Using Fibers causes epic crash

[withinboredom]

Minimal code to reproduce:

<?php

do {
    $running = false;
    //$running = frankenphp_handle_request(function (): void {
        $fiber = new Fiber(function() {
            echo "Starting Fiber\n";
        });
        $fiber->start();
    //});
} while ($running);

With some slight modifications, it can also be reproduced in worker mode.

[withinboredom]

@dunglas the following Docker file (props @cdaguerre in #374) appears to "fix" fibers. At least for this reproducer with manual testing. It needs more testing:

FROM dunglas/frankenphp:latest-builder-php8.3-alpine AS builder

COPY --from=caddy:builder-alpine /usr/bin/xcaddy /usr/bin/xcaddy

ENV CGO_ENABLED=1 XCADDY_SETCAP=1 CGO_CXXFLAGS=-fPIE CGO_CFLAGS=-fPIE CGO_LDFLAGS=-pie XCADDY_GO_BUILD_FLAGS='-buildmode=pie -ldflags="-w -s" -trimpath'
RUN xcaddy build \
    --output /usr/local/bin/frankenphp \
    --with github.com/dunglas/frankenphp=./ \
    --with github.com/dunglas/frankenphp/caddy=./caddy/ \
    --with github.com/dunglas/mercure/caddy \
    --with github.com/dunglas/vulcain/caddy

🥳 🤞 🤞 still testing...

[dunglas]

Great news! Don't hesitate to open a PR with this changes, so we can see if this fix the issue for all architectures.

[withinboredom]

I'll do some proper testing by Monday (by updating the fiber branch), but I haven't seen a crash yet via manual testing.

[piotrekkr]

@withinboredom I had issues with fibers so I could also test this on my Cloud Run service but not really sure where can I get docker image to use with this fix.

[withinboredom]

It doesn't fix it, per se, more-or-less just reduces the probability of a crash.

Edit to add: the best way to prevent a crash is to just not output anything at all inside a fiber.