Oracle8i Application Developer's Guide - Advanced Queuing
Release 2 (8.1.6)
Part Number A76938-01

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Oracle Advanced Queuing by Example, 8 of 8

AQ and Memory Usage

Create_types.sql : Create Payload Types and Queues in Scott's Schema

Note:

You may need to set up data structures for certain examples to work, such as: 

/* Create_types.sql */
CONNECT system/manager
GRANT AQ_ADMINISTRATOR_ROLE, AQ_USER_ROLE TO scott;
CONNECT scott/tiger
CREATE TYPE MESSAGE AS OBJECT (id NUMBER, data VARCHAR2(80));
EXECUTE DBMS_AQADM.CREATE_QUEUE_TABLE(
   queue_table        => 'qt', 
   queue_payload_type => 'message');
EXECUTE DBMS_AQADM.CREATE_QUEUE('msgqueue', 'qt');
EXECUTE DBMS_AQADM.START_QUEUE('msgqueue');
 

Enqueue Messages (Free Memory After Every Call) Using OCI

This program, enqnoreuse.c, dequeues each line of text from a queue 'msgqueue' that has been created in scott's schema via create_types.sql, above. Messages are enqueued using enqnoreuse.c or enqreuse.c (see below). If there are no messages, it waits for 60 seconds before timing out. In this program, the dequeue subroutine does not reuse client side objects' memory. It allocates the required memory before dequeue and frees it after the dequeue is complete. 

#ifndef OCI_ORACLE
#include <oci.h>
#endif

#include <stdio.h>

static void checkerr(OCIError *errhp, sword status);
static void deqmesg(text *buf, ub4 *buflen);

OCIEnv       *envhp;
OCIError     *errhp;
OCISvcCtx    *svchp;

struct message
{
  OCINumber    id;
  OCIString   *data;
};
typedef struct message message;

struct null_message
{
  OCIInd    null_adt;
  OCIInd    null_id;
  OCIInd    null_data;
};
typedef struct null_message null_message;

static void deqmesg(buf, buflen)
text  *buf;
ub4   *buflen;
{
  OCIType         *mesgtdo = (OCIType *)0;   /* type descr of SCOTT.MESSAGE */
  message         *mesg    = (dvoid *)0;     /* instance of SCOTT.MESSAGE */
  null_message    *mesgind = (dvoid *)0;     /* null indicator */
  OCIAQDeqOptions *deqopt  = (OCIAQDeqOptions *)0;
  ub4              wait    = 60;             /* timeout after 60 seconds */
  ub4              navigation = OCI_DEQ_FIRST_MSG;/* always get head of q */

 
  /* Get the type descriptor object for the type SCOTT.MESSAGE: */
  checkerr(errhp, OCITypeByName(envhp, errhp, svchp, 
           (CONST text *)"SCOTT", strlen("SCOTT"),
           (CONST text *)"MESSAGE", strlen("MESSAGE"), 
           (text *)0, 0, OCI_DURATION_SESSION, 
           OCI_TYPEGET_ALL, &mesgtdo));

  /* Allocate an instance of SCOTT.MESSAGE, and get its null indicator: */
  checkerr(errhp, OCIObjectNew(envhp, errhp, svchp, OCI_TYPECODE_OBJECT,
           mesgtdo, (dvoid *)0, OCI_DURATION_SESSION,
           TRUE, (dvoid **)&mesg));
  checkerr(errhp, OCIObjectGetInd(envhp, errhp, (dvoid *)mesg, 
           (dvoid **)&mesgind));

  /* Allocate a descriptor for dequeue options and set wait time, navigation: */
  checkerr(errhp, OCIDescriptorAlloc(envhp, (dvoid **)&deqopt, 
           OCI_DTYPE_AQDEQ_OPTIONS, 0, (dvoid **)0));
  checkerr(errhp, OCIAttrSet(deqopt, OCI_DTYPE_AQDEQ_OPTIONS, 
           (dvoid *)&wait, 0, OCI_ATTR_WAIT, errhp));
  checkerr(errhp, OCIAttrSet(deqopt, OCI_DTYPE_AQDEQ_OPTIONS, 
           (dvoid *)&navigation, 0, 
           OCI_ATTR_NAVIGATION, errhp));

