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If you are developing an application that subscribes
for a set of events that can be posted in high volume over a short
period, your program may occasionally be notified by the EVM daemon
that it has missed one or more events. This occurs if the program
has a significant amount of processing to do and is unable to handle
when a new event arrives immediately, causing unhandled events to
fill the connection buffers. It watches for notification of missed
events by including the EvmREASON_EVENTS_MISSED reason in its callback function and displays a message that includes
the number of events missed. For more information about missed events,
see “Missed Events”. Example 4-10 shows how to subscribe for all events and displays
each event on stdout as it arrives. Example 4-10 Dealing with Missed Events |
#include <stdio.h>
#include <evm/evm.h>
#include<unistd.h>
void EventCB(EvmConnection_t conn, EvmCallbackArg_t cbarg, EvmCallbackData_t *cbdata);
/*===============================================* Function: main()*===============================================*/
int main()
{ EvmConnection_t conn; EvmStatus_t status; int conn_fd;
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); }
status = EvmConnSubscribe(conn,NULL,"[name *]");
/* This code segment subscribes for notification of all events. */
if (status != EvmERROR_NONE)
{ fprintf(stderr,"Failed to subscribe for event notification\n");
exit(1); }
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)
{ char buff[256]; switch (cbdata->reason)
{ case EvmREASON_EVENT_DELIVERED:
EvmEventFormat(buff, sizeof(buff), cbdata->event);
fprintf(stdout,"Event: %s\n",buff);
EvmEventDestroy(cbdata->event);
/* To demonstrate missing events, sleep for one second after each event is received.
This simulates a heavy processing load and ensures that the input connection buffer will be filled if the
event load is heavy.*/
sleep(1);
break;
/* The callback function is invoked with reason code EvmREASON_EVENTS_MISSED if the daemon is unable to
send one or more missed events. The callback data member extension.eventMissedData.missedCount contains
a count of the number of missed events.*/
case EvmREASON_EVENTS_MISSED:
fprintf(stdout,"*** Missed %d incoming events\n",cbdata->extension.eventMissedData.missedCount);
break;
default: break; }} |
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