Pillow/mp_compile.py

# A monkey patch of the base distutils.ccompiler to use parallel builds
# Tested on 2.7, looks to be identical to 3.3.

from multiprocessing import Pool, cpu_count
from distutils.ccompiler import CCompiler
import os

try:
    MAX_PROCS = int(os.environ.get('MAX_CONCURRENCY', cpu_count()))
except:
    MAX_PROCS = None
        

# hideous monkeypatching.  but. but. but.
def _mp_compile_one(tp):
    (self, obj, build, cc_args, extra_postargs, pp_opts) = tp
    try:
        src, ext = build[obj]
    except KeyError:
        return
    self._compile(obj, src, ext, cc_args, extra_postargs, pp_opts)
    return


def _mp_compile(self, sources, output_dir=None, macros=None,
                include_dirs=None, debug=0, extra_preargs=None,
                extra_postargs=None, depends=None):
    """Compile one or more source files.

    see distutils.ccompiler.CCompiler.compile for comments.
    """
    # A concrete compiler class can either override this method
    # entirely or implement _compile().

    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)

    pool = Pool(MAX_PROCS)
    try:
        print ("Building using %d processes" % pool._processes)
    except:
        pass
    arr = [(self, obj, build, cc_args, extra_postargs, pp_opts)
           for obj in objects]
    pool.map_async(_mp_compile_one, arr)
    pool.close()
    pool.join()
    # Return *all* object filenames, not just the ones we just built.
    return objects

# explicitly don't enable if environment says 1 processor
if MAX_PROCS != 1:
    try:
        # bug, only enable if we can make a Pool. see issue #790 and
        # http://stackoverflow.com/questions/6033599/oserror-38-errno-38-with-multiprocessing
        pool = Pool(2)
        CCompiler.compile = _mp_compile
    except Exception as msg:
        print("Exception installing mp_compile, proceeding without: %s" %msg)
else:
    print("Single threaded build, not installing mp_compile: %s processes" %MAX_PROCS)