Re: [Boost-users] [asio] async_read and 100% CPU

Subject: Re: [Boost-users] [asio] async_read and 100% CPU
From: Etienne Philip Pretorius (icewolfhunter_at_[hidden])
Date: 2009-07-01 04:39:04

Zachary Turner wrote:
>> On Tue, Jun 30, 2009 at 2:24 PM, Etienne Philip Pretorius<icewolfhunter_at_[hidden]> wrote:
>>> Zachary Turner wrote:
>>> What is contained inside your buffer object?  If your buffer has a
>>> size of 0, then this seems like it would cause the problem.
>>>
>> yip, it has a size of 0. I hoped that the async receive would just increase
>> the size of the vector as it puts the contents into it, but that is not
>> happening.
> 
> I'm 99% sure this is your problem.  I haven't used asio with sockets,
> but I have used it with other types of input sources.  It doesn't know
> how much data to read unless you tell it.  The way you tell it is by
> giving it a buffer whose size is how much data you want to read.  That
> means that allocation / deletion of the buffer is also your
> responsibility.
> 
> boost::asio::const_buffer and boost::asio::mutable_buffer have no
> ownership over the memory contained in these buffers.  It seems like
> this makes the library a little less intuitive at first, I struggled
> for quite a while with buffer management in my own project, but in the
> end it is this way to help you.  Otherwise there would be excessive
> copying and allocation.  mutable_buffer and const_buffer are just very
> thin wrappers over a chunk of memory.  So you have to allocate a
> buffer up front that contains enough memory for whatever it is you're
> trying to read.  Then you pass that to async_receive and it should
> work.
> 
>                    const size_t expected = 4096;
>                    unsigned char* buf = new unsigned char[expected];
>                    boost::asio::mutable_buffer(buf, expected);
> 
>                    socket.async_receive(
>                        boost::asio::buffer(buffer),
>                        boost::bind(
>                            &client::handle_read,
>                            this,
>                            boost::asio::placeholders::error,
>                            boost::asio::placeholders::bytes_transferred
> 
> Now in your handler you will either need to free this buffer, release
> it to some cache, or whatever else you want to do with it.
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Not at my machine right now, but I am quite certain that you are 
correct. Thank you for your help, much appreciated.

Etienne