%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2006-2010. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
-module(snmpa_target_cache).
-behaviour(gen_server).
%% External exports
%% Avoid warning for local function demonitor/1 clashing with autoimported BIF.
-compile({no_auto_import,[demonitor/1]}).
-export([start_link/2, stop/0, verbosity/1]).
-export([
invalidate/0, % invalidate/1, invalidate/2,
targets/1, targets/2
]).
%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2,
code_change/3]).
-ifdef(snmp_qc).
-export([
lock/1,
unlock/0,
upgrade_lock/0,
downgrade_lock/0
]).
-endif.
-include("snmpa_internal.hrl").
-include("snmp_debug.hrl").
-include("snmp_verbosity.hrl").
-record(state,
{
active_count = 0,
writer = false, % Active or waiting write-lock
waiting = [] % Waiting lockers
}
).
-record(locker, {pid, from, mon_ref, type, state}).
-define(SERVER, ?MODULE).
-define(CACHE, ?MODULE).
-define(LOCKER_TAB, snmpa_target_cache_locker).
-ifndef(default_verbosity).
-define(default_verbosity,silence).
-endif.
-ifdef(snmp_debug).
-define(GS_START_LINK(Prio, Opts),
gen_server:start_link({local, ?SERVER}, ?MODULE,
[Prio, Opts], [{debug,[trace]}])).
-else.
-define(GS_START_LINK(Prio, Opts),
gen_server:start_link({local, ?SERVER}, ?MODULE,
[Prio, Opts], [])).
-endif.
%%%-------------------------------------------------------------------
%%% API
%%%-------------------------------------------------------------------
start_link(Prio, Opts) ->
?d("start_link -> entry with"
"~n Prio: ~p"
"~n Opts: ~p", [Prio, Opts]),
?GS_START_LINK(Prio, Opts).
stop() ->
call(stop).
verbosity(V) ->
call({verbosity, V}).
%% Targets -> notify_targets()
%% notify_targets() -> [notify_target()]
%% notify_target() -> {NotifyName, target()}
%% target() -> {DestAddr, TargetName, TargetParams, NotifyType}
targets(TargetsFun) when is_function(TargetsFun) ->
Pat = {{'_', '$1'}, '$2'},
get_targets(Pat, TargetsFun).
targets(TargetsFun, NotifyName) when is_function(TargetsFun) ->
Pat = {{NotifyName, '$1'}, '$2'},
get_targets(Pat, TargetsFun).
get_targets(Pat, TargetsFun) ->
lock(read), % Get a read lock
Targets =
case ets:lookup(?CACHE, state) of
[{state, invalid}] ->
upgrade_lock(), % Upgrade to write lock
%% Make sure it's still invalid
case ets:lookup(?CACHE, state) of
[{state, invalid}] ->
insert_all( TargetsFun() ),
ets:insert(?CACHE, {state, valid});
_ ->
ok % This means that someone got there before us
end,
downgrade_lock(), % Downgrade to read lock
get_targets(Pat);
[{state, valid}] ->
get_targets(Pat)
end,
unlock(), % Release the read lock
Targets.
get_targets(Pat) ->
NotifyTargets = ets:match(?CACHE, Pat),
[{DestAddr, TargetName, TargetParams, NotifyType} ||
[TargetName, {DestAddr, TargetParams, NotifyType}] <-
NotifyTargets].
invalidate() ->
lock(write),
case ets:lookup(?CACHE, state) of
[{state, invalid}] ->
ok;
[{state, valid}] ->
delete_all(),
ets:insert(?CACHE, {state, invalid})
end,
unlock(),
ok.