  /* Dequeue the message and commit: */
  checkerr(errhp, OCIAQDeq(svchp, errhp, (CONST text *)"msgqueue", 
           deqopt, 0, mesgtdo, (dvoid **)&mesg, 
           (dvoid **)&mesgind, 0, 0));

  checkerr(errhp, OCITransCommit(svchp, errhp, (ub4) 0));

  /* Copy the message payload text into the user buffer: */
  if (mesgind->null_data)
    *buflen = 0;
  else
    memcpy((dvoid *)buf, (dvoid *)OCIStringPtr(envhp, mesg->data), 
           (size_t)(*buflen = OCIStringSize(envhp, mesg->data)));

  /* Free the dequeue options descriptor: */
  checkerr(errhp, OCIDescriptorFree((dvoid *)deqopt, OCI_DTYPE_AQDEQ_OPTIONS));

  /* Free the memory for the objects: */
  Checkerr(errhp, OCIObjectFree(envhp, errhp, (dvoid *)mesg, 
           OCI_OBJECTFREE_FORCE));
}                           /* end deqmesg */

void main()
{
  OCIServer     *srvhp;
  OCISession    *usrhp;
  dvoid         *tmp;
  text           buf[80];                 /* payload text */
  ub4            buflen;

  OCIInitialize((ub4) OCI_OBJECT, (dvoid *)0,  (dvoid * (*)()) 0,
                (dvoid * (*)()) 0,  (void (*)()) 0 );
  
  OCIHandleAlloc((dvoid *) NULL, (dvoid **) &envhp, (ub4) OCI_HTYPE_ENV,
                 52, (dvoid **) &tmp);
  
  OCIEnvInit( &envhp, (ub4) OCI_DEFAULT, 21, (dvoid **) &tmp  );
  
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &errhp, (ub4) OCI_HTYPE_ERROR,
                 52, (dvoid **) &tmp);
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &srvhp, (ub4) OCI_HTYPE_SERVER,
                 52, (dvoid **) &tmp);
  
  OCIServerAttach(srvhp, errhp, (text *) 0, (sb4) 0, (ub4) OCI_DEFAULT);
  
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &svchp, (ub4) OCI_HTYPE_SVCCTX,
                 52, (dvoid **) &tmp);
  
  /* Set attribute server context in the service context: */
  OCIAttrSet((dvoid *) svchp, (ub4) OCI_HTYPE_SVCCTX, (dvoid *)srvhp, (ub4) 0,
             (ub4) OCI_ATTR_SERVER, (OCIError *) errhp);
  
  /* Allocate a user context handle: */
  OCIHandleAlloc((dvoid *)envhp, (dvoid **)&usrhp, (ub4) OCI_HTYPE_SESSION,
                 (size_t) 0, (dvoid **) 0);
  
  OCIAttrSet((dvoid *)usrhp, (ub4)OCI_HTYPE_SESSION,
             (dvoid *)"scott", (ub4)strlen("scott"), OCI_ATTR_USERNAME, errhp);
      
  OCIAttrSet((dvoid *)usrhp, (ub4)OCI_HTYPE_SESSION,
             (dvoid *)"tiger", (ub4)strlen("tiger"), OCI_ATTR_PASSWORD, errhp);
  
  checkerr(errhp, OCISessionBegin (svchp, errhp, usrhp, OCI_CRED_RDBMS, 
           OCI_DEFAULT));
  
  OCIAttrSet((dvoid *)svchp, (ub4)OCI_HTYPE_SVCCTX,
             (dvoid *)usrhp, (ub4)0, OCI_ATTR_SESSION, errhp);

  do {
    deqmesg(buf, &buflen);
    printf("%.*s\n", buflen, buf);
  } while(1);
}                         /* end main */

static void checkerr(errhp, status)
OCIError  *errhp;
sword      status;
{
  text errbuf[512];
  ub4  buflen;
  sb4 errcode;

  if (status == OCI_SUCCESS) return;

  switch (status)
  {
  case OCI_ERROR:
    OCIErrorGet ((dvoid *) errhp, (ub4) 1, (text *) NULL, &errcode,
                 errbuf, (ub4) sizeof(errbuf), (ub4) OCI_HTYPE_ERROR);
    printf("Error - %s\n", errbuf);
    break;
  case OCI_INVALID_HANDLE:
    printf("Error - OCI_INVALID_HANDLE\n");
    break;
  default:
    printf("Error - %d\n", status);
    break;
  }
  exit(-1);
}                          /* end checkerr */

Enqueue Messages (Reuse Memory) Using OCI

This program, enqreuse.c, enqueues each line of text into a queue 'msgqueue' that has been created in scott's schema by executing create_types.sql. Each line of text entered by the user is stored in the queue until user enters EOF. In this program the enqueue subroutine reuses the memory for the message payload, as well as the AQ message properties descriptor. 

