Fix profiling with C API

[mika-fischer]

Currently, when using OrtEnableProfiling to enable profiling using the C API,
the profile output file is created but is always empty.

The reason is that InferenceSession::EndProfiling() needs to be called to
write the profiling data to the output file.

However there's currently no way to call this function via the C API.

This adds a call to EndProfiling() to the descructor of the session if
profiling is enabled in the session options.

[raymondxyang]

/AzurePipelines run

[azure-pipelines]

Azure Pipelines successfully started running 7 pipeline(s).

[snnn]

Is it better to add an end profiling function in the C API?

[mika-fischer]

@snnn There is also no way to call StartProfiling from the C API. It's always done implicitly when creating the session. So I would find it strange to support only implicit start but explicit end. Either both should be implicit or both should be explicit.

I also think this implicit EndProfiling covers the vast majority of use-cases. And allowing explicit control of the profiling state would necessitate larger changes in the C API (removing the profiling option and introducing new functions).

So all in all I think this is fine as is.

[snnn]

Destructor shouldn't do any file io, including closing file.

[mika-fischer]

1. Why is that?
2. What alternative do you suggest? Do the call in OrtReleaseSession? I fail to see how that's any better.

[snnn]

Because destructor can't report error.

[mika-fischer]

True, but in this case an error is unlikely and logging would suffice IMO. It would be good to catch exceptions in the desrtuctor though. I'll update the pull request.

[mika-fischer]

Alright, I catch the (unlikely) exception now and log it. I also added a TODO that this is not optimal and maybe the C API should be refactored, so that profiling can be started and stopped explicitly.

But this pull request takes profiling via the C API from completetly broken to working as expected in most cases.

[RyanUnderhill]

Yeah, I think this is a good compromise for now.