use implementation identifier in init and shutdown functions

Signed-off-by: William Woodall <william@osrfoundation.org>

rmw/include/rmw/init.h

@@ -41,6 +41,8 @@ typedef struct RMW_PUBLIC_TYPE rmw_init_options_t {
    * It is designed to be used with `rcl_init()` and `rcl_get_instance_id()`.
    */
   uint64_t instance_id;
+  /// Implementation identifier, used to ensure two different implementations are not being mixed.
+  const char * implementation_identifier;
   /// Implementation defined init options.
   rmw_init_options_impl_t * impl;
 } rmw_init_options_t;
@@ -64,6 +66,8 @@ typedef struct rmw_init_context_impl_t rmw_init_context_impl_t;
 typedef struct RMW_PUBLIC_TYPE rmw_init_context_t {
   /// Locally (process local) unique ID that represents this init/shutdown cycle.
   uint64_t instance_id;
+  /// Implementation identifier, used to ensure two different implementations are not being mixed.
+  const char * implementation_identifier;
   /// Implementation defined init context information.
   rmw_init_context_impl_t * impl;
 } rmw_init_context_t;
@@ -94,6 +98,8 @@ rmw_get_zero_initialized_init_context(void);
  * \param[in] options initialization options to be used during initialization
  * \param[out] context resulting context struct
  * \return `RMW_RET_OK` if successful, or
+ * \return `RMW_RET_INCORRECT_RMW_IMPLEMENTATION` if the implementation
+ *   identifier does not match, or
  * \return `RMW_RET_INVALID_ARGUMENT` if any arguments are null or invalid, or
  * \return `RMW_RET_ERROR` if an unexpected error occurs.
  */
@@ -119,6 +125,8 @@ rmw_init(const rmw_init_options_t * options, rmw_init_context_t * context);
  *
  * \param[in] context resulting context struct
  * \return `RMW_RET_OK` if successful, or
+ * \return `RMW_RET_INCORRECT_RMW_IMPLEMENTATION` if the implementation
+ *   identifier does not match, or
  * \return `RMW_RET_INVALID_ARGUMENT` if the argument is null or invalid, or
  * \return `RMW_RET_ERROR` if an unexpected error occurs.
  */

rmw/include/rmw/types.h

@@ -39,6 +39,8 @@ typedef int rmw_ret_t;
 #define RMW_RET_BAD_ALLOC 10
 /// Invalid argument return code.
 #define RMW_RET_INVALID_ARGUMENT 11
+/// Incorrect rmw implementation.
+#define RMW_RET_INCORRECT_RMW_IMPLEMENTATION 12
 
 // 24 bytes is the most memory needed to represent the GID by any current
 // implementation. It may need to be increased in the future.