Re: [PR] Fix volatile qualifier discard and ensure safe access to PGPROC in lock [cloudberry]

["my-ship-it (via GitHub)" <gi...@apache.org>]

my-ship-it commented on code in PR #963:
URL: https://github.com/apache/cloudberry/pull/963#discussion_r1987094355


##########
src/backend/storage/lmgr/lock.c:
##########
@@ -936,19 +936,29 @@ LockAcquireExtended(const LOCKTAG *locktag,
 			if (lockHolderProcPtr == MyProc)
 			{
 				/* Find the guy who should manage our locks */
-				PGPROC * proc = FindProcByGpSessionId(gp_session_id);
+				volatile PGPROC * proc = FindProcByGpSessionId(gp_session_id);
 				int count = 0;
 				while(proc==NULL && count < 5)
 				{
 					pg_usleep( /* microseconds */ 2000);
 					count++;
 					CHECK_FOR_INTERRUPTS();
+					/*
+					 * The reason for using pg_memory_barrier() is to ensure memory ordering
+					 * constraints are respected. In concurrent programming, memory barriers
+					 * are used to prevent the compiler and CPU from reordering memory operations
+					 * in a way that could lead to race conditions or other synchronization issues.
+					 * By using pg_memory_barrier(), we can enforce a strict ordering of memory
+					 * accesses, which is crucial for the correct functioning of lock mechanisms
+					 * and other synchronization primitives in a multi-threaded environment.

Review Comment:
   multi-threaded? or multi processes



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