Need help woth thread support in ecpglib - Mailing list pgsql-hackers

Hi,

I recently got the following bug report. It appears to be a bug in
pthread implementation in ecpglib/connect.c where 

pthread_getspecific(actual_connection_key);

doesn't return the value of actual_connection, the variable used for
non-threaded mode. Problem is I never really used threading in my apps
and didn't do the threading patches. Maybe someone with more knowledge
than me could have a look at this. Thanks.

Michael

---

When using postgresql 8.0 compiled with --enable-thread-safety, new threads
no longer see the default ecpg connection.  That was not the case in 7.4.x
compiled with or without --enable-thread-safety.

TEST CASE

The program at the end of this mail sets up a database table named
"dbthreadtest" in the default database.  It then spawns 5 threads which each
do a select from that table using the default connection.

If the program is saved as dbthreadtest.pgc, compile with:

ecpg -t -o dbthreadtest.c dbthreadtest.pgc
gcc -Wall -o dbthreadtest dbthreadtest.c -lecpg -lpthread

Results under 7.4.x / 8.0 without --enable-thread-safety:

got id = 1
got id = 1
got id = 1
got id = 1
got id = 1

Results under 8.0 with --enable-thread-safety:

'No such connection NULL in line 76.', sqlcode = -220 select id

TEST PROGRAM

/* -*-C-*- */

#include <stdlib.h>
#include <pthread.h>

#define CHECK_SQL(fmt, args...)                \
do                            \
{                            \ if (sqlca.sqlcode != ECPG_NO_ERROR)            \   {                            \
fprintf(stderr, "'%s', sqlcode = %ld " fmt "\n",    \       sqlca.sqlerrm.sqlerrmc,            \       sqlca.sqlcode,
##args);            \     exit (1);                        \   }                            \}
 \
 
while (0)

#define FATAL(fmt, args...)            \
do                        \
{                        \ fprintf (stderr, fmt "\n", ## args);        \ exit (1);                    \
}                        \
while (0)

pthread_mutex_t global_lock;
pthread_t global_threads[5];

void
setup_db ()
{ exec sql begin declare section;   const char *_user; exec sql end declare section;
 pthread_mutex_lock (&global_lock);
 _user = getenv ("LOGNAME");
 exec sql connect to :_user; CHECK_SQL ("connect");
 exec sql create table dbthreadtest (id int); CHECK_SQL ("create dbthreadtest");
 exec sql insert into dbthreadtest (id) values (1); CHECK_SQL ("insert 1");
 pthread_mutex_unlock (&global_lock);
}

void
teardown_db ()
{ pthread_mutex_lock (&global_lock);
 exec sql drop table dbthreadtest; CHECK_SQL ("drop dbthreadtest");
 exec sql disconnect; CHECK_SQL ("disconnect");
 pthread_mutex_unlock (&global_lock);
}

void *query_db (void *ignorep)
{ exec sql begin declare section;   int _id; exec sql end declare section;
 pthread_mutex_lock (&global_lock); exec sql select id into :_id from dbthreadtest; CHECK_SQL ("select id");
 fprintf (stdout, "got id = %d\n", _id); pthread_mutex_unlock (&global_lock);
 return NULL;
}

int
main ()
{ int i;
 pthread_mutex_init (&global_lock, NULL);  setup_db ();
 for (i = 0; i < sizeof (global_threads) / sizeof (global_threads[0]);
++i)   {     if (pthread_create (&global_threads[i], NULL, query_db, NULL))FATAL ("pthread_create %d failed", i);   }
 for (i = 0; i < sizeof (global_threads) / sizeof (global_threads[0]);
++i)   {     if (pthread_join (global_threads[i], NULL))FATAL ("pthread_join %d failed", i);   }
 teardown_db ();  return 0;
}

----- End forwarded message -----

-- 
Michael Meskes
Email: Michael at Fam-Meskes dot De, Michael at Meskes dot (De|Com|Net|Org)
ICQ: 179140304, AIM/Yahoo: michaelmeskes, Jabber: meskes@jabber.org
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