-# $Id: Pod.pm,v 1.2 2006-05-09 12:03:37 mike Exp $
+# $Id: Pod.pm,v 1.22 2006-10-06 11:33:07 mike Exp $
package ZOOM::Pod;
use ZOOM;
+BEGIN {
+ # Just register the names: this doesn't turn the levels on
+ ZOOM::Log::mask_str("pod");
+ ZOOM::Log::mask_str("pod_unhandled");
+}
+
+=head1 NAME
+
+ZOOM::Pod - Perl extension for handling pods of concurrent ZOOM connections
+
=head1 SYNOPSIS
- $conn1 = new ZOOM::Connection("bagel.indexdata.com/gils");
- $conn2 = new ZOOM::Connection("z3950.loc.gov:7090/Voyager");
- $pod = new ZOOM::Pod($conn1, $conn2);
- $pod->callback(ZOOM::Event::RECV_SEARCH, \&show_result);
- $pod->search_pqf("mineral");
- $pod->wait();
+ use ZOOM::Pod;
+
+ $pod = new ZOOM::Pod("bagel.indexdata.com/gils",
+ "bagel.indexdata.com/marc");
+ $pod->callback(ZOOM::Event::RECV_SEARCH, \&completed_search);
+ $pod->callback(ZOOM::Event::RECV_RECORD, \&got_record);
+ $pod->search_pqf("the");
+ $err = $pod->wait();
+ die "$pod->wait() failed with error $err" if $err;
+
+ sub completed_search {
+ ($conn, undef, $rs) = @_;
+ print $conn->option("host"), ": found ", $rs->size(), " records\n";
+ $rs->records(0, 1, 0); # Queues a request for the record
+ return 0;
+ }
- sub show_result {
- ($conn, $rs, $event) = @_;
- print "$conn: found ", $rs->size(), " records\n";
+ sub got_record {
+ ($conn, undef, $rs) = @_;
+ $rec = $rs->record(0);
+ print $conn->option("host"), ": got $rec = '", $rec->render(), "'\n";
+ return 0;
}
+=head1 DESCRIPTION
+
+C<ZOOM:Pod> provides an API that simplifies asynchronous programming
+using ZOOM. A pod is a collection of asynchronous connections that
+are run simultaneously to achieve broadcast searching and retrieval.
+When a pod is created, a set of connections (or target-strings to
+connect to) are specified. Thereafter, they are treated as a unit,
+and methods for searching, option-setting, etc. that are invoked on
+the pod are delegated to each of its members.
+
+The key method on a pod is C<wait()>, which enters a loop accepting
+and dispatching events occurring on any of the connections in the pod.
+Unless interrupted,the loop runs until there are no more events left,
+i.e. no searches are outstanding and no requested records have still
+to be received.
+
+Event dispatching is done by means of callback functions, which can be
+registered for each event. A registered callback is invoked whenever
+a corresponding event occurs. A special callback can be nominated to
+handle errors.
+
+=head1 METHODS
+
+=head2 new()
+
+ $pod = new ZOOM::Pod($conn1, $conn2, $conn3);
+ $pod = new ZOOM::Pod("bagel.indexdata.com/gils",
+ "bagel.indexdata.com/marc");
+
+Creates a new pod containing one or more connections. Each connection
+may be specified either by an existing C<ZOOM::Connection> object,
+which I<must> be asynchronous; or by a ZOOM target string, in which
+case the pod module will make the connection object itself.
+
+Returns the new pod.
+
=cut
+# Functionality to be added:
+#
+# If the constructor's first argument is a number, then it is
+# taken as a limit on the number of connections to handle at any
+# one time. In this case, the pod initially multiplexes between
+# the first I<n> connections, and brings further connections
+# into the active subset whenever already-active connections are
+# closed.
+
sub new {
my $class = shift();
my(@conn) = @_;
+ die "$class with no connections" if @conn == 0;
foreach my $conn (@conn) {
if (!ref $conn) {
$conn = new ZOOM::Connection($conn, 0, async => 1);
+ # The $conn object is always made, even if no there's no
+ # server. Such errors are caught later, by the _check()
+ # call in wait().
}
}
}, $class;
}
+
+=head2 connections()
+
+ @c = $pod->connections();
+
+Returns a list of the connection objects in the pod.
+
+=cut
+
+sub connections {
+ my $this = shift();
+ return @{ $this->{conn} }
+}
+
+
+=head2 option()
+
+ $oldElemSet = $pod->option("elementSetName");
+ $pod->option(elementSetName => "b");
+
+Sets a specified option in all the connections in a pod. Returns the
+old value that the option had in first of the connections in the pod:
+be aware that this value was not necessarily shared by all the members
+of the pod ... but that is true often enough to be useful.
