5.26 DEVTMAX (Maximum number of device threads)
5.26.1 Function
DEVTMAX specifies the maximum number of device threads allowed.
5.26.2 Syntax
Descriptive
-1 -n
Diagram
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-1 ¬¬¬¬«
- n
5.26.3 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-
