increase default number of threads for blosc; resolves #33

Author: alimanfoo

docs/release.rst

@@ -11,6 +11,8 @@ Release notes
   section on :ref:`tutorial_compression` for an example.
 * When using the Blosc compressor, the default internal compression library
   is now 'lz4'.
+* The default number of internal threads for the Blosc compressor has been
+  increased to a maximum of 8 (previously 4).
 
 .. _release_1.0.0:
 

zarr/__init__.py

@@ -21,6 +21,5 @@
 else:
     ncores = multiprocessing.cpu_count()
     blosc.init()
-    # diminishing returns beyond 4 threads?
-    blosc.set_nthreads(min(4, ncores))
+    blosc.set_nthreads(min(8, ncores))
     atexit.register(blosc.destroy)