src/test/examples/testlibpq2.c

   1 /*
   2  * $PostgreSQL:$
   3  *
   4  *
   5  * testlibpq2.c
   6  *              Test of the asynchronous notification interface
   7  *
   8  * Start this program, then from psql in another window do
   9  *       NOTIFY TBL2;
  10  * Repeat four times to get this program to exit.
  11  *
  12  * Or, if you want to get fancy, try this:
  13  * populate a database with the following commands
  14  * (provided in src/test/examples/testlibpq2.sql):
  15  *
  16  *       CREATE TABLE TBL1 (i int4);
  17  *
  18  *       CREATE TABLE TBL2 (i int4);
  19  *
  20  *       CREATE RULE r1 AS ON INSERT TO TBL1 DO
  21  *         (INSERT INTO TBL2 VALUES (new.i); NOTIFY TBL2);
  22  *
  23  * and do this four times:
  24  *
  25  *       INSERT INTO TBL1 VALUES (10);
  26  */
  27 #include <stdio.h>
  28 #include <stdlib.h>
  29 #include <string.h>
  30 #include <errno.h>
  31 #include <sys/time.h>
  32 #include "libpq-fe.h"
  33
  34 static void
  35 exit_nicely(PGconn *conn)
  36 {
  37         PQfinish(conn);
  38         exit(1);
  39 }
  40
  41 int
  42 main(int argc, char **argv)
  43 {
  44         const char *conninfo;
  45         PGconn     *conn;
  46         PGresult   *res;
  47         PGnotify   *notify;
  48         int                     nnotifies;
  49
  50         /*
  51          * If the user supplies a parameter on the command line, use it as the
  52          * conninfo string; otherwise default to setting dbname=postgres and using
  53          * environment variables or defaults for all other connection parameters.
  54          */
  55         if (argc > 1)
  56                 conninfo = argv[1];
  57         else
  58                 conninfo = "dbname = postgres";
  59
  60         /* Make a connection to the database */
  61         conn = PQconnectdb(conninfo);
  62
  63         /* Check to see that the backend connection was successfully made */
  64         if (PQstatus(conn) != CONNECTION_OK)
  65         {
  66                 fprintf(stderr, "Connection to database failed: %s",
  67                                 PQerrorMessage(conn));
  68                 exit_nicely(conn);
  69         }
  70
  71         /*
  72          * Issue LISTEN command to enable notifications from the rule's NOTIFY.
  73          */
  74         res = PQexec(conn, "LISTEN TBL2");
  75         if (PQresultStatus(res) != PGRES_COMMAND_OK)
  76         {
  77                 fprintf(stderr, "LISTEN command failed: %s", PQerrorMessage(conn));
  78                 PQclear(res);
  79                 exit_nicely(conn);
  80         }
  81
  82         /*
  83          * should PQclear PGresult whenever it is no longer needed to avoid memory
  84          * leaks
  85          */
  86         PQclear(res);
  87
  88         /* Quit after four notifies are received. */
  89         nnotifies = 0;
  90         while (nnotifies < 4)
  91         {
  92                 /*
  93                  * Sleep until something happens on the connection.  We use select(2)
  94                  * to wait for input, but you could also use poll() or similar
  95                  * facilities.
  96                  */
  97                 int                     sock;
  98                 fd_set          input_mask;
  99
 100                 sock = PQsocket(conn);
 101
 102                 if (sock < 0)
 103                         break;                          /* shouldn't happen */
 104
 105                 FD_ZERO(&input_mask);
 106                 FD_SET(sock, &input_mask);
 107
 108                 if (select(sock + 1, &input_mask, NULL, NULL, NULL) < 0)
 109                 {
 110                         fprintf(stderr, "select() failed: %s\n", strerror(errno));
 111                         exit_nicely(conn);
 112                 }
 113
 114                 /* Now check for input */
 115                 PQconsumeInput(conn);
 116                 while ((notify = PQnotifies(conn)) != NULL)
 117                 {
 118                         fprintf(stderr,
 119                                         "ASYNC NOTIFY of '%s' received from backend pid %d\n",
 120                                         notify->relname, notify->be_pid);
 121                         PQfreemem(notify);
 122                         nnotifies++;
 123                 }
 124         }
 125
 126         fprintf(stderr, "Done.\n");
 127
 128         /* close the connection to the database and cleanup */
 129         PQfinish(conn);
 130
 131         return 0;
 132 }