Revert "Do not call empty closures."

This reverts commit 66b3430481fcb6fadffb392c6f7c845978b69b29.
Invoke methods.
bugfix: removed a typo
bugfix - PHP_INT_MAX 64int is bigger than Linux Semaphore int 32bit
range check is now in the right place
documentation fix
bugfix increment was in key() method instead of in the next() method
Do not call empty closures.