What does timer_getoverrun( ) do?

I am not very clear with 开发者_运维知识库this API from it's definition in man page: timer_getoverrun( ).

Can someone help me to explain, with the context of a timer?

Thanks in advance

If you create e.g. a 1ms timer, but due to various delays it takes e.g 4.5ms from the signal is generated until it is actually accepted by the application, there could have been 3 more signals issued in the meantime (but isn't, since only one signal is pending at a time). timer_getoverrun() retrieves the value 3 - the number of signals not generated.