A call to FCONTROL with a controlcode
value of 4 allows you to set a time limit on the next read from
a terminal. The timeout value is specified in seconds, with a maximum
value of 65535.
Any read that does not complete before the time limit expires
is transferred to the user buffer and the read length is returned.
A condition code of CCL is returned to the calling program. A call
to FCHECK after the timeout returns Error code 22, Software Timeout.
If you are setting a timeout value for a read posted against
a device connected through a PAD, DTC Telnet, or Telnet/iX, you
should take care to add enough time to compensate for any time delays
that might be caused by the network.
A timeout value should be used any time your program is reading
from an unattended device, to prevent "hangs"
that might occur if the device is not ready or a problem exists
with the device or its connection to the system. You can also use
a timeout value to terminate binary reads. Refer to the discussion
of FCONTROL(26,27) for more information on terminating reads in
binary mode.
The timeout value is in effect only for the next read from
the terminal, and must therefore be reissued for each read. A timeout
value of 0 cancels the timeout.
During block mode reads the timer halts when the DC2 character
is received. At this point, the block mode read timer is activated
by the system. The block mode read timer is set by the system software,
and its values are not user changeable.
