Fix: add check for nonfunctional multiprocessing (fixes #9047)

Add an additional check for a special case where semlock_open seemingly exists but doesn't work (OSError is raised because function is not implemented)

Author: richboss

news/9047.bugfix.rst

@@ -0,0 +1 @@
+Check for operativeness of multiprocessing. This takes care of systems where multiprocessing seems available but really is not.

src/pip/_internal/utils/parallel.py

@@ -43,7 +43,14 @@
 except ImportError:
     LACK_SEM_OPEN = True
 else:
-    LACK_SEM_OPEN = False
+    try:
+        p = ProcessPool()
+        p.terminate()
+        del p
+    except OSError:
+        LACK_SEM_OPEN = True
+    else:
+        LACK_SEM_OPEN = False
 
 # Incredibly large timeout to work around bpo-8296 on Python 2.
 TIMEOUT = 2000000