Re: [boost] Interprocess mutex & condition variable at process termination

Subject: Re: [boost] Interprocess mutex & condition variable at process termination
From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2017-02-16 12:31:03

Andrey Semashev wrote:
> On 02/15/17 20:42, Phil Endecott via Boost wrote:
>> I've just been surprised by the behaviour of the interprocess
>> mutex and condition variable on abnormal process termination, i.e.
>> they are not automatically released.

> There is a way to handle this case, but this API is not universally 
> supported:
>
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_mutexattr_getrobust.html

Thanks for pointing that out.  For some reason I thought that
"robust" mutexes solved some other problem.

I think that in my case where I have some processes that only
read the shared data, it would be possible to handle EOWNERDEAD
by either continuing if the previous lock were a read-lock, or
by throwing if it were a write lock.  I don't think Interprocess
does any of this, does it?

> The best solution to these problems, however, is to avoid locks 
> altogether and use lock-free algorithms in such a way that any data in 
> the shared memory is valid and can be handled.

Maybe, though my next concern would be how to implement the functionality
of a condition variable.  What happens if a process crashes while it
is waiting on a condition variable?  I did once know how Linux
implements condition variables using atomics and futexes, and I
think it's probably safe to crash in this situation, but I guess
there are no guarantees.

Thanks, Phil.