On Wed, May 25, 2016 at 10:30 PM, Per Hedbor () @ Pike (-) developers
forum <10...@lyskom.lysator.liu.se> wrote:
>>I think the biggest benefit is that your async programming becomes/or
>>looks more sequential/synchroneous which tend to be easier to follow,
>>or in other words less spaghetti-ish.
>
>
> And I definitely beg to differ that.
>
> Take this future-less code from a chat server:
>
> | void rpc_call_muc_join(ReturnCall x, mapping args )
> | {
> | [string muc,string who] = get_args(args,
> | "muc",stringp,
> | "inviter",ornull(stringp));
> |
> | Channel channel = get_destination( muc );
> | int when = now();
> |
> | channel->when_available()
> | {
> | if( !channel->exists() )
> | client_error(x, "No such channel" );
> |
> | channel->joined( user->id, when ) {
> | me->join_channel( channel ) {
> | channel->add_message( msg( "joined",
> | "user_ids",({format_destination(me)}),
> | "by",format_destination(me),
> | "when", now)) {
> | x(true); // return true.
> | };
> | };
> | };
> | };
> | }
>
>
> Todays quiz: Is it really harder to read, and how many asynchronous levels
> do you think there is in it? :)
If you want your asynchronous code to look truly clean, the way
synchronous code does, there needs to be a way to have a function
pause its execution and let something else carry on. Python can do
this, either with generator functions or with the new async/await
keywords. Adapting the style to Pike syntax, it'd be something like
this:
async string talk_to_socket(string msg)
{
array(string) ips = await resolv("destination.ip.address");
foreach (ips, string ip)
{
Stdio.File sock = Stdio.File();
sock->open_socket();
if (await sock->connect(ip, 5678)) break;
}
await sock->write("helo\n");
await sock->write(msg + "\n");
string data = await sock->read(1024, 1);
sock->close();
return data;
}
Whenever you say "await", you trigger a sub-action, and the current
call gets suspended. It functions pretty much like cooperative
threading; effectively, any 'await' can result in a context switch.
Without language support like that, everything's going to be a pile of
(probably lambda) functions, one way or another.
ChrisA
