[Boost-users] Asio::Async_read_some - bytes_transferred=0!

[Lloyd]

Hi,

 

I am using async_read_some() to read data from a tcp connection. In the "async_read_some" handler, sometimes the "bytes_transferred" is zero, and also sometimes causes an error in the read handler called "The I/O operation has been aborted because of either a thread exit or an application request"

 

What could be the reason? Is this an expected behavior?

Thanks,

  Lloyd

 

 

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[Igor R]

> I am using async_read_some() to read data from a tcp connection. In the
> "async_read_some" handler, sometimes the "bytes_transferred" is zero, and
> also sometimes causes an error in the read handler called "The I/O operation
> has been aborted because of either a thread exit or an application request"
>
> What could be the reason? Is this an expected behavior?

This error usually means that you called socket.close()
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[Lloyd]

>
> This error usually means that you called socket.close()

What surprises me here is -

*) The socket is not closed
*) The accept handler of initial async_read_some gets the error ("The I/O

operation has been aborted because of either a thread exit or an application

request")

*) After that I am able to wait on same socket and read the data from
socket. (The async_read_some is again called form the handler of the
"initial async_read_some 's accept handler in a recursive manner)

Could there be any other reason for this? This is a multi-threaded
application and each socket is created in a new thread, and thread would not
exit without completing its execution...

Thanks a lot for your hint,
Lloyd

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[Igor R]

> What surprises me here is -
>
> *) The socket is not closed
> *) The accept handler of initial async_read_some gets the error ("The I/O
> operation has been aborted because of either a thread exit or an application
> request")
>
> *) After that I am able to wait on same socket and read the data from
> socket. (The async_read_some is again called form the handler of the
> "initial async_read_some 's accept handler in a recursive manner)
>
> Could there be any other reason for this? This is a multi-threaded
> application and each socket is created in a new thread, and thread would not
> exit without completing its execution...

Maybe the thread that calls async_read exits before the relevant
completion handler is invoked?

By the way, using threads in the way you described in asio-based
program is usually a bad idea. The whole point of using async i/o is
to avoid such an "explicit" multithreading -- usually one spawns
multiple threads to scale for multiple CPUs only.
http://www.boost.org/doc/libs/1_43_0/doc/html/boost_asio/examples.html#boost_asio.examples.http_server_3
http://www.boost.org/doc/libs/1_43_0/doc/html/boost_asio/examples.html#boost_asio.examples.http_server_2

[Lloyd]

>
> Maybe the thread that calls async_read exits before the relevant
> completion handler is invoked?
>
>
> By the way, using threads in the way you described in asio-based
> program is usually a bad idea. The whole point of using async i/o is
> to avoid such an "explicit" multithreading -- usually one spawns
> multiple threads to scale for multiple CPUs only.
> http://www.boost.org/doc/libs/1_43_0/doc/html/boost_asio/examples.html#boost_asio.examples.http_server_3
> http://www.boost.org/doc/libs/1_43_0/doc/html/boost_asio/examples.html#boost_asio.examples.http_server_2

Yes, you are right, the thread is exiting before the async_read_some.

I would like to let you know why I am using threads. This is a server
application. The client can give any command, and the server will execute
it. Some commands may take much longer time. In this kind of situations, the
client may want to STOP the execution of that long job. With the help of
threading I am able to do this with the help "Interruption points and
interrupts". The server will receive a "STOP command with the thread ID"
from the client, So the server can interrupt the thread and stop the job.

Is there a better way to implement this? I would be very happy to know
that, than using this dirty way I am using now...

Thanks a lot,
Lloyd

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[Igor R]

> Yes, you are right, the thread is exiting before the async_read_some.

