Re: Is PREPARE of ecpglib thread safe?

At Thu, 14 Mar 2019 09:49:11 +0000, "Matsumura, Ryo" <matsumura.ryo@jp.fujitsu.com> wrote in
<03040DFF97E6E54E88D3BFEE5F5480F737AC3AD8@G01JPEXMBYT04>
> Horiguchi-san
> 
> Thank you for your comment.
> 
> > A connection cannot be concurrently used by multiple threads so
> > the programmer must guard connections using mutex [1] or
> > friends. If it is done by a single mutex (I suppose it is
> > common.), there's no race condition also on the prepared
> > statement storage. I'm not sure it is explicitly aimed but I
> > suppose that there's no problem in a common usage of the library.
> 
> I understand it, but current scope of StatementCache and DeclareStatementList seems not
> to be limitted within each connection, isn't it?

Yes, so I wrote that "if it is done by a single mutex". Feel free
to fix that if it is still problematic:)

> Therefore, I thought the operation on them must be thread safe.

I'm not against that.

> For example, scope of DescriptorList in descriptor.c is within thread (not connection)
> by using pthread_getspecific/ pthread_setspecific().

It seems like a local cache of server-side data, which is similar
to catcache on server side for each process. I don't think
prepared statements is in that category. A prepared statement is
bonded to a connection, not to a thread. Different threads can
execute the same prepared statement on the same connection.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center