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       Prima::File - asynchronous stream I/O.


         use strict;
         use Prima qw(Application);

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


       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.


       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
       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       However, if the system detects that a file handle is no longer valid,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.


       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:


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

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

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

           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.


       Dmitry Karasik, <>.


       Prima, Prima::Object