MSVC needs -D _HAS_EXCEPTIONS=1 for exceptions to work properly #85

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1. jasongin commented on Jul 21, 2017

   

   jasongin

   on Jul 21, 2017

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   Why? Can you explain what problem you're seeing without that define? There are tests of the exception behavior that seem to work fine without it.

   As far as I know, _HAS_EXCEPTIONS=1 is the default for MSVC. Some projects may override it to 0. But in that case, they'd probably want 'NAPI_DISABLE_CPP_EXCEPTIONS instead.
2. mika-fischer commented on Jul 21, 2017

   

   mika-fischer

   on Jul 21, 2017

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   Things work to some degree without it but there are subtle memory errors. I don't understand exactly what this flag causes but the effect is that objects are freed too early when handling an exception.

   For instance try this with _HAS_EXCEPTIONS=0 and _HAS_EXCEPTIONS=1:

   try
   {
       throw std::runtime_error(std::string("abc"));
   }
   catch (std::exception& e)
   {
       std::cout << "'" << e.what() << "'" << std::endl;
   }
   

   For me with MSVC 2015 this reliably prints '' with _HAS_EXCEPTIONS=0. But I've also encountered garbage memory in other cases. Needless to say this was a huge pain to debug and thus I think it should be much more prominently documented.

   The define comes from nodejs itself: https://github.com/nodejs/node/blob/master/common.gypi#L273

   See also nodejs/node-gyp#939 which led me to the solution.

   👍React with 👍1Reacted by Jordi Vallès
3. jasongin commented on Jul 21, 2017

   

   jasongin

   on Jul 21, 2017

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   Interesting. Thanks for the details. And I didn't realize node common.gypi set _HAS_EXCEPTIONS=0. I agree then it should be added to the README.
4. DBJDBJ commented on Jan 31, 2020

   

   DBJDBJ

   on Jan 31, 2020

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   Abstract

   The author measures size costs of error handling approaches. Exceptions are big, std::abort and integer error codes are small.
5. NickNaso commented on Jan 31, 2020

   

   NickNaso

   on Jan 31, 2020

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   Hi @DBJDBJ,
   thanks for reporting the paper about performance on error handling. node-addon-api allow you to enable or disable the exception mechanism.
   It is documented on the following sections:

   • Setup
   • Error handling

   If you enable the exceptions you will have a little overhead and it could be acceptable or not.

   I'm closing this because now the error handling for node-addon-api is documented like how it's possible to enable or disable the exception mechanism.
6. NickNaso

   closed this as completedon Jan 31, 2020
7. DBJDBJ commented on Jan 31, 2020

   

   DBJDBJ

   on Jan 31, 2020

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   If you enable the exceptions you will have a little overhead and it could be acceptable or not

   Many thanks for the quick comment. I appreciate the answer.

   I might be so bold to think we (the native node.js community and customers) do require a bit more precise size and performance results than "you will have a little overhead..." ... has anyone (tasked by node team) measured the impact of exceptions recently? on the 3 key platforms with the 3 key compilers. I am trying to stay high level here. :)
8. zbjornson commented on Sep 1, 2021

   

   zbjornson

   on Sep 1, 2021

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   @NickNaso This issue was closed but the documentation was never updated. Here's a simple example that doesn't catch correctly without "defines": ["_HAS_EXCEPTIONS=1"]:

   #include<new>
   
   Napi::Value test(const Napi::CallbackInfo& info) {
      Napi::Env env = info.Env();
      try {
         uint64_t* ptr = new uint64_t[0xFFFFFFFFFFFFUL];
         delete[] ptr;
      } catch(const std::bad_alloc& ba) {
         throw Napi::Error::New(env, ba.what());
      } catch(...) {
         throw Napi::Error::New(env, "This shouldn't be the one that catches");
      }
      return Napi::Number::New(env, 0);
   }
   
   Napi::Object Init(Napi::Env env, Napi::Object exports) {
   	exports.Set(Napi::String::New(env, "test"), Napi::Function::New(env, test));
   	return exports;
   }
   
   NODE_API_MODULE(xxx, Init)
9. NickNaso commented on Sep 1, 2021

   

   NickNaso

   on Sep 1, 2021

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   Hi @zbjornson,
   sorry I made a mistake on closing the issue. Now i'm preparing a PR to solve the problem. Thanks for your feedback.

   👍React with 👍1Reacted by Zach Bjornson
10. DBJDBJ commented on Sep 2, 2021

    

    DBJDBJ

    on Sep 2, 2021

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    Ok here is what precisely happens if one compiles with -D_HAS_EXCEPTIONS=0, on Windows.

    _CPPUNWIND becomes 0. Keywords try,throw, catch cease to exist and WIN32 SEH aka "Structured Exceptions Handling" is being used everywhere like for example in MS STL.

    This is primarily the side effect of using cl.exe (MSVC compiler) with the /kernel switch, to create kernel-mode DLL's.

    May thanks ...

    👍React with 👍1Reacted by Nicola Del Gobbo