[MRG] OpenMP support (#260)

* Added : OpenMP support
Restored : Epsilon and Debug mode
Replaced : parmap => multiprocessing is now replace by multithreading

* Commit clean up

* Number of CPUs correctly calculated on SLURM clusters

* Corrected number of processes for cluster slurm

* Mistake corrected

* parmap is now deprecated

* Now a different solver is used depending on the requested number of threads

* Tiny mistake corrected

* Folders are now in the ot library instead of at the root

* Helpers is now correctly placed

* Attempt to make compilation work smoothly

* OS compatible path

* NumThreads now defaults to 1

* Better flags

* Mistake corrected in case of OpenMP unavailability

* Revert OpenMP flags modification, which do not compile on Windows

* Test helper functions

* Helpers comments

* Documentation update

* File title corrected

* Warning no longer using print

* Last attempt for macos compilation

* pls work

* atempt

* solving a type error

* TypeError OpenMP

* Compilation finally working on Windows

* Bug solve, number of threads now correctly selected

* 64 bits solver to avoid overflows for bigger problems

* 64 bits EMD corrected

Co-authored-by: kguerda-idris <ssos023@jean-zay3.idris.fr>
Co-authored-by: ncassereau-idris <84033440+ncassereau-idris@users.noreply.github.com>
Co-authored-by: ncassereau <nathan.cassereau@idris.fr>
Co-authored-by: Rémi Flamary <remi.flamary@gmail.com>