%%%-------------------------------------------------------------------
%%% Callback functions from gen_server
%%%-------------------------------------------------------------------
%%--------------------------------------------------------------------
%% Func: init/1
%% Returns: {ok, State} |
%% {ok, State, Timeout} |
%% ignore |
%% {stop, Reason}
%%--------------------------------------------------------------------
init([Prio, Opts]) ->
case (catch do_init(Prio, Opts)) of
{ok, State} ->
?vdebug("started",[]),
{ok, State};
{error, Reason} ->
config_err("failed starting target-cache server: ~n~p", [Reason]),
{stop, {error, Reason}};
Error ->
config_err("failed starting target-cache server: ~n~p", [Error]),
{stop, {error, Error}}
end.
do_init(Prio, Opts) ->
process_flag(priority, Prio),
process_flag(trap_exit, true),
put(sname, tcs),
put(verbosity, get_opt(verbosity, Opts, ?default_verbosity)),
?vlog("starting",[]),
ets:new(?CACHE, [set, named_table, public]),
ets:insert(?CACHE, {state, invalid}),
ets:new(?LOCKER_TAB, [set, named_table, {keypos, #locker.pid}]),
{ok, #state{}}.
%%--------------------------------------------------------------------
%% Func: handle_call/3
%% Returns: {reply, Reply, State} |
%% {reply, Reply, State, Timeout} |
%% {noreply, State} |
%% {noreply, State, Timeout} |
%% {stop, Reason, Reply, State} | (terminate/2 is called)
%% {stop, Reason, State} (terminate/2 is called)
%%--------------------------------------------------------------------
%%%-----------------------------------------------------------------
%%
%% (1) As long as there are no _waiting_ or active write locks,
%% read-locks will allways be granted
%% (2) When there are no active readers, write-locks will be
%% granted.
%% (3) When there are active readers (clients with read-locks),
%% a write-lock will have to wait for _all_ the read-locks
%% to be released.
%% (4) If there is a waiting write-lock, all subsequent lock-
%% requests will have to wait.
%% (5) If there is an active write-lock, all subsequent lock-
%% requests will have to wait.
%%
monitor(Pid) -> erlang:monitor(process, Pid).
-ifdef(SNMP_R10).
demonitor(Ref) ->
erlang:demonitor(Ref),
receive
{_, Ref, _, _, _} ->
true
after 0 ->
true
end.
-else.
demonitor(Ref) ->
erlang:demonitor(Ref, [flush]).
-endif.
%% (1) No write_lock active or waiting
handle_call({lock, read = Type, infinity}, {Pid, _} = From,
#state{active_count = Cnt, writer = false} = State) ->
?vlog("lock(read, infinity) -> "
"entry when no waiting or active writer with"
"~n Pid: ~p"
"~n Cnt: ~p", [Pid, Cnt]),
MonRef = monitor(Pid),
Locker = #locker{pid = Pid,
from = From,
mon_ref = MonRef,
type = Type,
state = active},
ets:insert(?LOCKER_TAB, Locker),
%% ?vtrace("lock(read, infinity) -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{reply, ok, State#state{active_count = inc(Cnt)}};
%% (4,5) There is waiting or active write locks
handle_call({lock, read = Type, infinity}, {Pid, _} = From, State) ->
?vlog("lock(read, infinity) -> "
"entry when active or waiting write locks with"
"~n Pid: ~p", [Pid]),
MonRef = monitor(Pid),
Locker = #locker{pid = Pid,
from = From,
mon_ref = MonRef,
type = Type,
state = waiting},
ets:insert(?LOCKER_TAB, Locker),
Waiting = lists:append(State#state.waiting, [Pid]),
%% ?vtrace("lock(read, infinity) -> done when"
%% "~n Waiting: ~p"
%% "~n Lockers: ~p", [Waiting, ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{waiting = Waiting}};
%% (2) No active locks
%% Since there are no active lockers, that also means that
%% there is no lockers waiting.
