Threadsafe avro import (#175)

* Make the avro import magic threadsafe
* cache mypy on TravisCI

Author: mr-c

.travis.yml

@@ -1,6 +1,9 @@
 sudo: false
 language: python
-cache: pip
+cache:
+  pip: true
+  directories:
+    - .mypy_cache
 python:
   - 2.7
   - 3.4

schema_salad/__init__.py

@@ -3,6 +3,7 @@
 import os
 import sys
 import typing
+import threading
 
 import six
 
@@ -13,24 +14,27 @@
 _logger.addHandler(logging.StreamHandler())
 _logger.setLevel(logging.INFO)
 
+__TMPDIR_LOCK = threading.Lock()
+
 if six.PY3:
 
-    if onWindows:
+    if onWindows():
         # create '/tmp' folder if not present
         # required by autotranslate module
         # TODO: remove when https://github.com/PythonCharmers/python-future/issues/295
         # is fixed
         if not os.path.exists("/tmp"):
-            try:
-                os.makedirs("/tmp")
-            except OSError as exception:
-                _logger.error(u"Cannot create '\\tmp' folder in root needed for",
-                              "'cwltool' Python 3 installation.")
-                exit(1)
-
-    from past import autotranslate  # type: ignore
-    autotranslate(['avro', 'avro.schema'])
-    import avro
-    import avro.schema
-    from past.translation import remove_hooks  # type: ignore
-    remove_hooks()
+            with __TMPDIR_LOCK:
+                try:
+                    os.makedirs("/tmp")
+                except OSError as exception:
+                    _logger.error(u"Cannot create '\\tmp' folder in root needed for"
+                                  "'cwltool' Python 3 installation.")
+                    exit(1)
+    with __TMPDIR_LOCK:
+        from past import autotranslate  # type: ignore
+        from past.translation import remove_hooks  # type: ignore
+        autotranslate(['avro', 'avro.schema'])
+        import avro
+        import avro.schema  # pylint: disable=no-name-in-module,import-error
+        remove_hooks()