Re: Idea for an event loop library
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- Subject: Re: Idea for an event loop library
- From: Jorge <xxopxe@...>
- Date: 2012年5月11日 20:00:45 -0300
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