From 267987d01c9309fee7c3d607444147bf8bbce938 Mon Sep 17 00:00:00 2001
From: Wolfgang Lux <wolfgang.lux@gmail.com>
Date: Tue, 1 Sep 2020 15:24:16 +0200
Subject: [PATCH] Reinstate fix to avoid deadlock while purging pool

---
 ChangeLog   |  5 +++++
 SQLClient.m | 20 ++++++++++++--------
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 6ce0701..ad00798 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2020-09-01  Wolfgang Lux  <wolfgang.lux@gmail.com>
+
+	* SQLClient.m (release): Reinstate fix to avoid deadlock while
+	purging pool.
+
 2020-04-21 Richard Frith-Macdonald  <rfm@gnu.org>
 
 	* Postgres.m: Change notification code to de-duplicate notifications
diff --git a/SQLClient.m b/SQLClient.m
index b1d0e2c..d0136dd 100644
--- a/SQLClient.m
+++ b/SQLClient.m
@@ -2566,19 +2566,22 @@ static int	        poolConnections = 0;
 
 - (oneway void) release
 {
-  /* We lock the table while checking, to prevent
-   * another thread from grabbing this object while we are
-   * checking it.
-   * If we are going to deallocate the object, we first remove
-   * it from the table so that no other thread will find it
-   * and try to use it while it is being deallocated.
+  /* We lock the table while checking, to prevent another thread
+   * from grabbing this object while we are checking it.
    */
   [clientsLock lock];
   if (nil != _pool && [self retainCount] == 1)
     {
-      /* If this is the only reference to a client associated with
+      /* This is the only reference to a client associated with
        * a connection pool we put this client back to the pool.
        *
+       * That being the case, we know that this thread 'owns'
+       * the client and it's not going to be deallocated and not
+       * going to have the _pool iinstance variable changed, so it
+       * is safe to unlock clientsLock before returning the client
+       * to the pool.  This avoids a possible deadlock when a pool
+       * is being purged.
+       *
        * wl 2019-05-01: The original implementation was calling this code
        * when NSDecrementExtraRefCountWasZero returns YES, but
        * this does not work with newer versions of the GNUstep
@@ -2586,13 +2589,14 @@ static int	        poolConnections = 0;
        * Objective-C runtime, which both don't handle resurrection
        * gracefully for objects whose retain count has become zero.
        */
+      [clientsLock unlock];
       [_pool _swallowClient: self explicit: NO];
     }
   else
     {
       [super release];
+      [clientsLock unlock];
     }
-  [clientsLock unlock];
 }
 
 - (SQLClientPool*) pool