From 319ee643ad919b43f65eca4d98dfb3e12c89214a Mon Sep 17 00:00:00 2001
From: Steffen Vogel <info@steffenvogel.de>
Date: Mon, 12 Mar 2012 01:32:54 +0100
Subject: [PATCH] added registry to manage memory for string identifiers

---
 include/reading.h |  8 ++++++++
 src/reading.c     | 29 +++++++++++++++++++++++++++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/include/reading.h b/include/reading.h
index 500e0ad..9f8ee98 100644
--- a/include/reading.h
+++ b/include/reading.h
@@ -51,6 +51,14 @@ typedef struct reading {
 
 enum meter_procotol; /* forward declaration */
 
+/**
+ * Manages memory for string identifiers
+ *
+ * @param str string to lookup in the registry
+ * @return pointer to string in the regstry
+ */
+char * reading_id_registry(const char *str);
+
 /**
  * Parse two reading identifiers in a given protocol context
  *
diff --git a/src/reading.c b/src/reading.c
index cb01c46..a4dcfcb 100644
--- a/src/reading.c
+++ b/src/reading.c
@@ -25,10 +25,32 @@
 
 #include <stdlib.h>
 #include <math.h>
+#include <string.h>
 
 #include "reading.h"
 #include "meter.h"
 
+char * reading_id_registry(const char *str) {
+	static list_t strings;
+
+	char *found = NULL;
+
+	/* linear search in string list */
+	foreach(strings, it, char *) {
+		if (strcmp(it, str) == 0) {
+			found = it;
+			break;
+			}
+	}
+
+	if (!found) {
+		found = strdup(str);
+		list_push(strings, found);
+	}
+
+	return found;
+}
+
 int reading_id_compare(meter_protocol_t protocol, reading_id_t a, reading_id_t b) {
 	switch (protocol) {
 		case meter_protocol_d0:
@@ -40,7 +62,10 @@ int reading_id_compare(meter_protocol_t protocol, reading_id_t a, reading_id_t b
 
 		case meter_protocol_file:
 		case meter_protocol_exec:
-			return strcmp(a.string, b.string);
+			/* we only need to compare the base pointers here,
+			   because each identifer exists only once in the registry
+			   and has therefore a unique pointer */
+			return !(a.string == b.string);
 
 		default:
 			/* no channel id, adding all readings to buffer */
@@ -81,7 +106,7 @@ int reading_id_parse(meter_protocol_t protocol, reading_id_t *id, const char *st
 
 		case meter_protocol_file:
 		case meter_protocol_exec:
-			id->string = strdup(string); // TODO free() elsewhere
+			id->string = reading_id_registry(string);
 			break;
 
 		default: /* ignore other protocols which do not provide id's */