[FFmpeg-devel] libavutil/thread.h: Fixed g++ build error when ASSERT_LEVEL is greater than 1

[James Almer]

On 4/17/2017 5:39 AM, Clément Bœsch wrote:
> On Sun, Apr 16, 2017 at 05:20:02PM -0700, Aaron Levinson wrote:
>> From 9e6a9e2b8d58f17c661a3f455e03c95587ec7b18 Mon Sep 17 00:00:00 2001
>> From: Aaron Levinson <alevinsn at aracnet.com>
>> Date: Sun, 16 Apr 2017 17:13:31 -0700
>> Subject: [PATCH] libavutil/thread.h:  Fixed g++ build error when
>>  ASSERT_LEVEL is greater than 1
>>
>> Purpose: libavutil/thread.h: Fixed g++ build error when ASSERT_LEVEL
>> is greater than 1.  This is only relevant when thread.h is included by
>> C++ files.  In this case, the relevant code is only defined if
>> HAVE_PTHREADS is defined as 1.  Use configure --assert-level=2 to do
>> so.
>>
>> Note: Issue discovered as a result of Coverity build failure.  Cause
>> of build failure pinpointed by Hendrik Leppkes.
>>
>> Comments:
>>
>> -- libavutil/thread.h: Altered ASSERT_PTHREAD_NORET definition such
>>    that it uses av_make_error_string instead of av_err2str().
>>    av_err2str() uses a "parenthesized type followed by an initializer
>>    list", which is apparently not valid C++.  This issue started
>>    occurring because thread.h is now included by the DeckLink C++
>>    files.  The alteration does the equivalent of what av_err2str()
>>    does, but instead declares the character buffer as a local
>>    variable.
>> ---
>>  libavutil/thread.h | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavutil/thread.h b/libavutil/thread.h
>> index 6e57447..f108e20 100644
>> --- a/libavutil/thread.h
>> +++ b/libavutil/thread.h
>> @@ -36,8 +36,11 @@
>>  #define ASSERT_PTHREAD_NORET(func, ...) do {                            \
>>      int ret = func(__VA_ARGS__);                                        \
>>      if (ret) {                                                          \
>> +        char errbuf[AV_ERROR_MAX_STRING_SIZE] = "";                     \
>>          av_log(NULL, AV_LOG_FATAL, AV_STRINGIFY(func)                   \
>> -               " failed with error: %s\n", av_err2str(AVERROR(ret)));   \
>> +               " failed with error: %s\n",                              \
>> +               av_make_error_string(errbuf, AV_ERROR_MAX_STRING_SIZE,   \
>> +                                    AVERROR(ret)));                     \
>>          abort();                                                        \
>>      }                                                                   \
>>  } while (0)
> 
> I don't like limiting ourselves in the common C code of the project
> because C++ is a bad and limited language. Can't you solve this by bumping
> the minimal requirement of C++ version?

We're already using C++11 when available because of atomics on mediacodec.
Also, just tried and it seems to fail even with C++14, so it just doesn't
work with C++.

We could instead just make these strict assert wrappers work only on C
code by for example checking for defined(__cplusplus).