StatelessWriter: implement clean_history()

`PublisherHistory::add_pub_change()` calls `clean_history()` and considers history full if it returns false. Actually remove items from history, and return whether we actually removed anything.

for eProsima#34

include/fastrtps/rtps/writer/StatelessWriter.h

@@ -102,7 +102,7 @@ class StatelessWriter : public RTPSWriter
 	*/
 	inline size_t getMatchedReadersSize() const {return m_matched_readers.size();};
 
-    bool clean_history(unsigned int /*max = 0*/){ return false; }
+    bool clean_history(unsigned int max = 0);
 
 private:
 	//Duration_t resendDataPeriod; //FIXME: Not used yet.

src/cpp/rtps/writer/StatelessWriter.cpp

@@ -352,7 +352,31 @@ void StatelessWriter::unsent_changes_reset()
 //}
 
 
+bool StatelessWriter::clean_history(unsigned int max)
+{
+	boost::lock_guard<boost::recursive_mutex> guard(*mp_mutex);
+
+	bool removed = false;
+	if (max == 0) {
+		max = mp_history->getHistorySize();
+	}
+
+	while (max--) {
+		CacheChange_t *cc;
+		if (!mp_history->get_min_change(&cc)) {
+			break;
+		}
+		if (mp_history->remove_change(cc)) {
+			removed = true;
+		}
+	}
 
+	if (removed) {
+		unsent_changes_reset();
+	}
+
+	return removed;
+}