adds proper multi-threading

src/RdaReader/CMakeLists.txt

@@ -2,6 +2,8 @@ project(RdaReader)
 
 set(CMAKE_CXX_STANDARD 20)
 
+find_package(Threads REQUIRED)
+
 add_library(RdaReader src/RdaReader src/SharedIndex.cpp src/BucketedZstdData.cpp)
 target_include_directories(RdaReader PUBLIC include)
-target_link_libraries(RdaReader zstd)
+target_link_libraries(RdaReader PRIVATE zstd Threads::Threads)

src/RdaReader/src/RdaReader.cpp

@@ -6,6 +6,8 @@
 #include <execution>
 #include <algorithm>
 #include <atomic>
+#include <optional>
+#include <thread>
 
 void RdaReader::log(const std::string &string) {
 	if(logger) logger(string);
@@ -37,19 +39,40 @@ size_t RdaReader::readRda(std::istream &rda, uint64_t id, std::ostream &output)
 	return readRda(rda, id, output, dummyMutex);
 }
 
+std::optional<std::istream *> getVictimIfAvailable(std::vector<std::istream *> &victims, std::mutex &victimMutex) {
+	std::lock_guard lock(victimMutex);
+	if(victims.size() > 0) {
+		std::istream *tmp = victims.back();
+		victims.pop_back();
+		return tmp;
+	}
+	return {};
+}
+
 size_t RdaReader::readDataset(const std::vector<char> &datasetName, const std::vector<char> &sharedIndex, const std::vector<std::istream *> &rdas, std::ostream &output, std::mutex &outputMutex) {
 	log("Reading shared index... ");
 	SharedIndex sharedIndexReader(sharedIndex);
 
+	std::vector<std::istream *> victims = rdas;
+	std::mutex victimMutex;
+
 	if(std::optional<std::uint64_t> id = sharedIndexReader.getID(datasetName)) {
 		log("Found ID: " + std::to_string(id.value()) + '\n');
 		std::atomic_size_t totalEntries(0);
-		std::for_each(
-			std::execution::par,
-			rdas.begin(),
-			rdas.end(),
-			[this, &totalEntries, &id, &output, &outputMutex](std::istream * const &rda) {totalEntries += readRda(*rda, id.value(), output, outputMutex);}
+		std::vector<std::thread> threads(std::thread::hardware_concurrency());
+		for(int i = 0; i < std::thread::hardware_concurrency(); ++i) {
+			threads[i] = std::thread(
+				[&victims, &victimMutex, this, &totalEntries, &id, &output, &outputMutex](){
+					for(std::optional<std::istream *> victim; victim = getVictimIfAvailable(victims, victimMutex); ) {
+						totalEntries += readRda(*victim.value(), id.value(), output, outputMutex);
+					}
+				}
 			);
+		}
+		for(std::thread &thread : threads) {
+			thread.join();
+		}
+
 		return totalEntries;
 	}
 	log("No entries found\n");