Mutext handling (#90)

* namespace added on countly classes

* - queue processing flag added
- mutext unlock while attempting http requests

* compilation issue fixed!

* code reverted

* change log entry added
code formating

* adding comments

Co-authored-by: ArtursK <[email protected]>

CHANGELOG.md

@@ -3,6 +3,7 @@
 * !! Major breaking change !! We are extracting the 'Event' class out of the 'Countly' class which will change how that class can be referenced. 'Countly::Event' will not work, you will have to use 'cly::Event' instead.
 * !! Major breaking change !! Increased the compiler version required to compile the SDK. It's increased from version C++11 to C++14.
 * Making network requests has been reworked. They will now be sent on a separate thread. Requests will also be added in an internal queue and will be sent one at a time.
+* When making network requests, the SDK will now unlock it's mutex.
 * Fixed a bug that caused an exception on windows when encoding data that contains special characters. 
 
 22.02.0

include/countly.hpp

@@ -12,9 +12,7 @@
 #include <string>
 #include <thread>
 
-#ifndef COUNTLY_USE_SQLITE
 #include <deque>
-#endif
 
 #include "nlohmann/json.hpp"
 
@@ -203,6 +201,9 @@ class Countly : public cly::CountlyDelegates {
    * @return a vector object containing events.
    */
   const std::vector<std::string> debugReturnStateOfEQ() {
+#ifdef COUNTLY_USE_SQLITE
+    return {};
+#endif
     std::vector<std::string> v(event_queue.begin(), event_queue.end());
     return v;
   }
@@ -215,7 +216,7 @@ class Countly : public cly::CountlyDelegates {
   /**
    * Helper methods to fetch remote config from the server.
    */
-#pragma region  Remote_Config_Helper_Methods
+#pragma region Remote_Config_Helper_Methods
   void _fetchRemoteConfig(std::map<std::string, std::string> &data);
   void _updateRemoteConfigWithSpecificValues(std::map<std::string, std::string> &data);
 #pragma endregion Remote_Config_Helper_Methods
@@ -258,6 +259,8 @@ class Countly : public cly::CountlyDelegates {
   std::shared_ptr<cly::LoggerModule> logger;
 
   std::mutex mutex;
+
+  bool is_queue_being_processed = false;
   bool enable_automatic_session = false;
   bool stop_thread = false;
   bool running = false;

src/countly.cpp

@@ -787,21 +787,56 @@ std::string Countly::calculateChecksum(const std::string &salt, const std::strin
 #endif
 }
 
+  /**
+   * SDK central execution call for processing requests in the request queue.
+   * Only one sender is active at a time. Requests are processed in order.
+   */
 void Countly::processRequestQueue() {
+  mutex.lock();
+  //making sure that no other thread is processing the queue
+  if (is_queue_being_processed) {
+    mutex.unlock();
+    return;
+  }
+
+  //if this is the only thread, mark that processing is happening
+  is_queue_being_processed = true;
+  mutex.unlock();
 
-  while (!request_queue.empty()) {
+  while (true) {
     mutex.lock();
+    if (request_queue.empty()) {
+      //stop sending requests once the queue is empty
+      mutex.unlock();
+      break;
+    }
+
     std::string data = request_queue.front();
+    mutex.unlock();
+
     HTTPResponse response = sendHTTP("/i", data);
 
+    mutex.lock();
     if (!response.success) {
+      //if the request was not a success, abort sending and try again in the future
       mutex.unlock();
       break;
     }
 
-    request_queue.pop_front();
+
+    if (request_queue.front() == data) {
+      // we pop the front only if it is still the same request
+      // the queue might have changed while we were sending the request
+      request_queue.pop_front();
+    }
+
     mutex.unlock();
   }
+
+  mutex.lock();
+  //mark that no thread is processing the request queue
+  is_queue_being_processed = false;
+  mutex.unlock();
 }
 
 void Countly::addToRequestQueue(std::string &data) {
@@ -1029,8 +1064,8 @@ void Countly::enableRemoteConfig() {
 }
 
 void Countly::_fetchRemoteConfig(std::map<std::string, std::string> &data) {
-  mutex.lock();
   HTTPResponse response = sendHTTP("/o/sdk", serializeForm(data));
+  mutex.lock();
   if (response.success) {
     remote_config = response.data;
   }
@@ -1061,8 +1096,8 @@ nlohmann::json Countly::getRemoteConfigValue(const std::string &key) {
 }
 
 void Countly::_updateRemoteConfigWithSpecificValues(std::map<std::string, std::string> &data) {
-  mutex.lock();
   HTTPResponse response = sendHTTP("/o/sdk", serializeForm(data));
+  mutex.lock();
   if (response.success) {
     for (auto it = response.data.begin(); it != response.data.end(); ++it) {
       remote_config[it.key()] = it.value();