Lu's blog

Compile `folly` from source on Arch Linux

Lu Pan -

You first need to install all the dependencies as documented on the folly github page,

  • fmt
  • googletest,
  • boost
  • gflag
  • glog

These are pretty straightforward, as you can build them just fine by following the github page for each project respectively.

However I ran into some issues when building folly from source. I did the standard,

mkdir bin
cd bin
cmake ..
make -j 8

However it complains that gflag is redefined.

/home/lupan/folly/folly/portability/GFlags.h:66:7: error: redefinition of ‘class google::FlagSaver’           
   66 | class FlagSaver {};                                                                                   
      |       ^~~~~~~~~                                                                                       
In file included from /usr/local/include/glog/logging.h:86,                                                   
                 from /home/lupan/folly/folly/concurrency/UnboundedQueue.h:23,                                
                 from /home/lupan/folly/folly/executors/StrandExecutor.h:20,                                  
                 from /home/lupan/folly/folly/executors/StrandExecutor.cpp:17:                                
/usr/local/include/gflags/gflags.h:278:23: note: previous definition of ‘class google::FlagSaver’             
  278 | class GFLAGS_DLL_DECL FlagSaver {                                                                     
      |

folly/portability/GFlags.h depends on a macro called FOLLY_HAVE_LIBGFLAGS to tell if gflag is available or not. But we clearly have just installed gflag. If you grep this macro, you see that it's in the generated folly-config.h header file.

Turns out what happened was that I ran cmake once before gflag was properly installed in the folly directory, and it put a generated folly-config.h in folly/ directly. Because the file is in the .gitignore list, I missed it from git status. That's why even after gflag is properly installed, the folly-config.h in bin directory was always masked by the previous generated one in folly/ directory.

The fix is simple. I just deleted the bin/ directory and ran cmake in folly/ which overwrote the previous bad folly-config.h file, and fixed all the problems.