Bug fixes for sync flush and add_tracker (#91)

* fixes for sync flush and also add_tracker

* added flag for flush

include/cppkafka/utils/buffered_producer.h

@@ -185,20 +185,28 @@ public:
      * This will send all messages and keep waiting until all of them are acknowledged (this is
      * done by calling wait_for_acks).
      *
+     * \param preserve_order If set to True, each message in the queue will be flushed only when the previous
+     *                       message ack is received. This may result in performance degradation as messages
+     *                       are sent one at a time. This calls sync_produce() on each message in the buffer.
+     *                       If set to False, all messages are flushed in one batch before waiting for acks,
+     *                       however message reordering may occur if librdkafka setting 'messages.sent.max.retries > 0'.
+     *
      * \remark Although it is possible to call flush from multiple threads concurrently, better
      *         performance is achieved when called from the same thread or when serialized
      *         with respect to other threads.
      */
-    void flush();
+    void flush(bool preserve_order = false);
     
     /**
      * \brief Flushes the buffered messages and waits up to 'timeout'
      *
      * \param timeout The maximum time to wait until all acks are received
      *
+     * \param preserve_order True to preserve message ordering, False otherwise. See flush above for more details.
+     *
      * \return True if the operation completes and all acks have been received.
      */
-    bool flush(std::chrono::milliseconds timeout);
+    bool flush(std::chrono::milliseconds timeout, bool preserve_order = false);
 
     /**
      * Waits for produced message's acknowledgements from the brokers
@@ -404,13 +412,15 @@ private:
     };
     using TrackerPtr = std::shared_ptr<Tracker>;
     
+    // Returns existing tracker or creates new one
     template <typename BuilderType>
-    TrackerPtr add_tracker(BuilderType& builder) {
-        if (has_internal_data_ && !builder.internal()) {
-            // Add message tracker only if it hasn't been added before
-            TrackerPtr tracker = std::make_shared<Tracker>(SenderType::Async, max_number_retries_);
-            builder.internal(tracker);
-            return tracker;
+    TrackerPtr add_tracker(SenderType sender, BuilderType& builder) {
+        if (has_internal_data_) {
+            if (!builder.internal()) {
+                // Add message tracker only if it hasn't been added before
+                builder.internal(std::make_shared<Tracker>(sender, max_number_retries_));
+            }
+            return std::static_pointer_cast<Tracker>(builder.internal());
         }
         return nullptr;
     }
@@ -469,7 +479,7 @@ void BufferedProducer<BufferType>::add_message(const MessageBuilder& builder) {
 
 template <typename BufferType>
 void BufferedProducer<BufferType>::add_message(Builder builder) {
-    add_tracker(builder);
+    add_tracker(SenderType::Async, builder);
     do_add_message(move(builder), MessagePriority::Low, true);
 }
 
@@ -477,7 +487,7 @@ template <typename BufferType>
 void BufferedProducer<BufferType>::produce(const MessageBuilder& builder) {
     if (has_internal_data_) {
         MessageBuilder builder_clone(builder.clone());
-        add_tracker(builder_clone);
+        add_tracker(SenderType::Async, builder_clone);
         async_produce(builder_clone, true);
     }
     else {
@@ -489,7 +499,7 @@ template <typename BufferType>
 void BufferedProducer<BufferType>::sync_produce(const MessageBuilder& builder) {
     if (has_internal_data_) {
         MessageBuilder builder_clone(builder.clone());
-        TrackerPtr tracker = add_tracker(builder_clone);
+        TrackerPtr tracker = add_tracker(SenderType::Sync, builder_clone);
         // produce until we succeed or we reach max retry limit
         std::future<bool> should_retry;
         do {
@@ -526,15 +536,47 @@ void BufferedProducer<BufferType>::async_flush() {
 }
 
 template <typename BufferType>
-void BufferedProducer<BufferType>::flush() {
-    async_flush();
-    wait_for_acks();
+void BufferedProducer<BufferType>::flush(bool preserve_order) {
+    if (preserve_order) {
+        CounterGuard<size_t> counter_guard(flushes_in_progress_);
+        QueueType flush_queue; // flush from temporary queue
+        {
+            std::lock_guard<std::mutex> lock(mutex_);
+            std::swap(messages_, flush_queue);
+        }
+        while (!flush_queue.empty()) {
+            sync_produce(flush_queue.front());
+            flush_queue.pop_front();
+        }
+    }
+    else {
+        async_flush();
+        wait_for_acks();
+    }
 }
 
 template <typename BufferType>
-bool BufferedProducer<BufferType>::flush(std::chrono::milliseconds timeout) {
-    async_flush();
-    return wait_for_acks(timeout);
+bool BufferedProducer<BufferType>::flush(std::chrono::milliseconds timeout,
+                                         bool preserve_order) {
+    if (preserve_order) {
+        CounterGuard<size_t> counter_guard(flushes_in_progress_);
+        QueueType flush_queue; // flush from temporary queue
+        {
+            std::lock_guard<std::mutex> lock(mutex_);
+            std::swap(messages_, flush_queue);
+        }
+        auto start_time = std::chrono::high_resolution_clock::now();
+        while (!flush_queue.empty() &&
+               (std::chrono::duration_cast<std::chrono::milliseconds>
+                   (std::chrono::high_resolution_clock::now() - start_time) < timeout)) {
+            sync_produce(flush_queue.front());
+            flush_queue.pop_front();
+        }
+    }
+    else {
+        async_flush();
+        return wait_for_acks(timeout);
+    }
 }
 
 template <typename BufferType>

tests/producer_test.cpp

@@ -79,6 +79,19 @@ void flusher_run(BufferedProducer<string>& producer,
     producer.flush();
 }
 
+void async_flusher_run(BufferedProducer<string>& producer,
+                       int& exit_flag,
+                       int num_flush) {
+    while (!exit_flag) {
+        if (producer.get_buffer_size() >= (size_t)num_flush) {
+            producer.async_flush();
+        }
+        this_thread::sleep_for(milliseconds(10));
+    }
+    producer.async_flush();
+    producer.wait_for_acks();
+}
+
 void clear_run(BufferedProducer<string>& producer,
                condition_variable& clear) {
     mutex m;
@@ -377,7 +390,7 @@ TEST_CASE("replay async messages with errors", "[producer][buffered_producer][as
     ErrorProducer<string> producer(make_producer_config(),
                                    BufferedProducer<string>::TestParameters{false, true});
     producer.set_max_number_retries(num_retries);
-    thread flusher_thread(flusher_run, ref(producer), ref(exit_flag), 0);
+    thread flusher_thread(async_flusher_run, ref(producer), ref(exit_flag), 0);
     string payload = "Hello world";
     producer.produce(MessageBuilder(KAFKA_TOPICS[0]).payload(payload));
     this_thread::sleep_for(milliseconds(2000));