Re: [Boost-users] How to call destructor on thread object?

Subject: Re: [Boost-users] How to call destructor on thread object?
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2015-05-19 01:49:38

Mere moments ago, quoth I:
> On 19/05/2015 15:26, Lane wrote:
>>
>> I'm using the boost meta state machine and upon entry of this state, I
>> create two threads, and stop these threads in the on_exit().
>>
>> In on_entry(), I call the functors of each class and create threads and
>> add those to a boost thread_group. What I need to do now is call the
>> destructor of the objects on the threads ( of ClassA and ClassB) within
>> on_exit(). I'm unclear as to how the destructors of the objects
>> would/should be called when interrupting the threads. The destructors
>> are currently not being called.
>
> Since you are passing a copy of the object as the thread's state, the
> destructor for the local instances will be called in on_entry(), and the
> destructor for the instances owned by the thread will be called when the
> thread_group is destroyed, which is when MyEvent is destroyed.
>
> I'm not really familiar enough with Boost.MSM to know whether the event
> instance is destroyed when the event is handled (which if this were the
> case, you shouldn't be keeping threads in it), or when the containing
> state machine is destroyed, or only when the program exits.

Sorry, pressed Send too quickly.

If you want to destroy the threads in on_exit instead, then since 
thread_group lacks a means to remove a thread (unless you still have a 
reference to it), you will have to destroy the thread_group instead.

The simplest way to do that is to wrap it in a std::unique_ptr and 
reset() it in on_exit.