You mean "before async_read_some completion"? At least on Windows,
this would cause the following behavior:
"Note All I/O initiated by a given thread is canceled when that
thread exits. For overlapped sockets, pending asynchronous operations
can fail if the thread is closed before the operations complete. "
http://msdn.microsoft.com/en-us/library/ms741688(VS.85).aspx

> I would like to let you know why I am using threads. This is a server
> application. The client can give any command, and the server will execute
> it. Some commands may take much longer time. In this kind of situations, the
> client may want to STOP the execution of that long job. With the help of
> threading I am able to do this with the help "Interruption points and
> interrupts". The server will receive a "STOP command with the thread ID"
> from the client, So the server can interrupt the thread and stop the job.
>
> Is  there a better way to implement this? I would be very happy to know
> that, than using this dirty way I am using now...

Well, you can launch threads for your tasks -- still processing all
the i/o in one thread (where you call io_service::run()):

// pseudo code
// gotCommand is always being called from within a single thread,
where io_service::run() is running
void gotCommand(Command cmd)
{
Task task = makeTask(cmd);
launchThread(task);

[Lloyd]

----- Original Message -----
From: "Igor R" <boost...@gmail.com>
To: <boost...@lists.boost.org>
Sent: Monday, June 28, 2010 6:59 PM
Subject: Re: [Boost-users] Asio::Async_read_some - bytes_transferred=0!

>> Yes, you are right, the thread is exiting before the async_read_some.
> You mean "before async_read_some completion"? At least on Windows,this
> would cause the following behavior:"Note All I/O initiated by a given

> thread is canceled when thatthread exits. For overlapped sockets, pending
> asynchronous operationscan fail if the thread is closed before the

> operations complete.
> "http://msdn.microsoft.com/en-us/library/ms741688(VS.85).aspx
>
>> I would like to let you know why I am using threads. This is a server>
>> application. The client can give any command, and the server will
>> execute> it. Some commands may take much longer time. In this kind of
>> situations, the> client may want to STOP the execution of that long job.
>> With the help of> threading I am able to do this with the help
>> "Interruption points and> interrupts". The server will receive a "STOP
>> command with the thread ID"> from the client, So the server can interrupt
>> the thread and stop the job.>> Is there a better way to implement this? I
>> would be very happy to know> that, than using this dirty way I am using
>> now...

> Well, you can launch threads for your tasks -- still processing allthe i/o

> in one thread (where you call io_service::run()):

> // pseudo code// gotCommand is always being called from within a single
> thread,where io_service::run() is runningvoid gotCommand(Command cmd){

> Task task = makeTask(cmd);
> launchThread(task);}_______________________________________________Boost-users
> mailing

> listBoost-users@lists.boost.orghttp://lists.boost.org/mailman/listinfo.cgi/boost-users
>

I think I am doing it in a very similar manner as you have mentioned. The
socket is created in the main thread, where the io_service::run() is called.
>From the initil data received on the socket, the command is recognised, then
a new thread is created and the socket and io_service is passed to it as a
reference. Then, inside the thread, the job is performed in an asynchronous
manner. As the thread exists before async_read_some is called (I think so),
I think at first I get the error in the async_read_some handler, later it
works fine... I think a code snippet would be far better than the written
words...

main()
{
...
try
{
boost::asio::io_service IOService;
TCPServer Server(IOService);
IOService.run();
}
catch(std::exception& e)
{
}
}

TCPServer:: TCPServer ()
{
StartAccept();
}

TCPServer:: StartAccept()
{
...
...
//here createa new TCPConnection object , shared_from_this
//Then inside TCPConnection object, it waits for new connection using
async_accept

}

"All the code is copied from asio sample", and the async_read Handler does
the following

AsyncReadhandler()
{
...
boost::thread *th=new
boost::thread(boost::bind(&TCPConnection::ExecutionRoutine,....))
}

//This is a thread
int TCPConnection::ExecutionRoutine(string Command)
{
...
...
if(Command = = "BIG_OPERATION")
{
boost::shared_ptr<BigOp> bo(new BigOp(Socket,IOService));
bo->Operation();
}
//Thread exits here, but the "Operation" continues on socket and
io_service....
}

BigOp::Operation()
{
Socket.async_read_some(....);
}

What is your opinion about "signals and slots" in this kind of situation?

Thanks a lot,
Lloyd

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