#ifndef OCI_ORACLE
#include <oci.h>
#endif

#include <stdio.h>

static void checkerr(OCIError *errhp, sword status);
static void enqmesg(ub4 msgno, text *buf);

struct message
{
  OCINumber     id;
  OCIString    *data;
};
typedef struct message message;

struct null_message
{
  OCIInd    null_adt;
  OCIInd    null_id;
  OCIInd    null_data;
};
typedef struct null_message null_message;

/* Global data reused on calls to enqueue: */
OCIEnv             *envhp;
OCIError           *errhp;
OCISvcCtx          *svchp;
message             msg;
null_message        nmsg;
OCIAQMsgProperties *msgprop;

static void enqmesg(msgno, buf)
ub4     msgno;
text   *buf;
{
  OCIType          *mesgtdo = (OCIType *)0; /* type descr of SCOTT.MESSAGE */
  message          *mesg = &msg;            /* instance of SCOTT.MESSAGE */
  null_message     *mesgind = &nmsg;        /* null indicator */
  text              corrid[128];            /* correlation identifier */

  /* Get the type descriptor object for the type SCOTT.MESSAGE: */
  checkerr(errhp, OCITypeByName(envhp, errhp, svchp, 
           (CONST text *)"SCOTT", strlen("SCOTT"),
           (CONST text *)"MESSAGE", strlen("MESSAGE"), 
           (text *)0, 0, OCI_DURATION_SESSION, 
           OCI_TYPEGET_ALL, &mesgtdo));

  /* Fill in the attributes of SCOTT.MESSAGE: */
  checkerr(errhp, OCINumberFromInt(errhp, &msgno, sizeof(ub4), 0, &mesg->id));
  checkerr(errhp, OCIStringAssignText(envhp, errhp, buf, strlen(buf),
           &mesg->data));
  mesgind->null_adt = mesgind->null_id = mesgind->null_data = 0;

  /* Set the correlation id in the message properties descriptor: */
  sprintf((char *)corrid, "Msg#: %d", msgno);
  checkerr(errhp, OCIAttrSet(msgprop, OCI_DTYPE_AQMSG_PROPERTIES, 
           (dvoid *)&corrid, strlen(corrid), 
           OCI_ATTR_CORRELATION, errhp));
  
  /* Enqueue the message and commit: */
  checkerr(errhp, OCIAQEnq(svchp, errhp, (CONST text *)"msgqueue", 
           0, msgprop, mesgtdo, (dvoid **)&mesg, 
           (dvoid **)&mesgind, 0, 0));

  checkerr(errhp, OCITransCommit(svchp, errhp, (ub4) 0));
}                           /* end enqmesg */

void main()
{
  OCIServer    *srvhp;
  OCISession   *usrhp;
  dvoid        *tmp;
  text          buf[80];                /* user supplied text */
  int           msgno = 0;

  OCIInitialize((ub4) OCI_OBJECT, (dvoid *)0,  (dvoid * (*)()) 0,
                (dvoid * (*)()) 0,  (void (*)()) 0 );
  
  OCIHandleAlloc((dvoid *) NULL, (dvoid **) &envhp, (ub4) OCI_HTYPE_ENV,
                 52, (dvoid **) &tmp);
  
  OCIEnvInit( &envhp, (ub4) OCI_DEFAULT, 21, (dvoid **) &tmp  );
  
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &errhp, (ub4) OCI_HTYPE_ERROR,
                 52, (dvoid **) &tmp);
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &srvhp, (ub4) OCI_HTYPE_SERVER,
                 52, (dvoid **) &tmp);
  
  OCIServerAttach(srvhp, errhp, (text *) 0, (sb4) 0, (ub4) OCI_DEFAULT);
  
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &svchp, (ub4) OCI_HTYPE_SVCCTX,
                 52, (dvoid **) &tmp);
  
  /* Set attribute server context in the service context: */
  OCIAttrSet((dvoid *) svchp, (ub4) OCI_HTYPE_SVCCTX, (dvoid *)srvhp, (ub4) 0,
             (ub4) OCI_ATTR_SERVER, (OCIError *) errhp);
  
