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Kevin Ryde > X11-Protocol-Other > X11::Protocol::GrabServer



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X11::Protocol::GrabServer -- object-oriented server grabbing


 use X11::Protocol::GrabServer;
   my $grab = X11::Protocol::GrabServer->new ($X); 
   # UngrabServer when $grab destroyed


This is an object-oriented approach to GrabServer / UngrabServer on an X11::Protocol connection. A grab object represents a desired server grab and destroying it ungrabs.

The first grab object on a connection does a GrabServer() and the last destroyed does an UngrabServer(). The idea is that it's easier to manage the lifespan of a grabbing object in a block etc than to be sure of catching all exits.

Multiple grab objects can overlap or nest. A single GrabServer() is done and it remains until the last object is destroyed. This is good in a library or sub-function where an UngrabServer() should wait until the end of outermost desired grab.

A server grab is usually to make a few operations atomic, for instance something global like root window properties. A block-based temporary object like the synopsis above is typical. It's also possible to hold a grab object for an extended time, perhaps for some state driven interaction with the server.

Care must be taken not to grab for too long since other client programs are locked out. Also if a grabbing program hangs then the server will be unusable until the program is killed, or its TCP etc server connection is broken.

Weak $X

If Perl weak references are available (which means Perl 5.6 and up and Scalar::Util with its usual XS code), then a grab object holds only a weak reference to the target $X connection. This means the grab doesn't keep the connection alive once nothing else is interested. When a connection is destroyed the server ungrabs automatically and so there's no need for an explicit UngrabServer() in that case.

The main effect of the weakening is that $X can be garbage collected anywhere within a grabbing block, the same as if there was no grab. Without the weakening it would wait until the end of the block. In practice this only rarely makes a difference.

In the future if an X11::Protocol connection gets a notion of an explicit close then the intention would be to skip any UngrabServer() in that case too, ie. treat a closed connection the same as a weakened away connection.

Currently no attention is paid to whether the server has disconnected the link. A UngrabServer() is done on destroy in the usual way. If the server has disconnected then a SIGPIPE or EPIPE occurs the same as for any other request sent to the $X.


$g = X11::Protocol::GrabServer->new ($X)

$X is an X11::Protocol object. Create and return a $g object representing a grab of the $X server.

If this new $g is the first new grab on $X then an $X->GrabServer is done.

$g->ungrab ()

Ungrab the $g object explicitly. An ungrab is done automatically when $g is destroyed, but $g->ungrab() can do it sooner.

If $g is already ungrabbed then do nothing.

$g->grab ()

Re-grab with the $g object. This can be used after a $g->ungrab() to grab again with the same object, the same as if newly created.

If $g is already grabbing then do nothing.

$bool = $g->is_grabbed ()

Return true if $g is grabbing. This is true when first created, or false after a $g->ungrab().

This function is only the state of $g. There might be other GrabServer objects which grabbing the server.


X11::Protocol, X11::Protocol::Other



Copyright 2010, 2011, 2012, 2013, 2014 Kevin Ryde

X11-Protocol-Other is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

X11-Protocol-Other is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with X11-Protocol-Other. If not, see <>.

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