mainthread

Work handed to the main thread from any other. Pages and views live on the main thread, and so do bound methods and window events; a plugin's threads (an HTTP response, a WebSocket message, a file changed) give their results to them through this package. The fetch, websocket, watch, updater and terminal plugins depend on it.

The package is plugins/mainthread (module mainthread); it depends on nothing, not even myzig.

zig

const mainthread = @import("mainthread");

const Job = struct {
    window: *myzig.Window,
    result: []u8,

    fn run(ctx: ?*anyopaque) callconv(.c) void {
        const job: *Job = @ptrCast(@alignCast(ctx));
        // On the main thread: emit an event, change a view's state, ...
        _ = job;
    }
};

try mainthread.init(); // once, on the main thread (plugins' services do it when created)
if (!mainthread.post(job, Job.run)) {
    // Not queued (no init, or out of memory): the caller still owns `job`.
}

init() prepares the queue; calling it again does nothing.
post(ctx, func) runs func(ctx) on the main thread, soon. It is safe from any thread; jobs run in the order they were posted. func is a mainthread.Func, *const fn (?*anyopaque) callconv(.c) void.
runUntil(&done) runs the queue until an atomic flag is set, for tests and tools that have no event loop of their own (main thread only).

It is the main thread's own queue on each platform, so nothing polls:

platform	queue
macOS	libdispatch's main queue (`dispatch_async_f`)
Linux	GLib's default context (`g_idle_add`), which GTK's loop runs
Windows	a message-only window (`PostMessageW`), which the app's message loop runs

In browsers (wasm32-wasi) there is no other thread, and the package does not compile there.

Within myzig itself, work reaches the main thread through myzig.App.after (a timer) and, on macOS, objc.dispatchMain; see the architecture guide for the threading model.

cd plugins/mainthread
zig build test                              # on this machine
zig build check -Dtarget=x86_64-linux-gnu   # type-check another platform

mainthread ​

mainthread