created a new configuration caching API (config_changed).

applied this to some rules.

src/kernel/config.c

@@ -887,14 +887,23 @@ int rule_blessed_harvest(void)
 
 int rule_alliance_limit(void)
 {
-    int rule = config_get_int("rules.limit.alliance", 0);
+    static int cache_token;
+    static int rule = 0;
+
+    if (config_changed(&cache_token)) {
+        rule = config_get_int("rules.limit.alliance", 0);
+    }
     assert(rule >= 0);
     return rule;
 }
 
 int rule_faction_limit(void)
 {
-    int rule = config_get_int("rules.limit.faction", 0);
+    static int cache_token;
+    static int rule = 0;
+    if (config_changed(&cache_token)) {
+        rule = config_get_int("rules.limit.faction", 0);
+    }
     assert(rule >= 0);
     return rule;
 }
@@ -1053,8 +1062,19 @@ bool markets_module(void)
 }
 
 static struct param *configuration;
+static int config_cache_key = 1;
+
+bool config_changed(int *cache_key) {
+    assert(cache_key);
+    if (config_cache_key != *cache_key) {
+        *cache_key = config_cache_key;
+        return true;
+    }
+    return false;
+}
 
 void config_set(const char *key, const char *value) {
+    ++config_cache_key;
     set_param(&configuration, key, value);
 }
 

src/kernel/config.h

@@ -184,6 +184,7 @@ struct param;
     int config_get_int(const char *key, int def);
     double config_get_flt(const char *key, double def);
     bool config_token(const char *key, const char *tok);
+    bool config_changed(int *cache_key);
 
     char * join_path(const char *p1, const char *p2, char *dst, size_t len);
     bool ExpensiveMigrants(void);

src/kernel/config.test.c

@@ -190,9 +190,31 @@ static void test_default_order(CuTest *tc) {
     test_cleanup();
 }
 
+static void test_config_cache(CuTest *tc) {
+    int key = 0;
+
+    test_setup();
+    CuAssertTrue(tc, config_changed(&key));
+    config_set("hodor", "0");
+    CuAssertTrue(tc, config_changed(&key));
+    CuAssertTrue(tc, !config_changed(&key));
+    test_cleanup();
+}
+
+static void test_rules(CuTest *tc) {
+    CuAssertIntEquals(tc, 0, rule_alliance_limit());
+    config_set("rules.limit.alliance", "1");
+    CuAssertIntEquals(tc, 1, rule_alliance_limit());
+
+    CuAssertIntEquals(tc, 0, rule_faction_limit());
+    config_set("rules.limit.faction", "1000");
+    CuAssertIntEquals(tc, 1000, rule_faction_limit());
+}
+
 CuSuite *get_config_suite(void)
 {
     CuSuite *suite = CuSuiteNew();
+    SUITE_ADD_TEST(suite, test_config_cache);
     SUITE_ADD_TEST(suite, test_get_set_param);
     SUITE_ADD_TEST(suite, test_param_int);
     SUITE_ADD_TEST(suite, test_param_flt);
@@ -200,5 +222,6 @@ CuSuite *get_config_suite(void)
     SUITE_ADD_TEST(suite, test_getunit);
     SUITE_ADD_TEST(suite, test_read_unitid);
     SUITE_ADD_TEST(suite, test_default_order);
+    SUITE_ADD_TEST(suite, test_rules);
     return suite;
 }