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multiple threads using one connection

From: Robert Gruszka <rgruszka(at)power(dot)com(dot)pl>
To: pgsql-interfaces(at)postgresql(dot)org
Subject: multiple threads using one connection
Date: 2006-02-28 12:35:46
Message-ID: 440443A2.5080907@power.com.pl (view raw or flat)
Thread:
Lists: pgsql-interfaces
Hi,

I have multi-thread application written in Ada which uses APQ. All 
threads use the same connection (can't afford one connection per 
thread). I compiled libpq with --enable-thread-safty option.
When two threads try to execute a query at the same time one of them is 
blocked and even when the other one finishes it is not unblocked.

I wrote simple test in c to find out is it APQ fault. But the result was 
the same. Am I doing something wrong?

My libpq version is 8.0.4 and here's the code of this test:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include "libpq-fe.h"
#include <pthread.h>

/* for ntohl/htonl */
#include <netinet/in.h>
#include <arpa/inet.h>

PGconn     *conn;

  static void
exit_nicely(PGconn *conn)
{
  //PQfinish(conn);
}


void *run(void *ptr)
{
  char *message;
  PGresult   *res;
  message = (char *)ptr;
  res = PQexec(conn, "select * from foo;");

  if (PQresultStatus(res) != PGRES_TUPLES_OK)
  {
    fprintf(stderr, "select failed: %s\n", PQerrorMessage(conn));
    PQclear(res);
    exit_nicely(conn);
    return;
  }

  PQclear(res);
  printf ("%s completed\n", message);

}

  int
main(int argc, char **argv)
{
  const char *conninfo;
  pthread_t thread1, thread2;
  char *message1 = "Thread 1";
  char *message2 = "Thread 2";
  int  iret1, iret2;

    //TODO
  conninfo = "dbname =  user =  password = ";

  /* Make a connection to the database */
  conn = PQconnectdb(conninfo);

  /* Check to see that the backend connection was successfully made */
  if (PQstatus(conn) != CONNECTION_OK)
  {
    fprintf(stderr, "Connection to database failed: %s",
        PQerrorMessage(conn));
    exit_nicely(conn);
  }
  else
  {
    fprintf(stderr, "Connected.\n");
  }

  PGresult   *res;
  res = PQexec(conn, "drop table foo;create table foo(id int);");

  if (PQresultStatus(res) != PGRES_COMMAND_OK)
  {
    fprintf(stderr, "create table failed: %s\n", PQerrorMessage(conn));
    PQclear(res);
    exit_nicely(conn);
    return;
  }

  iret1 = pthread_create( &thread1, NULL, run, (void*) message1);
  iret2 = pthread_create( &thread2, NULL, run, (void*) message2);

  pthread_join( thread1, NULL);
  pthread_join( thread2, NULL);
  /* close the connection to the database and cleanup */
  PQfinish(conn);

  return 0;
}



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Next:From: Alvaro HerreraDate: 2006-02-28 15:09:50
Subject: Re: multiple threads using one connection
Previous:From: Tom LaneDate: 2006-02-28 06:42:26
Subject: Re: row description, protocol 3

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