- 01
- 02
- 03
- 04
- 05
- 06
- 07
- 08
- 09
- 10
- 11
- 12
- 13
- 14
- 15
- 16
- 17
- 18
- 19
- 20
- 21
- 22
- 23
- 24
- 25
- 26
- 27
- 28
- 29
- 30
- 31
- 32
- 33
- 34
- 35
- 36
- 37
- 38
- 39
- 40
- 41
- 42
- 43
- 44
- 45
- 46
- 47
- 48
- 49
- 50
- 51
- 52
- 53
- 54
- 55
- 56
- 57
- 58
- 59
- 60
- 61
- 62
- 63
- 64
- 65
- 66
- 67
- 68
- 69
- 70
- 71
- 72
- 73
- 74
- 75
%% Note: set and unset are not thread-safe.
-spec set(key(), value()) -> ok.
set(Key, Value) ->
case ets:lookup(?status_tab, Key) of
[{_, {set, _OldValue}}] ->
ets:insert(?status_tab, {Key, {set, Value}});
[{_, {unset, Pid}}] ->
MRef = monitor(process, Pid),
Pid ! {set, Value},
receive
{'DOWN', MRef, _, _, _} -> ok
end;
[] ->
case ets:insert_new(?status_tab, {Key, {set, Value}}) of
true ->
ok;
false ->
set(Key, Value)
end
end,
ok.
-spec unset(key()) -> ok.
unset(Key) ->
case ets:lookup(?status_tab, Key) of
[{_, {set, _OldValue}}] -> ets:delete(?status_tab, Key);
_ -> ok
end,
ok.
-spec read(key()) -> value().
read(Key) ->
case read_or_wait(Key) of
{set, Value} ->
Value;
{wait, MRef} ->
receive
{'DOWN', MRef, _, _, {cvar_set, Value}} ->
Value;
{'DOWN', MRef, _, _, noproc} ->
read(Key)
end
end.
-spec read_or_wait(key()) -> {set, value()} | {wait, reference()}.
read_or_wait(Key) ->
case ets:lookup(?status_tab, Key) of
[] ->
{Pid, MRef} = spawn_monitor(?MODULE, waker_entrypoint, [Key, self()]),
receive
{Pid, proceed} ->
{wait, MRef};
{'DOWN', MRef, _, _, Reason} ->
cvar_retry = Reason,
read_or_wait(Key)
end;
[{_, {set, Val}}] ->
{set, Val};
[{_, {unset, Pid}}] ->
{wait, monitor(process, Pid)}
end.
-spec waker_entrypoint(key(), pid()) -> no_return().
waker_entrypoint(Key, Parent) ->
case ets_insert_new({Key, {unset, self()}}) of
false ->
exit(cvar_retry);
true ->
Parent ! {self(), proceed},
receive
{set, Value} ->
ets_insert({Key, {set, Value}}),
exit({cvar_set, Value})
end
end.
Follow us!