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authorJohn Högberg <[email protected]>2017-11-03 11:49:27 +0100
committerJohn Högberg <[email protected]>2017-11-30 15:44:33 +0100
commitebbd26eeea4115c946d1254d94acd50f150b4455 (patch)
treeab2a8ba1023aa0684695dc36ff5567ae9e3f59c4 /lib/kernel/src/raw_file_io.erl
parent6cb62e44eba1db8d1917ebb0db84298e91582c4e (diff)
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Reimplement efile_drv as a dirty NIF
This improves the latency of file operations as dirty schedulers are a bit more eager to run jobs than async threads, and use a single global queue rather than per-thread queues, eliminating the risk of a job stalling behind a long-running job on the same thread while other async threads sit idle. There's no such thing as a free lunch though; the lowered latency comes at the cost of increased busy-waiting which may have an adverse effect on some applications. This behavior can be tweaked with the +sbwt flag, but unfortunately it affects all types of schedulers and not just dirty ones. We plan to add type-specific flags at a later stage. sendfile has been moved to inet_drv to lessen the effect of a nasty race; the cooperation between inet_drv and efile has never been airtight and the socket dying at the wrong time (Regardless of reason) could result in fd aliasing. Moving it to the inet driver makes it impossible to trigger this by closing the socket in the middle of a sendfile operation, while still allowing it to be aborted -- something that can't be done if it stays in the file driver. The race still occurs if the controlling process dies in the short window between dispatching the sendfile operation and the dup(2) call in the driver, but it's much less likely to happen now. A proper fix is in the works. -- Notable functional differences: * The use_threads option for file:sendfile/5 no longer has any effect. * The file-specific DTrace probes have been removed. The same effect can be achieved with normal tracing together with the nif__entry/nif__return probes to track scheduling. -- OTP-14256
Diffstat (limited to 'lib/kernel/src/raw_file_io.erl')
-rw-r--r--lib/kernel/src/raw_file_io.erl75
1 files changed, 75 insertions, 0 deletions
diff --git a/lib/kernel/src/raw_file_io.erl b/lib/kernel/src/raw_file_io.erl
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+++ b/lib/kernel/src/raw_file_io.erl
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+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2017. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%% http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%
+%% %CopyrightEnd%
+%%
+-module(raw_file_io).
+
+-export([open/2]).
+
+open(Filename, Modes) ->
+ %% Layers are applied in this order, and the listed modules will call this
+ %% function again as necessary. eg. a raw compressed delayed file in list
+ %% mode will walk through [_list -> _compressed -> _delayed -> _raw].
+ ModuleOrder = [{raw_file_io_list, fun match_list/1},
+ {raw_file_io_compressed, fun match_compressed/1},
+ {raw_file_io_delayed, fun match_delayed/1},
+ {raw_file_io_raw, fun match_raw/1}],
+ open_1(ModuleOrder, Filename, add_implicit_modes(Modes)).
+open_1([], _Filename, _Modes) ->
+ error(badarg);
+open_1([{Module, Match} | Rest], Filename, Modes) ->
+ case lists:any(Match, Modes) of
+ true ->
+ {Options, ChildModes} =
+ lists:partition(fun(Mode) -> Match(Mode) end, Modes),
+ Module:open_layer(Filename, ChildModes, Options);
+ false ->
+ open_1(Rest, Filename, Modes)
+ end.
+
+%% 'read' and 'list' mode are enabled unless disabled by another option, so
+%% we'll explicitly add them to avoid duplicating this logic in child layers.
+add_implicit_modes(Modes0) ->
+ Modes1 = add_unless_matched(Modes0, fun match_writable/1, read),
+ add_unless_matched(Modes1, fun match_binary/1, list).
+add_unless_matched(Modes, Match, Default) ->
+ case lists:any(Match, Modes) of
+ false -> [Default | Modes];
+ true -> Modes
+ end.
+
+match_list(list) -> true;
+match_list(_Other) -> false.
+
+match_compressed(compressed) -> true;
+match_compressed(_Other) -> false.
+
+match_delayed({delayed_write, _Size, _Timeout}) -> true;
+match_delayed(delayed_write) -> true;
+match_delayed(_Other) -> false.
+
+match_raw(raw) -> true;
+match_raw(_Other) -> false.
+
+match_writable(write) -> true;
+match_writable(append) -> true;
+match_writable(exclusive) -> true;
+match_writable(_Other) -> false.
+
+match_binary(binary) -> true;
+match_binary(_Other) -> false.