bluetooth read thread will not exit when bluetooth connection lost in c

Question

I am writing a "race box" in C that runs on an Intel Edison. It can send or receive bluetooth data with an Android app based on Bluetooth Chat. Everything works fine. I can send and receive. I can lose the connection and reacquire and the connection comes back and data flows from the C program to the Android app. All is good except once I reconnect I can no longer send data from C to Android. I have traced this to the read statement and I assume it never returns a value because it never exits the while loop. Specifically, this line:

while(bluetooth_up == 1 && (read(client, &aa, 1) == -1) ){

Will not exit even when I know bluetooth_up == 0 (another thread fprints bluetooth_up and it is 0 when bluetooth is down). My conclusion was that read was blocking so I attempted to fix that with the line

fcntl(s, F_SETFL,sock_flags|O_NONBLOCK);

The bluetooth connection is in the bluetooth write thread. But like I said, everything works except that this while loop will not exit when bluetooth_up is 0.

All I can figure out is that the read is blocking and what I cannot figure out is how to make it not blocking so it will return the -1 and the while loop can see that bluetooth_up == 0 and exit.

Here is the global definition of bluetooth_up

volatile int bluetooth_up = 0;

I would appreciate help on this as it needs to be robust and I don't want to require people to power cycle the race box to get bluetooth working again, although that does work.

    void *blueRead(void *arg){
    blue_read_up = 1;
    char aa;
    char buffer[500];
    int idx = 0;
    printf("\nBlue Read started\n");
    fcntl(s, F_SETFL,sock_flags|O_NONBLOCK);
    while(bluetooth_up == 1){
        if (new_blue_read_sentence == 0 && bluetooth_up == 1){
            while(bluetooth_up == 1 && (read(client, &aa, 1) == -1) ){
                    if(bluetooth_up == 0){
                        printf("\nExiting blue read\n");
                        blue_read_up = 0;
                        return NULL;
                    }
            }
            printf("%i",aa);
            if(aa != '\n')
            {
                buffer[idx++] = aa;
            }
            else
            {
                buffer[idx] = '\n';
                buffer[idx + 1] = '\0';
                idx = 0;
                strcpy( blue_read_buffer, buffer);
                new_blue_read_sentence = 1;
            }
        }
    }
    printf("\nExiting blue read 2\n");
    blue_read_up = 0;
    return NULL;
}

I think the bluetooth connection code is pretty standard but here it is

        // allocate socket
    s = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
    printf("\nsocket = %i\n", s);

    // bind socket to port 1 of the first available local bluetooth adapter
    loc_addr.rc_family = AF_BLUETOOTH;
    loc_addr.rc_bdaddr = *BDADDR_ANY;
    loc_addr.rc_channel = (uint8_t)1;
    retval = bind(s, (struct sockaddr*)&loc_addr, sizeof(loc_addr));
    printf("\nbind = %i\n", retval);

    // put socket into listening mode
    //listen(s, 1);
    retval = listen(s, 1);
    printf("\nlisten = %i\n", retval);

    // accept one connection
    client = accept(s, (struct sockaddr*)&rem_addr, &opt);

    sock_flags = fcntl(s,F_GETFL,0);
    fcntl(s, F_SETFL,sock_flags|O_NONBLOCK);

    printf("\n1 - client connect = %i socket %i\n", client, s);

Answer 1

You are setting O_NONBLOCK on the listening socket (s). Try instead on the accept socket (client) which is the one that is actually being read from.