Question

I am programming a C++ extension for Python and I am using distutils to compile the project. As the project grows, rebuilding it takes longer and longer. Is there a way to speed up the build process?

I read that parallel builds (as with make -j) are not possible with distutils. Are there any good alternatives to distutils which might be faster?

I also noticed that it’s recompiling all object files every time I call python setup.py build, even when I only changed one source file. Should this be the case or might I be doing something wrong here?

In case it helps, here are some of the files which I try to compile: https://gist.github.com/2923577

Thanks!

Answer 1

1. Try building with environment variable CC="ccache gcc", that will speed up build significantly when the source has not changed. (strangely, distutils uses CC also for c++ source files). Install the ccache package, of course.

2. Since you have a single extension which is assembled from multiple compiled object files, you can monkey-patch distutils to compile those in parallel (they are independent) – put this into your setup.py (adjust the N=2 as you wish):

   # monkey-patch for parallel compilation
   def parallelCCompile(self, sources, output_dir=None, macros=None, include_dirs=None, debug=0, extra_preargs=None, extra_postargs=None, depends=None):
       # those lines are copied from distutils.ccompiler.CCompiler directly
       macros, objects, extra_postargs, pp_opts, build = self._setup_compile(output_dir, macros, include_dirs, sources, depends, extra_postargs)
       cc_args = self._get_cc_args(pp_opts, debug, extra_preargs)
       # parallel code
       N=2 # number of parallel compilations
       import multiprocessing.pool
       def _single_compile(obj):
           try: src, ext = build[obj]
           except KeyError: return
           self._compile(obj, src, ext, cc_args, extra_postargs, pp_opts)
       # convert to list, imap is evaluated on-demand
       list(multiprocessing.pool.ThreadPool(N).imap(_single_compile,objects))
       return objects
   import distutils.ccompiler
   distutils.ccompiler.CCompiler.compile=parallelCCompile
   

3. For the sake of completeness, if you have multiple extensions, you can use the following solution:

   import os
   import multiprocessing
   try:
       from concurrent.futures import ThreadPoolExecutor as Pool
   except ImportError:
       from multiprocessing.pool import ThreadPool as LegacyPool
   
       # To ensure the with statement works. Required for some older 2.7.x releases
       class Pool(LegacyPool):
           def __enter__(self):
               return self
   
           def __exit__(self, *args):
               self.close()
               self.join()
   
   def build_extensions(self):
       """Function to monkey-patch
       distutils.command.build_ext.build_ext.build_extensions
   
       """
       self.check_extensions_list(self.extensions)
   
       try:
           num_jobs = os.cpu_count()
       except AttributeError:
           num_jobs = multiprocessing.cpu_count()
   
       with Pool(num_jobs) as pool:
           pool.map(self.build_extension, self.extensions)
   
   def compile(
       self, sources, output_dir=None, macros=None, include_dirs=None,
       debug=0, extra_preargs=None, extra_postargs=None, depends=None,
   ):
       """Function to monkey-patch distutils.ccompiler.CCompiler"""
       macros, objects, extra_postargs, pp_opts, build = self._setup_compile(
           output_dir, macros, include_dirs, sources, depends, extra_postargs
       )
       cc_args = self._get_cc_args(pp_opts, debug, extra_preargs)
   
       for obj in objects:
           try:
               src, ext = build[obj]
           except KeyError:
               continue
           self._compile(obj, src, ext, cc_args, extra_postargs, pp_opts)
   
       # Return *all* object filenames, not just the ones we just built.
       return objects
   
   
   from distutils.ccompiler import CCompiler
   from distutils.command.build_ext import build_ext
   build_ext.build_extensions = build_extensions
   CCompiler.compile = compile