Post-fix 567c0973

Do *not* check if socket is closed by another thread. This is
race-condition prone, unnecessary, and harmful. VIO state was introduced
to debug the errors, not to change the behavior.

Rather than checking if socket is closed, add a DBUG_ASSERT that it is
*not* closed, because this is an actual logic error, and can potentially
lead to all sorts of funny behavior like writing error packets to Innodb
files.

Unlike closesocket(), shutdown(2) is not actually race-condition prone,
and it breaks poll() and read(), and it worked for longer than a decade,
and it does not need any state check in the code.

vio/viosocket.c

@@ -560,8 +560,7 @@ vio_should_retry(Vio *vio)
   DBUG_ENTER("vio_should_retry");
   DBUG_PRINT("info", ("vio_errno: %d  state: %d",
                       vio_errno(vio), (int) vio->state));
-  DBUG_RETURN(vio_errno(vio) == SOCKET_EINTR &&
-              vio->state < VIO_STATE_SHUTDOWN);
+  DBUG_RETURN(vio_errno(vio) == SOCKET_EINTR);
 }
 
 
@@ -931,14 +930,7 @@ int vio_io_wait(Vio *vio, enum enum_vio_io_event event, int timeout)
                        (int) mysql_socket_getfd(vio->mysql_socket),
                        timeout));
 
-  if (vio->state >= VIO_STATE_SHUTDOWN)
-  {
-    DBUG_PRINT("info", ("vio deactivated. state: %ld", (int) vio->state));
-    /* Socket is shutdown or closed */
-    errno= EIO;
-    DBUG_RETURN(-1);
-  }
-
+  DBUG_ASSERT(vio->state != VIO_STATE_CLOSED);
   memset(&pfd, 0, sizeof(pfd));
 
   pfd.fd= sd;
@@ -999,14 +991,7 @@ int vio_io_wait(Vio *vio, enum enum_vio_io_event event, int timeout)
   fd_set readfds, writefds, exceptfds;
   MYSQL_SOCKET_WAIT_VARIABLES(locker, state) /* no ';' */
   DBUG_ENTER("vio_io_wait");
-
-  if (vio->state >= VIO_STATE_SHUTDOWN)
-  {
-    DBUG_PRINT("info", ("vio deactive. state: %ld", (int) vio->state));
-    /* Socket is shutdown or closed */
-    errno= EIO;
-    DBUG_RETURN(-1);
-  }
+  DBUG_ASSERT(vio->state != VIO_STATE_CLOSED);
 
   /* Convert the timeout, in milliseconds, to seconds and microseconds. */
   if (timeout >= 0)
@@ -1180,9 +1165,7 @@ my_bool vio_is_connected(Vio *vio)
 {
   uint bytes= 0;
   DBUG_ENTER("vio_is_connected");
-
-  if (vio->state >= VIO_STATE_SHUTDOWN)
-    DBUG_RETURN(FALSE);
+  DBUG_ASSERT(vio->state != VIO_STATE_CLOSED);
 
   /*
     The first step of detecting an EOF condition is verifying