[erlang-patches] Optimize communication with file io server

[Anthony Ramine]

Hello Björn,

I found a way to make it backwards compatible with the old protocol right now.

The file module communicates with a file io server with the following protocol for file operations:

> {file_request,From,ReplyAs,Request}
< {file_reply,ReplyAs,Reply}

The ReplyAs value is sent by the client side to match against when receiving the reply and is otherwise left untouched and passed as is by the server.

The amended commit changes the protocol to:

> {file_request,From,MonitorRef,Request}
< {file_reply,MonitorRef,Reply}

As the shape of the messages is not changed, backwards compatibility is not a concern.

Unfortunately, the following patch fails to compile because of a bug in the optimization pass. I've submitted two other patches; the first fixes beam_receive by teaching it how to track a set of registers instead of a single one, making it able to cope with the Core Erlang code generated by the inliner, the second improves sys_core_fold and makes it simplifies what is outputted by said inliner.

Please refetch.

Regards,

-- 
Anthony Ramine

Le 9 avr. 2013 à 12:12, Björn Gustavsson a écrit :

> The patch looks fine and it would be a good thing to do.
> 
> Unfortunately, there is the pesky question of backward
> compatibility.
> 
> Someone can open a file on an R15 system, send the
> file descriptor (=a pid) to an R16B01 system with your
> patch and the R16B01 system will attempt to do file
> operations on the file.
> 
> The backward compatible way to do this is to first introduce
> a file_io_server module that can handle both the new
> and the old messages. Two releases later the file module
> can be changed to use the new message format.
> 
> Strictly speaking, two releases forward means R19
> to allow the original R16B release to communicate
> with an R18 release.
> 
> /Bjorn