need to find the best way to exit a thread that is blocked on read

Hello,

I have a driver with two threads. Write is easy, as I use signals to wake it up for write events and write event of 0 is an exit. The read is giving me problems, as I use block on read read(). I don't know the best way to stop the thread. I use fcntl to setup my stream as blocked on read. I use pthread_kill(read_thread, 0); to stop the read thread right now.
Please advice

Do you need to block on a read()? You could try to set up the stream as non-blocking.

Another alternative, is to use select() to determine whether you should read in the first place. A timeout value can be used with select() so that if no activity is detected in a certain delta of time, your thread gets control back, to perhaps look at a semaphore or other flag to determine if it should exit.

For example:

...

fd_set savefds;
FD_ZERO(&savefds);
FD_SET(fd, &savefds);

while (run)
{
  fd_set readfds = savefds;
  struct timeval timeout = {1,0};

  int sel = select(fd + 1, &readfds, 0, 0, &timeout);
  if (sel > 0)
  {
    // read
  }
}

...

The 'run' flag can be set by your main thread to 'true' under nominal circumstances, or 'false' otherwise.

Thanks for the advice. I have not used select yet. I will build a version and run a test.

I could not find a way to stop the thread from reading, when it was blocked on read. I don't know, if closing the fd would pull the rag on the blocked on read thread.

I ended up rewriting the interface to use usleep and read every so often. I will attempt the select method as well.

Thanks again for the advice.

The select version worked perfect. I wanted to ask you how would you use the select approach, if you had multiple fd's in the set? Would you read each, or is there a better approach such as setting an individual fd set for each select call? Would you call select individually per stream or combine streams in a single call?

Thanks

You can add more file descriptors to your fd_set using FD_SET(). When select() reports that there is activity, you can use FD_ISSET() to determine which file descriptor requires attention.

There's a basic example given in the man-page for select().

man 2 select