When using WaitOne with a timeout (Int32 or TimeSpan), the method can exit before the expected time.

The smallest time element is a tick. A tick is not always a second multiple. Internally WaitOne convert the timeout in tick and round it under.

On very fast machine you can exit before expected time (some micro second before + very fast machine = expected time is not correct).

Remi, the paramter for WaitOne(Int32) is clearly documented as milliseconds. I wonder if you have any evidence that it's tick count instead?

Here is WaitOne(Int32)'s documented signature in C#:

public virtual bool WaitOne(
int millisecondsTimeout
)