analysis.md

title	Embedded rcutils analysis
permalink	/docs/concepts/client_library/rcutils_analysis/

Proposed changes

The main issues found when porting rcutils package to embedded systems with RTOS during micro*ROS development were:

• the lack of filesystem
• dynamic memory allocations out of the RTOS control (usually with standard library implementations of malloc and free)
• the POSIX API dependency

This document addresses the first two items.

To avoid the filesystem dependency without modifying high*level layers (such as rcl or rmw), it is proposed to use a combination between the available rcl_logging_noop package and a modified version of the filesystem dependencies in rcutils. This approach is enabled using the RCUTILS_NO_FILESYSTEM flag in compilation time.

Dynamic memory allocation must be bounded to ROS2 custom allocators. rcl and rmw layers usually rely on rcutils_get_default_allocator function to obtain allocators, so a setter function is proposed. This way, using rcutils_set_default_allocator function is possible to modify the defaults easing the use of custom memory management in embedded systems.

Dynamic memory allocation is also found when dealing with error handling in rcutils. By using RCUTILS_AVOID_DYNAMIC_ALLOCATION some string related memmove functions along the error handling are avoided.

Dependencies in rcl, rcutils and rmw

Test folders are excluded.

error_handling.h

• Macro RCUTILS_SAFE_FWRITE_TO_STDERR in rcutils error_handling.h: Check here

  • Problem: use fwrite to print to stderr and relies on a filesytem
  • Appears in:
    • rcl/rcl/src/rcl/expand_topic_name.c
    • rcl/rcl/src/rcl/logging_rosout.c
    • rcl/rcl/src/rcl/logging.c
    • rcl/rcl/src/rcl/context.c
    • rcl/rcl_yaml_param_parser/src/parser.c
    • rcutils/src/split.c
    • rcutils/src/error_handling.c
    • rcutils/src/allocator.c
    • rcutils/src/logging.c
    • rcutils/src/error_handling_helpers.h
    • rcutils/include/rcutils/logging.h
    • rcutils/include/rcutils/error_handling.h
    • rcl/rcl/src/rcl/expand_topic_name.c
    • rcl/rcl/src/rcl/logging_rosout.c
    • rcl/rcl/src/rcl/logging.c
    • rcl/rcl/src/rcl/context.c
    • rcl/rcl_yaml_param_parser/src/parser.c
    • rmw/rmw/include/rmw/error_handling.h

• Macro RCUTILS_SET_ERROR_MSG in rcutils error_handling.h: Check here

  • Problem: use inconditionally memmove inside __rcutils_copy_string() inside rcutils_set_error_state. It implies dynamic memory allocation.
  • Dependecies:
    • rcl/rcl/include/rcl/error_handling.h
    • rcutils/src/security_directory.c
    • rcutils/src/time_unix.c
    • rcutils/src/split.c
    • rcutils/src/error_handling.c
    • rcutils/src/time.c
    • rcutils/src/string_map.c
    • rcutils/src/uint8_array.c
    • rcutils/src/hash_map.c
    • rcutils/src/char_array.c
    • rcutils/src/logging.c
    • rcutils/src/string_array.c
    • rcutils/src/array_list.c
    • rcutils/include/rcutils/types/array_list.h
    • rcutils/include/rcutils/types/hash_map.h
    • rcutils/include/rcutils/allocator.h
    • rcutils/include/rcutils/error_handling.h
    • rcl/rcl/include/rcl/error_handling.h
    • rmw/rmw/include/rmw/error_handling.h

• Macro RCUTILS_SET_ERROR_MSG_WITH_FORMAT_STRING in rcutils error_handling.h:. Check here

  • Problem: use RCUTILS_SET_ERROR_MSG, see above.
  • Dependecies:
    • rcl/rcl/include/rcl/error_handling.h
    • rcutils/src/security_directory.c
    • rcutils/src/string_map.c
    • rcutils/src/logging.c
    • rcutils/include/rcutils/error_handling.h
    • rcl/rcl/include/rcl/error_handling.h
    • rmw/rmw/include/rmw/error_handling.h

security_directory.c (moved from rcl to rcutils)

• Function get_best_matching_directory in rcutils security_directory.c Check here

  • Problem: use tinydir library which relies on filesytem
  • Dependecies:
    • rcutils/src/security_directory.c
    • rcl/rcl/src/rcl/security_directory.c

• Function prefix_match_lookup. Check here

  • Problem: use tinydir library which relies on filesytem
  • Dependencies:
    • rcutils/src/security_directory.c
    • rcl/rcl/src/rcl/security_directory.c

allocator.c

• Function rcutils_get_default_allocator. Check here
• Problem: use static allocated default_allocator which uses malloc/free. rcutils_set_default_allocator is proposed.
• Dependecies:
  • rcl/rcl/include/rcl/allocator.h
  • rcl/rcl/include/rcl/expand_topic_name.h
  • rcutils/src/allocator.c
  • rcutils/src/logging.c
  • rcutils/include/rcutils/types/string_map.h
  • rcutils/include/rcutils/types/array_list.h
  • rcutils/include/rcutils/types/string_array.h
  • rcutils/include/rcutils/types/hash_map.h
  • rcutils/include/rcutils/allocator.h
  • rmw_implementation/rmw_implementation/src/functions.cpp
  • rcl/rcl/include/rcl/allocator.h
  • rcl/rcl/include/rcl/expand_topic_name.h
  • rmw/rmw/src/allocators.c

filesystem.c

• Functions rcutils_get_cwd, rcutils_is_directory, rcutils_is_file, rcutils_exists, rcutils_is_readable, rcutils_is_writable and rcutils_is_readable_and_writable. Check here
  • Problem: rely on filesystem
  • Dependecies rcutils_get_cwd():
    • rcutils/src/filesystem.c
    • rcutils/include/rcutils/filesystem.h
  • Dependecies rcutils_is_directory():
    • rcutils/src/security_directory.c
    • rcutils/src/filesystem.c
    • rcutils/include/rcutils/filesystem.h
    • rcl/rcl/src/rcl/security_directory.c
  • Dependecies rcutils_is_file():
    • rcutils/src/filesystem.c
    • rcutils/include/rcutils/filesystem.h
  • Dependencies rcutils_exists():
    • rcutils/src/filesystem.c
    • rcutils/include/rcutils/filesystem.h
  • Dependencies rcutils_is_readable():
    • rcutils/src/filesystem.c
    • rcutils/include/rcutils/filesystem.h
  • Dependencies rcutils_is_writable():
    • rcutils/src/filesystem.c
    • rcutils/include/rcutils/filesystem.h
  • Dependencies rcutils_is_readable_and_writable():
    • rcutils/src/filesystem.c
    • rcutils/include/rcutils/filesystem.h