From beba95a43a39711a11663024f7065375095e22e6 Mon Sep 17 00:00:00 2001
From: Jake Smith <jake.smith@lexisnexisrisk.com>
Date: Mon, 10 Jul 2023 17:40:43 +0100
Subject: [PATCH] HPCC-29923 Avoid CRowServer cancel if not running

This avoids an inherent delay being introduced by the MP layer.

CRowServer is used by Global Group, Global TopN and a refactoring
form of IndexWrite (where is merges down to less parts).

Signed-off-by: Jake Smith <jake.smith@lexisnexisrisk.com>
---
 thorlcr/thorutil/thormisc.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/thorlcr/thorutil/thormisc.cpp b/thorlcr/thorutil/thormisc.cpp
index 7d8c76fa284..d216db1aef7 100644
--- a/thorlcr/thorutil/thormisc.cpp
+++ b/thorlcr/thorutil/thormisc.cpp
@@ -1371,8 +1371,12 @@ class CRowServer : public CSimpleInterface, implements IThreaded, implements IRo
 #ifdef TRACE_GLOBAL_GROUP
         ActPrintLog(activity, "%s", __func__);
 #endif
-        running = false;
-        comm.cancel(RANK_ALL, mpTag);
+        bool wanted = true;
+        if (running.compare_exchange_strong(wanted, false))
+        {
+            running = false;
+            comm.cancel(RANK_ALL, mpTag);
+        }
     }
 };