Re: [PATCH v4] lib: Simplify close and codify aborting atomic section

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+From: Austin Clements <aclements@csail.mit.edu>\r
+To: "W. Trevor King" <wking@tremily.us>\r
+Subject: Re: [PATCH v4] lib: Simplify close and codify aborting atomic section\r
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+Date: Thu, 02 Oct 2014 16:39:41 -0400\r
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+\r
+On Thu, 02 Oct 2014, "W. Trevor King" <wking@tremily.us> wrote:\r
+> On Thu, Oct 02, 2014 at 03:19:08PM -0400, Austin Clements wrote:\r
+>> This patch simplifies notmuch_database_close to explicitly abort any\r
+>> outstanding transaction and then just call Database::close.  This\r
+>> works for both read-only and read/write databases, takes care of\r
+>> committing changes, unifies the exception handling path, and codifies\r
+>> aborting outstanding transactions.\r
+>\r
+> I don't expect atomic blocks are particularly useful for read-only\r
+> connections.  If they aren't, I'd quibble with the =E2=80=9CThis works for\r
+> both read-only=E2=80=A6=E2=80=9D wording above.  If they are, I'd drop th=\r
+e read/write\r
+\r
+It's true that atomic sections aren't very useful on a read-only\r
+database, but we do allow them for symmetry.  We also keep track of how\r
+deeply nested we are so notmuch_database_end_atomic can return a proper\r
+error message regardless of whether the database is read/write or\r
+read-only.\r
+\r
+But all I'm saying in the commit message is that Xapian::Database::close\r
+works for both read-only and read/write databases and will flush if\r
+necessary, so we don't have to worry about that.\r
+\r
+> check below:\r
+>\r
+>> +       /* If there's an outstanding transaction, it's unclear if\r
+>> +        * closing the Xapian database commits everything up to\r
+>> +        * that transaction, or may discard committed (but\r
+>> +        * unflushed) transactions.  To be certain, explicitly\r
+>> +        * cancel any outstanding transaction before closing. */\r
+>> +       if (notmuch->mode =3D=3D NOTMUCH_DATABASE_MODE_READ_WRITE &&\r
+>> +           notmuch->atomic_nesting)\r
+>> +           (static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db))\r
+>> +               ->cancel_transaction ();\r
+\r
+The notmuch->mode check here is necessary because atomic_nesting can be\r
+non-zero on a read-only database (for the reason I mentioned above), but\r
+we had better not cast xapian_db to a WritableDatabase if it isn't a\r
+WritableDatabase.\r
+\r
+> Thats a very minor quibble though, and I'd be glad to see this patch\r
+> land as is.\r
+>\r
+> Cheers,\r
+> Trevor\r
+>\r
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