bug: make boto3 calls thread safe

Closes #1081

.travis.yml

@@ -12,7 +12,7 @@ matrix:
     - python: 2.7
       env: TOXENV=py27 DDB=true CODECOV=true
     - python: pypy
-      env: TOXENV=pypy DDB=true CODECOV=true
+      env: TOXENV=pypy DDB=true CODECOV=true AWS_LOCAL_DYNAMODB=http://127.0.0.1:8000
     - env: TOXENV=flake8 WITH_RUST=false
     - python: 3.6
       env: TOXENV=py36-mypy WITH_RUST=false

autopush/config.py

@@ -176,6 +176,9 @@ class AutopushConfig(object):
     # Don't cache ssl.wrap_socket's SSLContexts
     no_sslcontext_cache = attrib(default=False)  # type: bool
 
+    # DynamoDB endpoint override
+    aws_ddb_endpoint = attrib(default=None)  # type: str
+
     def __attrs_post_init__(self):
         """Initialize the Settings object"""
         # Setup hosts/ports/urls

autopush/constants.py

@@ -0,0 +1,4 @@
+"""Shared constants which might produce circular includes"""
+
+# Number of concurrent threads / AWS Session resources
+THREAD_POOL_SIZE = 50