Adapt event exec_once_mutex to asyncio

The pool makes use of a threading.Lock() for the
"first_connect" event.  if the pool is async make sure this
is a greenlet-adapted asyncio lock.

Fixes: #5581
Change-Id: If52415839c7ed82135465f1fe93b95d86c305820

2 files changed, 15 insertions, 0 deletions

diff --git a/lib/sqlalchemy/util/_concurrency_py3k.py b/lib/sqlalchemy/util/_concurrency_py3k.py
index 3b112ff7d..82125b771 100644
--- a/lib/sqlalchemy/util/_concurrency_py3k.py
+++ b/lib/sqlalchemy/util/_concurrency_py3k.py
@@ -96,6 +96,17 @@ try:
             del context.driver
         return result
 
+    class AsyncAdaptedLock:
+        def __init__(self):
+            self.mutex = asyncio.Lock()
+
+        def __enter__(self):
+            await_fallback(self.mutex.acquire())
+            return self
+
+        def __exit__(self, *arg, **kw):
+            self.mutex.release()
+
 
 except ImportError:  # pragma: no cover
     greenlet = None
diff --git a/lib/sqlalchemy/util/concurrency.py b/lib/sqlalchemy/util/concurrency.py
index 4c4ea20d1..e0883aa68 100644
--- a/lib/sqlalchemy/util/concurrency.py
+++ b/lib/sqlalchemy/util/concurrency.py
@@ -7,6 +7,7 @@ if compat.py3k:
     from ._concurrency_py3k import await_fallback
     from ._concurrency_py3k import greenlet
     from ._concurrency_py3k import greenlet_spawn
+    from ._concurrency_py3k import AsyncAdaptedLock
 else:
     asyncio = None
     greenlet = None
@@ -19,3 +20,6 @@ else:
 
     def greenlet_spawn(fn, *args, **kw):
         raise ValueError("Cannot use this function in py2.")
+
+    def AsyncAdaptedLock(*args, **kw):
+        raise ValueError("Cannot use this function in py2.")