Re: Idea for an event loop library

[Jorge <xxopxe@...>]

On 11/05/12 16:21, Jay Carlson wrote:
> Here's the problem case:
>
> function web_server:handle_login_html(req)
>      -- Grab the current session and ensure it's valid
>      local session_data = this:find_session(req) or this:die()
>      -- Log the request
>      this:log(req)
>      -- delegate to session
>      session_data:handle_login(req)
> end
>
> The problem is "this:log(req)". Logging could be implemented by
> writing to a socket--and you can't tell by looking at this code. If it
> writes to a socket, the socket may want to block. In a simple socket
> coroutine system, operations which would block instead are suspended
> until the socket can be read or written. Waiting for this:log() could
> take arbitrarily long. The session_data we grabbed at the top may be
> stale by then.

In my library you handle this case the obvious 2 ways: you create 
separate task when invoking the log function, or have a separate logging 
task running and signal it when you want to log something.

--Option A:
local function log(req)
    --whatever
end
function handle_login_html(req)
    local session=find_session(req) or error()
    sched.run(log, req)
    session_data.handle_login(req)
end

--Option B
sched.sigrun(function(req)
        --whatever
    end,
    {events={"logthis!"}}
)
function handle_login_html(req)
    local session=find_session(req) or error()
    sched.signal("logthis!", req)
    session_data.handle_login(req)
end

In both cases if the logging function blocks, control will be dispatched 
back (eventually). In other words, if you want synchronous, then do 
function calls. If you want asynchronous, create tasks or signals.
Of course, this makes no sense if i live under the fear that any 
function call i do can turn into a horrible beast. But anyway I can 
handle only so much complexity and levels of indirection. The whole 
reason behind this library was to see if I can cram everyhing needed in 
such a compact package that i can handle an application completelly. It 
is still cooperative multitasking, after all.


Jorge