handle_call({lock, write = Type, infinity}, {Pid, _} = From,
#state{active_count = 0, writer = false} = State) ->
?vlog("lock(write, infinity) -> "
"entry when no active lockers with"
"~n Pid: ~p", [Pid]),
MonRef = monitor(Pid),
Locker = #locker{pid = Pid,
from = From,
mon_ref = MonRef,
type = Type,
state = active},
ets:insert(?LOCKER_TAB, Locker),
%% ?vtrace("lock(write, infinity) -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{reply, ok, State#state{active_count = 1, writer = true}};
%% (3) No waiting or active writers, but at least one active reader
handle_call({lock, write = Type, infinity}, {Pid, _} = From,
#state{writer = false} = State) ->
?vlog("lock(write, infinity) -> "
"entry when active lockers with"
"~n Pid: ~p", [Pid]),
MonRef = monitor(Pid),
Locker = #locker{pid = Pid,
from = From,
mon_ref = MonRef,
type = Type,
state = waiting},
ets:insert(?LOCKER_TAB, Locker),
Waiting = lists:append(State#state.waiting, [Pid]),
%% ?vtrace("lock(write, infinity) -> done when"
%% "~n Waiting: ~p"
%% "~n Lockers: ~p", [Waiting, ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{waiting = Waiting, writer = true}};
handle_call({lock, write = Type, infinity}, {Pid, _} = From,
#state{writer = true} = State) ->
?vlog("lock(write, infinity) -> entry with"
"~n Pid: ~p", [Pid]),
MonRef = monitor(Pid),
Locker = #locker{pid = Pid,
from = From,
mon_ref = MonRef,
type = Type,
state = waiting},
ets:insert(?LOCKER_TAB, Locker),
Waiting = lists:append(State#state.waiting, [Pid]),
%% ?vtrace("lock(write, infinity) -> done when"
%% "~n Waiting: ~p"
%% "~n Lockers: ~p", [Waiting, ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{waiting = Waiting}};
handle_call({verbosity, Verbosity}, _From, State) ->
?vlog("verbosity: ~p -> ~p", [get(verbosity), Verbosity]),
Old = put(verbosity, ?vvalidate(Verbosity)),
{reply, Old, State};
%% If there are no more active read'ers, and no waiting,
%% then set to writer and reply now
handle_call({upgrade_lock, Pid}, _From,
#state{active_count = 1, waiting = []} = State) ->
?vlog("upgrade_lock -> "
"entry when one active locker and no waiting with"
"~n Pid: ~p", [Pid]),
case ets:lookup(?LOCKER_TAB, Pid) of
[#locker{type = read} = Locker] ->
ets:insert(?LOCKER_TAB, Locker#locker{type = write}),
%% ?vtrace("upgrade_lock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{reply, ok, State#state{writer = true}};
[#locker{type = write}] ->
{reply, ok, State}
end;
%% If there are no more active read'ers, and no waiting,
%% then set to writer and reply now
handle_call({upgrade_lock, Pid}, {Pid, _} = From,
#state{active_count = 1, waiting = Waiting} = State) ->
?vlog("upgrade_lock -> "
"entry when one active locker with"
"~n Pid: ~p"
"~n Waiting: ~p", [Pid, Waiting]),
case ets:lookup(?LOCKER_TAB, Pid) of
[#locker{type = read} = Locker] ->
case active_waiting_writer(Waiting) of
{true, StillWaiting} ->
?vtrace("upgrade_lock -> activated when"
"~n StillWaiting: ~p", [StillWaiting]),
ets:insert(?LOCKER_TAB, Locker#locker{from = From,
type = write,
state = waiting}),
%% ?vtrace("upgrade_lock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{waiting = StillWaiting ++ [Pid]}};
{false, []} ->
?vtrace("upgrade_lock -> none activated, "
"so we can let the upgrader in", []),
ets:insert(?LOCKER_TAB, Locker#locker{type = write}),
%% ?vtrace("upgrade_lock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{reply, ok, State#state{writer = true,
waiting = []}}
end;
[#locker{type = write}] ->
{reply, ok, State};
_ ->
{reply, {error, not_found}, State}
end;
%% There are active and waiting locker's
handle_call({upgrade_lock, Pid}, {Pid, _} = From,
#state{active_count = Cnt, waiting = Waiting} = State) ->
?vlog("upgrade_lock -> entry with"
"~n Pid: ~p"
"~n Waiting: ~p", [Pid, Waiting]),
case ets:lookup(?LOCKER_TAB, Pid) of
[#locker{type = read} = Locker] ->
ets:insert(?LOCKER_TAB, Locker#locker{from = From,
type = write,
state = waiting}),
%% ?vtrace("upgrade_lock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{active_count = dec(Cnt),
waiting = Waiting ++ [Pid]}};
[#locker{type = write}] ->
{reply, ok, State};
_ ->
{reply, {error, not_found}, State}
end;
handle_call(stop, _From, State) ->
?vlog("stop",[]),
{stop, normal, stopped, State};
handle_call(Req, _From, State) ->
warning_msg("received unknown request: ~n~p", [Req]),
Reply = {error, {unknown, Req}},
{reply, Reply, State}.
