Applied Till's fix for lp:1581212

documentation/RELEASE_NOTES.html

@@ -13,6 +13,20 @@
 
 <!-- Insert new items immediately below here ... -->
 
+<h3>Making IOC ca_get operations atomic</h3>
+
+<p>When a CA client gets data from an IOC record using a compound data type such
+as <tt>DBR_TIME_DOUBLE</tt> the value field is fetched from the database in a
+separate call than the other metadata, without keeping the record locked. This
+allows some other thread such as a periodic scan thread a chance to interrupt
+the get operation and process the record in between. CA monitors have always
+been atomic as long as the value data isn't a string or an array, but this race
+condition in the CA get path has now been fixed so the record will stay locked
+between the two fetch operations.</p>
+
+<p>This fixes <a href="https://bugs.launchpad.net/epics-base/+bug/1581212">
+Launchpad bug #1581212</a>, thanks to Till Strauman and Dehong Zhang.</p>
+
 <h3>New CONFIG_SITE variable for running self-tests</h3>
 
 <p>The 'make runtests' and 'make tapfiles' build targets normally only run the

src/db/db_access.c

@@ -32,6 +32,7 @@
 #include "dbCommon.h"
 #include "errMdef.h"
 #include "recSup.h"
+#include "dbLock.h"
 #include "alarm.h"
 #define db_accessHFORdb_accessC
 #include "db_access.h"
@@ -182,6 +183,8 @@ int epicsShareAPI db_get_field_and_count(
     * in the dbAccess.c dbGet() and getOptions() routines.
     */
 
+    dbScanLock(paddr->precord);
+
     switch(buffer_type) {
     case(oldDBR_STRING):
         status = dbGetField(paddr, DBR_STRING, pbuffer, &zero, nRequest, pfl);
@@ -820,8 +823,12 @@ int epicsShareAPI db_get_field_and_count(
         }
         break;
     default:
-        return -1;
+        status = -1;
+        break;
     }
+
+    dbScanUnlock(paddr->precord);
+
     if (status) return -1;
     return 0;
 }