Thread: BackendPidGetProc doesn't return PGPROC for background worker?
Hi
I am trying to start bgworker from bgworker and create communication between these process. I have a code based on test_shm_mq. This code fails because BackendPidGetProc doesn't find related bgworker process, although the registrant process is livingregistrant = BackendPidGetProc(MyBgworkerEntry->bgw_notify_pid)
On 2015-05-15 AM 05:01, Pavel Stehule wrote: > > I am trying to start bgworker from bgworker and create communication > between these process. I have a code based on test_shm_mq. This code fails > because BackendPidGetProc doesn't find related bgworker process, although > the registrant process is living > One reason for this may be that the worker was not started with the flag BGWORKER_SHMEM_ACCESS which is necessary to perform InitProcess() that would initialize a PGPROC entry for it. But if you'd used the same method for initializing workers as test_shm_mq_setup(), then it should have. Thanks, Amit
On 2015-05-15 AM 10:39, Amit Langote wrote: > On 2015-05-15 AM 05:01, Pavel Stehule wrote: >> >> I am trying to start bgworker from bgworker and create communication >> between these process. I have a code based on test_shm_mq. This code fails >> because BackendPidGetProc doesn't find related bgworker process, although >> the registrant process is living >> > > One reason for this may be that the worker was not started with the flag > BGWORKER_SHMEM_ACCESS which is necessary to perform InitProcess() that would > initialize a PGPROC entry for it. But if you'd used the same method for > initializing workers as test_shm_mq_setup(), then it should have. > It seems in addition, a BackgroundWorkerInitializeConnection() is also necessary for the PGPROC entry of the worker to be visible to others. I do not see that done anywhere in test_shm_mq(); so perhaps that's missing? Thanks, Amit
On 2015-05-15 AM 10:59, Amit Langote wrote: > On 2015-05-15 AM 10:39, Amit Langote wrote: >> On 2015-05-15 AM 05:01, Pavel Stehule wrote: >>> >>> I am trying to start bgworker from bgworker and create communication >>> between these process. I have a code based on test_shm_mq. This code fails >>> because BackendPidGetProc doesn't find related bgworker process, although >>> the registrant process is living >>> >> >> One reason for this may be that the worker was not started with the flag >> BGWORKER_SHMEM_ACCESS which is necessary to perform InitProcess() that would >> initialize a PGPROC entry for it. But if you'd used the same method for >> initializing workers as test_shm_mq_setup(), then it should have. >> > > It seems in addition, a BackgroundWorkerInitializeConnection() is also > necessary for the PGPROC entry of the worker to be visible to others. I do not > see that done anywhere in test_shm_mq(); so perhaps that's missing? > And these conditions apply to the bgworker that started another bgworker, that is the registrant bgworker. I think such a pattern does not exist in existing code. That is, normally all workers are started by a user backend that has a valid shared PGPROC entry. Thanks, Amit
2015-05-15 3:39 GMT+02:00 Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>:
On 2015-05-15 AM 05:01, Pavel Stehule wrote:
>
> I am trying to start bgworker from bgworker and create communication
> between these process. I have a code based on test_shm_mq. This code fails
> because BackendPidGetProc doesn't find related bgworker process, although
> the registrant process is living
>
One reason for this may be that the worker was not started with the flag
BGWORKER_SHMEM_ACCESS which is necessary to perform InitProcess() that would
initialize a PGPROC entry for it. But if you'd used the same method for
initializing workers as test_shm_mq_setup(), then it should have.
I have it
Thanks,
Amit
On 2015-05-15 PM 02:13, Pavel Stehule wrote: > 2015-05-15 3:39 GMT+02:00 Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>: >> One reason for this may be that the worker was not started with the flag >> BGWORKER_SHMEM_ACCESS which is necessary to perform InitProcess() that >> would >> initialize a PGPROC entry for it. But if you'd used the same method for >> initializing workers as test_shm_mq_setup(), then it should have. >> > > I have it > See my other (the last) email. You said you created a bgworker from bgworker, so if the parent bgworker did not perform BackgroundWorkerInitializeConnection, then it would not be found in ProcArray. Thanks, Amit