Fix #177

ImageD11/cImageD11.py

@@ -1,9 +1,7 @@
-
-
 # import cImageD11 compiled module and patch the docstrings
 
-import sys
 import struct
+import warnings
 from ImageD11 import cImageD11_docstrings
 
 try:
@@ -19,43 +17,95 @@
     print("   python setup.py build_ext --inplace")
     raise
 
+# Check for the use of openmp interactions with os.fork and multiprocessing
+
+def check_multiprocessing():
+    """ You cannot safely use os.fork together with threads.
+    But the cImageD11 codes uses threads via openmp.
+    So please use forkserver or spawn for multiprocessing.
+
+    https://discuss.python.org/t/concerns-regarding-deprecation-of-fork-with-alive-threads/33555
+    https://github.com/FABLE-3DXRD/ImageD11/issues/177
+
+    > Developers should respond by adjusting their use of multiprocessing or concurrent.futures
+    > to explicitly specify either the "forkserver" or "spawn" start methods via a context.
+    """
+    import multiprocessing
+    # Problem cases are:
+    #     child processes -> we will set num threads to 1
+    parent = None
+    if hasattr(multiprocessing,"parent_process"):
+        parent = multiprocessing.parent_process()
+        # only for python 3.8 and up
+        cimaged11_omp_set_num_threads( 1 ) 
+        # people wanting Nprocs * Mthreads need to reset after import
+        # OMP_NUM_THREADS is not going to work for them
+        # how are we going to remember this in the future??
+    #
+    # now check for the fork issue
+    if ((multiprocessing.get_start_method(allow_none=False) == 'fork') and    # we have the problem
+        (multiprocessing.get_start_method(allow_none=True) is None) and       # by accident
+         ('forkserver' in multiprocessing.get_all_start_methods())):          # so fix it
+            multiprocessing.set_start_method('forkserver')
+    if ((multiprocessing.get_start_method(allow_none=False) == 'fork') and    #  we have the problem
+        (parent is not None)):
+        # Tell them about it.
+        warnings.warn(__doc__)
+
+
+
+if cimaged11_omp_get_max_threads() == 0:
+    # The code was compiled without openmp
+    OPENMP = False
+else:
+    # Openmp threading can be used
+    OPENMP = True
+    check_multiprocessing()
+
+
 # For 32 or 64 bits
-nbyte = struct.calcsize("P") # 4 or 8
+nbyte = struct.calcsize("P")  # 4 or 8
 
 if nbyte == 8:
-    def put_incr(*a,**k):
-        """ redirects to put_incr64 """
-        return put_incr64(*a,**k)
+
+    def put_incr(*a, **k):
+        """redirects to put_incr64"""
+        return put_incr64(*a, **k)
+
 
 if nbyte == 4:
-    def put_incr(*a,**k):
-        """ redirects to put_incr32 """
-        return put_incr32(*a,**k)
+
+    def put_incr(*a, **k):
+        """redirects to put_incr32"""
+        return put_incr32(*a, **k)
+
 
 # Add / fix the docstrings
 
-def fix_doc( oldstring, to_be_added ):
-    """ Adds a description of the function to the f2py string """
+
+def fix_doc(oldstring, to_be_added):
+    """Adds a description of the function to the f2py string"""
     if oldstring.find("Wrapper for"):
         try:
             head, tail = oldstring.split("Wrapper for")
         except:
-            print( oldstring )
-            print( to_be_added )
+            print(oldstring)
+            print(to_be_added)
             raise
         iname = tail.find("\n")
         return head + tail[:iname] + " " + to_be_added + tail[iname:]
     else:
         return oldstring + to_be_added
 
+
 def fill_in_docstrings():
     for name in cImageD11_docstrings.__all__:
-        doc = getattr( cImageD11_docstrings, name )
+        doc = getattr(cImageD11_docstrings, name)
         if name in globals():
             func = globals()[name]
-            func.__doc__ = fix_doc( func.__doc__, doc )
+            func.__doc__ = fix_doc(func.__doc__, doc)
+
 
 fill_in_docstrings()
 
 assert verify_rounding(20) == 0, "Problem with cImageD11 fast rounding code"
-