Re: [Boost-users] [Asio] Socket Read/Write Thread-Safety

Subject: Re: [Boost-users] [Asio] Socket Read/Write Thread-Safety
From: Timothy Liang (timothy003_at_[hidden])
Date: 2011-01-31 06:30:23

> <<In the case of composed asynchronous operations, such as async_read() or
> async_read_until(), if a completion handler goes through a strand, then
> all intermediate handlers should also go through the same strand. This is
> needed to ensure thread safe access for any objects that are shared
> between the caller and the composed operation (in the case of async_read()
> it's the socket, which the caller can close() to cancel the operation).
> This is done by having hook functions for all intermediate handlers which
> forward the calls to the customisable hook associated with the final
> handler>>
> http://www.boost.org/doc/libs/1_45_0/doc/html/boost_asio/overview/core/strands.html

Ah!  It also says, "The io_service::strand::wrap() function creates a new 
completion handler that defines asio_handler_invoke so that the function 
object is executed through the strand."  And the composed operations have a 
hook on their intermediate handlers that call asio_handler_invoke with the 
completion handler's context.  So I simply need to pass the wrapped handler 
object directly to the composed operations as the completion handler.  Cool.

Now I'm beginning to wonder if this will work with my design.  I want my 
program to run handlers as concurrently as possible.  I'm currently using a 
single io_service and setting up a thread pool like the HTTP Server 3 
example.  Since the io_service doesn't know if a handler would be blocked by 
a strand, it could needlessly assign an about-to-be-blocked handler to a 
free thread.  How do I fix that?