Re: [Bluez-devel] Problem detecting closed connection

[Mikael Bengtsson <micke_b.b@hotmail.com>]

I have an example of this problem. The following code snippet show a thread that controls a SCO connection. 


...
do
{
     poll_result = poll(ufds, 1, 1000);
     printf("Hello\n");
     if (poll_result == -1)
     {
          printf("Device got POLL-ERROR\n");
     }
     else if (poll_result == 0)
     {
          printf("Timeout\n");
     }
     else if (ufds[0].revents & POLLIN)
     {
         memset(buffer, 0, sizeof(buffer));
         bytes_read = read(ufds[0].fd, buffer, sizeof(buffer));
         printf("bytes_read == %d\n", bytes_read);
         if (bytes_read == 0)
            exit(1);
         ....
     }
} while (poll_result> 0);

Since this is a SCO connection, the read operation will always return 60 bytes every 3.75 ms. I observe that "Hello" and "bytes_read == %60" is written which is correct. When i switch off the slave, "Hello" and "bytes_read = 60" will continue for about 20 about seconds. This is also correct since it may take that long for a connection to be disconnected. After this, only the text "Hello" is written. However, I expected that the timeout event also should occur, that is, poll_result should have returned 0, or that the text "bytes_read == 0" should occur, and in that case the program should end. But the program prints "Hello" endlessly. Why doesn't this work?

I'm thinking of doing a thread with low level checks on the connections, I have two SCO and three ACL connections. This thread may check the connections periodically, but I don't have a clue what low level functions in BlueZ I should use.

I used hcitool to check what happened with a connection when switching off a slave. This program detected a closed connection after about 20 seconds. Maybe I could use something from that program?

-Mikael
________________________________
From: micke_b.b@hotmail.com
To: bluez-devel@lists.sourceforge.net
Date: Wed, 3 Oct 2007 10:40:08 +0200
Subject: [Bluez-devel] Problem detecting closed connection

Hello!

I have a problem detecting a device that has closed it's connection.

The software I'm developing sends and receives data through sockets to a slave device. When I switch of the slave device I expect that send and receive should return the value 0, as in ordinary sockets programming for TCP and UDP sockets. But instead send happily always returns a value which is bigger than 0. Why? Shouldn't Bluetooth sockets behave the same way as ordinary sockets? I have a quite old Bluez, version 2.15. Is there another way of detecting closed connections?

Regards:
-Mikael

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