Обсуждение: seg fault on dsm_create call
Hello,
sorry for my repost from psql-novice, probably it was not a right place
for my question.
I'm trying to understand how to work with dynamic shared memory, message
queues and workers.
The problem is I can not initialize any dsm segment -
void _PG_init() { ... dsm_segment *seg = dsm_create(32768, 0); // Segmentation fault
here ... BackgroundWorker worker; sprintf(worker.bgw_name, "mystem wrapper process");
worker.bgw_flags= BGWORKER_SHMEM_ACCESS; worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
worker.bgw_restart_time= BGW_NEVER_RESTART; worker.bgw_main = mainProc; worker.bgw_notify_pid = 0;
RegisterBackgroundWorker(&worker); }
Also I was trying to move dsm_create call to a worker, but with the same
result -
static void mainProc(Datum) { ... dsm_segment *seg = dsm_create(32768, 0); // Segmentation fault
here ... pqsignal(SIGTERM, mystemSigterm); BackgroundWorkerUnblockSignals(); ...
What could be a reason and what am I doing wrong?
PS
test/modules/test_shm_mq works fine...
dynamic_shared_memory_type = posix
OSX 10.11.5
PostgreSQL 9.5.3
--
Best regards,
Max Fomichev
On Tue, Jun 28, 2016 at 10:11 AM, Max Fomichev <max.fomitchev@gmail.com> wrote:
> Hello,
> sorry for my repost from psql-novice, probably it was not a right place for
> my question.
>
> I'm trying to understand how to work with dynamic shared memory, message
> queues and workers.
> The problem is I can not initialize any dsm segment -
>
> void _PG_init() {
> ...
> dsm_segment *seg = dsm_create(32768, 0); // Segmentation fault here
> ...
> BackgroundWorker worker;
> sprintf(worker.bgw_name, "mystem wrapper process");
> worker.bgw_flags = BGWORKER_SHMEM_ACCESS;
> worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
> worker.bgw_restart_time = BGW_NEVER_RESTART;
> worker.bgw_main = mainProc;
> worker.bgw_notify_pid = 0;
> RegisterBackgroundWorker(&worker);
> }
>
> Also I was trying to move dsm_create call to a worker, but with the same
> result -
>
> static void mainProc(Datum) {
> ...
> dsm_segment *seg = dsm_create(32768, 0); // Segmentation fault here
> ...
> pqsignal(SIGTERM, mystemSigterm);
> BackgroundWorkerUnblockSignals();
> ...
>
> What could be a reason and what am I doing wrong?
I think there are two problems.
1. You need to set up a ResourceOwner before you can attach to a DSM
segment. Something like: CurrentResourceOwner =
ResourceOwnerCreate(NULL, "name of my extension").
2. You can't do this from inside a _PG_init() block. That will run in
every process that loads this, which is probably not what you want,
and it will run in the postmaster also, which will not work: the
postmaster cannot use DSM.
Actually, I'd like to change #1 at some point, so that if
CurrentResourceOwner = NULL and you create or attach to a DSM, you
just get a backend-lifespan mapping. The current setup is annoying
rather than helpful. But currently that's how it is.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
On 28/06/16 19:24, Robert Haas wrote:
> On Tue, Jun 28, 2016 at 10:11 AM, Max Fomichev <max.fomitchev@gmail.com> wrote:
>> Hello,
>> sorry for my repost from psql-novice, probably it was not a right place for
>> my question.
>>
>> I'm trying to understand how to work with dynamic shared memory, message
>> queues and workers.
>> The problem is I can not initialize any dsm segment -
>>
>> void _PG_init() {
>> ...
>> dsm_segment *seg = dsm_create(32768, 0); // Segmentation fault here
>> ...
>> BackgroundWorker worker;
>> sprintf(worker.bgw_name, "mystem wrapper process");
>> worker.bgw_flags = BGWORKER_SHMEM_ACCESS;
>> worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
>> worker.bgw_restart_time = BGW_NEVER_RESTART;
>> worker.bgw_main = mainProc;
>> worker.bgw_notify_pid = 0;
>> RegisterBackgroundWorker(&worker);
>> }
>>
>> Also I was trying to move dsm_create call to a worker, but with the same
>> result -
>>
>> static void mainProc(Datum) {
>> ...
>> dsm_segment *seg = dsm_create(32768, 0); // Segmentation fault here
>> ...
>> pqsignal(SIGTERM, mystemSigterm);
>> BackgroundWorkerUnblockSignals();
>> ...
>>
>> What could be a reason and what am I doing wrong?
> I think there are two problems.
>
> 1. You need to set up a ResourceOwner before you can attach to a DSM
> segment. Something like: CurrentResourceOwner =
> ResourceOwnerCreate(NULL, "name of my extension").
>
> 2. You can't do this from inside a _PG_init() block. That will run in
> every process that loads this, which is probably not what you want,
> and it will run in the postmaster also, which will not work: the
> postmaster cannot use DSM.
>
> Actually, I'd like to change #1 at some point, so that if
> CurrentResourceOwner = NULL and you create or attach to a DSM, you
> just get a backend-lifespan mapping. The current setup is annoying
> rather than helpful. But currently that's how it is.
>
Thanks.
It works now with CurrentResourceOwner = ResourceOwnerCreate(NULL, "name
of my extension")
I am a little bit confused about test/modules/test_shm_mq, where
CurrentResourceOwner is set up before dsm_attach, not dsm_create -
/* * Connect to the dynamic shared memory segment. * * The backend that registered this worker passed
usthe ID of a shared * memory segment to which we must attach for further instructions. In * order to attach
todynamic shared memory, we need a resource owner. * Once we've mapped the segment in our address space, attach to
the table * of contents so we can locate the various data structures we'll
need to * find within the segment. */ CurrentResourceOwner = ResourceOwnerCreate(NULL, "test_shm_mq
worker"); seg = dsm_attach(DatumGetInt32(main_arg));
--
Best regards,
Max Fomichev
On Tue, Jun 28, 2016 at 12:45 PM, Max Fomichev <max.fomitchev@gmail.com> wrote: > On 28/06/16 19:24, Robert Haas wrote: > Thanks. > It works now with CurrentResourceOwner = ResourceOwnerCreate(NULL, "name of > my extension") > > I am a little bit confused about test/modules/test_shm_mq, where > CurrentResourceOwner is set up before dsm_attach, not dsm_create - You need a resource owner for either dsm_attach or dsm_create. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company