# $Id: Pod.pm,v 1.22 2006-10-06 11:33:07 mike Exp $ package ZOOM::Pod; use strict; use warnings; 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 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"; $rs->records(0, 1, 0); # Queues a request for the record return 0; } sub got_record { ($conn, undef, $rs) = @_; $rec = $rs->record(0); print $conn->option("host"), ": got $rec = '", $rec->render(), "'\n"; return 0; } =head1 DESCRIPTION C 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, 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 object, which I 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 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(). } } return bless { conn => \@conn, rs => [], callback => {}, }, $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: $@\n"; return 0 } ); Registers a callback to be invoked by the pod when an event happens. Callback functions are invoked by C (q.v.). When registering a callback, the first argument is an event-code - one of those defined in the C enumeration - and the second is a function reference, or equivalently an inline code-fragment. It is acceptable to nominate the same function as the callback for multiple events, by multiple invocations of C. When an event occurs during the execution of C, the relevant callback function is called with four arguments: the connection that the event happened on; the argument that was passed into C; the result-set associated with the connection (if there is one); and the event-type (so that a single function that handles events of multiple types can switch on the code where necessary). The callback function can handle the event as it wishes, finishing up by returning an integer. If this is zero, then C continues as normal; if it is anything else, then that value is immediately returned from C. So a simple event-handler might look like this: sub got_event { ($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-Eisa("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<$@>. Exception-handling callbacks may of course re-throw the exception using C. So a simple error-handler might look like this: sub got_error { ($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. 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; 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 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 Cing on the pod. B 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) { 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, then that same argument is also passed to each callback invocation. If that function returns a non-zero value, then C 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. 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 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 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 (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(); 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, $arg, $this->{rs}->[$i-1], $ev); last if $res != 0; } else { ZOOM::Log::log("pod_unhandled", "connection ", $i-1, ": unhandled event $ev ($evstr)"); } } return $res; } =head1 LOGGING This module generates logging messages using C, 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 environment variable to C. =head1 SEE ALSO The underlying C module (part of the C distribution). =head1 AUTHOR Mike Taylor, Emike@indexdata.comE =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;