Re: [boost] [interprocess][process] Synchronizing libraries and efforts (+ bugs)

From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2008-09-01 11:52:52

Boris wrote:
> On Sun, 31 Aug 2008 23:20:10 +0200, Ion Gaztañaga <igaztanaga_at_[hidden]> 
> wrote:
> 
>> [...]I understand async I/O should be tied with ASIO. I think 
>> Boost.Iostreams
> 
> To give you an idea how asynchronous I/O with Boost.Process and 
> Boost.Asio currently looks like:
> 
> boost::process::child child; // somehow launched
> #if defined(_WIN32)
>   boost::asio::windows::stream_handle out(io_service, 
> child.get_stdin().handle().release());
>   boost::asio::windows::stream_handle in(io_service, 
> child.get_stdout().handle().release());
> #else
>   boost::asio::posix::stream_descriptor out(io_service, 
> child.get_stdin().handle().release());
>   boost::asio::posix::stream_descriptor in(io_service, 
> child.get_stdout().handle().release());
> #endif
> in.async_read_some(...);

I don't know ASIO but it's a shame that it does not offer a portable 
interface for async I/O.

>> [...]I can wait ;-) Since you are working hard on the library, I think 
>> it's better to wait until you consider the library mature enough. Feel 
>> free to contact me if you have any question.
> 
> OK, I'll tell you once I'm done (as I said I expect until mid 
> September). The code is nearly done. But with all the changes which I 
> had to merge I definitely need to update the documentation and samples.

Ok.

> By the way, I would be very interested in a communication channel 
> between a parent and a child process based on Boost.Interprocess. I need 
> asynchronous I/O though. Before I picked up Boost.Process I had created 
> a Boost.Asio extension boost::asio::shared_memory which can be used like 
> boost::asio::socket. The only (but big :) problem I haven't solved yet 
> is how to handle more than one communication channel. As read/write 
> operations in Boost.Interprocess need to be synchronized the calls might 
> block. A parent process with many children will then have to use at 
> least one thread per child. What would be required is a demultiplexer 
> which would work like select() for file descriptors. Then I think 
> asynchronous I/O could be done with Boost.Interprocess. The question is 
> though what would that demultiplexer look like? You are not working on 
> supporting asynchronous I/O in Boost.Interprocess? ;)

I don't have much idea about async I/O but we can try to write something 
once we know what we need. I might be completly wrong but 
boost::interprocess::shared_memory_object is based on a file descriptor 
(shm_open in unix and a plan file on windows) so we can just obtain the 
handle and see if select() and WaitForMultipleObject() work on them. 
After all, write() should work on UNIX with a shared memory object 
descritor.

Regards,

Ion