  /* Allocate a user context handle: */
  OCIHandleAlloc((dvoid *)envhp, (dvoid **)&usrhp, (ub4) OCI_HTYPE_SESSION,
                 (size_t) 0, (dvoid **) 0);
  
  OCIAttrSet((dvoid *)usrhp, (ub4)OCI_HTYPE_SESSION,
             (dvoid *)"scott", (ub4)strlen("scott"), OCI_ATTR_USERNAME, errhp);
      
  OCIAttrSet((dvoid *)usrhp, (ub4)OCI_HTYPE_SESSION,
             (dvoid *)"tiger", (ub4)strlen("tiger"), OCI_ATTR_PASSWORD, errhp);
  
  checkerr(errhp, OCISessionBegin (svchp, errhp, usrhp, OCI_CRED_RDBMS, 
           OCI_DEFAULT));
  
  OCIAttrSet((dvoid *)svchp, (ub4)OCI_HTYPE_SVCCTX,
             (dvoid *)usrhp, (ub4)0, OCI_ATTR_SESSION, errhp);

  /* Allocate a message properties descriptor to fill in correlation id :*/
  checkerr(errhp, OCIDescriptorAlloc(envhp, (dvoid **)&msgprop, 
           OCI_DTYPE_AQMSG_PROPERTIES, 
           0, (dvoid **)0));
  do {
    printf("Enter a line of text (max 80 chars):");
    if (!gets((char *)buf))
      break;
    enqmesg((ub4)msgno++, buf);
  } while(1);

  /* Free the message properties descriptor: */
  checkerr(errhp, OCIDescriptorFree((dvoid *)msgprop, 
           OCI_DTYPE_AQMSG_PROPERTIES));

}                         /* end main */

static void checkerr(errhp, status)
OCIError   *errhp;
sword      status;
{
  text errbuf[512];
  ub4  buflen;
  sb4  errcode;

  if (status == OCI_SUCCESS) return;

  switch (status)
  {
  case OCI_ERROR:
    OCIErrorGet ((dvoid *) errhp, (ub4) 1, (text *) NULL, &errcode,
                 errbuf, (ub4) sizeof(errbuf), (ub4) OCI_HTYPE_ERROR);
    printf("Error - %s\n", errbuf);
    break;
  case OCI_INVALID_HANDLE:
    printf("Error - OCI_INVALID_HANDLE\n");
    break;
  default:
    printf("Error - %d\n", status);
    break;
  }
  exit(-1);
}                          /* end checkerr */

Dequeue Messages (Free Memory After Every Call) Using OCI

This program, deqnoreuse.c, dequeues each line of text from a queue 'msgqueue' that has been created in scott's schema by executing create_types.sql. Messages are enqueued using enqnoreuse or enqreuse. If there are no messages, it waits for 60 seconds before timing out. In this program the dequeue subroutine does not reuse client side objects' memory. It allocates the required memory before dequeue and frees it after the dequeue is complete. 

#ifndef OCI_ORACLE
#include <oci.h>
#endif

#include <stdio.h>

static void checkerr(OCIError *errhp, sword status);
static void deqmesg(text *buf, ub4 *buflen);

OCIEnv       *envhp;
OCIError     *errhp;
OCISvcCtx    *svchp;

struct message
{
  OCINumber     id;
  OCIString    *data;
};
typedef struct message message;

struct null_message
{
  OCIInd    null_adt;
  OCIInd    null_id;
  OCIInd    null_data;
};
typedef struct null_message null_message;

static void deqmesg(buf, buflen)
text      *buf;
ub4       *buflen;
{
  OCIType          *mesgtdo = (OCIType *)0;  /* type descr of SCOTT.MESSAGE */
  message          *mesg = (dvoid *)0;       /* instance of SCOTT.MESSAGE */
  null_message     *mesgind   = (dvoid *)0;       /* null indicator */
  OCIAQDeqOptions  *deqopt    = (OCIAQDeqOptions *)0;
  ub4               wait      = 60;               /* timeout after 60 seconds */
  ub4              navigation = OCI_DEQ_FIRST_MSG;/* always get head of q */

   /* Get the type descriptor object for the type SCOTT.MESSAGE: */
  checkerr(errhp, OCITypeByName(envhp, errhp, svchp, 
           (CONST text *)"SCOTT", strlen("SCOTT"),
           (CONST text *)"MESSAGE", strlen("MESSAGE"), 
           (text *)0, 0, OCI_DURATION_SESSION, 
           OCI_TYPEGET_ALL, &mesgtdo));

