Custom main and event loop

A vibe.0 process is a main() you wrote, a LibasyncDriver the module constructor started, one or more listenHTTP calls on that first thread, and runEventLoop() which does not return until something calls exitEventLoop(). There is no implicit main. source/vibe/appmain.d compiles only under VibeDefaultMain and not VibeCustomMain, and when it compiles it static asserts. The engine’s webserver/dub.sdl sets VibeCustomMain. Generated apps must too.

Process start

vibe.core.core shared static this() (process):

• Initialises the log module.
• Allocates VibeDriverCore and the thread registry mutex/condition.
• Installs SIGINT/SIGTERM/SIGPIPE (POSIX) or SIGABRT/SIGTERM/SIGINT (Windows).
• Names the main thread "V|Main". Threads whose name does not start with "V|" are ignored by later per-thread setup.
• Calls setupDriver() → new LibasyncDriver(core).
• Creates a process-wide ManualEvent used as a cross-thread wake.
• Optionally registers --uid / --gid (unless VibeNoDefaultArgs).
• If newStdConcurrency, installs VibedScheduler into std.concurrency.

Per "V|…" thread, static this() allocates a CoreTask fiber slot and calls setupDriver() again so workers get their own LibasyncDriver / EventLoop. getEventDriver() is typed as returning LibasyncDriver, not EventDriver. The abstraction is documentary: you cannot swap backends without editing that module. Residual version(VibeLibeventDriver) branches elsewhere are leftover.

listenHTTP then runEventLoop

void main()
{
    auto settings = new HTTPServerSettings;
    settings.port = 8080;
    settings.bindAddresses = ["127.0.0.1"];
 
    auto router = new URLRouter;
    router.registerWebInterface(new UsersPageServer);
 
    listenHTTP(settings, router);
    runEventLoop();
}

Listening may only happen on the thread that first called listenHTTP (g_ctor). “Listening from multiple threads is unsupported.” listenHTTP allocates an HTTPServerContext in ThreadMem, optionally installs an ALPN chooser (h2 / h2-16 / h2-14 / http/1.1, or always http/1.1 if disableHTTP2), and listenTCPs each bind address. A second listenHTTP on the same (addr, port) is a virtual host.

runEventLoop() sets s_eventLoopRunning, notifies idle, and delegates to LibasyncDriver.runEventLoop():

while (!exitFlag && getEventLoop().loop(-1.seconds)) {
    processTimers();
    getDriverCore().notifyIdle();
}

libasync EventLoop.loop is the OS wait (IOCP / epoll / kqueue). Socket readiness resumes the waiting fiber via DriverCore.resumeTask. Exit: exitEventLoop() triggers an AsyncSignal. Process teardown waits for non-daemon "V|…" threads and logs leftover connections / HTTP/2 sessions.

runTask either recycles a CoreTask from s_availableFibers or ThreadMem.alloc!CoreTask. It resumes the fiber synchronously until the first yield (typically the first socket read). Tasks stay on their thread.

Versions that change the boot

DisableDebugger, TLSGC, and SQLite appear in README examples and are not matched in source/. @safe is not part of the interface; the fork does not use it.

What svelte-d’s host main actually does

Engine webserver/source/app.d is the golden. It builds a URLRouter, optionally setupDebugger(), hangs GC endpoints, registerWebInterfaces the installation API and every generated kit class under /__svelte-d/host/, serveStaticFiles("../public/") before the Vite reverse-proxy, then listenHTTP and runEventLoop(). Sessions may be RedisSessionStore. TLS is botan when certs are present. svelte-d writes only between the marked import and route regions. It does not rewrite the rest of main, and it does not add a second event loop.