1 # $Id: Pod.pm,v 1.12 2006-06-07 10:43:22 mike Exp $
11 # Just register the name
12 ZOOM::Log::mask_str("pod");
13 ZOOM::Log::mask_str("pod_unhandled");
18 ZOOM::Pod - Perl extension for handling pods of concurrent ZOOM connections
24 $pod = new ZOOM::Pod("bagel.indexdata.com/gils",
25 "bagel.indexdata.com/marc");
26 $pod->callback(ZOOM::Event::RECV_SEARCH, \&completed_search);
27 $pod->callback(ZOOM::Event::RECV_RECORD, \&got_record);
28 $pod->search_pqf("the");
30 die "$pod->wait() failed with error $err" if $err;
32 sub completed_search {
33 ($conn, undef, $rs) = @_;
34 print $conn->option("host"), ": found ", $rs->size(), " records\n";
35 $rs->records(0, 1, 0); # Queues a request for the record
40 ($conn, undef, $rs) = @_;
41 $rec = $rs->record(0);
42 print $conn->option("host"), ": got $rec = '", $rec->render(), "'\n";
48 C<ZOOM:Pod> provides an API that simplifies asynchronous programming
49 using ZOOM. A pod is a collection of asynchronous connections that
50 are run simultaneously to achieve broadcast searching and retrieval.
51 When a pod is created, a set of connections (or target-strings to
52 connect to) are specified. Thereafter, they are treated as a unit,
53 and methods for searching, option-setting, etc. that are invoked on
54 the pod are delegated to each of its members.
56 The key method on a pod is C<wait()>, which enters a loop accepting
57 and dispatching events occurring on any of the connections in the pod.
58 Unless interrupted,the loop runs until there are no more events left,
59 i.e. no searches are outstanding and no requested records have still
62 Event dispatching is done by means of callback functions, which can be
63 registered for each event. A registered callback is invoked whenever
64 a corresponding event occurs. A special callback can be nominated to
71 $pod = new ZOOM::Pod($conn1, $conn2, $conn3);
72 $pod = new ZOOM::Pod("bagel.indexdata.com/gils",
73 "bagel.indexdata.com/marc");
75 Creates a new pod containing one or more connections. Each connection
76 may be specified either by an existing C<ZOOM::Connection> object,
77 which I<must> be asynchronous; or by a ZOOM target string, in which
78 case the pod module will make the connection object itself.
84 # Functionality to be added:
86 # If the constructor's first argument is a number, then it is
87 # taken as a limit on the number of connections to handle at any
88 # one time. In this case, the pod initially multiplexes between
89 # the first I<n> connections, and brings further connections
90 # into the active subset whenever already-active connections are
97 die "$class with no connections" if @conn == 0;
98 my @state; # Hashrefs with application state associated with connections
99 foreach my $conn (@conn) {
101 $conn = new ZOOM::Connection($conn, 0, async => 1);
102 # The $conn object is always made, even if no there's no
103 # server. Such errors are caught later, by the _check()
119 $oldElemSet = $pod->option("elementSetName");
120 $pod->option(elementSetName => "b");
122 Sets a specified option in all the connections in a pod. Returns the
123 old value that the option had in first of the connections in the pod:
124 be aware that this value was not necessarily shared by all the members
125 of the pod ... but that is true often enough to be useful.
131 my($key, $value) = @_;
133 my $old = $this->{conn}->[0]->option($key);
134 foreach my $conn (@{ $this->{conn} }) {
135 $conn->option($key, $value);
143 $pod->callback(ZOOM::Event::RECV_SEARCH, \&completed_search);
144 $pod->callback("exception", sub { print "never mind: $@\n"; return 0 } );
146 Registers a callback to be invoked by the pod when an event happens.
147 Callback functions are invoked by C<wait()> (q.v.).
149 When registering a callback, the first argument is an event-code - one
150 of those defined in the C<ZOOM::Event> enumeration - and the second is
151 a function reference, or equivalently an inline code-fragment. It is
152 acceptable to nominate the same function as the callback for multiple
153 events, by multiple invocations of C<callback()>.