  /* Allocate an instance of SCOTT.MESSAGE, and get its null indicator: */
  checkerr(errhp, OCIObjectNew(envhp, errhp, svchp, OCI_TYPECODE_OBJECT,
           mesgtdo, (dvoid *)0, OCI_DURATION_SESSION,
           TRUE, (dvoid **)&mesg));
  checkerr(errhp, OCIObjectGetInd(envhp, errhp, (dvoid *)mesg, 
           (dvoid **)&mesgind));

  /* Allocate a descriptor for dequeue options and set wait time, navigation: */
  checkerr(errhp, OCIDescriptorAlloc(envhp, (dvoid **)&deqopt, 
           OCI_DTYPE_AQDEQ_OPTIONS, 0, (dvoid **)0));
  checkerr(errhp, OCIAttrSet(deqopt, OCI_DTYPE_AQDEQ_OPTIONS, 
           (dvoid *)&wait, 0, OCI_ATTR_WAIT, errhp));
  checkerr(errhp, OCIAttrSet(deqopt, OCI_DTYPE_AQDEQ_OPTIONS, 
           (dvoid *)&navigation, 0, 
           OCI_ATTR_NAVIGATION, errhp));

  /* Dequeue the message and commit: */
  checkerr(errhp, OCIAQDeq(svchp, errhp, (CONST text *)"msgqueue", 
           deqopt, 0, mesgtdo, (dvoid **)&mesg, 
           (dvoid **)&mesgind, 0, 0));

  checkerr(errhp, OCITransCommit(svchp, errhp, (ub4) 0));

  /* Copy the message payload text into the user buffer: */
  if (mesgind->null_data)
    *buflen = 0;
  else
    memcpy((dvoid *)buf, (dvoid *)OCIStringPtr(envhp, mesg->data), 
           (size_t)(*buflen = OCIStringSize(envhp, mesg->data)));

  /* Free the dequeue options descriptor: */
  checkerr(errhp, OCIDescriptorFree((dvoid *)deqopt, OCI_DTYPE_AQDEQ_OPTIONS));

  /* Free the memory for the objects: */
  checkerr(errhp, OCIObjectFree(envhp, errhp, (dvoid *)mesg, 
           OCI_OBJECTFREE_FORCE));
}                                       /* end deqmesg */

void main()
{
  OCIServer    *srvhp;
  OCISession   *usrhp;
  dvoid        *tmp;
  text          buf[80];                 /* payload text */
  ub4           buflen;

  OCIInitialize((ub4) OCI_OBJECT, (dvoid *)0,  (dvoid * (*)()) 0,
                (dvoid * (*)()) 0,  (void (*)()) 0 );
  
  OCIHandleAlloc((dvoid *) NULL, (dvoid **) &envhp, (ub4) OCI_HTYPE_ENV,
                 52, (dvoid **) &tmp);
  
  OCIEnvInit( &envhp, (ub4) OCI_DEFAULT, 21, (dvoid **) &tmp  );
  
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &errhp, (ub4) OCI_HTYPE_ERROR,
                 52, (dvoid **) &tmp);
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &srvhp, (ub4) OCI_HTYPE_SERVER,
                 52, (dvoid **) &tmp);
  
  OCIServerAttach(srvhp, errhp, (text *) 0, (sb4) 0, (ub4) OCI_DEFAULT);
  
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &svchp, (ub4) OCI_HTYPE_SVCCTX,
                 52, (dvoid **) &tmp);
  
  /* Set attribute server context in the service context: */
  OCIAttrSet((dvoid *) svchp, (ub4) OCI_HTYPE_SVCCTX, (dvoid *)srvhp, (ub4) 0,
             (ub4) OCI_ATTR_SERVER, (OCIError *) errhp);
  
  /* Allocate a user context handle: */
  OCIHandleAlloc((dvoid *)envhp, (dvoid **)&usrhp, (ub4) OCI_HTYPE_SESSION,
                 (size_t) 0, (dvoid **) 0);
  
  OCIAttrSet((dvoid *)usrhp, (ub4)OCI_HTYPE_SESSION,
             (dvoid *)"scott", (ub4)strlen("scott"), OCI_ATTR_USERNAME, errhp);
      
