Interrupts are like threads, except worse because you have also reentrancy issues (e.g., can IRQ A happen while the handler for IRQ A is still running, possibly outside of IRQ context). Volatile is not sufficient for several reasons, not the least because insertion/removal into a linked list is not an atomic operation. As I see it you have two choices:

Introduce fine-grained locking of list nodes by customizing boost.intrusive (you have to be careful because it’s easy to end up in a deadlock due to reentrancy issues – unless you have some constraints, like IRQ levels, that can prevent this.)
Use a lock-free list

You should read about how operating systems (Windows, Linux) tackle these issues.

From: Boost-users <boost-users-bounces@lists.boost.org> On Behalf Of nat ersoz via Boost-users
Sent: Sunday, November 25, 2018 18:38
To: boost-users@lists.boost.org
Cc: nat ersoz <natersoz@gmail.com>
Subject: [Boost-users] Boost intrusive list volatile hook

I intend to use the boost intrusive list to implement an observer pattern.

The list will cross interrupt boundaries; meaning one interrupt will produce the notifications and the other interrupt will observer the notifications.

The observer, in response to a notification, might detach itself from the list using the the hook's unlink() function.

I think that I will need the hook to be declared volatile in order to accommodate this.

I have a minimal code sample here: https://github.com/natersoz/patterns/blob/master/observer/intrusive_list_member/test_observer_minimal.cc

My list hook member declaration:

    using list_hook_type = boost::intrusive::list_member_hook<

        boost::intrusive::link_mode<boost::intrusive::auto_unlink>

>;

    list_hook_type hook;

My list declaration:

    using list_type =

    boost::intrusive::list<

        Observer<NotificationType>,

        boost::intrusive::constant_time_size<false>,

        boost::intrusive::member_hook<

            Observer<NotificationType>,

            typename Observer<NotificationType>::list_hook_type,

            &Observer<NotificationType>::hook>

>;

If I a the volatile keyword to the list hood type, I cannot figure out how to get the list_type declaration to fit into the list template list.

Is it possible?

Thank you.

Nat Ersoz
425-417-5182 (cell)