HP-UX Event ManagerProgrammer's Guide

for each type of connection: posting, listening (subscribing), or availing service. For more
information about this function, see EvmConnection(5) and EvmConnCreate(3).
• EvmEventPost — Posts an event to EVM. For more information about this function, see
EvmEventPost(3).
• EvmConnDestroy — Destroys a specified connection. For more information about this
function, see EvmConnDestroy(3).
You can use the simpler EvmConnCreatePoster macro in place of EvmConnCreate to create
a posting connection. This macro requires fewer arguments than EvmConnCreate. Although it
offers fewer connection options, it is suitable for use by most applications that need to post events
to the local system.
If your program uses transient EVM connections, you can omit calls to EvmConnCreate or
EvmConnDestroy and pass NULL as the connection argument to EvmEventPost. Connections
use significant processing time to establish, so you must use only transient connections if they
are appropriate for your program. For more information about connections, see “Choosing a
Connection Policy” (page 34) and EvmEventPost(3).
You can create, post, and destroy an event in a single call using the EvmEventPostVa function.
For more information about this function, see EvmEventPost(3).
Example 4-4 Posting Events
#include <stdio.h>
#include <evm/evm.h>
int main()
{ EvmEvent_t event;
EvmStatus_t status;
EvmConnection_t conn;
EvmItemValue_t itemval_name;
/* You can create a connection to the EVM daemon using EvmConnCreate() function. The connectionremains in place
until your program exits, or until you explicitly destroy it with EvmConnDestroy(). The first two arguments to
EvmConnCreate() function specify that the connection will be used for posting events. This function waits for
the daemon to acknowledge acceptance of the event before returning, so that you can take action if the attempt
fails.
(See EvmConnCreate(3) for other response options.) The NULL value for the third argument indicates that you are
making
a connection to the EVM daemon running on the local system. The fourth and fifth values are used for other
response types,
and should always be NULL for wait-mode responses. The final argument receives the handle to the connection.
You
must supply the returned value in all future calls being made on this connection.*/
status = EvmConnCreate(EvmCONNECTION_POST, EvmRESPONSE_WAIT,NULL,NULL,NULL,&conn);
if (status != EvmERROR_NONE)
{ fprintf(stderr,"Failed to create EVM posting connection\n");
exit(1); } /* Create an event and post it. */
itemval_name.NAME="sys.unix.evm";
EvmEventCreateVa(&event, EvmITEM_NAME, itemval_name,EvmITEM_NONE);
status = EvmEventPost(conn,event);
if (status != EvmERROR_NONE)
{ fprintf(stderr,"Failed to post event\n");
exit(1); }
/* Clean up by destroying the event and the connection. If you expect posting events periodically, it may be
better
not to destroy the connection, but to reuse it for all future events. This will save you the overhead of
re-establishing
the connection each time you have something to post.*/
EvmEventDestroy(event);
EvmConnDestroy(conn);}
Reading and Writing Events
You must use the EVM read and write functions to write a program that performs any of the
following operations:
• Stores events in a file
• Passes events to another process through a pipe or socket connection
• Analyzes events stored in a file
• Receives events from a process other than the EVM daemon
You cannot write events directly using the standard UNIX write functions, because the event
handle contains only a pointer to the body of the event and because the location of the body can
42 Sample EVM Programming Operations