logging: write log to a memory buffer

Instead of writing every line of the log to the file (and, consequently,
to the disk), write to a memory buffer first and after the log finishes
flush from memory to disk. This improve the performance of the tool, since
it avoids making the program blocked by disk IO.

src/logging.h

@@ -10,16 +10,16 @@ using namespace std;
 
 string os, cpu, gpu, ram, kernel, driver;
 bool sysInfoFetched = false;
-int gpuLoadLog = 0, cpuLoadLog = 0, log_period = 0;
+int gpuLoadLog = 0, cpuLoadLog = 0, log_period = 0, elapsedLog;
 
 struct logData{
   double fps;
-  double cpu;
-  double gpu;
-  double previous;
+  int cpu;
+  int gpu;
+  int previous;
 };
 
-double fps, elapsedLog;
+double fps;
 std::vector<logData> logArray;
 ofstream out;
 const char* log_period_env = std::getenv("LOG_PERIOD");
@@ -27,15 +27,15 @@ int num;
 bool loggingOn;
 uint64_t log_start;
 
-// void writeFile(string date){
-// 	out.open(mangohud_output_env + date, ios::out | ios::app);
+void writeFile(string filename){
+  out.open(filename, ios::out | ios::app);
 
-// 	for (size_t i = 0; i < logArray.size(); i++) {
-//      out << logArray[i].fps << "," << logArray[i].cpu  << "," << logArray[i].gpu << endl;
-//   }
-// 	out.close();
-// 	logArray.clear();
-// }
+  for (size_t i = 0; i < logArray.size(); i++)
+    out << logArray[i].fps << "," << logArray[i].cpu  << "," << logArray[i].gpu << "," << logArray[i].previous << endl;
+
+  out.close();
+  logArray.clear();
+}
 
 void *logging(void *params_void){
   overlay_params *params = reinterpret_cast<overlay_params *>(params_void);
@@ -51,18 +51,19 @@ void *logging(void *params_void){
   out.open(params->output_file + date, ios::out | ios::app);
   out << "os," << "cpu," << "gpu," << "ram," << "kernel," << "driver" << endl;
   out << os << "," << cpu << "," << gpu << "," << ram << "," << kernel << "," << driver << endl;
+  out.close();
+
   while (loggingOn){
     uint64_t now = os_time_get();
-    elapsedLog = (double)(now - log_start);
-    out << fps << "," << cpuLoadLog << "," << gpuLoadLog << "," <<  now - log_start << endl;
-    // logArray.push_back({fps, cpuLoadLog, gpuLoadLog, 0.0f});
+    elapsedLog = now - log_start;
+    logArray.push_back({fps, cpuLoadLog, gpuLoadLog, elapsedLog});
 
     if ((elapsedLog) >= params->log_duration * 1000000 && params->log_duration)
       loggingOn = false;
-    
+
     this_thread::sleep_for(chrono::milliseconds(log_period));
   }
-  // writeFile(date);
-  out.close();
+
+  writeFile(params->output_file + date);
   return NULL; 
 }