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MQACH – API exit chain header

 

The MQACH structure describes the header information that must be present at the start of each exit chain area.

• The address of the first area in the chain in given by the ExitChainAreaPtr field in MQAXP. If there is no chain, ExitChainAreaPtr is the null pointer.

• The address of the next area in the chain is given by the NextChainAreaPtr field in MQACH. For the last area in the chain, NextChainAreaPtr is the null pointer.

Any exit function can create a chain area in dynamically-obtained storage (for example, by using malloc), and add that area to the chain at the desired location (start, middle, or end). The exit function must ensure that it sets all fields in MQACH to valid values.

The exit suite that creates the chain area is responsible for destroying that chain area before termination (the MQ_TERM_EXIT function is a convenient point at which to do this). However, adding and removing chain areas from the chain must be done only by an exit function when it is invoked by the queue manager; this restriction is necessary to avoid serialization problems.

Exit chain areas are made available to all exit suites, and must not be used to hold private data. Use ExitUserArea in MQAXP to hold private data.

In general there is no correspondence between the chain of exit functions that are invoked for an API call, and the chain of exit chain areas:

• Some exit functions might not have chain areas.

• Other exit functions might each have multiple chain areas.

• The order of the chain areas might be different from the order of the exit functions that own those chain areas.

• Fields
  

• C declaration
  

 

Parent topic:

API exit reference information

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