Add comment to explain why PGReserveSemaphores() is called early

hlinnaka · hlinnaka · commit 75ec47c38bcf · 2025-11-06T14:20:58.000+02:00
Before commit e256266, PGReserveSemaphores() had to be called before SpinlockSemaInit() because spinlocks were implemented using semaphores on some platforms (--disable-spinlocks). Add a comment explaining that. Author: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com> Discussion: https://www.postgresql.org/message-id/CAExHW5seSZpPx-znjidVZNzdagGHOk06F+Ds88MpPUbxd1kTaA@mail.gmail.com Backpatch-to: 18
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
@@ -225,7 +225,9 @@ CreateSharedMemoryAndSemaphores(void)
 	InitShmemAccess(seghdr);
 
 	/*
-	 * Create semaphores
+	 * Create semaphores.  (This is done here for historical reasons.  We used
+	 * to support emulating spinlocks with semaphores, which required
+	 * initializing semaphores early.)
 	 */
 	PGReserveSemaphores(numSemas);
 
