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…le creation Previous to this change, the OS pid was used to lock the bitcask database and prevent two bitcask instances performing write operations at the same time. However, if bitcask is not able to clean up the write locks because of a hard shutdown and another process takes that the pid in written to the lock file, bitcask is not able to take the lock even though it is the only running instance. This change uses the flock system call to obtain exclusive write access to the file across OS processes, as long as the other processes use flock to obtain the lock.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,9 +1,10 @@ | ||
| .eunit/* | ||
| deps/* | ||
| deps | ||
| ebin | ||
| priv/*.so | ||
| *.o | ||
| *.beam | ||
| *~ | ||
| .local_dialyzer_plt | ||
| log/ | ||
| erl_crash.dump |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,88 @@ | ||
| %% ------------------------------------------------------------------- | ||
| %% | ||
| %% Copyright (c) 2018 Workday, Inc. | ||
| %% | ||
| %% This file is provided to you 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. | ||
| %% | ||
| %% ------------------------------------------------------------------- | ||
| -module(bitcask_lockops_tests). | ||
|
|
||
| -include_lib("eunit/include/eunit.hrl"). | ||
|
|
||
| -export([bitcask_locker_vm_main/0]). | ||
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| lock_cannot_be_obtained_on_already_locked_file_within_same_os_process_test() -> | ||
| Dir = "/tmp", | ||
| Filename = bitcask_lockops:lock_filename(write,Dir), | ||
| ok = file_delete(Filename), | ||
| ok = file:write_file(Filename, ""), | ||
| {ok, _Lock} = bitcask_lockops:acquire(write, Dir), | ||
| ?assertEqual( | ||
| {error, locked}, | ||
| bitcask_lockops:acquire(write, Dir) | ||
| ). | ||
|
|
||
| lock_can_be_obtained_on_already_locked_file_is_unlocked_test() -> | ||
| Dir = "/tmp", | ||
| Filename = bitcask_lockops:lock_filename(write,Dir), | ||
| ok = file_delete(Filename), | ||
| ok = file:write_file(Filename, ""), | ||
| {ok, Lock} = bitcask_lockops:acquire(write, Dir), | ||
| bitcask_lockops:release(Lock), | ||
| ?assertMatch( | ||
| {ok, _}, | ||
| bitcask_lockops:acquire(write, Dir) | ||
| ). | ||
|
|
||
| lock_cannot_be_obtained_on_already_locked_file_across_os_process_test() -> | ||
| os:cmd("mkdir -p /tmp/lockbitcask"), | ||
| os:cmd("rm -rf /tmp/lockbitcask/*"), | ||
| %% start another erlang vm that will open the DB and obtain a write | ||
| %% lock, then, when we try to obtain a write lock on the current vm | ||
| %% it should fail. | ||
| Eval1 = | ||
| "erl -pa ebin -pa deps/*/ebin -noinput -noshell " | ||
| "-eval \"bitcask_lockops_tests:bitcask_locker_vm_main().\"", | ||
| spawn_link( | ||
| fun() -> | ||
| Output = os:cmd(Eval1), | ||
| ?debugFmt("\nCMD OUTPUT: ~s", [Output]) | ||
| end), | ||
| timer:sleep(1000), | ||
| DB = bitcask:open("/tmp/lockbitcask",[read_write]), | ||
| ?assertEqual( | ||
| {error,{error,locked}}, | ||
| bitcask:put(DB, <<"k">>, <<"v">>) | ||
| ). | ||
|
|
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| %% entry function for another vm to lock a bitcask DB | ||
| bitcask_locker_vm_main() -> | ||
| case (catch bitcask:open("/tmp/lockbitcask", [read_write,{open_timeout,1000}])) of | ||
| {error, Error} -> | ||
| io:format("ERROR: ~p", [Error]); | ||
| DB -> | ||
| %% DB is locked on the first write operation | ||
| ok = bitcask:put(DB, <<"k">>, <<"v">>), | ||
| io:format('~p',[os:getpid()]), | ||
| timer:sleep(3000), | ||
| erlang:halt() | ||
| end. | ||
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||
| file_delete(Filename) -> | ||
| case file:delete(Filename) of | ||
| ok -> ok; | ||
| {error,enoent} -> ok | ||
| end. | ||
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