155 When an event occurs during the execution of C<wait()>, the relevant
156 callback function is called with four arguments: the connection that the
157 event happened on; a state hash-reference associated with the
158 connection; the result-set associated with the connection; and the
159 event-type (so that a single function that handles events of multiple
160 types can switch on the code where necessary). The callback function
161 can handle the event as it wishes, finishing up by returning an
162 integer. If this is zero, then C<wait()> continues as normal; if it
163 is anything else, then that value is immediately returned from
166 So a simple event-handler might look like this:
169 ($conn, $state, $rs, $event) = @_;
170 print "event $event on connection ", $conn->option("host"), "\n";
171 print "Found ", $rs->size(), " records\n"
172 if $event == ZOOM::Event::RECV_SEARCH;
176 In addition to the event-type callbacks discussed above, there is a
177 special callback, C<"exception">, which is invoked if an exception
178 occurs. This will nearly always be a ZOOM error, but this can be
179 tested using C<$exception-E<gt>isa("ZOOM::Exception")>. This callback is
180 invoked with the same arguments as described above, except that
181 instead of the event-type, the fourth argument is a copy of the
182 exception, C<$@>. Exception-handling callbacks may of course re-throw
183 the exception using C<die $exception>.
185 So a simple error-handler might look like this:
188 ($conn, $state, $rs, $exception) = @_;
189 if ($exception->isa("ZOOM::Exception")) {
190 print "Caught error $exception - continuing";
196 The C<$state> argument is a reference to an initially empty hash,
197 which the application can use as it sees fit, to store its own
198 connection-relation information. For example, an application might
199 use C<$state-E<gt>{last}> to keep a record of which was the last record
200 retrieved from the associated connection. The pod module itself does
201 not use the state hash at all, and applications are also welcome to
202 ignore it if they do not need it.
208 my($event, $sub) = @_;
210 my $old = $this->{callback}->{$event};
211 $this->{callback}->{$event} = $sub
219 $pod->search_pqf("@attr 1=1003 wedel");
221 Submits the specified query to each of the connections in a pod,
222 delegating to the same-named method of the C<ZOOM::Connection> class
223 and storing each result in a result-set object associated with the
224 connection that generated it. Returns no value: success or failure
225 must subsequently be detected by inspecting the events and exceptions
226 generated by C<wait()>ing on the pod.
229 An important simplifying assumption is that each connection can only
230 have one search active on it at a time: this allows the pod to
231 maintain the one-to-one mapping between connections and result-sets.
232 Submitting a new search on a connection before the old one has
233 completed will result in a total failure in the nature of causality,
234 and the spontaneous existence-failure of the universe. Do not do
243 foreach my $i (0..@{ $this->{conn} }-1) {
244 $this->{rs}->[$i] = $this->{conn}->[$i]->search_pqf($pqf);
251 die "$pod->wait() failed with error $err" if $err;
253 Waits for events on the connections that make up the pod, usually
254 continuing until there are no more events left and then returning
255 zero. Whenever an event occurs, a callback function is dispatched as
257 that function returns a non-zero value, then C<wait()> terminates
258 immediately, whether or not any events remain, and returns that value.
260 If an error occurs on one of the connection in the pod, then it is
261 normally thrown as a C<ZOOM::Exception>. If, however, there is a
262 special C<"exception"> callback registered, then the exception object
263 is passed to this instead. As usual, the return value of the callback
264 indicates whether C<wait()> should continue (return-value 0) or return
265 immediately (any other value). Exception-handling callbacks may of
266 course re-throw the exception.
274 while ((my $i = ZOOM::event($this->{conn})) != 0) {
275 my $conn = $this->{conn}->[$i-1];
276 my $ev = $conn->last_event();
277 my $evstr = ZOOM::event_str($ev);
278 ZOOM::Log::log("pod", "connection ", $i-1, ": event $ev ($evstr)");
283 my $sub = $this->{callback}->{exception};
284 die $@ if !defined $sub;
285 $res = &$sub($conn, $this->{state}->[$i-1],
286 $this->{rs}->[$i-1], $@);
291 my $sub = $this->{callback}->{$ev};
293 $res = &$sub($conn, $this->{state}->[$i-1],
294 $this->{rs}->[$i-1], $ev);
297 ZOOM::Log::log("pod_unhandled", "connection ", $i-1, ": unhandled event $ev ($evstr)");
307 This module generates logging messages using C<ZOOM::Log::log()>,
308 which in turn relies on the YAZ logging facilities. It uses two
319 Logs unhandled events, i.e. events of types for which no callback has
324 These logging levels can be turned on by setting the C<YAZ_LOG>
325 environment variable to C<pod,pod_unhandled>.
337 Mike Taylor, E<lt>mike@indexdata.comE<gt>
339 =head1 COPYRIGHT AND LICENCE
341 Copyright (C) 2006 by Index Data.
343 This library is free software; you can redistribute it and/or modify
344 it under the same terms as Perl itself, either Perl version 5.8.4 or,
345 at your option, any later version of Perl 5 you may have available.