moving process state - copy on write - heap memory increase - Erlang Programming

The old Google Groups will be going away soon, but your browser is incompatible with the new version.
Message from discussion moving process state - copy on write - heap memory increase
Received-SPF: pass (google.com: domain of erlang-questions-boun...@erlang.org designates 192.121.151.104 as permitted sender) client-ip=192.121.151.104;
Message-ID: <504FB0EE.6010208@student.tuwien.ac.at>
Date: Tue, 11 Sep 2012 23:45:18 +0200
From: Roland <roland.koel...@student.tuwien.ac.at>
User-Agent: Mozilla/5.0 (X11; Linux x86_64;
 rv:15.0) Gecko/20120827 Thunderbird/15.0
MIME-Version: 1.0
To: erlang-questi...@erlang.org
Subject: [erlang-questions] moving process state - copy on write - heap
	memory increase
Precedence: list
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset="us-ascii"; Format="flowed"
Errors-To: erlang-questions-boun...@erlang.org
Sender: erlang-questions-boun...@erlang.org

Hello!

I want to move the state of my process to another process. Unfortunately 
this is not possible without a huge increase in memory consumption as by 
copying the state the "copy on write semantics" are lost.

This behaviour is demonstrated in my attached simplified t_process module.

-> {ok, Pid} = t_process:start_link().
-> t_process:bloat(Pid). --> memory consumption of the process is at 
6657256 after "bloat" is finished
-> t_process:reload_bag(P1). --> memory consumption is at 26295176 (4 
times as much)

No data has not been modified in any way, the data stays the same.

My question is: Despite what i want to do with this state transfer, is 
there any way to copy the state of a process without losing the "copy on 
write semantics", so that the target process has the same memory 
footprint as the original one?

Can someone point me to any direction/documentation on how i can get 
arround this issue?

Thank you!

-module(t_process).

-behaviour(gen_server).

-export([start_link/0, init/1, handle_call/3, handle_cast/2, 
handle_info/2, terminate/2, code_change/3, bloat/1, reload_bag/1]).

-record(process, {bag = []}).

start_link() ->
	gen_server:start_link(?MODULE, [], []).

bloat(Pid) ->
     gen_server:cast(Pid, bloat).

reload_bag(Pid) ->
     gen_server:call(Pid, reload_bag).

init([]) ->
	{ok, #process{}}.

handle_call(reload_bag, _From, State) ->
     BinaryBag = erlang:term_to_binary(State#process.bag), % simulate 
state transfer / loss of semantics
     io:format("Bag size is ~w.", [erlang:size(BinaryBag)]),
     {reply, ok, State#process{bag = erlang:binary_to_term(BinaryBag)}};

handle_call(_Call, _From, State) ->
     {reply, ok, State}.

handle_cast(bloat, State) ->
     NewBag = lists:concat([State#process.bag, lists:foldl(fun(_C, List) 
-> List ++ [{"ABCDEFGHIJKLMNOPQRSTUVWXYZ"}] end, [], lists:seq(1, 50000))]),
     io:format("Bloating finished."),
     {noreply, State#process{bag = NewBag}};

handle_cast(_Cast, State) ->
     {noreply, State}.

handle_info(_Info, State) ->
     {noreply, State}.

terminate(_Reason, _State) ->
     ok.

code_change(_OldVsn, State, _Extra) ->
     {ok, State}.

_______________________________________________
erlang-questions mailing list
erlang-questi...@erlang.org
http://erlang.org/mailman/listinfo/erlang-questions
Create a group - Google Groups - Google Home - Terms of Service - Privacy Policy
Account Options
