Sending Asynchronous Messages

This section explains how to:

The type of asynchronous processing discussed in this section is sometimes referred to as fan-out parallelism because it allows a client's requests to be distributed (or "fanned out") simultaneously to several services for processing.

Sending an Asynchronous Request

int
tpacall(char *svc, char *data, long len, long flags) 

The following table describes the arguments to the tpacall() function.

tpacall( ) Function Arguments

Argument	Description
svc	Pointer to the name of the service offered by your application.
data	Pointer that contains the address of the data portion of the request. The pointer must reference a typed buffer that was allocated by a prior call to tpalloc(). Note that the type (and optionally the subtype) of idata must match the type (and optionally the subtype) expected by the service routine. If the types do not match, the system sets tperrno to TPEITYPE and the function call fails. If the request requires no data, set data to the NULL pointer. This setting means that the parameter can be ignored. If no data is being sent with the request, you do not need to allocate a buffer for data.
len	Length of the request data in the buffer referenced by data. If the buffer is a self-defining type, that is, an FML, FML32, VIEW, VIEW32, X_COMMON, X_C_TYPE, or STRING buffer, you can set this argument to zero, indicating that the argument should be ignored.
flags	Flag options. You can list a group of flags by using the logical OR operator. If you set this value to zero, the communication is conducted in the default manner. For a list of valid flags and defaults, refer to tpacall(3c) in the BEA Tuxedo ATMI C Function Reference.

Example: Sending an Asynchronous Message with TPNOTRAN | TPNOREPLY

Sending an Asynchronous Message with TPNOREPLY | TPNOTRAN

#include <stdio.h>
#include "atmi.h"
 
main()
 
{
char *rbuf;         /* report buffer */
long rlen, rrlen;   /* buffer lengths of send, reply buffers for report */
 
join application
 
if (rbuf = tpalloc("STRING", NULL, 0) == NULL) /* allocate space for report */
 error
(void)strcpy(rbuf, "REPORT=accrcv DBNAME=accounts");/* send parms of report */
rlen = strlen(rbuf)+1;  /* length of request */
 
start transaction
 
if (tpcall("REPORT", rbuf, rlen, &rbuf, &rrlen, 0)
   == -1) /* get report print stream */

   error
if (tpacall("PRINTER", rbuf, rrlen, TPNOTRAN|TPNOREPLY)
   == -1) /* send report to printer */
   error

. . .
commit transaction
free buffer
leave application
}

Example: Sending Asynchronous Requests

The following example shows a series of asynchronous calls that make up the total bank balance query. Because the banking application data is distributed among several database sites, an SQL query needs to be executed against each one. The application performs these queries by selecting one branch identifier per database site, and calling the ABAL or TBAL service for each site. The branch identifier is not used in the actual SQL query, but it enables the BEA Tuxedo system to route each request to the proper site. In the following code, the for loop invokes tpacall() once for each site.

Sending Asynchronous Requests

audv->balance = 0.0;
(void)strcpy(audv->ermsg, "");
 
for (i=0; i<NSITE; i++) {
 
  /* Prepare aud structure */
 
  audv->b_id = sitelist[i];    /* routing done on this field */
 
  /* Do tpacall */
 
  if ((cd[i]=tpacall(sname, (char *)audv, sizeof(struct aud), 0))
     == -1) {
     (void)fprintf (stderr,
        "%s: %s service request failed for site rep %ld\n",
        pgmname, sname, sitelist[i]);
        tpfree((char *)audv);
        return(-1);
  }
}

Getting an Asynchronous Reply

Use the following signature to call the tpgetrply() function:

int
tpgetrply(int *cd, char **data, long *len, long flags) 

The following table describes the arguments to the tpgetrply() function.

tpgetrply( ) Function Arguments

Argument	Description
cd	Pointer to the call descriptor returned by the tpacall() function.
*data	Address of a pointer to the output buffer that receives the reply. You must allocate the output buffer using the tpalloc() function. If the reply message contains no data, upon successful return from tpcall(), the system sets *data to zero. The pointer and the contents of the output buffer remain unchanged. You can use the same buffer for both the request and reply messages. If you do, then you must set odata to the address of the pointer returned when you allocated the input buffer. It is an error for this parameter to point to NULL.
len	Pointer to the length of the reply data. It is an error for this parameter to point to NULL.
flags	Flag options. You can list a group of flags using the logical OR operator. If you set this value to zero, the communication is conducted in the default manner. For a list of valid flags and defaults, refer to tpcall(3c)) in the BEA Tuxedo ATMI C Function Reference.