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You must not use EvmEventWait()to write a program that perform functions other than listening for
events. For example, you may want to use the select system call to wait for I/O activity on multiple file descriptors,
including the EVM connection. Example 4-7 illustrates how to handle the EVM connection in conjunction with
the input from stdin. Example 4-7 introduces the following functions: EvmConnFdGet — Returns the file descriptor (file number) associated with
a specified connection. For more information about this function,
see EvmConnFdGet(3). EvmConnCheck — Checks whether any I/O activity is outstanding on a specified
connection. For more information about this function, see EvmConnCheck(3).
Example 4-7 Handling Multiple
I/O Sources |
#include <stdio.h>
#include <sys/time.h>
#include <evm/evm.h>
#include <string.h>
void HandleInput();
void EventCB(EvmConnection_t conn, EvmCallbackArg_t cbarg, EvmCallbackData_t *cbdata);
/*===============================================* Function: main()*===============================================*/
int main()
{ EvmConnection_t conn;
EvmStatus_t status;
fd_set read_fds;
int conn_fd;
EvmBoolean_t io_waiting;
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 sys.unix.evm.msg.user]");
if(status != EvmERROR_NONE)
{fprintf(stderr,"Failed to subscribe for event notification\n");
exit(1); }
/* Use EvmConnFdGet() to find the file descriptor assigned to the connection. */
EvmConnFdGet(conn,&conn_fd);
/* In this example, select is used to wait for I/O activity because this allows waiting on multiple file
descriptors. When the select call returns, check to see which of the file descriptors has activity,
and deal with it appropriately.*/
for (;;)
{FD_ZERO(&read_fds);
FD_SET(fileno(stdin),&read_fds);
FD_SET(conn_fd,&read_fds);
select(FD_SETSIZE,&read_fds,NULL,NULL,NULL);
if (FD_ISSET(fileno(stdin),&read_fds))
HandleInput();
/* EvmConnCheck() is used here to determine whether any activity is outstanding on the EVM connection.
Because the connection's file descriptor is known, FD_ISSET() could have been used for the same purpose.*/
status = EvmConnCheck(conn,&io_waiting);
if (status != EvmERROR_NONE)
{fprintf(stderr,"Connection error\n");
exit(1); }
if (io_waiting)
{status = EvmConnDispatch(conn);
if (status != EvmERROR_NONE)
{fprintf(stderr,"Connection dispatch error\n");
exit(1); } } }}
/*===============================================* Function: HandleInput()*=====================================*/
/* The HandleInput() function reads lines of input from stdin and echoes them to stdout.
It terminates the program on error or if an empty line is read. */
void HandleInput()
{ char buff[256]; if (feof(stdin))
exit(0);
if (fgets(buff,sizeof(buff),stdin) == NULL)
exit(0);
if (buff[0] == '\n')
exit(0);
fprintf(stdout,buff);}
/*===============================================* Function: EventCB()*===============================================*//*
The event callback function is identical to the one used in the previous example. */
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);
break;
default: break; }} |
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