $input, $wheel_id) = @_[HEAP, ARG0, ARG1];
print "Echoing input from wheel $wheel_id: $input\n";
$heap->{wheel}->put($input); # Echo it back.
}
FlushedEvent contains the event that ReadWrite emits whenever its output queue becomes empty. This signals that all pending data has been written, and it's often used to wait for "goodbye" messages to be sent before a session shuts down.
FlushedEvent comes with a single parameter, ARG0, that indicates
which wheel flushed its buffer.
A sample FlushedEvent handler:
sub flushed_state {
# Stop a wheel after all outgoing data is flushed.
# This frees the wheel's resources, including the
# filehandle, and closes the connection.
delete $_[HEAP]->{wheel}->{$_[ARG0]};
}
ErrorEvent contains the event that ReadWrite emits whenever an error occurs. Every ErrorEvent comes with four parameters:
ARG0 contains the name of the operation that failed. This usually
is 'read'. Note: This is not necessarily a function name. The wheel
doesn't know which function its Driver is using.
ARG1 and ARG2 hold numeric and string values for $!,
respectively.
ARG3 contains the wheel's unique ID.
A sample ErrorEvent handler:
sub error_state {
my ($operation, $errnum, $errstr, $wheel_id) = @_[ARG0..ARG3];
warn "Wheel $wheel_id generated $operation error $errnum: $errstr\n";
delete $_[HEAP]->{wheels}->{$wheel_id}; # shut down that wheel
}
ReadWrite emits a HighEvent when a wheel's pending output queue has grown to be at least HighMark octets. A LowEvent is emitted when a wheel's pending octet count drops below the value of LowMark.
HighEvent and LowEvent flip-flop. Once a HighEvent has been emitted, it won't be emitted again until a LowEvent is emitted. Likewise, LowEvent will not be emitted again until HighEvent is. ReadWrite always starts in a low-water state.
Sessions which stream output are encouraged to use these events for flow control. Sessions can reduce their transmission rates or stop transmitting altogether upon receipt of a HighEvent, and they can resume full-speed transmission once LowEvent arrives.
POE::Wheel.
The SEE ALSO section in POE contains a table of contents covering the entire POE distribution.
Oh, probably some.
Please see POE for more information about authors and contributors.