[erlang-questions] NIF+device problem moving R18->R19 / Mac 10.11->10.12

[Fisher, Paul]

Complete wild guess, but is there a difference in nif initialization running off the main thread in non-working version? This would be a problem for some low-level Mach related things. Not near laptop to look through the code to see if that changed.


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From: erlang-questions-bounces@REDACTED <erlang-questions-bounces@REDACTED> on behalf of Igor Clark <igor.clark@REDACTED>
Sent: Monday, April 17, 2017 4:38:11 PM
To: erlang-questions@REDACTED
Subject: [erlang-questions] NIF+device problem moving R18->R19 / Mac 10.11->10.12

Hi all,

I'm having problems updating a NIF to work correctly with R19 and/or
MacOS Sierra (10.12). The NIF uses Mac OS C API calls to talk to some
hardware. It's been working just fine with R18 on El Capitan, but it
fails in a manner I don't understand when I trying to run it on R19 or
Sierra. I'm pretty baffled as to what's going on, and wonder if any of
the following might ring bells or set off a spider-sense for anyone here?

- The code continues to work 100% as expected on R18 / Mac OS El Capitan
(10.11), as it has for the last year or so.

- On R19 on El Capitan, 99% of the C code works as before, but one
particular MacOS C API call fails unexpectedly. It doesn't crash or
cause errors directly, but it returns null instead of a valid value as
before. There are no build errors or warnings. (I'm using 'pc' plugin
version 1.5.0 with rebar3). Other MacOS API calls talking to the same
hardware work as expected, sending correct commands, getting the
hardware to carry out operations as expected and returning expected
values, without any problems.

- On both R18 & R19 on Sierra, exactly the same problem occurs as above
in R19 on El Capitan.

- If I make the failing/null-returning OS API call in a plain,
simple-as-possible C file compiled with gcc (Apple LLVM/clang), it works
as expected, *on both OS versions*.

- If I paste that same simple-as-possible C code verbatim into the NIF,
as the first line in the load() function, and run it on R18/El Capitan,
it continues to work as expected.

- If I then try to run that identical pasted-verbatim NIF code with no
changes on R18/Sierra or on R19 & either OS version, this one particular
function call fails, as above.

I realise it could be many things, and my initial thought was that it
must be the OS change or even the hardware failing - but the hardware
and C API call continue to work just fine on both OS versions when the
NIF stuff is taken out of the picture, and on El Capitan, the
previously-not-happening problem reliably (and only) starts happening
when I switch from R18 to R19.

Did anything change between R18 and R19 that might somehow make some,
but not all, external C function calls fail on El Capitan/clang 8.0.0?
And could that be something that also makes the same thing happen on
both R18 and R19 under Sierra/clang 8.1.0? Could it perhaps be something
do with the port compiler & LD/CXX flags?

Any ideas as to where else I could look to try to track this down, or
what might be causing this?

(BTW, I'm using homebrew erlang, and I've tried all the above with
versions 18.1, 18.3, 19.0.2 and 19.3 on both OS versions. The gcc/clang
version on El Capitan is from Xcode 8.1, "Apple LLVM version 8.0.0
(clang-800.0.42.1)". On Sierra it's from Xcode 8.3.1, "Apple LLVM
version 8.1.0 (clang-802.0.41)" - but as above, the plain/non-NIF C code
works perfectly and identically on both versions.)

Thanks very much,
Igor
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