Provided by: libfuture-io-perl_0.11-3_all 
NAME
"Future::IO" - Future-returning IO methods
SYNOPSIS
use Future::IO;
my $delay = Future::IO->sleep( 5 );
# $delay will become done in 5 seconds time
my $input = Future::IO->sysread( \*STDIN, 4096 );
# $input will yield some input from the STDIN IO handle
DESCRIPTION
This package provides a few basic methods that behave similarly to the same-named core
perl functions relating to IO operations, but yield their results asynchronously via
Future instances.
This is provided primarily as a decoupling mechanism, to allow modules to be written that
perform IO in an asynchronous manner to depend directly on this, while allowing
asynchronous event systems to provide an implementation of these operations.
Default Implementation
If the "override_impl" method is not invoked, a default implementation of these operations
is provided. This implementation allows a single queue of "sysread" or "syswrite" calls on
a single filehandle only, combined with "sleep" calls. It does not support "waitpid".
It is provided for the simple cases where modules only need one filehandle (most likely a
single network socket or hardware device handle), allowing such modules to work without
needing a better event system.
If there are both read/write and "sleep" futures pending, the implementation will use
"select()" to wait for either. This may be problematic on MSWin32, depending on what type
of filehandle is involved.
For cases where multiple filehandles are required, or for doing more involved IO
operations, a real implementation based on an actual event loop should be provided. The
following are known to exist; CPAN may provide others:
• Future::IO::Impl::Glib
• Future::IO::Impl::IOAsync
• Future::IO::Impl::UV
Unit Testing
The replaceable implementation is also useful for writing unit test scripts. If the
implementation is set to an instance of some sort of test fixture or mocking object, a
unit test can check that the appropriate IO operations happen as part of the test.
A testing module which does this is provided by Test::Future::IO.
METHODS
accept
$f = Future::IO->accept( $fh )
Since version 0.11.
Returns a Future that will become done when a new connection has been accepted on the
given filehandle, which should represent a listen-mode socket.
alarm
$f = Future::IO->alarm( $epoch )
Since version 0.08.
Returns a Future that will become done at a fixed point in the future, given as an epoch
timestamp (such as returned by "time()"). This value may be fractional.
connect
$f = Future::IO->connect( $fh, $name )
Since version 0.11.
Returns a Future that will become done when a "connect()" has succeeded on the given
filehandle to the given sockname address.
sleep
$f = Future::IO->sleep( $secs )
Returns a Future that will become done a fixed delay from now, given in seconds. This
value may be fractional.
sysread
$f = Future::IO->sysread( $fh, $length )
$bytes = $f->get
Returns a Future that will become done when at least one byte can be read from the given
filehandle. It may return up to $length bytes. On EOF, the returned future will yield an
empty list (or "undef" in scalar context). On any error (other than "EAGAIN" /
"EWOULDBLOCK" which are ignored), the future fails with a suitable error message.
Note specifically this may perform only a single "sysread()" call, and thus is not
guaranteed to actually return the full length.
sysread_exactly
$f = Future::IO->sysread_exactly( $fh, $length )
$bytes = $f->get
Since version 0.03.
Returns a Future that will become done when exactly the given number of bytes have been
read from the given filehandle. It returns exactly $length bytes. On EOF, the returned
future will yield an empty list (or "undef" in scalar context), even if fewer bytes have
already been obtained. These bytes will be lost. On any error (other than "EAGAIN" /
"EWOULDBLOCK" which are ignored), the future fails with a suitable error message.
This may make more than one "sysread()" call.
syswrite
$f = Future::IO->syswrite( $fh, $bytes )
$written_len = $f->get
Since version 0.04.
Returns a Future that will become done when at least one byte has been written to the
given filehandle. It may write up to all of the bytes. On any error (other than "EAGAIN" /
"EWOULDBLOCK" which are ignored) the future fails with a suitable error message.
Note specifically this may perform only a single "syswrite()" call, and thus is not
guaranteed to actually return the full length.
syswrite_exactly
$f = Future::IO->syswrite_exactly( $fh, $bytes )
$written_len = $f->get
Since version 0.04.
Returns a Future that will become done when exactly the given bytes have been written to
the given filehandle. On any error (other than "EAGAIN" / "EWOULDBLOCK" which are ignored)
the future fails with a suitable error message.
This may make more than one "syswrite()" call.
waitpid
$f = Future::IO->waitpid( $pid )
$wstatus = $f->get
Since version 0.09.
Returns a Future that will become done when the given child process terminates. The future
will yield the wait status of the child process. This can be inspected by the usual
bitshifting operations as per $?:
if( my $termsig = ($wstatus & 0x7f) ) {
say "Terminated with signal $termsig";
}
else {
my $exitcode = ($wstatus >> 8);
say "Terminated with exit code $exitcode";
}
override_impl
Future::IO->override_impl( $impl )
Sets a new implementation for "Future::IO", replacing the minimal default internal
implementation. This can either be a package name or an object instance reference, but
must provide the methods named above.
This method is intended to be called by event loops and other similar places, to provide a
better integration. Another way, which doesn't involve directly depending on "Future::IO"
or loading it, is to use the $IMPL variable; see below.
Can only be called once, and only if the default implementation is not in use, therefore a
module that wishes to override this ought to invoke it as soon as possible on program
startup, before any of the main "Future::IO" methods may have been called.
HAVE_MULTIPLE_FILEHANDLES
$has = Future::IO->HAVE_MULTIPLE_FILEHANDLES
Since version 0.11.
Returns true if the underlying IO implementation actually supports multiple filehandles.
Most real support modules will return true here, but this returns false for the internal
minimal implementation.
await
$f = $f->await
Since version 0.07.
Blocks until this future is ready (either by success or failure). Does not throw an
exception if failed.
THE $IMPL VARIABLE
Since version 0.02.
As an alternative to setting an implementation by using override_impl, a package variable
is also available that allows modules such as event systems to opportunistically provide
an implementation without needing to depend on the module, or loading it "require". Simply
directly set that package variable to the name of an implementing package or an object
instance.
Additionally, implementors may use a name within the "Future::IO::Impl::" namespace,
suffixed by the name of their event system.
For example, something like the following code arrangement is recommended.
package Future::IO::Impl::BananaLoop;
{
no warnings 'once';
( $Future::IO::IMPL //= __PACKAGE__ ) eq __PACKAGE__ or
warn "Unable to set Future::IO implementation to " . __PACKAGE__ .
" as it is already $Future::IO::IMPL\n";
}
sub sleep
{
...
}
sub sysread
{
...
}
sub syswrite
{
...
}
sub waitpid
{
...
}
Optionally, you can also implement "sysread_exactly" and "syswrite_exactly":
sub sysread_exactly
{
...
}
sub syswrite_exactly
{
...
}
If not, they will be emulated by "Future::IO" itself, making multiple calls to the
non-"_exactly" versions.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>