Re: [Boost-users] Boost.ASIO calling handler guarantees

Subject: Re: [Boost-users] Boost.ASIO calling handler guarantees
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2014-08-22 08:30:28

On 22 Aug 2014 at 16:20,   wrote:

> I'm playing with Boost.ASIO framework and failed to find a complete
> answer on the following question. 
> [snip]
> Looking at least at async_write() implementation, it cannot be relied upon:
>  - async_write executes a chain of boost::asio::detail::write_op() operations:
>  - if asio_handler_allocate() may throw then
>  - write_op::stream_.async_write_some() may throw then
>  - write_op.handler_() might never be called
> 
> So, either we should never rely on this assumption, or there's a bug in async_write().
> Not relying on this assumption what is the reliable way of building applications with Boost.Asio?

I can't speak for ASIO, but AFIO explicitly makes no guarantees if a 
bad_alloc exception is ever thrown. Otherwise it guarantees exception 
safety.

I would be highly surprised if ASIO can do any better than AFIO here. 
Handling bad_alloc is extremely tough when your exception handling 
paths have no choice but to allocate memory, which for something 
involving async i/o they must.

The traditional solution is to feed the code an allocator which will 
never, ever run out of memory. That may be useful for ASIO too.

Niall

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