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References: <20100925112640.3FF8123889DD@eris.apache.org>
	<DA577861-DB97-47B7-95A3-EC59F95F6C3D@apache.org>
Date: Mon, 27 Sep 2010 16:48:45 +0100
Message-ID: <AANLkTikOU45rdB36HzORz4-D=MPp+e6WEQR94Bbsn_3p@mail.gmail.com>
Subject: Re: svn commit: r1001196 - /couchdb/trunk/src/couchdb/couch_file.erl
From: Filipe David Manana <fdmanana@apache.org>
To: dev@couchdb.apache.org
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On Mon, Sep 27, 2010 at 3:34 PM, Adam Kocoloski <kocolosk@apache.org> wrote=
:
> Hi Filipe, I'm quite certain that the file_descriptor is closed when couc=
h_file dies. =C2=A0I believe what the man page means by that statement is t=
hat if you don't supply the 'raw' option, Erlang will spawn a process to ha=
ndle IO for the file. =C2=A0That is, couch_file will send a message to anot=
her process which owns the port, rather than couch_file owning the port its=
elf. =C2=A0Regards,

Right.

Digging into OTP's code (R14B actually, but I guess it didn't change
much from R13), when the option 'raw' is not given, file.erl (
lib/kernel/src/file.erl) will use a process (the gen_server defined in
lib/kernel/src/file_server.erl) to access the file. This server will
handle process EXIT messages and do the necessary cleanups.

When using the 'raw' flag, file.erl will do the file operations
through a port (erts/preloaded/src/prim_file.erl) - this is why I have
a hunch that in this case we need to explicitely close the file, which
will send the 'close' command to the port and close the port. From
prim_file.erl:

close(#file_descriptor{module =3D ?MODULE, data =3D {Port, _}}) ->
    case drv_command(Port, <<?FILE_CLOSE>>) of
        ok ->
            drv_close(Port);
        Error ->
            Error
    end;


I'm not 100% sure of course, but anyway, it doesn't hurt to
explicitely close the file.

cheers


>
> Adam
>
> On Sep 25, 2010, at 7:26 AM, fdmanana@apache.org wrote:
>
>> Author: fdmanana
>> Date: Sat Sep 25 11:26:39 2010
>> New Revision: 1001196
>>
>> URL: http://svn.apache.org/viewvc?rev=3D1001196&view=3Drev
>> Log:
>> Explicitely close the file descriptor. It doesn't hurt.
>> Also, since we open the file in 'raw' mode, I suspect the file descripto=
r is not closed when the couch_file server dies.
>>
>> From erl -man file:
>>
>> "The raw option allows faster access to a file, because no Erlang proces=
s is needed to handle the file."
>>
>> For me, no Erlang process handling the file means that it's likely the f=
ile is not closed by any other process.
>>
>>
>>
>> Modified:
>> =C2=A0 =C2=A0couchdb/trunk/src/couchdb/couch_file.erl
>>
>> Modified: couchdb/trunk/src/couchdb/couch_file.erl
>> URL: http://svn.apache.org/viewvc/couchdb/trunk/src/couchdb/couch_file.e=
rl?rev=3D1001196&r1=3D1001195&r2=3D1001196&view=3Ddiff
>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D
>> --- couchdb/trunk/src/couchdb/couch_file.erl (original)
>> +++ couchdb/trunk/src/couchdb/couch_file.erl Sat Sep 25 11:26:39 2010
>> @@ -278,8 +278,8 @@ maybe_track_open_os_files(FileOptions) -
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 couch_stats_collector:track_process_count({c=
ouchdb, open_os_files})
>> =C2=A0 =C2=A0 end.
>>
>> -terminate(_Reason, _Fd) ->
>> - =C2=A0 =C2=A0ok.
>> +terminate(_Reason, #file{fd =3D Fd}) ->
>> + =C2=A0 =C2=A0ok =3D file:close(Fd).
>>
>>
>> handle_call({pread_iolist, Pos}, _From, File) ->
>>
>>
>
>


--=20
Filipe David Manana,
fdmanana@gmail.com, fdmanana@apache.org

"Reasonable men adapt themselves to the world.
=C2=A0Unreasonable men adapt the world to themselves.
=C2=A0That's why all progress depends on unreasonable men."