do not throw exception if trying to dequeue an empty intra-process buffer (#2061)

Signed-off-by: Alberto Soragna <[email protected]>

Signed-off-by: Alberto Soragna <[email protected]>

Author: alsora

rclcpp/include/rclcpp/experimental/buffers/ring_buffer_implementation.hpp

@@ -86,8 +86,7 @@ class RingBufferImplementation : public BufferImplementationBase<BufferT>
     std::lock_guard<std::mutex> lock(mutex_);
 
     if (!has_data_()) {
-      RCLCPP_ERROR(rclcpp::get_logger("rclcpp"), "Calling dequeue on empty intra-process buffer");
-      throw std::runtime_error("Calling dequeue on empty intra-process buffer");
+      return BufferT();
     }
 
     auto request = std::move(ring_buffer_[read_index_]);

rclcpp/include/rclcpp/experimental/subscription_intra_process.hpp

@@ -109,8 +109,14 @@ class SubscriptionIntraProcess
 
     if (any_callback_.use_take_shared_method()) {
       shared_msg = this->buffer_->consume_shared();
+      if (!shared_msg) {
+        return nullptr;
+      }
     } else {
       unique_msg = this->buffer_->consume_unique();
+      if (!unique_msg) {
+        return nullptr;
+      }
     }
     return std::static_pointer_cast<void>(
       std::make_shared<std::pair<ConstMessageSharedPtr, MessageUniquePtr>>(
@@ -138,7 +144,7 @@ class SubscriptionIntraProcess
   execute_impl(std::shared_ptr<void> & data)
   {
     if (!data) {
-      throw std::runtime_error("'data' is empty");
+      return;
     }
 
     rmw_message_info_t msg_info;