8.54 DEVTMAX (Display or set maximum device threads)

8.54.1 Function

The DEVTMAX command displays the current setting of the DEVTMAX system parameter along with the
actual device threads statistics. As an additional argument a new value for the maximum device threads
may be specified.

8.54.2 Syntax

Descriptive

- - n]

Diagram

¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬ÊÍ

-1 ¬¬¬¬«

- n

8.54.3 Parameter

0

Specify 0 to create an unlimited number of ‘semi-permanent’ threads on an ‘as-
needed’ basis. This is the default. With this option, a thread is created to service an
I/O request for a device if one does not already exist. When the I/O is complete the
thread enters an idle state waiting for new work. If a new I/O request for the device
arrives before the timeout period expires the existing thread will be reused. The
timeout value is currently hard coded at 5 minutes.

Note that this option can cause one thread (or possibly more) to be created for
each de vice in your configuration. Specifying 0 means there is no limit to the num-
ber of threads that can be created.

-1

Specify -1 to cause ‘one time only’ temporary threads to be created to service each
I/O request to a device. Once the I/O request is complete, the thread exits. Subse-
quent I/Os to the same device will cause another worker thread to be created
again.

1-n

Specify a value from 1 to n to set an upper limit to the number of threads that can
be created to service any I/O request to any device. Like the “0” option, each thread
once finished servicing an I/O request enters an idle state. If a new request arrives
before the timeout period expires, the thread is reused.

If all threads are busy when a new I/O request arrives a new thread is created only
if the specified maximum number of threads have not yet been reached. If the spe-
cified maximum number of threads already has been reached then the I/O request

is placed in a queue and will be serviced by the first available thread (eg. by which-
ever thread becomes idle first).

This option was created to address a threading issue, possibly related to the Cyg-
win phtreads implementation on Windows systems. On Windows systems positive
DEVTMAX values are currently not honoured and are treated identically as if the
value 0 had been specified. The default for non-Windows systems is 0.

8.54.4 Examples

Example 1:

Display the maximum allowed device threads along with the current statistics.

HHC00013I Herc command: 'devtmax'

HHC02241I Max device threads: 0, current: 5, most: 5, waiting: 4, max exceeded: 0

Figure 110: DEVTMAX command (list maximum allowed device threads)

Example 2:

Set the maximum allowed device threads to 25.

HHC00013I Herc command: 'devtmax 25'

Figure 111: DEVTMAX command (set maximum allowed device threads)