%%--------------------------------------------------------------------
%% Func: handle_cast/2
%% Returns: {noreply, State} |
%% {noreply, State, Timeout} |
%% {stop, Reason, State} (terminate/2 is called)
%%--------------------------------------------------------------------
handle_cast({unlock, Pid},
#state{active_count = Cnt, waiting = []} = State) ->
?vlog("unlock -> entry when no waiting with"
"~n Pid: ~p"
"~n Cnt: ~p", [Pid, Cnt]),
case ets:lookup(?LOCKER_TAB, Pid) of
[#locker{mon_ref = MonRef, type = read}] ->
?vdebug("unlock -> found read locker"
"~n MonRef: ~p", [MonRef]),
demonitor(MonRef),
ets:delete(?LOCKER_TAB, Pid),
%% ?vtrace("unlock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{active_count = dec(Cnt)}};
[#locker{mon_ref = MonRef, type = write}] ->
?vdebug("unlock -> found write locker"
"~n MonRef: ~p", [MonRef]),
demonitor(MonRef),
ets:delete(?LOCKER_TAB, Pid),
%% ?vtrace("unlock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{active_count = dec(Cnt), writer = false}};
_ ->
{noreply, State}
end;
handle_cast({unlock, Pid},
#state{active_count = Cnt, waiting = Waiting} = State) ->
?vlog("unlock -> entry when waiting with"
"~n Pid: ~p"
"~n Cnt: ~p", [Pid, Cnt]),
case ets:lookup(?LOCKER_TAB, Pid) of
%% Last active reader: Time to let the waiting in
%% The first of the waiting _has_ to be a write-lock
%% (read-locks will only be set waiting if there is
%% a waiting or active write).
[#locker{mon_ref = MonRef, type = read}] when (Cnt == 1) ->
?vdebug("unlock -> found read locker"
"~n MonRef: ~p", [MonRef]),
demonitor(MonRef),
ets:delete(?LOCKER_TAB, Pid),
case active_waiting_writer(Waiting) of
{true, StillWaiting} ->
?vtrace("unlock -> activated when"
"~n StillWaiting: ~p", [StillWaiting]),
%% ?vtrace("unlock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{active_count = 1,
writer = true,
waiting = StillWaiting}};
{false, []} ->
?vtrace("unlock -> none activated", []),
%% ?vtrace("unlock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{active_count = 0,
writer = false,
waiting = []}}
end;
[#locker{mon_ref = MonRef, type = read}] ->
?vdebug("unlock -> found read locker"
"~n MonRef: ~p", [MonRef]),
demonitor(MonRef),
ets:delete(?LOCKER_TAB, Pid),
%% ?vtrace("unlock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{active_count = dec(Cnt)}};
[#locker{mon_ref = MonRef, type = write}] ->
%% Release the hord (maybe)
?vdebug("unlock -> found write locker"
"~n MonRef: ~p", [MonRef]),
demonitor(MonRef),
ets:delete(?LOCKER_TAB, Pid),
{Active, StillWaiting, Writer} =
activate_waiting_readers_or_maybe_writer(Waiting),
?vtrace("unlock -> new reader(s) or maybe writer activated:"
"~n Active: ~p"
"~n StillWaiting: ~p"
"~n Writer: ~p", [Active, StillWaiting, Writer]),
%% ?vtrace("unlock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{active_count = Active,
writer = Writer,
waiting = StillWaiting}};
%% If we have no active lockers, this may be a bug and therefor
%% see if we can activate some of the waiting
_ when (State#state.active_count == 0) ->
?vdebug("unlock -> could not find locker", []),
{Active, StillWaiting, Writer} =
activate_waiting_readers_or_maybe_writer(Waiting),