  OCIAttrSet((dvoid *)usrhp, (ub4)OCI_HTYPE_SESSION,
             (dvoid *)"tiger", (ub4)strlen("tiger"), OCI_ATTR_PASSWORD, errhp);
  
  checkerr(errhp, OCISessionBegin (svchp, errhp, usrhp, OCI_CRED_RDBMS, 
           OCI_DEFAULT));
  
  OCIAttrSet((dvoid *)svchp, (ub4)OCI_HTYPE_SVCCTX,
             (dvoid *)usrhp, (ub4)0, OCI_ATTR_SESSION, errhp);

  do {
    deqmesg(buf, &buflen);
    printf("%.*s\n", buflen, buf);
  } while(1);
}                         /* end main */

static void checkerr(errhp, status)
OCIError   *errhp;
sword      status;
{
  text errbuf[512];
  ub4  buflen;
  sb4  errcode;

  if (status == OCI_SUCCESS) return;

  switch (status)
  {
  case OCI_ERROR:
    OCIErrorGet ((dvoid *) errhp, (ub4) 1, (text *) NULL, &errcode,
                 errbuf, (ub4) sizeof(errbuf), (ub4) OCI_HTYPE_ERROR);
    printf("Error - %s\n", errbuf);
    break;
  case OCI_INVALID_HANDLE:
    printf("Error - OCI_INVALID_HANDLE\n");
    break;
  default:
    printf("Error - %d\n", status);
    break;
  }
  exit(-1);
}                          /* end checkerr */

Dequeue Messages (Reuse Memory) Using OCI

This program, deqreuse.c, dequeues each line of text from a queue 'msgqueue' that has been created in scott's schema by executing create_types.sql. Messages are enqueued using enqnoreuse.c or enqreuse.c. If there are no messages, it waits for 60 seconds before timing out. In this program, the dequeue subroutine reuses client side objects' memory between invocation of OCIAQDeq. During the first call to OCIAQDeq, OCI automatically allocates the memory for the message payload. During subsequent calls to OCIAQDeq, the same payload pointers are passed and OCI will automatically resize the payload memory if necessary. 

#ifndef OCI_ORACLE
#include <oci.h>
#endif

#include <stdio.h>

static void checkerr(OCIError *errhp, sword status);
static void deqmesg(text *buf, ub4 *buflen);

struct message
{
  OCINumber    id;
  OCIString   *data;
};
typedef struct message message;

struct null_message
{
  OCIInd    null_adt;
  OCIInd    null_id;
  OCIInd    null_data;
};
typedef struct null_message null_message;

/* Global data reused on calls to enqueue: */
OCIEnv          *envhp;
OCIError        *errhp;
OCISvcCtx       *svchp;
OCIAQDeqOptions *deqopt;
message         *mesg = (message *)0;
null_message    *mesgind = (null_message *)0;

static void deqmesg(buf, buflen)
text       *buf;
ub4        *buflen;
{



  OCIType        *mesgtdo    = (OCIType *)0; /* type descr of SCOTT.MESSAGE */
  ub4             wait       = 60;           /* timeout after 60 seconds */
  ub4             navigation = OCI_DEQ_FIRST_MSG;/* always get head of q */

  /* Get the type descriptor object for the type SCOTT.MESSAGE: */
  checkerr(errhp, OCITypeByName(envhp, errhp, svchp, 
           (CONST text *)"SCOTT", strlen("SCOTT"),
           (CONST text *)"MESSAGE", strlen("MESSAGE"), 
           (text *)0, 0, OCI_DURATION_SESSION, 
           OCI_TYPEGET_ALL, &mesgtdo));

  /* Set wait time, navigation in dequeue options: */
  checkerr(errhp, OCIAttrSet(deqopt, OCI_DTYPE_AQDEQ_OPTIONS, 
           (dvoid *)&wait, 0, OCI_ATTR_WAIT, errhp));
  checkerr(errhp, OCIAttrSet(deqopt, OCI_DTYPE_AQDEQ_OPTIONS, 
           (dvoid *)&navigation, 0, 
           OCI_ATTR_NAVIGATION, errhp));

  /* 
   * Dequeue the message and commit. The memory for the payload will be
   * automatically allocated/resized by OCI:
   */
  checkerr(errhp, OCIAQDeq(svchp, errhp, (CONST text *)"msgqueue", 
           deqopt, 0, mesgtdo, (dvoid **)&mesg, 
           (dvoid **)&mesgind, 0, 0));

  checkerr(errhp, OCITransCommit(svchp, errhp, (ub4) 0));

