# Copyright 2018 The gRPC Authors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Patches the compile() to allow enable parallel compilation of C/C++.

build_ext has lots of C/C++ files and normally them one by one.
Enabling parallel build helps a lot.
"""

import distutils.ccompiler
import os

try:
    BUILD_EXT_COMPILER_JOBS = int(
        os.environ.get('GRPC_PYTHON_BUILD_EXT_COMPILER_JOBS', '1'))
except ValueError:
    BUILD_EXT_COMPILER_JOBS = 1


# monkey-patch for parallel compilation
def _parallel_compile(self,
                      sources,
                      output_dir=None,
                      macros=None,
                      include_dirs=None,
                      debug=0,
                      extra_preargs=None,
                      extra_postargs=None,
                      depends=None):
    # setup the same way as distutils.ccompiler.CCompiler
    # https://github.com/python/cpython/blob/31368a4f0e531c19affe2a1becd25fc316bc7501/Lib/distutils/ccompiler.py#L564
    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)

    def _compile_single_file(obj):
        try:
            src, ext = build[obj]
        except KeyError:
            return
        self._compile(obj, src, ext, cc_args, extra_postargs, pp_opts)

    # run compilation of individual files in parallel
    import multiprocessing.pool
    multiprocessing.pool.ThreadPool(BUILD_EXT_COMPILER_JOBS).map(
        _compile_single_file, objects)
    return objects


def monkeypatch_compile_maybe():
    """Monkeypatching is dumb, but the build speed gain is worth it."""
    if BUILD_EXT_COMPILER_JOBS > 1:
        distutils.ccompiler.CCompiler.compile = _parallel_compile
