All of the message enqueue and dequeue routines make use of context variables. Each enqueue context variable is used to keep track of a single "thread" of message enqueue operations. Likewise for each dequeue context variable. Through the use of multiple context variables, a program may manage and effect several simultaneous message enqueue and dequeue operations. While each enqueue context controls only a single message submission, each dequeue context controls an entire series of message dequeues (e.g., with a single dequeue context all message for a given channel may be processed and dequeued).
Note:
The ability to use multiple contexts was enabled in PMDF V4.3. Code written prior to PMDF V4.3 will continue to operate normally without any changes. The same code may make use of multiple enqueue contexts without requiring any changes to how the API message enqueue routines are called. However, code wishing to use multiple dequeue contexts must be changed to create a dequeue context with PMDF_dequeue_initialize and to destroy that context with PMDF_dequeue_end.