fix pool bug

eventlet/db_pool.py

@@ -175,19 +175,6 @@ def _safe_close(self, conn, quiet=False):
     def get(self):
         conn = super(BaseConnectionPool, self).get()
 
-        # None is a flag value that means that put got called with
-        # something it couldn't use
-        if conn is None:
-            try:
-                conn = self.create()
-            except Exception:
-                # unconditionally increase the free pool because
-                # even if there are waiters, doing a full put
-                # would incur a greenlib switch and thus lose the
-                # exception stack
-                self.current_size -= 1
-                raise
-
         # if the call to get() draws from the free pool, it will come
         # back as a tuple
         if isinstance(conn, tuple):

eventlet/pools.py

@@ -75,22 +75,33 @@ def __init__(self, min_size=0, max_size=4, order_as_stack=False, create=None):
             self.current_size += 1
             self.free_items.append(self.create())
 
+    def _safe_create(self):
+        try:
+            return self.create()
+        except Exception as e:
+            if not self.waiting():
+                self.current_size -= 1
+                raise
+            else:
+                # put will cause a greenlet switch which destroys the
+                # exception info, so we have to raise the exception explicitly
+                self.put(None)
+                raise e
+
     def get(self):
         """Return an item from the pool, when one is available.  This may
         cause the calling greenthread to block.
         """
         if self.free_items:
-            return self.free_items.popleft()
-        self.current_size += 1
-        if self.current_size <= self.max_size:
-            try:
-                created = self.create()
-            except:
-                self.current_size -= 1
-                raise
-            return created
-        self.current_size -= 1 # did not create
-        return self.channel.get()
+            item = self.free_items.popleft()
+        elif self.current_size < self.max_size:
+            self.current_size += 1
+            item = self._safe_create()
+        else:
+            item = self.channel.get()
+            if item is None:
+                item = self._safe_create()
+        return item
 
     @contextmanager
     def item(self):