/ 
PAGI-0.002000
/ examples/16-foreign-loop/README.md

Example 16 — PAGI::Server under a Foreign (EV-backed) Loop

Demonstrates running PAGI::Server under an EV-backed IO::Async loop, and verifies that Future::IO operations actually tick on that loop.

The diagnostic

The HTTP handler does await Future::IO->sleep(1) before sending a response. If the response arrives after ~1 second, Future::IO is correctly driven by the EV loop. If the request hangs, it is not.

How the wiring works

BEGIN { $ENV{IO_ASYNC_LOOP} = 'EV' }   # (1) select the EV backend globally
use IO::Async::Loop;
use Future::IO::Impl::IOAsync;          # (2) wire Future::IO to IO::Async
use PAGI::Server;

my $loop   = IO::Async::Loop->new;      # IO::Async::Loop::EV
my $server = PAGI::Server->new(app => $app, port => 5016);
$loop->add($server);
$server->listen->get;   # bind without starting the loop
$loop->run;             # the host app owns the loop

Three things must be in place:

  1. IO_ASYNC_LOOP=EV (or BEGIN block) — IO::Async::Loop->new reads this env var and constructs IO::Async::Loop::EV instead of the default poll/epoll backend.
  2. Future::IO::Impl::IOAsync — loaded by the embedder, this routes all Future::IO calls (including Future::IO->sleep) through the shared IO::Async loop, which is now EV-backed.
  3. $loop->add($server) before $server->listen->get — PAGI::Server is an IO::Async::Notifier; it must be added to the loop before it binds.

Observed outcome (SUCCESS)

loop backend: IO::Async::Loop::EV
PAGI Server listening on http://127.0.0.1:5016/ (loop: EV, ...)

$ time curl -s localhost:5016/
PAGI::Server is running under the EV loop; Future::IO ticked

real    0m1.019s

Response arrived in ~1.019 s — the Future::IO->sleep(1) resolved correctly on the EV-backed loop. Both server I/O and Future::IO are driven by EV.

Running

perl examples/16-foreign-loop/server.pl
# In another terminal:
curl localhost:5016/

From an uninstalled PAGI-Server checkout, add -I /path/to/PAGI-Server/lib:

perl -I /path/to/PAGI-Server/lib examples/16-foreign-loop/server.pl

See also