Replace boost.bimap with std::unordered_map

Author: tstenner

src/stream_info_impl.cpp

@@ -188,34 +188,56 @@ void stream_info_impl::from_fullinfo_message(const std::string &m) {
 	read_xml(doc_);
 }
 
-/**
-* Test whether this stream info matches the given query string.
-*/
-bool stream_info_impl::matches_query(const string &query) {
+/// Test whether this stream info matches the given query string.
+bool stream_info_impl::matches_query(const string &query, bool nocache) {
+	return cached_.matches_query(doc_, query, nocache);
+}
+
+bool query_cache::matches_query(const xml_document &doc, const std::string query, bool nocache) {
 	lslboost::lock_guard<lslboost::mutex> lock(cache_mut_);
-    query_cache::left_iterator it = cached_.left.find(query);
-	if (it != cached_.left.end()) {
-		// found in cache
-		bool is_match = it->second.second;
+
+	decltype(cache)::iterator it;
+	if (!nocache && (it = cache.find(query)) != cache.end()) {
+		// the sign bit encodes if the query matches or not
+		bool matches = it->second > 0;
 		// update the last-use time stamp
-		cached_.left.replace_data(it,std::make_pair(lsl_clock(),is_match));
-		return is_match;
-	} else {
-		// not found in cache
-		try {
-			// compute whether it matches
-			string fullquery = (string("/info[") += query) += "]";
-			bool result = !doc_.select_nodes(fullquery.c_str()).empty();
-			// insert result into cache
-			cached_.left.insert(std::make_pair(query,std::make_pair(lsl_clock(),result)));
-			// remove oldest results until we're within capacity
-			while ((int)cached_.size() > api_config::get_instance()->max_cached_queries())
-				cached_.right.erase(cached_.right.begin());
-			// return result
-			return result;
-		} catch(...) {
-			return false; // error: unsupported query
+		it->second = ++query_cache_age * (matches ? 1 : -1);
+		// return cached match
+		return matches;
+	}
+
+	// not found in cache
+	try {
+		// compute whether it matches
+		bool matched = pugi::xpath_query(query.c_str()).evaluate_boolean(doc.first_child());
+
+		auto max_cached = (std::size_t)api_config::get_instance()->max_cached_queries();
+		if(nocache || max_cached == 0)
+			return matched;
+
+		cache.insert(std::make_pair(query, ++query_cache_age * (matched ? 1 : -1)));
+
+		// remove n/2 oldest results to make room for new entries
+		if (cache.size() > max_cached) {
+			// Find out the median cache entry age
+			std::vector<int> agevec;
+			agevec.reserve(cache.size());
+			for (auto &val : cache) agevec.push_back(std::abs(val.second));
+			auto middle = agevec.begin() + max_cached / 2;
+			std::nth_element(agevec.begin(), middle, agevec.end());
+			auto oldest_to_keep = *middle;
+
+			// Remove all elements older than the median age
+			for (auto it = cache.begin(); it != cache.end();)
+				if (abs(it->second) <= oldest_to_keep)
+					it = cache.erase(it);
+				else
+					++it;
 		}
+		return matched;
+	} catch (std::exception &e) {
+		LOG_F(WARNING, "Query error: %s", e.what());
+		return false;
 	}
 }
 

src/stream_info_impl.h

@@ -2,19 +2,26 @@
 #define STREAM_INFO_IMPL_H
 
 #include "common.h"
-#include <boost/bimap.hpp>
-#include <boost/thread/mutex.hpp>
 #include "pugixml/pugixml.hpp"
+#include <boost/thread/mutex.hpp>
+#include <unordered_map>
 
 namespace lsl {
 
+/// LRU cache for queries
+class query_cache {
+	std::unordered_map<std::string, int> cache;
+	int query_cache_age{0};
+	lslboost::mutex cache_mut_;
+public:
+	bool matches_query(const pugi::xml_document& doc, const std::string query, bool nocache);
+};
+
 	/**
 	* Actual implementation of the stream_info class.
 	* The stream_info class forwards all operations to an instance of this class.
 	*/
 	class stream_info_impl {
-		/// The query cache is a (bidirectional) mapping between query-strings and pairs of (last-use-timestamp, matching-true/false)
-		typedef lslboost::bimap<std::string,std::pair<double,bool> > query_cache;
 	public:
 
