= async

This is a simple asynchronous demo, that demonstrates use of the RAW
option with a server, along with async message handling, to obtain a
very high level of asynchronous operation, suitable for use in a highly
concurrent server application.

== Compiling

You can override the level of concurrency with the `PARALLEL`
define.  This determines how many requests the server will accept
at a time, and keep outstanding.  Note that for our toy
implementation, we create this many "logical" flows of execution
(these are _NOT_ threads), where a request is followed by a reply.

The value of `PARALLEL` must be at least one, and may be as large
as your memory will permit.  (The default value is 32.)

On UNIX-style systems:

[source, bash]
----
% export CPPFLAGS="-D PARALLEL=32 -I /usr/local/include"
% export LDFLAGS="-L /usr/local/lib -lnng"
% export CC="cc"
% ${CC} ${CPPFLAGS} async.c -o async ${LDFLAGS}
----

== Running

To run the server, use the arguments `__url__ -s`.

To run the client, use the arguments `__url__ __msec__`.

The _msec_ is a "delay" time that server will wait before responding.
We have these delays so simulate long running work.

In the following example, all of the clients should complete within
2 seconds.  (Assuming `PARALLEL` is defined to be large enough.)

[source,bash]
----
% export URL="tcp://127.0.0.1:55995"
# start the server
% ./async $URL -s &
# start a bunch of clients
# Note that these all run concurrently!
% ./async $URL 2 &
% ./async $URL 2 &
% ./async $URL 2 &
% ./async $URL 2 &
% ./async $URL 2 &
----