+
+=cut
+
+sub option {
+ my $this = shift();
+ my($key, $value) = @_;
+
+ my $old = $this->{conn}->[0]->option($key);
+ foreach my $conn (@{ $this->{conn} }) {
+ $conn->option($key, $value);
+ }
+
+ return $old;
+}
+
+=head2 callback()
+
+ $pod->callback(ZOOM::Event::RECV_SEARCH, \&completed_search);
+ $pod->callback("exception", sub { print "never mind: $@\n"; return 0 } );
+
+Registers a callback to be invoked by the pod when an event happens.
+Callback functions are invoked by C<wait()> (q.v.).
+
+When registering a callback, the first argument is an event-code - one
+of those defined in the C<ZOOM::Event> enumeration - and the second is
+a function reference, or equivalently an inline code-fragment. It is
+acceptable to nominate the same function as the callback for multiple
+events, by multiple invocations of C<callback()>.
+
+When an event occurs during the execution of C<wait()>, the relevant
+callback function is called with four arguments: the connection that the
+event happened on; the argument that was passed into C<wait()>;
+the result-set associated with the connection (if there is one); and the
+event-type (so that a single function that handles events of multiple
+types can switch on the code where necessary). The callback function
+can handle the event as it wishes, finishing up by returning an
+integer. If this is zero, then C<wait()> continues as normal; if it
+is anything else, then that value is immediately returned from
+C<wait()>.
+
+So a simple event-handler might look like this:
+
+ sub got_event {
+ ($conn, $arg, $rs, $event) = @_;
+ print "event $event on connection ", $conn->option("host"), "\n";
+ print "Found ", $rs->size(), " records\n"
+ if $event == ZOOM::Event::RECV_SEARCH;
+ return 0;
+ }
+
+In addition to the event-type callbacks discussed above, there is a
+special callback, C<"exception">, which is invoked if an exception
+occurs. This will nearly always be a ZOOM error, but this can be
+tested using C<$exception-E<gt>isa("ZOOM::Exception")>. This callback is
+invoked with the same arguments as described above, except that
+instead of the event-type, the fourth argument is a copy of the
+exception, C<$@>. Exception-handling callbacks may of course re-throw
+the exception using C<die $exception>.
+
+So a simple error-handler might look like this:
+
+ sub got_error {
+ ($conn, $arg, $rs, $exception) = @_;
+ if ($exception->isa("ZOOM::Exception")) {
+ print "Caught error $exception - continuing";
+ return 0;
+ }
+ die $exception;
+ }
+
+The C<$arg> argument could be anything at all - it is whatever the
+application code passed into C<wait()>. For example, it could be
+a reference to a hash indexed by the host string of the connections to
+yield some per-connection state information.
+An application might use such information
+to keep a record of which was the last record
+retrieved from the associated connection.
+
+=cut
+
sub callback {
my $this = shift();
my($event, $sub) = @_;
my $old = $this->{callback}->{$event};
- $this->{callback}->{$event} = $sub
- if defined $sub;
+ $this->{callback}->{$event} = $sub;
return $old;
}
+=head2 remove_callbacks()
+
+ $pod->remove_callbacks();
+
+Removes all registed callbacks from the pod. This is useful when the
+pod has completed one operation and is about to start the next.
+
+=cut
+
+sub remove_callbacks {
+ my $this = shift();
+ $this->{callback} = {};
+}
+
+=head2 search_pqf()
+
+ $pod->search_pqf("@attr 1=1003 wedel");
+
+Submits the specified query to each of the connections in a pod,
+delegating to the same-named method of the C<ZOOM::Connection> class
+and storing each result in a result-set object associated with the
+connection that generated it. Returns no value: success or failure
+must subsequently be detected by inspecting the events and exceptions
+generated by C<wait()>ing on the pod.
+
+B<WARNING!>
+An important simplifying assumption is that each connection can only
+have one search active on it at a time: this allows the pod to
+maintain the one-to-one mapping between connections and result-sets.
+Submitting a new search on a connection before the old one has
+completed will result in a total failure in the nature of causality,
+and the spontaneous existence-failure of the universe. Try to avoid
+doing this too often.
