Re: Can a background worker exist without shared memory access for EXEC_BACKEND cases?

On Wed, Aug 5, 2020 at 5:16 PM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Wed, Aug 5, 2020 at 7:24 AM Bharath Rupireddy
> <bharath.rupireddyforpostgres@gmail.com> wrote:
> > In EXEC_BACKEND cases, right after PGSharedMemoryDetach(), the bg
> > worker will no longer be able to access the backend parameters, see
> > below(I tried this on my Ubuntu machine with a bgworker with no
> > BGWORKER_SHMEM_ACCESS flag and defined EXEC_BACKEND macro in
> > pg_config_manual.h) :
> >
> > (gdb) p *MyLatch
> > Cannot access memory at address 0x7fd60424a6b4
> > (gdb) p *ShmemVariableCache
> > Cannot access memory at address 0x7fd58427bf80
> > (gdb) p ProcStructLock
> > $10 = (slock_t *) 0x7fd60429bd00 <error: Cannot access memory at
> > address 0x7fd60429bd00>
> > (gdb) p *AuxiliaryProcs
> > Cannot access memory at address 0x7fd60424cc60
> > (gdb) p *ProcGlobal
> > Cannot access memory at address 0x7fd604232880
>
> Well all of those are pointers into the main shared memory segment,
> which is expected to be inaccessible after it is detached. Hopefully
> nobody should be surprised that if you don't specify
> BGWORKER_SHMEM_ACCESS, you can't access data stored in shared memory.
>

Right.

Will the proposed patch(v2) having some info in bgworker.sgml and
bgworker.h be ever useful to the users in some way?

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com