Re: [Boost-users] [asio] Async (or sync) in threads

Subject: Re: [Boost-users] [asio] Async (or sync) in threads
From: Anthony Foiani (tkil_at_[hidden])
Date: 2013-07-25 03:30:34

Michael Powell <mwpowellhtx_at_[hidden]> writes:

> Most of the examples are one main being the sole main thread hosting
> the io_service. Would that this were the case with me. This has to
> be one worker among several other workers running in the same
> process.

There's no requirement that there be only one io_service per process,
nor that it be dealt with in the main (original) thread.

My current design actually has a bit of an explosion of io_service
instances: for each client, I end up with one input + thread and one
output + thread, to make sure that the input processing / data
generation doesn't overwhelm the output bandwidth (and hence cause
memory exhuastion by generating data faster than we can send it).

> Wouldn't mind if there were a couple of ideas recommending what I
> might explore next.

Hopefully obvious, but the main reason for seg faults is when threads
expect an object to exist somewhere, but a different thread has
already destroyed ("destructed") the object.

>     boost::thread runner_([&server_]() {
>         server_->start_server();
>     });
>     runner_.start_thread();

Boost.thread starts automatically, I thought?

For that matter, where does "start_thread" even exist?  It's not in
the current documentation...

Ah, looks like it was removed about a year ago.  Fair enough.  Just
use creation as start.

>     while (!timer_.has_elapsed_query_wait(wait_timeout_,
> elapsed_milliseconds_)) {
>         //...
>     }
>
>     runner_.interrupt();
>     runner_.join();

Given that thread interruption is a bit dicey, you might consider
doing the timeout work in the thread / io_service itself.  That way,
the controller only needs to launch the thread, then join it.

>         boost::system::error_code ec_;
>         a_.accept((*s_), ec_);
>         if (!ec_) return;

Since you're catching exceptions *anyway*, don't bother with error
codes unless you're detecting specific values (as you do for eof
elsewhere).

> void server2::session(socket_pointer s) {

>     while (true) {
>         {

No reason for this extra scope, either.

>            std::vector<byte> buffer_;
>            size_t length_ = s_.read_some(boost::asio::buffer(buffer_), ec_);

This is fishy.  buffer_ has length 0, yet you're trying to read into
it.  Maybe add a "buffer_.resize( 1024 )" (or whatever sounds good to
you).

Good luck,
t.