+
+=cut
+
sub search_pqf {
my $this = shift();
my($pqf) = @_;
foreach my $i (0..@{ $this->{conn} }-1) {
- $this->{rs}->[$i] = $this->{conn}->[$i]->search_pqf($pqf);
+ my $conn = $this->{conn}->[$i];
+ $this->{rs}->[$i] = $conn->search_pqf($pqf)
+ if !$conn->option("pod_omit");
}
}
+=head2 wait()
+
+ $err = $pod->wait();
+ # or
+ $err = $pod->wait($arg);
+ die "$pod->wait() failed with error $err" if $err;
+
+Waits for events on the connections that make up the pod, usually
+continuing until there are no more events left and then returning
+zero. Whenever an event occurs, a callback function is dispatched as
+described above; if an argument was passed to C<wait()>, then that
+same argument is also passed to each callback invocation. If
+that function returns a non-zero value, then C<wait()> terminates
+immediately, whether or not any events remain, and returns that value.
+
+If an error occurs on one of the connection in the pod, then it is
+normally thrown as a C<ZOOM::Exception>. If, however, there is a
+special C<"exception"> callback registered, then the exception object
+is passed to this instead. As usual, the return value of the callback
+indicates whether C<wait()> should continue (return-value 0) or return
+immediately (any other value). Exception-handling callbacks may of
+course re-throw the exception.
+
+Connections that have the C<pod_omit> option set are omitted from
+consideration. This is useful if, for example, a connection that is
+part of a pod is known to have encountered an unrecoverable error.
+
+=cut
+
sub wait {
my $this = shift();
+ my($arg) = @_;
+
my $res = 0;
- while ((my $i = ZOOM::event($this->{conn})) != 0) {
+ while (1) {
+ my @conn;
+ my @idxmap; # maps indexes into conn to global indexes
+ foreach my $i (0 .. @{ $this->{conn} }-1) {
+ my $conn = $this->{conn}->[$i];
+ if ($conn->option("pod_omit")) {
+ #ZOOM::Log::log("pod", "connection $i omitted (",
+ #$conn->option("host"), ")");
+ } else {
+ push @conn, $conn;
+ push @idxmap, $i;
+ #ZOOM::Log::log("pod", "connection $i included (",
+ #$conn->option("host"), ")");
+ }
+ }
+
+ last if @conn == 0;
+ my $i0 = ZOOM::event(\@conn);
+ last if $i0 == 0;
+ my $i = 1+$idxmap[$i0-1];
my $conn = $this->{conn}->[$i-1];
+ die "connection-mapping screwup" if $conn ne $conn[$i0-1];
+
my $ev = $conn->last_event();
- print("connection ", $i-1, ": ", ZOOM::event_str($ev), "\n");
+ my $evstr = ZOOM::event_str($ev);
+ ZOOM::Log::log("pod", "connection ", $i-1, ": event $ev ($evstr)");
+
+ eval {
+ $conn->_check();
+ }; if ($@) {
+ my $sub = $this->{callback}->{exception};
+ die $@ if !defined $sub;
+ $res = &$sub($conn, $arg, $this->{rs}->[$i-1], $@);
+ last if $res != 0;
+ next;
+ }
+
my $sub = $this->{callback}->{$ev};
if (defined $sub) {
- $res = &$sub($conn, $this->{rs}->[$i-1], $ev);
+ $res = &$sub($conn, $arg, $this->{rs}->[$i-1], $ev);
last if $res != 0;
+ } else {
+ ZOOM::Log::log("pod_unhandled", "connection ", $i-1, ": unhandled event $ev ($evstr)");
}
}
}
+=head1 LOGGING
+
+This module generates logging messages using C<ZOOM::Log::log()>,
+which in turn relies on the YAZ logging facilities. It uses two
+logging levels:
+
+=over 4
+
+=item pod
+
+Logs all events.
+
+=item pod_unhandled
+
+Logs unhandled events, i.e. events of types for which no callback has
+been registered.
+
+=back
+
+These logging levels can be turned on by setting the C<YAZ_LOG>
+environment variable to C<pod,pod_unhandled>.
+
+=head1 SEE ALSO
+
+The underlying
+C<ZOOM>
+module (part of the
+C<Net::Z3950::ZOOM>
+distribution).
+
+=head1 AUTHOR
+
+Mike Taylor, E<lt>mike@indexdata.comE<gt>
+
+=head1 COPYRIGHT AND LICENCE
+
+Copyright (C) 2006 by Index Data.
+
+This library is free software; you can redistribute it and/or modify
+it under the same terms as Perl itself, either Perl version 5.8.4 or,
+at your option, any later version of Perl 5 you may have available.
+
+=cut
+
+
1;
projects / irspy-moved-to-github.git / blobdiff