From b35064d26ccc2d94e95331225f8638a5f02777d0 Mon Sep 17 00:00:00 2001
From: Michael Davidsaver <mdavidsaver@gmail.com>
Date: Sun, 23 Jun 2019 10:36:52 -0700
Subject: [PATCH] Revert "dbEvent simplify db_close_events() with join"

This reverts commit 37a76b433a9e7d5a8d26a13fd21ad62f20a0c1c1.

# Conflicts:
#	modules/database/src/ioc/db/dbEvent.c
---
 modules/database/src/ioc/db/dbEvent.c | 74 ++++++++++++++++++---------
 1 file changed, 51 insertions(+), 23 deletions(-)

diff --git a/modules/database/src/ioc/db/dbEvent.c b/modules/database/src/ioc/db/dbEvent.c
index 7342a0852..65e3488ad 100644
--- a/modules/database/src/ioc/db/dbEvent.c
+++ b/modules/database/src/ioc/db/dbEvent.c
@@ -84,6 +84,7 @@ struct event_user {
     epicsMutexId        lock;
     epicsEventId        ppendsem;       /* Wait while empty */
     epicsEventId        pflush_sem;     /* wait for flush */
+    epicsEventId        pexitsem;       /* wait for event task to join */
 
     EXTRALABORFUNC      *extralabor_sub;/* off load to event task */
     void                *extralabor_arg;/* parameter to above */
@@ -122,6 +123,8 @@ static char *EVENT_PEND_NAME = "eventTask";
 
 static struct evSubscrip canceledEvent;
 
+static epicsMutexId stopSync;
+
 static unsigned short ringSpace ( const struct event_que *pevq )
 {
     if ( pevq->evque[pevq->putix] == EVENTQEMPTY ) {
@@ -260,6 +263,10 @@ int dbel ( const char *pname, unsigned level )
  */
 void db_init_event_freelists (void)
 {
+    if (!stopSync) {
+        stopSync = epicsMutexMustCreate();
+    }
+
     if (!dbevEventUserFreeList) {
         freeListInitPvt(&dbevEventUserFreeList,
             sizeof(struct event_user),8);
@@ -299,6 +306,9 @@ dbEventCtx db_init_events (void)
         return NULL;
     }
 
+    /* Flag will be cleared when event task starts */
+    evUser->pendexit = TRUE;
+
     evUser->firstque.evUser = evUser;
     evUser->firstque.writelock = epicsMutexCreate();
     if (!evUser->firstque.writelock)
@@ -313,6 +323,9 @@ dbEventCtx db_init_events (void)
     evUser->lock = epicsMutexCreate();
     if (!evUser->lock)
         goto fail;
+    evUser->pexitsem = epicsEventCreate(epicsEventEmpty);
+    if (!evUser->pexitsem)
+        goto fail;
 
     evUser->flowCtrlMode = FALSE;
     evUser->extraLaborBusy = FALSE;
@@ -327,6 +340,8 @@ fail:
         epicsEventDestroy (evUser->ppendsem);
     if(evUser->pflush_sem)
         epicsEventDestroy (evUser->pflush_sem);
+    if(evUser->pexitsem)
+        epicsEventDestroy (evUser->pexitsem);
     freeListFree(dbevEventUserFreeList,evUser);
     return NULL;
 }
@@ -347,6 +362,7 @@ DBCORE_API void db_cleanup_events(void)
     dbevFieldLogFreeList = NULL;
 }
 
+    /* intentionally leak stopSync to avoid possible shutdown races */
 /*
  *  DB_CLOSE_EVENTS()
  *
@@ -368,15 +384,30 @@ void db_close_events (dbEventCtx ctx)
      * hazardous to the system's health.
      */
     epicsMutexMustLock ( evUser->lock );
-    evUser->pendexit = TRUE;
+    if(!evUser->pendexit) { /* event task running */
+        evUser->pendexit = TRUE;
+        epicsMutexUnlock ( evUser->lock );
+
+        /* notify the waiting task */
+        epicsEventSignal(evUser->ppendsem);
+        /* wait for task to exit */
+        epicsEventMustWait(evUser->pexitsem);
+
+        epicsMutexMustLock ( evUser->lock );
+    }
+
     epicsMutexUnlock ( evUser->lock );
 
-    /* notify the waiting task */
-    epicsEventSignal(evUser->ppendsem);
+    epicsMutexMustLock (stopSync);
 
-    if(evUser->taskid)
-        epicsThreadMustJoin(evUser->taskid);
-    /* evUser has been deleted by the worker */
+    epicsEventDestroy(evUser->pexitsem);
+    epicsEventDestroy(evUser->ppendsem);
+    epicsEventDestroy(evUser->pflush_sem);
+    epicsMutexDestroy(evUser->lock);
+
+    epicsMutexUnlock (stopSync);
+
+    freeListFree(dbevEventUserFreeList, evUser);
 }
 
 /*
@@ -1063,18 +1094,17 @@ static void event_task (void *pParm)
         }
     }
 
-    epicsEventDestroy(evUser->ppendsem);
-    epicsEventDestroy(evUser->pflush_sem);
-    epicsMutexDestroy(evUser->lock);
-
-    if (dbevEventUserFreeList)
-        freeListFree(dbevEventUserFreeList, evUser);
-    else
-        fprintf(stderr, "%s exiting but dbevEventUserFreeList already NULL\n",
-                __FUNCTION__);
-
     taskwdRemove(epicsThreadGetIdSelf());
 
+    /* use stopSync to ensure pexitsem is not destroy'd
+     * until epicsEventSignal() has returned.
+     */
+    epicsMutexMustLock (stopSync);
+
+    epicsEventSignal(evUser->pexitsem);
+
+    epicsMutexUnlock(stopSync);
+
     return;
 }
 
@@ -1086,11 +1116,6 @@ int db_start_events (
     void *init_func_arg, unsigned osiPriority )
 {
      struct event_user * const evUser = (struct event_user *) ctx;
-     epicsThreadOpts opts = EPICS_THREAD_OPTS_INIT;
-
-     opts.stackSize = epicsThreadGetStackSize(epicsThreadStackMedium);
-     opts.priority = osiPriority;
-     opts.joinable = 1;
 
      epicsMutexMustLock ( evUser->lock );
 
@@ -1108,12 +1133,15 @@ int db_start_events (
      if (!taskname) {
          taskname = EVENT_PEND_NAME;
      }
-     evUser->taskid = epicsThreadCreateOpt (
-         taskname, event_task, (void *)evUser, &opts);
+     evUser->taskid = epicsThreadCreate (
+         taskname, osiPriority, 
+         epicsThreadGetStackSize(epicsThreadStackMedium),
+         event_task, (void *)evUser);
      if (!evUser->taskid) {
          epicsMutexUnlock ( evUser->lock );
          return DB_EVENT_ERROR;
      }
+     evUser->pendexit = FALSE;
      epicsMutexUnlock ( evUser->lock );
      return DB_EVENT_OK;
 }