spawn

    fn spawn(config: SpawnConfig, comptime f: anytype, args: anytype) !Impl {
        const Args = @TypeOf(args);
        const allocator = std.heap.c_allocator;

        const Instance = struct {
            fn entryFn(raw_arg: ?*anyopaque) callconv(.c) ?*anyopaque {
                const args_ptr: *Args = @ptrCast(@alignCast(raw_arg));
                defer allocator.destroy(args_ptr);
                return callFn(f, args_ptr.*);
            }
        };

        const args_ptr = try allocator.create(Args);
        args_ptr.* = args;
        errdefer allocator.destroy(args_ptr);

        var attr: c.pthread_attr_t = undefined;
        if (c.pthread_attr_init(&attr) != .SUCCESS) return error.SystemResources;
        defer assert(c.pthread_attr_destroy(&attr) == .SUCCESS);

        // Use the same set of parameters used by the libc-less impl.
        const stack_size = @max(config.stack_size, 16 * 1024);
        assert(c.pthread_attr_setstacksize(&attr, stack_size) == .SUCCESS);
        assert(c.pthread_attr_setguardsize(&attr, std.heap.pageSize()) == .SUCCESS);

        var handle: c.pthread_t = undefined;
        switch (c.pthread_create(
            &handle,
            &attr,
            Instance.entryFn,
            @ptrCast(args_ptr),
        )) {
            .SUCCESS => return Impl{ .handle = handle },
            .AGAIN => return error.SystemResources,
            .PERM => unreachable,
            .INVAL => unreachable,
            else => |err| return posix.unexpectedErrno(err),
        }
    }