From a99697e2c829d4979a79c7aab086184389b591a6 Mon Sep 17 00:00:00 2001
From: Michael Davidsaver <mdavidsaver@gmail.com>
Date: Mon, 15 Apr 2024 14:42:15 -0700
Subject: [PATCH] asTrapWriteRegisterListener() safe lazy init

---
 modules/libcom/src/as/asTrapWrite.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/modules/libcom/src/as/asTrapWrite.c b/modules/libcom/src/as/asTrapWrite.c
index ec5f0d1478..1bb3134127 100644
--- a/modules/libcom/src/as/asTrapWrite.c
+++ b/modules/libcom/src/as/asTrapWrite.c
@@ -22,6 +22,7 @@
 
 #include "ellLib.h"
 #include "freeList.h"
+#include "epicsThread.h"
 #include "cantProceed.h"
 #include "epicsMutex.h"
 #include "ellLib.h"
@@ -57,9 +58,10 @@ typedef struct asTrapWritePvt
     epicsMutexId lock;
 }asTrapWritePvt;
 
+static epicsThreadOnceId asTrapWriteOnce = EPICS_THREAD_ONCE_INIT;
 static asTrapWritePvt *pasTrapWritePvt = 0;
 
-static void asTrapWriteInit(void)
+static void asTrapWriteInit(void *unused)
 {
     pasTrapWritePvt = callocMustSucceed(1,sizeof(asTrapWritePvt),"asTrapWriteInit");
     ellInit(&pasTrapWritePvt->listenerList);
@@ -75,7 +77,7 @@ asTrapWriteId epicsStdCall asTrapWriteRegisterListener(
     asTrapWriteListener func)
 {
     listener *plistener;
-    if(pasTrapWritePvt==0) asTrapWriteInit();
+    epicsThreadOnce(&asTrapWriteOnce, &asTrapWriteInit, NULL);
     plistener = callocMustSucceed(1,sizeof(listener),"asTrapWriteRegisterListener");
     plistener->func = func;
     epicsMutexMustLock(pasTrapWritePvt->lock);