User`s guide

4: FMP Link Conﬁguration Options

DC 900-1339H 91

4.15 Queue Limit Option (21)

The queue limit option is used to prevent the ICP message buffer pool from being

exhausted. Message buffers for all links on the ICP are taken from the same memory

pool. This method allows each link to draw buffers as demand increases. However, if a

process on the client were to stop reading on one link without disabling the link, incom-

ing messages could deplete the buffer supply and the other links would not be able to

obtain buffers.

To prevent this from occurring, a queue limit can be placed on the FMP-to-client mes-

sage queue for a particular link. When the queue limit is reached, the last buffer on the

queue is marked with the

DLI_ICP_ERR_QFULL error code, and all subsequent blocks

from the link are discarded until the client program begins reading messages from the

queue. Control blocks such as status report, that cannot be placed on the queue, are dis-

carded. When the client program receives the

DLI_ICP_ERR_QFULL error, it should check

the sequence number to determine how much data, if any, was lost.

The client program speciﬁes the maximum number of buffers to be placed in the FMP-

to-client queue for a particular link. The queue limit applies to all sessions for a given

link. For example, if a queue limit of ten is set on a link that has a Manager and a Control

session established (Section 2.2 on page 32), the FMP software will queue ten master

buffers and ten control buffers. The queue limit is also independent for each type of ses-

sion; for example, if the Manager session has all ten buffers queued and waiting to be

read, this will not affect the Control session’s ten-buffer limit.

Specify a zero value to disable queue limiting for that link.

To set this option using the DLI conﬁguration ﬁle, use the

qLimit parameter; for exam-

ple,

qLimit = 0. See Table 5–1 on page 104.