Provided by: libfuture-io-perl_0.15-1_all bug

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.

       If "select()" is not being used then the default implementation will temporarily set
       filehandles into blocking mode (by switching off the "O_NONBLOCK" flag) while performing
       IO on them.

       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
          $socketfh = await 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.  The returned future will
       yield the newly-accepted client socket filehandle.

   alarm
          await 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
          await 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
          await 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
          $bytes = await Future::IO->sysread( $fh, $length );

       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
          $bytes = await Future::IO->sysread_exactly( $fh, $length );

       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.

   sysread_until_eof
          $f = Future::IO->sysread_until_eof( $fh );

       Since version 0.12.

       Returns a Future that will become done when the given filehandle reaches the EOF
       condition. The returned future will yield all of the bytes read up until that point.

   syswrite
          $written_len = await Future::IO->syswrite( $fh, $bytes );

       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
          $written_len = await Future::IO->syswrite_exactly( $fh, $bytes );

       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
          $wstatus = await Future::IO->waitpid( $pid );

       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>