?vtrace("unlock -> new reader(s) or maybe writer activated:"
"~n Active: ~p"
"~n StillWaiting: ~p"
"~n Writer: ~p", [Active, StillWaiting, Writer]),
%% ?vtrace("unlock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply,
State#state{active_count = Active,
writer = Writer,
waiting = StillWaiting}};
_ ->
{noreply, State}
end;
handle_cast({downgrade_lock, Pid}, #state{waiting = Waiting} = State) ->
?vlog("downgrade_lock -> entry when waiting with"
"~n Pid: ~p", [Pid]),
case ets:lookup(?LOCKER_TAB, Pid) of
[#locker{type = read}] ->
{noreply, State};
[#locker{type = write} = Locker] ->
%% We need to check if this is the only write(r),
%% in that case we must update the writer field
ets:insert(?LOCKER_TAB, Locker#locker{type = read}),
{Cnt, NewWaiting} = activate_waiting_readers(Waiting),
?vtrace("downgrade_lock -> entry when waiting with"
"~n Cnt: ~p"
"~n NewWaiting: ~p", [Cnt, NewWaiting]),
%% ?vtrace("downgrade_lock -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{active_count = Cnt,
waiting = NewWaiting,
writer = is_writer(NewWaiting)}}
end;
handle_cast(Msg, State) ->
warning_msg("received unknown message: ~n~p", [Msg]),
{noreply, State}.
%%--------------------------------------------------------------------
%% Func: handle_info/2
%% Returns: {noreply, State} |
%% {noreply, State, Timeout} |
%% {stop, Reason, State} (terminate/2 is called)
%%--------------------------------------------------------------------
%% This must be a glitch
handle_info({'DOWN', _MonRef, process, Pid, Reason},
#state{active_count = 0, waiting = []} = State) ->
?vlog("received DOWN message from ~p when no active and no waiting"
"~n exited for reason: ~n~p", [Pid, Reason]),
{noreply, State};
handle_info({'DOWN', _MonRef, process, Pid, Reason},
#state{active_count = Cnt, waiting = []} = State) ->
?vlog("received DOWN message from ~p when active but no waiting"
"~n exited for reason: ~n~p", [Pid, Reason]),
case handle_maybe_active_down(Cnt, Pid) of
{NewCnt, write} ->
%% ?vtrace("DOWN -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{active_count = NewCnt, writer = false}};
{NewCnt, read} ->
%% ?vtrace("DOWN -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, State#state{active_count = NewCnt}}
end;
handle_info({'DOWN', _MonRef, process, Pid, Reason}, State) ->
?vlog("received DOWN message from ~p"
"~n exited for reason: ~n~p", [Pid, Reason]),
NewState = handle_maybe_active_or_waiting_down(Pid, State),
%% ?vtrace("DOWN -> done when"
%% "~n Lockers: ~p", [ets:tab2list(?LOCKER_TAB)]),
{noreply, NewState};
handle_info({'EXIT', Pid, Reason}, S) ->
%% The only other process we should be linked to is
%% our supervisor, so die...
{stop, {received_exit, Pid, Reason}, S};
handle_info(Info, State) ->
warning_msg("received unknown info: ~n~p", [Info]),
{noreply, State}.
%%--------------------------------------------------------------------
%% Func: terminate/2
%% Purpose: Shutdown the server
%% Returns: any (ignored by gen_server)
%%--------------------------------------------------------------------
terminate(Reason, State) ->
?vlog("terminate ->"
"~n Reason: ~p"
"~n State: ~p", [Reason, State]),
ets:delete(?CACHE),
ets:delete(?LOCKER_TAB),
ok.
