Merge pull request #37 from smitchell556/issue_36_race_condition

Fix race condition in `get_resource`

CHANGELOG.md

@@ -11,6 +11,7 @@ project adheres to [Semantic Versioning](http://semver.org).
 - Dropped support for Python 3.3. This does not mean it won't work for Python
   3.3, but it will no longer be tested.
 - Add support for Python 3.7 and 3.8.
+- Fix race condition in `get_resource` see [issue #36](https://github.com/smitchell556/cuttlepool/issues/36).
 
 ## [0.8.0] - 2018-02-28
 ### Added

cuttlepool.py

@@ -297,51 +297,52 @@ def get_resource(self, resource_wrapper=None):
         if resource_wrapper is None:
             resource_wrapper = self._resource_wrapper
 
-        if self.empty():
-            self._harvest_lost_resources()
-
-        try:
-            rtracker = self._get(0)
-        except PoolEmptyError:
-            pass
-
-        if rtracker is None:
-            # Could not find resource, try to make one.
-            try:
-                rtracker = self._make_resource()
-            except PoolFullError:
-                pass
+        with self._lock:
+            if self.empty():
+                self._harvest_lost_resources()
 
-        if rtracker is None:
-            # Could not find or make resource, so must wait for a resource
-            # to be returned to the pool.
             try:
-                rtracker = self._get(timeout=self._timeout)
+                rtracker = self._get(0)
             except PoolEmptyError:
                 pass
 
-        if rtracker is None:
-            raise PoolEmptyError
-
-        # Ensure resource is active.
-        if not self.ping(rtracker.resource):
-            # Lock here to prevent another thread creating a resource in the
-            # index that will have this resource removed. This ensures there
-            # will be space for _make_resource() to place a newly created
-            # resource.
-            with self._lock:
-                self._remove(rtracker)
-                rtracker = self._make_resource()
-
-        # Ensure all resources leave pool with same attributes.
-        # normalize_connection() is used since it calls
-        # normalize_resource(), so if a user implements either one, the
-        # resource will still be normalized. This will be changed in 1.0 to
-        # call normalize_resource() when normalize_connection() is
-        # removed.
-        self.normalize_connection(rtracker.resource)
-
-        return rtracker.wrap_resource(self, resource_wrapper)
+            if rtracker is None:
+                # Could not find resource, try to make one.
+                try:
+                    rtracker = self._make_resource()
+                except PoolFullError:
+                    pass
+
+            if rtracker is None:
+                # Could not find or make resource, so must wait for a resource
+                # to be returned to the pool.
+                try:
+                    rtracker = self._get(timeout=self._timeout)
+                except PoolEmptyError:
+                    pass
+
+            if rtracker is None:
+                raise PoolEmptyError
+
+            # Ensure resource is active.
+            if not self.ping(rtracker.resource):
+                # Lock here to prevent another thread creating a resource in the
+                # index that will have this resource removed. This ensures there
+                # will be space for _make_resource() to place a newly created
+                # resource.
+                with self._lock:
+                    self._remove(rtracker)
+                    rtracker = self._make_resource()
+
+            # Ensure all resources leave pool with same attributes.
+            # normalize_connection() is used since it calls
+            # normalize_resource(), so if a user implements either one, the
+            # resource will still be normalized. This will be changed in 1.0 to
+            # call normalize_resource() when normalize_connection() is
+            # removed.
+            self.normalize_connection(rtracker.resource)
+
+            return rtracker.wrap_resource(self, resource_wrapper)
 
     def normalize_connection(self, connection):
         """For compatibility with older versions, will be removed in 1.0."""