  /* Copy the message payload text into the user buffer: */
  if (mesgind->null_data)
    *buflen = 0;
  else
    memcpy((dvoid *)buf, (dvoid *)OCIStringPtr(envhp, mesg->data), 
           (size_t)(*buflen = OCIStringSize(envhp, mesg->data)));
}                           /* end deqmesg */

void main()
{
  OCIServer    *srvhp;
  OCISession   *usrhp;
  dvoid        *tmp;
  text          buf[80];                 /* payload text */
  ub4           buflen;

  OCIInitialize((ub4) OCI_OBJECT, (dvoid *)0,  (dvoid * (*)()) 0,
                (dvoid * (*)()) 0,  (void (*)()) 0 );
  
  OCIHandleAlloc((dvoid *) NULL, (dvoid **) &envhp, (ub4) OCI_HTYPE_ENV,
                 52, (dvoid **) &tmp);
  
  OCIEnvInit( &envhp, (ub4) OCI_DEFAULT, 21, (dvoid **) &tmp  );
  
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &errhp, (ub4) OCI_HTYPE_ERROR,
                 52, (dvoid **) &tmp);
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &srvhp, (ub4) OCI_HTYPE_SERVER,
                 52, (dvoid **) &tmp);
  
  OCIServerAttach(srvhp, errhp, (text *) 0, (sb4) 0, (ub4) OCI_DEFAULT);
  
  OCIHandleAlloc((dvoid *) envhp, (dvoid **) &svchp, (ub4) OCI_HTYPE_SVCCTX,
                 52, (dvoid **) &tmp);
  
  /* set attribute server context in the service context */
  OCIAttrSet((dvoid *) svchp, (ub4) OCI_HTYPE_SVCCTX, (dvoid *)srvhp, (ub4) 0,
             (ub4) OCI_ATTR_SERVER, (OCIError *) errhp);
  
  /* allocate a user context handle */
  OCIHandleAlloc((dvoid *)envhp, (dvoid **)&usrhp, (ub4) OCI_HTYPE_SESSION,
                 (size_t) 0, (dvoid **) 0);
  
  OCIAttrSet((dvoid *)usrhp, (ub4)OCI_HTYPE_SESSION,
             (dvoid *)"scott", (ub4)strlen("scott"), OCI_ATTR_USERNAME, errhp);
      
  OCIAttrSet((dvoid *)usrhp, (ub4)OCI_HTYPE_SESSION,
             (dvoid *)"tiger", (ub4)strlen("tiger"), OCI_ATTR_PASSWORD, errhp);
  
  checkerr(errhp, OCISessionBegin (svchp, errhp, usrhp, OCI_CRED_RDBMS, 
           OCI_DEFAULT));
  
  OCIAttrSet((dvoid *)svchp, (ub4)OCI_HTYPE_SVCCTX,
             (dvoid *)usrhp, (ub4)0, OCI_ATTR_SESSION, errhp);

  /* allocate the dequeue options descriptor */
  checkerr(errhp, OCIDescriptorAlloc(envhp, (dvoid **)&deqopt, 
           OCI_DTYPE_AQDEQ_OPTIONS, 0, (dvoid **)0));

  do {
    deqmesg(buf, &buflen);
    printf("%.*s\n", buflen, buf);
  } while(1);

  /* 
   * This program never reaches this point as the dequeue timesout & exits.
   * If it does reach here, it will be a good place to free the dequeue
   * options descriptor using OCIDescriptorFree and free the memory allocated
   * by OCI for the payload using OCIObjectFree
   */
}                         /* end main */

static void checkerr(errhp, status)
OCIError *errhp;
sword      status;
{
  text errbuf[512];
  ub4  buflen;
  sb4  errcode;

  if (status == OCI_SUCCESS) return;

  switch (status)
  {
  case OCI_ERROR:
    OCIErrorGet ((dvoid *) errhp, (ub4) 1, (text *) NULL, &errcode,
                 errbuf, (ub4) sizeof(errbuf), (ub4) OCI_HTYPE_ERROR);
    printf("Error - %s\n", errbuf);
    break;
  case OCI_INVALID_HANDLE:
    printf("Error - OCI_INVALID_HANDLE\n");
    break;
  default:
    printf("Error - %d\n", status);
    break;
  }
  exit(-1);
}                          /* end checkerr */
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