On Mon, Jul 22, 2019 at 12:54 PM Robert Engels <reng...@ix.netcom.com> wrote:
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> -----Original Message-----
> >From: Burak Serdar <bser...@ieee.org>
> >Sent: Jul 22, 2019 11:55 AM
> >To: Robert Engels <reng...@ix.netcom.com>
> >Cc: Tong Sun <suntong...@gmail.com>, golang-nuts
> ><golang-nuts@googlegroups.com>
> >Subject: Re: [go-nuts] Variable life time -- sql.DB connection defer closing
> >question
> >
> >On Mon, Jul 22, 2019 at 10:37 AM Robert Engels <reng...@ix.netcom.com> wrote:
> >>
> >>
> >>
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> >>
> >>
> >> -----Original Message-----
> >> >From: Burak Serdar <bser...@ieee.org>
> >> >Sent: Jul 22, 2019 11:13 AM
> >> >To: Tong Sun <suntong...@gmail.com>
> >> >Cc: golang-nuts <golang-nuts@googlegroups.com>
> >> >Subject: Re: [go-nuts] Variable life time -- sql.DB connection defer
> >> >closing question
> >> >
> >> >On Mon, Jul 22, 2019 at 9:35 AM Tong Sun <suntong...@gmail.com> wrote:
> >> >>
> >> >> All SQL DB statements need a sql.DB connection:
> >> >>
> >> >> var conn *sql.DB = ...
> >> >> defer conn.Close()
> >> >>
> >> >> statement, err := conn.Prepare(SQL)
> >> >>
> >> >>
> >> >> My question is, if I want to reuse the `conn` variable later on in the
> >> >> same function,
> >> >>
> >> >> conn, err = sql.Open("mssql", NewConnString)
> >> >
> >> >If you didn't close conn here, then it will leak. The defer will close
> >> >the second connection, not the first.
> >> >You can add a second defer after opening the second connection. Or,
> >> >use a different variable and defer closing of that as well.
> >> >
> >> >Closing the first connection manually before opening the second won't
> >> >work. The first defer will try to close the first connection. Defer
> >> >evaluates its arguments when it is declared, not when it runs.
> >> >
> >> >
> >> >>
> >> >>
> >> >> Do I need to put another `defer conn.Close()` after it, or the first
> >> >> `defer conn.Close()` still applies? Or I should call `conn.Close()`
> >> >> explicitly beforehand?
> >> >>
> >> >> thanks
> >> >>
> >> >> --
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> >> >
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> >>
> >> I don't think that is true. The first defer will be scheduled with the
> >> first conn arg (since it is evaluated at call time). You need another
> >> defer after the second open. You will end up with Close being called twice
> >> from defer which is what you want.
> >
> >
> >I thought that's what I said as well. What part is wrong?
> >
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> I think it was this statement:
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> >> If you didn't close conn here, then it will leak. The defer will close
> >> the second connection, not the first.
>
> The first defer closes the first conn. A second defer is needed to close the
> second conn.
You're right, my mistake. Defer will close the first, not the second.
>
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