randomMainThread

fn randomMainThread(t: *Threaded, buffer: []u8) void {
    mutexLock(&t.mutex);
    defer mutexUnlock(&t.mutex);

    if (!t.csprng.isInitialized()) {
        @branchHint(.unlikely);
        var seed: [Csprng.seed_len]u8 = undefined;
        {
            mutexUnlock(&t.mutex);
            defer mutexLock(&t.mutex);

            const prev = swapCancelProtection(t, .blocked);
            defer _ = swapCancelProtection(t, prev);

            randomSecure(t, &seed) catch |err| switch (err) {
                error.Canceled => unreachable,
                error.EntropyUnavailable => fallbackSeed(t, &seed),
            };
        }
        t.csprng.rng = .init(seed);
    }

    t.csprng.rng.fill(buffer);
}