More efficient way for reading CAN data in while loop - c++

Question

I have 3 devices which send 8 bytes of data over CAN interface. To read the buffer from CAN I am using a while loop which looks something like this:
void CanServer::ReadFromCAN() {
data_from_buffer_.clear();
can_frame frame;
read_can_port_ = read(soc_, &frame, sizeof(struct can_frame));
if (read_can_port_ < 0) return;
id_ = frame.can_id&0x1FFFFFFF;
dlc_ = frame.can_dlc;
for (const auto& byte : frame.data)
data_from_buffer_.push_back(byte);
}
while (ros::ok()) {
std_msgs::Int32MultiArray tachometer_array;
std::vector<__u8> data_from_can;
/***
* Read for the Radar1
*/
this->ReadFromCAN();
if (read_can_port_ < 0) continue;
//ROS_INFO("Read from CAN");
if (id_ == can_id::RadarFrame1)
for (int i = 0; i < dlc_; i++) {
radar1_bytes_[i] = data_from_buffer_[i];
radar1_buffer_.push_back(data_from_buffer_[i]);
}
if (IsMagicWord(radar1_bytes_, 0)) {
frame_id = "radar1_link";
this->PulbishRadarPCL(frame_id, radar1_pub_, radar1_buffer_, 0);
radar1_buffer_.clear();
canFrame_.can_dlc = 0;
}
}
if (id_ == can_id::RadarFrame2) {
for (int i = 0; i < dlc_; i++) {
radar2_bytes_[i] = data_from_buffer_[i];
radar2_buffer_.push_back(data_from_buffer_[i]);
}
if (IsMagicWord(radar2_bytes_, 1)) {
frame_id = "radar2_link";
this->PulbishRadarPCL(frame_id, radar2_pub_, radar2_buffer_, 1);
radar2_buffer_.clear();
canFrame_.can_dlc = 0;
}
}
if (id_ == can_id::RadarFrame3) {
for (int i = 0; i < dlc_; i++) {
radar3_bytes_[i] = data_from_buffer_[i];
radar3_buffer_.push_back(data_from_buffer_[i]);
}
if (IsMagicWord(radar3_bytes_, 2)) {
frame_id = "radar3_link";
this->PulbishRadarPCL(frame_id, radar3_pub_, radar3_buffer_, 2);
radar3_buffer_.clear();
canFrame_.can_dlc = 0;
}
}
rate.sleep();
}
Where rate.sleep() is similar to sleep() function in C++.
Right now, I am running this while loop in 5 MHz however I think this is an overkill and I am getting almost 100% CPU usage on a 1 core.
I tried to play around with the delay time but I think this is highly inefficient and I wonder is there any other way to handle this?

Answer 1

It turns out that poll is what you need. Here is my example.
First, create a pollfd structure from <poll.h> header in Linux. I have decided to create a class member but you can create however you like:
pollfd poll_;
poll_.fd = soc_;
poll_.events = POLLIN;
poll_.revents = 0;
Here, soc_ is a socket and POLLIN means that you want to read from the socket.
Then, in my while loop, instead of delaying I just used this function at the beginning of my while loop:
poll_int = poll(&poll_, 1, 100);
if (poll_int <= 0) continue;
So poll() function returns value of 1 if the read was succesful and I made a timeout of 100ms (just a random number, I know that the data are coming at much higher rate)
With that, you will only read the data from socket whenever poll returns a value greater that 0.
Results? 3% CPU usage and if you want to add more data into your socket flow, poll will optimize for you so this is a scalable way of reading something like CAN bus.