%%%-------------------------------------------------------------------
%%% Internal functions
%%%-------------------------------------------------------------------
%% Locks are initially exclusive which means that it is possible
%% to both read _and_ write. After a downgrade, it is only possible
%% to read. But since, by then, the process already has a lock, it
%% can just go ahead and read.
lock(Type) ->
call({lock, Type, infinity}).
%% Upgrade from read to lock write
upgrade_lock() ->
call({upgrade_lock, self()}).
%% Downgrade from write to read lock
downgrade_lock() ->
cast({downgrade_lock, self()}).
unlock() ->
cast({unlock, self()}).
insert_all(Targets) ->
Fun = fun({NotifyName, Data}) -> insert(NotifyName, Data) end,
lists:foreach(Fun, Targets).
insert(NotifyName, {DestAddr, TargetName, TargetParams, NotifyType}) ->
Key = {NotifyName, TargetName},
Data = {DestAddr, TargetParams, NotifyType},
ets:insert(?CACHE, {Key, Data}).
delete_all() ->
ets:delete_all_objects(?CACHE).
%%----------------------------------------------------------
%% This function is called when we have active but no waiting
%% lockers. So, if we have it stored, it's an active locker.
handle_maybe_active_down(Cnt, Pid) ->
case ets:lookup(?LOCKER_TAB, Pid) of
[#locker{type = Type}] ->
ets:delete(?LOCKER_TAB, Pid),
{dec(Cnt), Type};
_ ->
{Cnt, read}
end.
handle_maybe_active_or_waiting_down(Pid,
#state{active_count = Cnt,
waiting = Waiting} = State) ->
case ets:lookup(?LOCKER_TAB, Pid) of
[#locker{state = active, type = read}] when (Cnt == 1) ->
%% 1) This means that the writer must be waiting
%% 2) The last reader terminated,
%% time to activate the wating writer
%% If this was the last one, then we must
%% activate the waiting writer.
ets:delete(?LOCKER_TAB, Pid),
case active_waiting_writer(Waiting) of
{true, StillWaiting} ->
%% active count is still 1, so no need to update that
State#state{writer = true,
waiting = StillWaiting};
{false, []} ->
State#state{active_count = 0,
writer = false,
waiting = []}
end;
[#locker{state = active, type = read}] ->
%% 1) This means that the writer must be waiting
%% 2) More then one (read-) locker active, just
%% clean up.
ets:delete(?LOCKER_TAB, Pid),
State#state{active_count = dec(Cnt)};
[#locker{state = active, type = write}] ->
ets:delete(?LOCKER_TAB, Pid),
{Active, StillWaiting, Writer} =
activate_waiting_readers_or_maybe_writer(Waiting),
State#state{active_count = Active,
writer = Writer,
waiting = StillWaiting};
[#locker{state = waiting, type = read}] ->
ets:delete(?LOCKER_TAB, Pid),
State#state{waiting = lists:delete(Pid, Waiting)};
[#locker{state = waiting, type = write}] ->
%% We need to check if this is the only waiting writer.
%% If it is we shall set the writer field to false
ets:delete(?LOCKER_TAB, Pid),
NewWaiting = lists:delete(Pid, Waiting),
Writer =
case ets:match_object(?LOCKER_TAB,
#locker{state = active,
type = write,
_ = '_'}) of
[] ->
is_writer(NewWaiting);
_ ->
true
end,
State#state{writer = Writer,
waiting = NewWaiting};
_Other ->
State
end.
is_writer([]) ->
false;
is_writer([Pid|Pids]) ->
case ets:lookup(?LOCKER_TAB, Pid) of
[#locker{type = write}] ->
true;
_Other ->
is_writer(Pids)
end.
