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%% This Source Code Form is subject to the terms of the Mozilla Public
%% License, v. 2.0. If a copy of the MPL was not distributed with this
%% file, You can obtain one at https://mozilla.org/MPL/2.0/.
%%
%% Copyright (c) 2007-2020 VMware, Inc. or its affiliates. All rights reserved.
%%
-module(mnesia_sync).
%% mnesia:sync_transaction/3 fails to guarantee that the log is flushed to disk
%% at commit. This module is an attempt to minimise the risk of data loss by
%% performing a coalesced log fsync. Unfortunately this is performed regardless
%% of whether or not the log was appended to.
-behaviour(gen_server).
-export([sync/0]).
-export([start_link/0, init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
-define(SERVER, ?MODULE).
-record(state, {waiting, disc_node}).
%%----------------------------------------------------------------------------
-spec sync() -> 'ok'.
%%----------------------------------------------------------------------------
start_link() ->
gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).
sync() ->
gen_server:call(?SERVER, sync, infinity).
%%----------------------------------------------------------------------------
init([]) ->
{ok, #state{disc_node = mnesia:system_info(use_dir), waiting = []}}.
handle_call(sync, _From, #state{disc_node = false} = State) ->
{reply, ok, State};
handle_call(sync, From, #state{waiting = Waiting} = State) ->
{noreply, State#state{waiting = [From | Waiting]}, 0};
handle_call(Request, _From, State) ->
{stop, {unhandled_call, Request}, State}.
handle_cast(Request, State) ->
{stop, {unhandled_cast, Request}, State}.
handle_info(timeout, #state{waiting = Waiting} = State) ->
ok = disk_log:sync(latest_log),
_ = [gen_server:reply(From, ok) || From <- Waiting],
{noreply, State#state{waiting = []}};
handle_info(Message, State) ->
{stop, {unhandled_info, Message}, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
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