move pid assignment to the last operation of the reset() method

1 files changed, 11 insertions, 1 deletions

diff --git a/redis/connection.py b/redis/connection.py
index fffdc1a..4d4f405 100755
--- a/redis/connection.py
+++ b/redis/connection.py
@@ -1094,12 +1094,22 @@ class ConnectionPool(object):
         )
 
     def reset(self):
-        self.pid = os.getpid()
         self._lock = threading.RLock()
         self._created_connections = 0
         self._available_connections = []
         self._in_use_connections = set()
 
+        # this must be the last operation in this method. while reset() is
+        # called when holding _fork_lock, other threads in this process
+        # can call _checkpid() which compares self.pid and os.getpid() without
+        # holding any lock (for performance reasons). keeping this assignment
+        # as the last operation ensures that those other threads will also
+        # notice a pid difference and block waiting for the first thread to
+        # release _fork_lock. when each of these threads eventually acquire
+        # _fork_lock, they will notice that another thread already called
+        # reset() and they will immediately release _fork_lock and continue on.
+        self.pid = os.getpid()
+
     def _checkpid(self):
         # _checkpid() attempts to keep ConnectionPool fork-safe on modern
         # systems. this is called by all ConnectionPool methods that