%%----------------------------------------------------------
%% This is just a utility function to make sure we don't
%% end up in a lockout situation.
active_waiting_writer([]) ->
{false, []};
active_waiting_writer([H|T]) ->
case ets:lookup(?LOCKER_TAB, H) of
[#locker{from = From} = L] ->
ets:insert(?LOCKER_TAB, L#locker{state = active}),
gen_server:reply(From, ok),
{true, T};
[] ->
%% Oups
error_msg("Could not find locker record for ~p", [H]),
active_waiting_writer(T)
end.
%% Activate waiting read(ers)
activate_waiting_readers(Waiting) ->
activate_waiting_readers(Waiting, 1).
activate_waiting_readers([], Cnt) ->
{Cnt, []};
activate_waiting_readers([H|T] = Waiting, Cnt) ->
case ets:lookup(?LOCKER_TAB, H) of
[#locker{from = From, type = read} = L] ->
ets:insert(?LOCKER_TAB, L#locker{state = active}),
gen_server:reply(From, ok),
activate_waiting_readers(T, inc(Cnt));
%% Found a writer, time to stop starting readers
[#locker{type = write}] ->
{Cnt, Waiting};
[] ->
%% Oups
error_msg("Could not find locker record for ~p", [H]),
activate_waiting_readers(T, Cnt)
end.
activate_waiting_readers_or_maybe_writer(Waiting) ->
activate_waiting_readers_or_maybe_writer(Waiting, 0).
activate_waiting_readers_or_maybe_writer([], Cnt) ->
{Cnt, [], false};
activate_waiting_readers_or_maybe_writer([H|T] = Waiting, Cnt) ->
case ets:lookup(?LOCKER_TAB, H) of
[#locker{from = From, type = read} = L] ->
ets:insert(?LOCKER_TAB, L#locker{state = active}),
gen_server:reply(From, ok),
activate_waiting_readers_or_maybe_writer(T, inc(Cnt));
%% Only active writer only if it's the first
[#locker{from = From, type = write} = L] when (Cnt == 0) ->
ets:insert(?LOCKER_TAB, L#locker{state = active}),
gen_server:reply(From, ok),
{1, T, true};
%% Found a writer, time to stop starting readers
[#locker{type = write}] ->
{Cnt, Waiting, false};
[] ->
%% Oups
error_msg("Could not find locker record for ~p", [H]),
activate_waiting_readers_or_maybe_writer(T, Cnt)
end.
%%----------------------------------------------------------
%% Code change
%%----------------------------------------------------------
%% downgrade
%%
%% code_change({down, _Vsn}, S1, downgrade_to_pre_4_7) ->
%% #state{dets = D, ets = E, notify_clients = NC, backup = B} = S1,
%% stop_backup_server(B),
%% S2 = {state, D, E, NC},
%% {ok, S2};
%% upgrade
%%
%% code_change(_Vsn, S1, upgrade_from_pre_4_7) ->
%% {state, D, E, NC} = S1,
%% S2 = #state{dets = D, ets = E, notify_clients = NC},
%% {ok, S2};
code_change(_Vsn, State, _Extra) ->
{ok, State}.
%%------------------------------------------------------------------
inc(Cnt) ->
Cnt + 1.
dec(Cnt) when (Cnt =< 0) ->
0;
dec(Cnt) ->
Cnt - 1.
%%------------------------------------------------------------------
%% This functions retrieves option values from the Options list.
%%------------------------------------------------------------------
get_opt(Key, Opts, Def) ->
snmp_misc:get_option(Key, Opts, Def).
%%------------------------------------------------------------------
%% info_msg(F, A) ->
%% ?snmpa_info("Target cache server: " ++ F, A).
warning_msg(F, A) ->
?snmpa_warning("Target cache server: " ++ F, A).
error_msg(F, A) ->
?snmpa_error("Target cache server: " ++ F, A).
%% ---
%% user_err(F, A) ->
%% snmpa_error:user_err(F, A).
config_err(F, A) ->
snmpa_error:config_err(F, A).
%% error(Reason) ->
%% throw({error, Reason}).
%% ----------------------------------------------------------------
call(Req) ->
gen_server:call(?SERVER, Req, infinity).
cast(Msg) ->
gen_server:cast(?SERVER, Msg).
