Question about Threads

AgentM,

The treads are joined back together by the master. I did try to debug, but
have to say I hard a hard time with it. I have tried to debug, but didn't
get very far. Debugging Threads is not my forte. :(

Here is the code from :
/src/backend/optimizer/geqo/geqo_main.c

for (i=0;i<thread_count;i++)
{
geqo_params[i].root = copyObject(root);
geqo_params[i].number_of_rels = number_of_rels;
geqo_params[i].initial_rels = copyObject(initial_rels);

geqo_params[i].root->base_rel_list =
listCopy(root->base_rel_list);
geqo_params[i].root->other_rel_list =
listCopy(root->other_rel_list);
geqo_params[i].root->join_rel_list =
listCopy(root->join_rel_list);
geqo_params[i].root->equi_key_list =
listCopy(root->equi_key_list);
geqo_params[i].root->query_pathkeys =
listCopy(root->query_pathkeys);

geqo_params[i].myid = i;

pthread_create(&thread_list[i],
NULL,
(void *(*)(void *)) geqo_single , (void *)
&geqo_params[i]);
}

// join all thread and get results
for (i=0;i<thread_count;i++)
{
elog(DEBUG1, "geqo: trying to join back thread %d", i);
pthread_join(thread_list[i],(void *) results[i]);
// sort results
if (best_so_far == -1)
{
elog(DEBUG1, "geqo: thread %d is first thread we
see", i);
best_so_far = i;
}
else
{
if
(results[best_so_far]->cheapest_total_path->total_cost >
results[i]->cheapest_total_path->total_cost)
{
elog(DEBUG1, "geqo: thread %d is better than
thread %d ", i, best_so_far);
best_so_far = i;

}
}

Leon

Leon Oosterwijk wrote:

All,

I'm working on a school project that involves genetic algorithms. We thought
it would be neat to parralelize the genetic algorithm in postgresql's query
optimiser. We used pthreads and are able to spawn threads to deal with the
query optimization, however on exit of the thread the postmaster blows up.
Before we get into details is there any obvious reason postgres doesn't like
to deal with threads?

Yes, the backend code is not thread-safe.

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