Prefetch enum variants

bus/m_epics_ca.h

@@ -7,6 +7,7 @@
 #include <menuAlarmStat.h>
 #include <optional>
 #include <string>
+#include <vector>
 
 /**
  * @brief Holds information about the CA channel: Value type and element count.
@@ -305,6 +306,10 @@ template <typename T> class mEpicsCa {
     */
     std::optional<T> _cached;
 
+    // Vector holding the possible enum variants, if the record is an enum
+    // record like e.g. bo. For all other record types, this is empty.
+    std::vector<std::string> _enumVariants;
+
     // Status and severity of the last read (or subscription callback)
     menuAlarmStat _status;
     menuAlarmSevr _severity;

bus/m_epics_ca.tpp

@@ -171,7 +171,8 @@ template <typename T>
 mEpicsCa<T>::mEpicsCa(std::string_view chanName, bool subscribe, double timeout)
     : _timeout(timeout), _pChanID(nullptr), _chanName(chanName),
       _subscribe(subscribe), _eventId(nullptr), _cached(std::nullopt),
-      _status(menuAlarmStatUDF), _severity(menuAlarmSevrNO_ALARM) {
+      _enumVariants(std::vector<std::string>()), _status(menuAlarmStatUDF),
+      _severity(menuAlarmSevrNO_ALARM) {
 
     // Compile time check of T
     dbfFromType<T>();
@@ -580,23 +581,36 @@ template <bool S>
 int mEpicsCa<T>::putRaw(const char *buf, u_long len) {
 
     if constexpr (dbfFromType<T>() == DBF_ENUM) {
-        // Check if the given string corresponds to one of the enum variants
-        // and fetch the corresponding index, if it does. Otherwise, create
-        // a nice error message.
-        struct dbr_ctrl_enum data;
-        ca_get(DBR_CTRL_ENUM, this->_pChanID, &data);
-        ca_pend_io(_timeout);
 
+        // Prefetch all enum variants if the vector is currently empty. We
+        // cannot do this at connection time, because this results in a segfault
+        // (likely because we are trying to use ca_get while being inside a
+        // callback).
+        if (_enumVariants.empty()) {
+            struct dbr_ctrl_enum data;
+            ca_get(DBR_CTRL_ENUM, _pChanID, &data);
+            ca_pend_io(_timeout);
+
+            for (int i = 0; i < data.no_str; ++i) {
+                _enumVariants.push_back(data.strs[i]);
+            }
+        }
+
+        // Check if the given string matches one of the enum variants
+        for (size_t i = 0; i < _enumVariants.size(); i++) {
+            if (_enumVariants[i] == buf) {
+                uint16_t idx = i;
+                return putRaw<S>(&idx);
+            }
+        }
+
+        // If we didn't exit from the loop, the given buffer is not one of the
+        // enum variants. Hence, we now create an error message (looping again).
         std::string variants;
-
-        for (int i = 0; i < data.no_str; ++i) {
+        for (size_t i = 0; i < _enumVariants.size(); i++) {
             if (i > 0)
                 variants += ", ";
-
-            variants += data.strs[i];
-
-            if (strcmp(data.strs[i], buf) == 0)
-                return putRaw<S>(&i);
+            variants += _enumVariants[i];
         }
 
         // Given string did not match any of the variants ->  return an
@@ -692,6 +706,7 @@ void mEpicsCa<T>::connStateCallback(struct connection_handler_args args) {
     } else {
         // Any other event -> assume the channel is disconnected and reset the
         // internal fields
+        self->_enumVariants.clear();
         self->_channelInfo.reset();
         self->_cached.reset();
         cm_msg(MDEBUG, __FILE__, "PV %s disconnected", self->_chanName.c_str());