HP-UX SNAplus2 R7 LUA Programmer's Guide

Designing and Writing LUA Applications

LUA Entry Points for HP-UX Applications

happens, the verb returns synchronously; the primary return code is set to a value other than

LUA_IN_PROGRESS,

and the lua_ﬂag2.async bit is set to 0 (zero). (For information about these returned parameters, see Chapter 4, RUI

Verbs or Chapter 5, SLI Verbs.)

At other times, LUA must wait for information from the remote LU or from the node before it can complete the

verb. In this case, the verb returns asynchronously; the primary return code is set to

LUA_IN_PROGRESS, and the

lua_ﬂag2.async bit is set to 1. The application can now perform other processing, or wait for notiﬁcation from

LUA that the verb has completed. LUA issues this notiﬁcation by setting the primary return code to its ﬁnal value,

leaving lua_ﬂag2.async set to 1.

As part of the supplied VCB, the application supplies a pointer to a callback routine (in the

lua_post_handle

parameter). If the verb completes synchronously, LUA does not call the callback routine. If the verb completes

asynchronously, LUA indicates the verb completion by calling the callback routine with one parameter—a pointer to

the original verb control block (VCB). For more information, see Section 2.1.6, Callback Routine for Asynchronous

Verb Completion.

Notes

1. It is not possible for an application to predict whether a particular verb will complete

synchronously or asynchronously.

2. If the lua_ﬂag2.async parameter indicates that the verb will complete asynchronously,

the program’s main thread of execution should not access any other parameters in the

VCB at this point. When LUA calls the callback routine, the application can then access

the VCB parameters.

3. Because of the way HP-UX callback routines operate, it is possible that the application’s

callback routine will be called before control returns to the application from its initial

function call for the verb. This means that, if the callback routine modiﬁes or deletes

the returned VCB, the program’s main thread of execution may be unable to check the

VCB parameters to determine that the verb is operating asynchronously. You may need

to take account of this in your application design.

2.1.6 Callback Routine for Asynchronous Verb Completion

To enable an LUA verb to complete asynchronously, the application must supply a pointer to a callback routine.

This section describes how SNAplus2 uses this routine, and the functions that it must perform.

Function Call

void callback (verb)

LUA_VERB_RECORD * verb;

}

Supplied Parameters

SNAplus2 calls the routine with the following parameter:

verb

Pointer to the VCB supplied by the application, including the returned parameters set by SNAplus2. The

callback routine may perform all the necessary processing on the returned parameters in the VCB, or may

simply set a variable to inform the main program that the verb has completed.