document the buildtime environment variables

Author: ksimpson-work

cuda_bindings/docs/source/install.md

@@ -46,6 +46,12 @@ During the build process, environment variable `CUDA_HOME` or `CUDA_PATH` are us
 export CUDA_HOME=/usr/local/cuda
 ```
 
+Some other build time environment variables are as follows:
+
+`CUDA_PYTHON_PARSER_CACHING` : bool, toggles the caching of parsed header files during the cuda-bindings build process. If caching is enabled (`CUDA_PYTHON_PARSER_CACHING` is True), the cache path is set to ./cache_<library_name>, where <library_name> is derived from the cuda toolkit libraries used to build cuda-bindings.
+
+`CUDA_PYTHON_PARALLEL_LEVEL` (previously `PARALLEL_LEVEL`) : int, sets the number of threads used in the compilation of cython files. This is passed as the `nthreads` argument to :meth:`cython.cythonize` and as the parallel attribute for building extension modules.
+
 ### In-place
 
 To compile the extension in-place, run:

cuda_bindings/setup.py

@@ -15,6 +15,7 @@
 import sys
 import sysconfig
 import tempfile
+from warnings import warn
 
 from Cython import Tempita
 from Cython.Build import cythonize
@@ -32,7 +33,13 @@
     raise RuntimeError("Environment variable CUDA_HOME or CUDA_PATH is not set")
 
 CUDA_HOME = CUDA_HOME.split(os.pathsep)
-nthreads = int(os.environ.get("PARALLEL_LEVEL", "0") or "0")
+if os.environ.get("PARALLEL_LEVEL") is not None:
+    warn(
+        "Environment variable PARALLEL_LEVEL is deprecated. Use CUDA_PYTHON_PARALLEL_LEVEL instead",
+        DeprecationWarning,
+        stacklevel=1,
+    )
+nthreads = int(os.environ.get("CUDA_PYTHON_PARALLEL_LEVEL", "0") or "0")
 PARSER_CACHING = os.environ.get("CUDA_PYTHON_PARSER_CACHING", False)
 PARSER_CACHING = bool(PARSER_CACHING)
 
@@ -80,7 +87,7 @@
 found_values = []
 
 include_path_list = [os.path.join(path, "include") for path in CUDA_HOME]
-print(f'Parsing headers in "{include_path_list}" (Caching {PARSER_CACHING})')
+print(f'Parsing headers in "{include_path_list}" (Caching = {PARSER_CACHING})')
 for library, header_list in header_dict.items():
     header_paths = []
     for header in header_list:
@@ -308,9 +315,9 @@ def build_extension(self, ext):
             # Allow extensions to discover libraries at runtime
             # relative their wheels installation.
             if ext.name == "cuda.bindings._bindings.cynvrtc":
-                ldflag = f"-Wl,--disable-new-dtags,-rpath,$ORIGIN/../../../nvidia/cuda_nvrtc/lib"
+                ldflag = "-Wl,--disable-new-dtags,-rpath,$ORIGIN/../../../nvidia/cuda_nvrtc/lib"
             elif ext.name == "cuda.bindings._internal.nvjitlink":
-                ldflag = f"-Wl,--disable-new-dtags,-rpath,$ORIGIN/../../../nvidia/nvjitlink/lib"
+                ldflag = "-Wl,--disable-new-dtags,-rpath,$ORIGIN/../../../nvidia/nvjitlink/lib"
             else:
                 ldflag = None
 
@@ -326,7 +333,7 @@ def build_extension(self, ext):
 cmdclass = {
     "bdist_wheel": WheelsBuildExtensions,
     "build_ext": ParallelBuildExtensions,
-    }
+}
 
 # ----------------------------------------------------------------------
 # Setup