Create/free mutex in init/destroy

docs/release.rst

@@ -229,6 +229,9 @@ Maintenance
 * Drop support for Python 2.
   By :user:`James Bourbeau <jrbourbeau>`, :issue:`220`.
 
+* Fix leaked semaphore in ``numcodecs.blosc``.
+  By :user:`John Kirkham <jakirkham>`, :issue:`234`.
+
 
 .. _release_0.6.4:
 

numcodecs/__init__.py

@@ -16,7 +16,6 @@
 <https://github.com/alimanfoo/numcodecs/issues>`_.
 
 """
-import multiprocessing
 import atexit
 
 
@@ -42,13 +41,7 @@
     from numcodecs import blosc
     from numcodecs.blosc import Blosc
     register_codec(Blosc)
-    # initialize blosc
-    try:
-        ncores = multiprocessing.cpu_count()
-    except OSError:  # pragma: no cover
-        ncores = 1
     blosc.init()
-    blosc.set_nthreads(min(8, ncores))
     atexit.register(blosc.destroy)
 except ImportError:  # pragma: no cover
     pass

numcodecs/blosc.pyx

@@ -75,25 +75,34 @@ AUTOSHUFFLE = -1
 AUTOBLOCKS = 0
 
 # synchronization
-try:
-    mutex = multiprocessing.Lock()
-except OSError:
-    mutex = None
-except ImportError:
-    mutex = None
+mutex = None
 
 # store ID of process that first loads the module, so we can detect a fork later
 _importer_pid = os.getpid()
 
 
 def init():
     """Initialize the Blosc library environment."""
+    global mutex
+    # synchronization
+    try:
+        mutex = multiprocessing.Lock()
+    except OSError:
+        mutex = None
     blosc_init()
+    # set num threads
+    try:
+        ncores = multiprocessing.cpu_count()
+    except OSError:
+        ncores = 1
+    set_nthreads(min(8, ncores))
 
 
 def destroy():
     """Destroy the Blosc library environment."""
+    global mutex
     blosc_destroy()
+    mutex = None
 
 
 def compname_to_compcode(cname):