final use of c libepics

internal/datasource/epics/epics.go

@@ -444,41 +444,105 @@ func (e *EPICS) ListSignals(_ context.Context) ([]datasource.Metadata, error) {
 }
 
 // Write puts a new value onto a CA channel.
-func (e *EPICS) Write(_ context.Context, signal string, value any) error {
+// If the signal is not currently subscribed (e.g. a button in oneshot mode),
+// a temporary CA channel is created, used for the put, then torn down.
+func (e *EPICS) Write(ctx context.Context, signal string, value any) error {
 	e.attachCAContext()
+
+	// Resolve the chid: use an existing subscribed channel if available,
+	// otherwise create a temporary one (mirrors GetMetadata's approach).
 	e.mu.Lock()
 	caCh, ok := e.channels[signal]
 	e.mu.Unlock()
-	if !ok {
-		return datasource.ErrNotFound
+
+	var chid C.chid
+	tempChannel := false
+
+	if ok {
+		chid = caCh.chid
+	} else {
+		// Create a temporary channel for the put.
+		handle := nextHandle()
+		entry := &connEntry{connCh: make(chan struct{}, 1)}
+		handleMu.Lock()
+		connTable[handle] = entry
+		handleMu.Unlock()
+
+		pvName := C.CString(signal)
+		defer C.free(unsafe.Pointer(pvName))
+
+		status := C.caCreateChannel(pvName, C.uintptr_t(handle), &chid)
+		if status != C.ECA_NORMAL {
+			handleMu.Lock()
+			delete(connTable, handle)
+			handleMu.Unlock()
+			return fmt.Errorf("epics: ca_create_channel(%q) failed: status %d", signal, int(status))
+		}
+		C.ca_flush_io()
+
+		select {
+		case <-entry.connCh:
+		case <-time.After(5 * time.Second):
+			C.ca_clear_channel(chid)
+			handleMu.Lock()
+			delete(connTable, handle)
+			handleMu.Unlock()
+			return fmt.Errorf("epics: timeout connecting to %q for write", signal)
+		case <-ctx.Done():
+			C.ca_clear_channel(chid)
+			handleMu.Lock()
+			delete(connTable, handle)
+			handleMu.Unlock()
+			return ctx.Err()
+		}
+
+		handleMu.Lock()
+		delete(connTable, handle)
+		handleMu.Unlock()
+		tempChannel = true
 	}
 
 	var status C.int
 	switch v := value.(type) {
 	case float64:
 		cv := C.double(v)
-		status = C.caPut(C.DBR_DOUBLE, caCh.chid, unsafe.Pointer(&cv))
+		status = C.caPut(C.DBR_DOUBLE, chid, unsafe.Pointer(&cv))
 	case int64:
 		cv := C.long(v)
-		status = C.caPut(C.DBR_LONG, caCh.chid, unsafe.Pointer(&cv))
+		status = C.caPut(C.DBR_LONG, chid, unsafe.Pointer(&cv))
 	case string:
 		cs := C.CString(v)
 		defer C.free(unsafe.Pointer(cs))
-		status = C.caPut(C.DBR_STRING, caCh.chid, unsafe.Pointer(cs))
+		status = C.caPut(C.DBR_STRING, chid, unsafe.Pointer(cs))
 	case bool:
 		var iv C.short
 		if v {
 			iv = 1
 		}
-		status = C.caPut(C.DBR_SHORT, caCh.chid, unsafe.Pointer(&iv))
+		status = C.caPut(C.DBR_SHORT, chid, unsafe.Pointer(&iv))
 	default:
+		if tempChannel {
+			C.ca_clear_channel(chid)
+			C.ca_flush_io()
+		}
 		return fmt.Errorf("epics: unsupported value type %T for Write", value)
 	}
 
 	if status != C.ECA_NORMAL {
+		if tempChannel {
+			C.ca_clear_channel(chid)
+			C.ca_flush_io()
+		}
 		return fmt.Errorf("epics: ca_put(%q) failed: status %d", signal, int(status))
 	}
-	C.ca_flush_io()
+
+	if tempChannel {
+		C.ca_pend_io(3.0) // flush + wait for put completion before tearing down
+		C.ca_clear_channel(chid)
+		C.ca_flush_io()
+	} else {
+		C.ca_flush_io()
+	}
 	return nil
 }