NAME

       Prima::File - asynchronous stream I/O.

SYNOPSIS

         use strict;
         use Prima qw(Application);

         # create pipe and autoflush the writer end
         pipe(READ, WRITE) or die "pipe():$!\n";
         select WRITE;
         $|=1;
         select STDOUT;

         # create Prima listener on the reader end
         my $read = Prima::File-> new(
             file => \*READ,
             mask => fe::Read,
             onRead => sub {
                $_ = <READ>;
                print "read:$_\n";
             },
         );

         print WRITE "line\n";
         run Prima;

DESCRIPTION

       Prima::File provides access to the I/O stream events, that are called when a file handle
       becomes readable, writable or if an exception occurred. Registering file handles to
       Prima::File objects makes possible the stream operations coexist with the event loop.

USAGE

       Prima::File is a descendant of Prima::Component.  Objects of Prima::File class must be
       binded to a valid file handle object, before the associated events can occur:

         my $f = Prima::File-> create();
         $f-> file( *STDIN);

       When a file handle, binded via the "::file" property becomes readable, writable or when an
       exception signaled, one of three correspondent events called - "Read", "Write" or
       "Exception". When a handle is always readable, or always writable, or, some of these
       events are desired to be blocked, the file event mask can be set via the "::mask"
       property:

         $f-> mask( fe::Read | fe::Exception);

       NB. Due to different system implementations, the only handles, currently supported on all
       systems, are socket handle and disk file handles. Pipes only work on unix platforms. The
       example file socket.pl elucidates the use of sockets together with Prima::File.

       When a file handle is not needed anymore, it is expected to be detached from an object
       explicitly:

         $f-> file( undef);

       However, if the system detects that a file handle is no longer valid, it is automatically
       detached. It is possible to check, if a file handle is still valid by calling the
       "is_active()" method.

       Prima::File events are basically the same I/O callbacks, provided by a system "select()"
       call. See documentation of your system's select() for the implementation details.

API

   Properties
       file HANDLE
           Selects a file handle, that is to be monitored for stream I/O events.  If HANDLE is
           "undef", object is returned to a passive state, and the previously binded file handle
           is de-selected.

       mask EVENT_MASK
           Selects a event mask, that is a combination of "fe::XXX" integer constants, each
           representing an event:

              fe::Read
              fe::Write
              fe::Exception

           The omitted events are effectively excluded from the system file event multiplexing
           mechanism.

   Methods
       get_handle
           Returns "sprintf("0x%08x", fileno( file ))" string.  If "::file" is "undef", -1 is
           used instead fileno() result.

       is_active AUTODETACH = 0
           Returns a boolean flag, indicating if a file handle is valid.  If AUTODETACH is 1, and
           the file handle is not valid, "file(undef)" is called.

   Events
       Read
           Called when a file handle becomes readable. The callback procedure is expected to call
           a non-blocking read() on the file handle.

       Write
           Called when a file handle becomes writable. The callback procedure is expected to call
           a non-blocking write() on the file handle.

       Exception
           Called when an exception is signaled on a file handle.  The exceptions are specific to
           handle type and the operating system.  For example, a unix socket signals "Exception"
           when a control status data for a pseudo terminal or an out-of-band data arrives.

AUTHOR

       Dmitry Karasik, <dmitry@karasik.eu.org>.

SEE ALSO

       Prima, Prima::Object