2 files changed, 172 insertions, 0 deletions

diff --git a/ot/helpers/openmp_helpers.py b/ot/helpers/openmp_helpers.py
new file mode 100644
index 0000000..a6ad38b
--- /dev/null
+++ b/ot/helpers/openmp_helpers.py
@@ -0,0 +1,85 @@
+"""Helpers for OpenMP support during the build."""
+
+# This code is adapted for a large part from the astropy openmp helpers, which
+# can be found at: https://github.com/astropy/extension-helpers/blob/master/extension_helpers/_openmp_helpers.py  # noqa
+
+
+import os
+import sys
+import textwrap
+import subprocess
+
+from distutils.errors import CompileError, LinkError
+
+from pre_build_helpers import compile_test_program
+
+
+def get_openmp_flag(compiler):
+    """Get openmp flags for a given compiler"""
+
+    if hasattr(compiler, 'compiler'):
+        compiler = compiler.compiler[0]
+    else:
+        compiler = compiler.__class__.__name__
+
+    if sys.platform == "win32" and ('icc' in compiler or 'icl' in compiler):
+        omp_flag = ['/Qopenmp']
+    elif sys.platform == "win32":
+        omp_flag = ['/openmp']
+    elif sys.platform in ("darwin", "linux") and "icc" in compiler:
+        omp_flag = ['-qopenmp']
+    elif sys.platform == "darwin" and 'openmp' in os.getenv('CPPFLAGS', ''):
+        omp_flag = []
+    else:
+        # Default flag for GCC and clang:
+        omp_flag = ['-fopenmp']
+        if sys.platform.startswith("darwin"):
+            omp_flag += ["-Xpreprocessor", "-lomp"]
+    return omp_flag
+
+
+def check_openmp_support():
+    """Check whether OpenMP test code can be compiled and run"""
+
+    code = textwrap.dedent(
+        """\
+        #include <omp.h>
+        #include <stdio.h>
+        int main(void) {
+        #pragma omp parallel
+        printf("nthreads=%d\\n", omp_get_num_threads());
+        return 0;
+        }
+        """)
+
+    extra_preargs = os.getenv('LDFLAGS', None)
+    if extra_preargs is not None:
+        extra_preargs = extra_preargs.strip().split(" ")
+        extra_preargs = [
+            flag for flag in extra_preargs
+            if flag.startswith(('-L', '-Wl,-rpath', '-l'))]
+
+    extra_postargs = get_openmp_flag
+
+    try:
+        output, compile_flags = compile_test_program(
+            code,
+            extra_preargs=extra_preargs,
+            extra_postargs=extra_postargs
+        )
+
+        if output and 'nthreads=' in output[0]:
+            nthreads = int(output[0].strip().split('=')[1])
+            openmp_supported = len(output) == nthreads
+        elif "PYTHON_CROSSENV" in os.environ:
+            # Since we can't run the test program when cross-compiling
+            # assume that openmp is supported if the program can be
+            # compiled.
+            openmp_supported = True
+        else:
+            openmp_supported = False
+
+    except (CompileError, LinkError, subprocess.CalledProcessError):
+        openmp_supported = False
+        compile_flags = []
+    return openmp_supported, compile_flags
diff --git a/ot/helpers/pre_build_helpers.py b/ot/helpers/pre_build_helpers.py
new file mode 100644
index 0000000..93ecd6a
--- /dev/null
+++ b/ot/helpers/pre_build_helpers.py
@@ -0,0 +1,87 @@
+"""Helpers to check build environment before actual build of POT"""
+
+import os
+import sys
+import glob
+import tempfile
+import setuptools  # noqa
+import subprocess
+
+from distutils.dist import Distribution
+from distutils.sysconfig import customize_compiler
+from numpy.distutils.ccompiler import new_compiler
+from numpy.distutils.command.config_compiler import config_cc
+
+
+def _get_compiler():
+    """Get a compiler equivalent to the one that will be used to build POT
+    Handles compiler specified as follows:
+        - python setup.py build_ext --compiler=<compiler>
+        - CC=<compiler> python setup.py build_ext
+    """
+    dist = Distribution({'script_name': os.path.basename(sys.argv[0]),
+                         'script_args': sys.argv[1:],
+                         'cmdclass': {'config_cc': config_cc}})
+
+    cmd_opts = dist.command_options.get('build_ext')
+    if cmd_opts is not None and 'compiler' in cmd_opts:
+        compiler = cmd_opts['compiler'][1]
+    else:
+        compiler = None
+
+    ccompiler = new_compiler(compiler=compiler)
+    customize_compiler(ccompiler)
+
+    return ccompiler
+
+
+def compile_test_program(code, extra_preargs=[], extra_postargs=[]):
+    """Check that some C code can be compiled and run"""
+    ccompiler = _get_compiler()
+
+    # extra_(pre/post)args can be a callable to make it possible to get its
+    # value from the compiler
+    if callable(extra_preargs):
+        extra_preargs = extra_preargs(ccompiler)
+    if callable(extra_postargs):
+        extra_postargs = extra_postargs(ccompiler)
+
+    start_dir = os.path.abspath('.')
+
+    with tempfile.TemporaryDirectory() as tmp_dir:
+        try:
+            os.chdir(tmp_dir)
+
+            # Write test program
+            with open('test_program.c', 'w') as f:
+                f.write(code)
+
+            os.mkdir('objects')
+
+            # Compile, test program
+            ccompiler.compile(['test_program.c'], output_dir='objects',
+                              extra_postargs=extra_postargs)
+
+            # Link test program
+            objects = glob.glob(
+                os.path.join('objects', '*' + ccompiler.obj_extension))
+            ccompiler.link_executable(objects, 'test_program',
+                                      extra_preargs=extra_preargs,
+                                      extra_postargs=extra_postargs)
+
+            if "PYTHON_CROSSENV" not in os.environ:
+                # Run test program if not cross compiling
+                # will raise a CalledProcessError if return code was non-zero
+                output = subprocess.check_output('./test_program')
+                output = output.decode(
+                    sys.stdout.encoding or 'utf-8').splitlines()
+            else:
+                # Return an empty output if we are cross compiling
+                # as we cannot run the test_program
+                output = []
+        except Exception:
+            raise
+        finally:
+            os.chdir(start_dir)
+
+    return output, extra_postargs