How to use SHM in mico-ROS (Using docker) #206

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1. pablogs9 commented on Sep 4, 2023

   

   pablogs9

   on Sep 4, 2023

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   Cyclone DDS is not compatible with micro-ROS. Please recheck with Fast DDS.
2. victor-velezmoro commented on Sep 4, 2023

   

   victor-velezmoro

   on Sep 4, 2023

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   Thanks for the answer. I now tried Fast DDS. With the Agent running, the communication works (but using the Agent). If I launch the nodes without the Agent, the nodes abort after a short time.
   This i the error message i get:

   root@docker-desktop:/microros_ws# ros2 run micro_ros_demos_rclc LIDAR
   [ERROR 1693841179.668659857]: [rclc_init] Error in rcl_init: error not set, at ./src/rcl/init.c:218
   
   Failed status on line 66: 1. Aborting.
   

   In line 66 of my code is this:
   RCCHECK(rclc_support_init(&support, argc, argv, &allocator));

   and i use the default allocator:

   rcl_allocator_t allocator = rcl_get_default_allocator();
   rclc_support_t support;
   

   All nodes are sourced and run on rmw_microxrcedds:

   source /opt/ros/humble/setup.bash
   source install/local_setup.bash
   export RMW_IMPLEMENTATION=rmw_microxrcedds
   ros2 run micro_ros_demos_rclc LIDAR
   

   Any idea why is does not work ?
3. victor-velezmoro commented on Sep 4, 2023

   

   victor-velezmoro

   on Sep 4, 2023

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   i did not change the code of my nodes for the use of SHM. Do i have to do that ?
   this is e.g. the code for my publisher node at the beginning of the chain:

   #include <rcl/rcl.h>
   #include <rcl/error_handling.h>
   #include <rclc/rclc.h>
   #include <rclc/executor.h>
   #include <errno.h>
   #include <std_msgs/msg/string.h>
   #include <sys/time.h>
   #include <stdio.h>
   #include <time.h>
   #include <math.h>
   #include <string.h>
   
   #define ARRAY_LEN 200
   
   #define RCCHECK(fn) { rcl_ret_t temp_rc = fn; if((temp_rc != RCL_RET_OK)){printf("Failed status on line %d: %d. Aborting.\n",__LINE__,(int)temp_rc); return 1;}}
   #define RCSOFTCHECK(fn) { rcl_ret_t temp_rc = fn; if((temp_rc != RCL_RET_OK)){printf("Failed status on line %d: %d. Continuing.\n",__LINE__,(int)temp_rc);}}
   
   rcl_publisher_t publisher;
   rcl_timer_t timer;
   std_msgs__msg__String msg;
   int msg_count = 0;  // Variable to hold the current message count
   
   FILE* pub_file;
   
   void get_timestamp(char* timestamp, size_t size)
   {
       struct timeval tv;
       
       // Get the current time
       gettimeofday(&tv, NULL);
       
       // Convert the time to microseconds
       unsigned long long current_time_microseconds = (unsigned long long)(tv.tv_sec) * 1000000 + tv.tv_usec;
       
       snprintf(timestamp, size, "%llu", current_time_microseconds);
   }
   
   void timer_callback(rcl_timer_t * timer, int64_t last_call_time)
   {
       if (timer != NULL) {
           snprintf(msg.data.data, ARRAY_LEN, "%d", msg_count++); // Fill msg.data with incrementing numbers
           msg.data.size = strlen(msg.data.data);
           msg.data.capacity = ARRAY_LEN;
   
           RCSOFTCHECK(rcl_publish(&publisher, &msg, NULL));
   
           char timestamp_pub[26];
           get_timestamp(timestamp_pub, sizeof(timestamp_pub));
   
           int res = fprintf(pub_file, "%s - %s\n", msg.data.data, timestamp_pub);
           if (res < 0) {
           perror("Failed to write to micro_pub.csv");
           } else {
           fflush(pub_file);
           }
   
           printf("Publishing (Controller, '%s'): ' %s'\n", timestamp_pub, msg.data.data);
       }
   }
   
   int main(int argc, const char * const * argv)
   {
   	rcl_allocator_t allocator = rcl_get_default_allocator();
   	rclc_support_t support;
   
   	RCCHECK(rclc_support_init(&support, argc, argv, &allocator));
   
   	rcl_node_t node;
   	RCCHECK(rclc_node_init_default(&node, "string_node", "", &support));
   
   	RCCHECK(rclc_publisher_init_best_effort(
   		&publisher,
   		&node,
   		ROSIDL_GET_MSG_TYPE_SUPPORT(std_msgs, msg, String),
   		"/sensor_data"));
   
   	const unsigned int timer_timeout_ms = 100;
   	RCCHECK(rclc_timer_init_default(
   		&timer,
   		&support,
   		RCL_MS_TO_NS(timer_timeout_ms),
   		timer_callback));
   
   	rclc_executor_t executor = rclc_executor_get_zero_initialized_executor();
   
   	RCCHECK(rclc_executor_init(&executor, &support.context, 1, &allocator));
   	RCCHECK(rclc_executor_add_timer(&executor, &timer));
   
   	msg.data.data = (char * ) malloc(ARRAY_LEN * sizeof(char));
   	msg.data.size = 0;
   	msg.data.capacity = ARRAY_LEN;
   
       if (msg.data.data == NULL) {
       fprintf(stderr, "Failed to allocate memory for msg.\n");
       return 1;
       }
   
       pub_file = fopen("/microros_ws/src/_csv_files/lidar_sensor_pub.csv", "w");
       if (pub_file == NULL) {
           perror("Failed to open micro_pub.csv");
           return 1;
       }
       fprintf(pub_file, "Lidar-PUB\n");
   
   	rclc_executor_spin(&executor);
   
   	fclose(pub_file);
   
   	RCCHECK(rcl_publisher_fini(&publisher, &node));
   	RCCHECK(rcl_timer_fini(&timer));
   	RCCHECK(rcl_node_fini(&node));
   
   	return 0;
   }
   
   
4. pablogs9 commented on Sep 5, 2023

   

   pablogs9

   on Sep 5, 2023

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   The micro-ROS client needs an agent to init the session, the SHM mechanism is a way of communicating entities inside an up-and-running XRCE session (that needs an agent to be valid).