init

pub fn init(
    /// Must be threadsafe. Only used for the following functions:
    /// * `Io.VTable.async`
    /// * `Io.VTable.concurrent`
    /// * `Io.VTable.groupAsync`
    /// * `Io.VTable.groupConcurrent`
    /// If these functions are avoided, then `Allocator.failing` may be passed
    /// here.
    gpa: Allocator,
    options: InitOptions,
) Threaded {
    if (builtin.single_threaded) return .{
        .allocator = gpa,
        .stack_size = options.stack_size,
        .async_limit = options.async_limit orelse init_single_threaded.async_limit,
        .cpu_count_error = init_single_threaded.cpu_count_error,
        .concurrent_limit = options.concurrent_limit,
        .old_sig_io = undefined,
        .old_sig_pipe = undefined,
        .have_signal_handler = init_single_threaded.have_signal_handler,
        .argv0 = options.argv0,
        .environ_initialized = options.environ.block.isEmpty(),
        .environ = .{ .process_environ = options.environ },
        .worker_threads = init_single_threaded.worker_threads,
        .disable_memory_mapping = options.disable_memory_mapping,
    };

    const cpu_count = std.Thread.getCpuCount();

    var t: Threaded = .{
        .allocator = gpa,
        .stack_size = options.stack_size,
        .async_limit = options.async_limit orelse if (cpu_count) |n| .limited(n - 1) else |_| .nothing,
        .concurrent_limit = options.concurrent_limit,
        .cpu_count_error = if (cpu_count) |_| null else |e| e,
        .old_sig_io = undefined,
        .old_sig_pipe = undefined,
        .have_signal_handler = false,
        .argv0 = options.argv0,
        .environ_initialized = options.environ.block.isEmpty(),
        .environ = .{ .process_environ = options.environ },
        .worker_threads = .init(null),
        .disable_memory_mapping = options.disable_memory_mapping,
    };

    if (posix.Sigaction != void) {
        // This causes sending `posix.SIG.IO` to thread to interrupt blocking
        // syscalls, returning `posix.E.INTR`.
        const act: posix.Sigaction = .{
            .handler = .{ .handler = doNothingSignalHandler },
            .mask = posix.sigemptyset(),
            .flags = 0,
        };
        if (have_sig_io) posix.sigaction(.IO, &act, &t.old_sig_io);
        if (have_sig_pipe) posix.sigaction(.PIPE, &act, &t.old_sig_pipe);
        t.have_signal_handler = true;
    }

    return t;
}