parallel build

Author: mayeut

.github/workflows/build.yml

@@ -253,6 +253,7 @@ jobs:
       - name: Install SDist
         env:
           CMAKE_ARGS: "-DBUILD_CMAKE_FROM_SOURCE:BOOL=OFF"
+          CMAKE_BUILD_PARALLEL_LEVEL: "4"
         run: |
           python -m pip install -v --no-binary='cmake,ninja' dist/*.tar.gz
           rm -rf dist

_build_backend/backend.py

@@ -96,14 +96,17 @@ def _bootstrap_build(temp_path: str, config_settings: dict[str, list[str] | str]
     with tarfile.open(source_tarball) as tar:
         tar.extractall(path=temp_path_, **tar_filter_kwargs)
 
+    parallel_str = env.get("CMAKE_BUILD_PARALLEL_LEVEL", "1")
+    parallel = max(0, int(parallel_str) if parallel_str.isdigit() else 1) or os.cpu_count() or 1
+
     bootstrap_path = next(temp_path_.glob("cmake-*/bootstrap"))
     prefix_path = temp_path_ / "cmake-install"
-    bootstrap_args = [f"--prefix={prefix_path}", "--no-qt-gui", "--no-debugger"]
+    bootstrap_args = [f"--prefix={prefix_path}", "--no-qt-gui", "--no-debugger", "--parallel={parallel}"]
     previous_cwd = Path().absolute()
     os.chdir(bootstrap_path.parent)
     try:
         subprocess.run([bootstrap_path, *bootstrap_args], env=env, check=True)
-        subprocess.run([make_path], env=env, check=True)
+        subprocess.run([make_path, "-j", f"{parallel}"], env=env, check=True)
         subprocess.run([make_path, "install"], env=env, check=True)
     finally:
         os.chdir(previous_cwd)