I frequently suffer from Java’s complete lack of assistance when it comes to asynchronous programming, but this little multi-phase maneuver really brings home the pain:
protected void findFriends (final Socks.Network sock, Group contents) {
contents.removeAll();
final Label status = UI.wrapLabel(_msgs.findingFriends);
contents.add(status);
class FriendFinder {
public void start () {
// make sure we've authenticated with this network
sock.authenticate(new Callback<Socks.Member>() {
public void onSuccess (Socks.Member self) { gotSelf(self); }
public void onFailure (Throwable err) { fail(_msgs.authErrPre, err); }
});
}
protected void gotSelf (Socks.Member self) {
// note our own name and id on this network for posterity
Global.persist.player().socksIds.put(sock.id(), self);
// get full list of friends for this social network...
sock.getFriends(new Callback<List<Socks.Member>>() {
public void onSuccess (List<Socks.Member> friends) { gotFriends(friends); }
public void onFailure (Throwable err) { fail(_msgs.getFriendsErrPre, err); }
});
}
protected void gotFriends (List<Socks.Member> friends) {
Json.Writer writer = json().newWriter();
writer.array();
for (Socks.Member friend : friends) writer.value(friend.userId);
writer.end();
final Map<String,Socks.Member> fmap = Maps.newHashMap();
for (Socks.Member friend : friends) fmap.put(friend.userId, friend);
// filter our full list of friends, to obtain those that play d11s
net().post(Global.serviceURL("filter"), writer.write(), new Callback<String>() {
public void onSuccess (String data) { gotFiltered(fmap, data); }
public void onFailure (Throwable err) { fail(_msgs.filterErrPre, err); }
});
}
protected void gotFiltered (Map<String,Socks.Member> fmap, String data) {
try {
List<Socks.Member> filtered = Lists.newArrayList();
Json.Array fids = json().parseArray(data);
for (int ii = 0, ll = fids.length(); ii < ll; ii++) {
Socks.Member friend = fmap.get(fids.getString(ii));
if (friend != null) filtered.add(friend);
else log.warning("Got unknown friend from server",
"id", fids.getString(ii), "fmap", fmap);
}
// store the filtered friends locally
Global.persist.socks().storeFriends(sock.id(), filtered);
// and finally update the user interface and report success
int added = addFriends(sock.id(), filtered);
setStatus(_msgs.foundFriends(added, SocksUI.name(sock)));
} catch (Exception e) {
log.warning("Failed to parse filtered friends", "data", data, e);
fail(_msgs.filterParseErrPre, e);
}
}
protected void fail (String prefix, Throwable cause) {
setStatus(prefix + ": " + cause.getMessage());
}
protected void setStatus (String message) {
status.text.update(message);
}
}
new FriendFinder().start();
}
I’ve already taken great liberties with “Java style” to achieve a level of concision that allows at least some of the control flow to remain visible, but it still burns the eyes.
Just for fun, let’s imagine what that might look like if Java supported
something like C#’s async mechanism (wherein the resulting code is the same
as the above, but the compiler takes care of the boilerplate behind the
scenes):
protected void findFriends (final Socks.Network sock, Group contents) {
contents.removeAll();
final Label status = UI.wrapLabel(_msgs.findingFriends);
contents.add(status);
String errpre = _msgs.authErrPre;
try {
Socks.Member self = await sock.authenticate();
// note our own name and id on this network for posterity
Global.persist.player().socksIds.put(sock.id(), self);
// get full list of friends for this social network...
errpre = _msgs.getFriendsErrPre;
List<Socks.Member> friends = await sock.getFriends();
Map<String,Socks.Member> fmap = Maps.newHashMap();
for (Socks.Member friend : friends) fmap.put(friend.userId, friend);
// filter our full list of friends, to obtain those that play d11s
Json.Writer writer = json().newWriter();
writer.array();
for (Socks.Member friend : friends) writer.value(friend.userId);
writer.end();
errpre = _msgs.filterErrPre;
String data = await net().post(Global.serviceURL("filter"), writer.write());
Json.Array fids = json().parseArray(data);
List<Socks.Member> filtered = Lists.newArrayList();
for (int ii = 0, ll = fids.length(); ii < ll; ii++) {
Socks.Member friend = fmap.get(fids.getString(ii));
if (friend != null) filtered.add(friend);
else log.warning("Got unknown friend from server",
"id", fids.getString(ii), "fmap", fmap);
}
// store the filtered friends locally
Global.persist.socks().storeFriends(sock.id(), filtered);
// and finally update the user interface and report success
int added = addFriends(sock.id(), filtered);
status.text.update(_msgs.foundFriends(added, SocksUI.name(sock)));
} catch (Exception e) {
status.text.update(errpre + ": " + e.getMessage());
}
}
While we’re dreaming, let’s rewrite it all in Scala (assuming the use of the delimited continuations plugin to do the appropriate rewriting):
def findFriends (sock :Socks.Network, contents :Group) {
contents.removeAll()
val status = UI.wrapLabel(_msgs.findingFriends)
contents.add(status)
var errpre = _msgs.authErrPre
try {
val self = await sock.authenticate
// note our own name and id on this network for posterity
Global.persist.player.socksIds.put(sock.id, self)
// get full list of friends for this social network...
errpre = _msgs.getFriendsErrPre
val friends = await sock.getFriends
// filter our full list of friends, to obtain those that play d11s
errpre = _msgs.filterErrPre
val json = json.newWriter.array(friends map(_.userId)).write
val farray = json.parseArray(await net.post(Global.serviceURL("filter"), json))
val fids = (0 to farray.length) map(farray.getString) toSet
val fmap = friends map(f => f.userId -> f) toMap
val filtered = fmap filterKeys(fids) values
if (fids.size != filtered.size) {
log.warnning("Got unknown friends(s) from server", "friends", friends,
"ids", (fids -- filtered.map(_.userId)))
}
// store the filtered friends locally
Global.persist.socks.storeFriends(sock.id, filtered)
// and finally update the user interface and report success
val added = addFriends(sock.id, filtered)
status.text.update(_msgs.foundFriends(added, SocksUI.name(sock)))
} catch {
case e => status.text.update(errpre + ": " + e.getMessage)
}
}
Alas, I can’t use Scala on my current project. I’ll shut up now and get back to the salt mines.