diff --git a/envs/win-37.yml b/envs/win-37.yml
index 904389d6a..8e5e4a038 100644
--- a/envs/win-37.yml
+++ b/envs/win-37.yml
@@ -22,5 +22,5 @@ dependencies:
   - mkl
   - mkl-devel
   - mkl_fft
-  - opencv>=3.4
+  - opencv>=3.4,<4.2
   - pytest
diff --git a/source/tomopy/recon/algorithm.py b/source/tomopy/recon/algorithm.py
index d2992013f..ecf844657 100644
--- a/source/tomopy/recon/algorithm.py
+++ b/source/tomopy/recon/algorithm.py
@@ -439,9 +439,15 @@ def _dist_recon(tomo, center, recon, algorithm, args, kwargs, ncore, nchunk):
         else:
             # execute recon on ncore threads
             with cf.ThreadPoolExecutor(ncore) as e:
-                for slc in use_slcs:
+                futures = [
                     e.submit(algorithm, tomo[slc], center[slc], recon[slc],
-                             *args, **kwargs)
+                             *args, **kwargs) for slc in use_slcs
+                ]
+            done, _ = cf.wait(futures, return_when=cf.ALL_COMPLETED)
+            for f in done:
+                if f.exception() is not None:
+                    raise f.exception()
+
 
     if pythreads is not None:
         # reset to default
diff --git a/source/tomopy/util/extern/__init__.py b/source/tomopy/util/extern/__init__.py
index 79cb809ea..80e4e7148 100644
--- a/source/tomopy/util/extern/__init__.py
+++ b/source/tomopy/util/extern/__init__.py
@@ -58,16 +58,21 @@ def c_shared_lib(lib_name, error=True):
 
     The ctypes.util.find_library function preprends "lib" to the name.
     """
-    load_dll = ctypes.cdll.LoadLibrary
-    ext = '.so'
-    if sys.platform == 'darwin':
-        ext = '.dylib'
     if os.name == 'nt':
-        ext = '.dll'
         load_dll = ctypes.windll.LoadLibrary
+    else:
+        load_dll = ctypes.cdll.LoadLibrary
+
+    # Returns None or a library name
     sharedlib = ctypes.util.find_library(lib_name)
-    if sharedlib and os.path.exists(sharedlib):
-        return load_dll(sharedlib)
+
+    if sharedlib is not None:
+        try:
+            # No error if sharedlib is None; error if library name wrong
+            return load_dll(sharedlib)
+        except OSError:
+            pass
+
     explanation = (
         'TomoPy links to compiled components which are installed separately'
         ' and loaded using ctypes.util.find_library().'
@@ -79,7 +84,8 @@ def c_shared_lib(lib_name, error=True):
     warnings.warn(
         explanation +
         'Some functionality is unavailable because an optional shared'
-        f' library, {sharedlib}, is missing.', ImportWarning)
+        f' library, {lib_name}, is missing.', ImportWarning)
+    return None
 
 
 def _missing_library(function):
diff --git a/source/tomopy/util/mproc.py b/source/tomopy/util/mproc.py
index 406361ffd..ab8f780f1 100644
--- a/source/tomopy/util/mproc.py
+++ b/source/tomopy/util/mproc.py
@@ -87,7 +87,7 @@ def get_rank():
         from mpi4py import MPI
         comm_w = MPI.COMM_WORLD
         return comm_w.Get_rank()
-    except:
+    except ModuleNotFoundError:
         return 0
 
 
@@ -97,7 +97,7 @@ def get_nproc():
         from mpi4py import MPI
         comm_w = MPI.COMM_WORLD
         return comm_w.Get_size()
-    except:
+    except ModuleNotFoundError:
         return 1
 
 def barrier():
@@ -106,7 +106,7 @@ def barrier():
         from mpi4py import MPI
         comm_w = MPI.COMM_WORLD
         comm_w.Barrier()
-    except:
+    except ModuleNotFoundError:
         pass