HP-UX Event ManagerProgrammer's Guide

Example 4-8 Using Filter Evaluators
#include <stdio.h>
#include <sys/time.h>
#include <evm/evm.h>
#include<string.h>
void EventCB(EvmConnection_t conn, EvmCallbackArg_t cbarg, EvmCallbackData_t *cbdata);
/* This section of code defines three simple filter strings. The first two filter by name alone,
but the third stringselects events with either of the two names, provided they have a priority of at least
300.*/
#define FILTER_1 "[name *.user]"
#define FILTER_2 "[name *.msg]"
#define FILTER_3 "([name *.msg] | [name *.mark]) & [priority >= 300]"
/*===============================================* Function:
main()*===============================================*/
int main()
{ EvmConnection_t conn;
EvmStatus_t status;
int conn_fd;char *filter_string;
status = EvmConnCreate(EvmCONNECTION_LISTEN, EvmRESPONSE_CALLBACK,NULL,EventCB,NULL,&conn);
if (status != EvmERROR_NONE)
{ fprintf(stderr,"Failed to create EVM listening connection\n");
exit(1); }
/* This section of code combines the three filter strings into a single logical expression, surrounding each
substring with parentheses and separating them with the logical OR operator. This will cause the daemon to
notify
you of any event that matches at least one of the substrings.*/
filter_string = (char *)malloc(strlen(FILTER_1) + strlen(FILTER_2) + strlen(FILTER_3) + 30);
sprintf(filter_string,"(%s) | (%s) | (%s)",FILTER_1,FILTER_2,FILTER_3);
/* Use the combined string to subscribe for the events, and then, because the string is no longer useful to
you, free its space. If you have to resubscribe for any reason, you can always recombine the substrings.*/
status = EvmConnSubscribe(conn,NULL,filter_string);
if (status != EvmERROR_NONE)
{ fprintf(stderr,"Failed to subscribe for event notification\n");
exit(1); }
free(filter_string);
/* After the evaluators have been established, retain it so that you can use them for all events that you receive
(that is, make them static entities). Alternatively,you could create a new set of evaluators each time you
receive
an event, and destroy them as you exit the function. However, retaining them avoids the repeated setup and
teardown overhead.*/
for (;;)
{ status = EvmConnWait(conn,NULL);
if (status != EvmERROR_NONE)
{ fprintf(stderr,"Connection error\n");
exit(1); }
if (EvmConnDispatch(conn) != EvmERROR_NONE)
{ fprintf(stderr,"Connection dispatch error\n");
exit(1); } }}
/*===============================================* Function:
EventCB()*===============================================*/
void EventCB(EvmConnection_t conn, EvmCallbackArg_t cbarg, EvmCallbackData_t *cbdata)
{ EvmBoolean_t match;
/* This section of code creates three filter evaluators using EvmFilterCreate() and loads them with the
three filter strings. For clarity, only the return status for the first filter is checked in this example,
but in production code it is important to check it in each case. This code is executed only the first time
we receive an event.*/
static EvmFilter_t f1,f2,f3;
static EvmBoolean_t filters_initialized = EvmFALSE;
if (! filters_initialized)
{ if (EvmFilterCreate(&f1) != EvmERROR_NONE)
{ fprintf(stderr,"Failed to create filter evaluator\n");
exit(1); }
if (EvmFilterSet(f1,FILTER_1) != EvmERROR_NONE)
{ fprintf(stderr,"Failed to set filter evaluator\n");
exit(1); }
EvmFilterCreate(&f2);
EvmFilterSet(f2,FILTER_2);
EvmFilterCreate(&f3);
EvmFilterSet(f3,FILTER_3);
filters_initialized = EvmTRUE; }
/* This section of code tests each incoming event against each of the three filter evaluators established in
the
previous section, and prints a different message for each evaluator that is matched by the event. It is quite
possible that some events will match more than one evaluator; in which case, more than one message is printed.*/
switch (cbdata->reason)
{ case EvmREASON_EVENT_DELIVERED: EvmFilterTest(f1,cbdata->event,&match);
if (match)
fprintf(stdout,"Filter 1 event received\n");
EvmFilterTest(f2,cbdata->event,&match);
if (match)
fprintf(stdout,"Filter 2 event received\n");
EvmFilterTest(f3,cbdata->event,&match);
if (match)
fprintf(stdout,"Filter 3 event received\n");
EvmEventDestroy(cbdata->event);
break;
default:
break; }}
50 Sample EVM Programming Operations