Is ManualResetEventSlim with spinCount = 0 the same as ManualResetEvent?

Question

As far as I know, slim versions of synchronization primitives use spin waits before using resources of the kernel.

Is it true that ManualResetEventSlim with spinCount = 0 is the same as the usual ManualResetEvent?

new ManualResetEventSlim(initialState: false, spinCount: 0);

If no, what is the essential difference between them? Do we have any benefits of using the slim-version without spin waits?

Answer 1

Looking at the source for Wait if you set the spin count to 0 then it's basically a ManualResetEvent but instead of using a kernel wait event it actually uses a monitor.

The kernel wait event is only allocated if you explicitly ask for it, which save a transition into kernel mode to allocate it and set/reset it.

It's worth considering that although the ManualResetEventSlim won't spin if you set the spin count to 0 it's highly likely that the call to Monitor.Wait will spin, so I suspect you're not actually avoiding a spin.