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