 		/**
@@ -80,7 +87,7 @@ namespace lsl {
 		* The info "matches" if the given XPath 1.0 query string returns a non-empty node set.
 		* @return Whether stream info is matched by the query string.
 		*/
-		bool matches_query(const std::string &query);
+		bool matches_query(const std::string &query, bool nocache = false);
 
 
 		//
@@ -255,7 +262,6 @@ namespace lsl {
 		pugi::xml_document doc_;
 		// cached query results
 		query_cache cached_;
-		lslboost::mutex cache_mut_;
 	};
 
 

testing/CMakeLists.txt

@@ -5,10 +5,17 @@ project(lsltests
 	)
 cmake_minimum_required (VERSION 3.12)
 enable_testing()
+
+option(LSL_BENCHMARKS "Enable benchmarks in unit tests" OFF)
+
 add_library(catch_main OBJECT catch_main.cpp)
 target_compile_features(catch_main PUBLIC cxx_std_11)
 
 target_compile_definitions(catch_main PRIVATE LSL_VERSION_INFO=${LSL_VERSION_INFO})
+if(LSL_BENCHMARKS)
+	target_compile_definitions(catch_main PUBLIC CATCH_CONFIG_ENABLE_BENCHMARKING)
+endif()
+
 add_executable(lsl_test_exported
 	DataType.cpp
 	discovery.cpp
@@ -21,6 +28,7 @@ add_executable(lsl_test_internal
 	asiocancel.cpp
 	inireader.cpp
 	stringfuncs.cpp
+	streaminfo.cpp
 )
 target_link_libraries(lsl_test_internal PRIVATE lslobj lslboost catch_main)
 

testing/streaminfo.cpp

@@ -0,0 +1,52 @@
+#include "../src/stream_info_impl.h"
+#include "../src/api_config.h"
+#include "catch.hpp"
+
+TEST_CASE("streaminfo matching via XPath", "[basic][streaminfo][xml]") {
+	lsl::stream_info_impl info(
+		"streamname", "streamtype", 8, 500, lsl_channel_format_t::cft_string, "sourceid");
+	auto channels = info.desc().append_child("channels");
+	for(int i=0; i< 4;++i)
+		channels.append_child("channel").append_child("type").append_child(pugi::node_pcdata).set_value("EEG");
+	for(int i=0; i< 4;++i)
+		channels.append_child("channel").append_child("type").append_child(pugi::node_pcdata).set_value("EOG");
+
+#ifdef CATCH_CONFIG_ENABLE_BENCHMARKING
+	// Append lots of dummy channels for performance tests
+	for(int i=0; i<50000; ++i)
+		channels.append_child("chn").append_child("type").append_child(pugi::node_pcdata).set_value("foobar");
+	for(int i=0; i<2000; ++i) {
+		channels = channels.append_child("chn");
+		channels.append_child(pugi::node_pcdata).set_value("1");
+	}
+
+	BENCHMARK("trivial query") {
+		return info.matches_query("name='streamname' and type='streamtype'", true);
+	};
+	BENCHMARK("complicated query") {
+		return info.matches_query("count(desc/channels/channel[type='EEG'])>3", true);
+	};
+	BENCHMARK("Cached query") {
+		return info.matches_query("count(desc/channels/channel[type='EEG'])>3", false);
+	};
+
+	// test how well the cache copes with lots of different queries
+	BENCHMARK("partially cached queries (x1000)") {
+		int matches = 0;
+		for (int j = 0; j < 1000; ++j)
+			matches += info.matches_query(("0<=" + std::to_string(j)).c_str());
+		return matches;
+	};
+
+#endif
+
+	INFO(info.to_fullinfo_message());
+	REQUIRE(info.matches_query("name='streamname'"));
+	REQUIRE(info.matches_query("name='streamname' and type='streamtype'"));
+	REQUIRE(info.matches_query("channel_count > 5"));
+	REQUIRE(info.matches_query("nominal_srate >= 499"));
+	REQUIRE(info.matches_query("count(desc/channels/channel[type='EEG'])>3"));
+
+	REQUIRE(!info.matches_query("in'va'lid"));
+	REQUIRE(!info.matches_query("name='othername'"));
+}