rclcpp/context lacking a const method for `shutdown_reason`

[Blast545]

Adding coverage tests for context module (#1321), we have realized there is no const method for the shutdown_reason method. See link to the code

This issue is to track the conversation here and get some feedback.

[brawner]

Link to .cpp (

rclcpp/rclcpp/src/rclcpp/context.cpp

Lines 289 to 294 in 3a4ac0c

	std::string
	Context::shutdown_reason()
	{
	std::lock_guard<std::recursive_mutex> lock(init_mutex_);
	return shutdown_reason_;
	}

). This function requires locking the init_mutex_ which prevents it from being const. I suggested @Blast545 open this issue, just to see if others thought there might be more preferred ways of doing this.

One possible solution would be to make init_mutex_ and perhaps other mutexes mutable.

[suab321321]

@clalancette should I follow @brawner and make it the init_mutex_ mutable?
and open a PR

[clalancette]

@clalancette should I follow @brawner and make it the init_mutex_ mutable?
and open a PR

Yeah, that is the usual way to deal with this problem. Making init_mutex_ mutable seems totally reasonable to me.

[fujitatomoya]

done with #1578