getCpuCount

    fn getCpuCount() !usize {
        switch (native_os) {
            .linux => {
                return LinuxThreadImpl.getCpuCount();
            },
            .emscripten => {
                return @as(usize, @intCast(std.os.emscripten.emscripten_num_logical_cores()));
            },
            .openbsd => {
                var count: c_int = undefined;
                var count_size: usize = @sizeOf(c_int);
                const mib = [_]c_int{ std.c.CTL.HW, std.c.HW.NCPUONLINE };
                posix.sysctl(&mib, &count, &count_size, null, 0) catch |err| switch (err) {
                    error.NameTooLong, error.UnknownName => unreachable,
                    else => |e| return e,
                };
                return @as(usize, @intCast(count));
            },
            .illumos, .serenity => {
                // The "proper" way to get the cpu count would be to query
                // /dev/kstat via ioctls, and traverse a linked list for each
                // cpu. (illumos)
                const rc = c.sysconf(@backingInt(std.c._SC.NPROCESSORS_ONLN));
                return switch (posix.errno(rc)) {
                    .SUCCESS => @as(usize, @intCast(rc)),
                    else => |err| posix.unexpectedErrno(err),
                };
            },
            .haiku => {
                var system_info: std.c.system_info = undefined;
                return switch (std.c.get_system_info(&system_info)) {
                    0 => @as(usize, @intCast(system_info.cpu_count)),
                    else => error.Unexpected,
                };
            },
            else => {
                var count: c_int = undefined;
                var count_len: usize = @sizeOf(c_int);
                const name = comptime if (target.os.tag.isDarwin()) "hw.logicalcpu" else "hw.ncpu";
                switch (posix.errno(posix.system.sysctlbyname(name, &count, &count_len, null, 0))) {
                    .SUCCESS => return @intCast(count),
                    .FAULT => unreachable,
                    .PERM => return error.PermissionDenied,
                    .NOMEM => return error.SystemResources,
                    .NOENT => unreachable,
                    else => |err| return posix.unexpectedErrno(err),
                }
            },
        }
    }