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/* Copyright 2023 The Matrix.org Foundation C.I.C |
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* |
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* Licensed under the Apache License, Version 2.0 (the "License"); |
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* you may not use this file except in compliance with the License. |
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* You may obtain a copy of the License at |
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* |
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* http://www.apache.org/licenses/LICENSE-2.0 |
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* |
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* Unless required by applicable law or agreed to in writing, software |
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* distributed under the License is distributed on an "AS IS" BASIS, |
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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* See the License for the specific language governing permissions and |
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* limitations under the License. |
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*/ |
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-- Remove a previous attempt to avoid deadlocks |
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DROP TRIGGER IF EXISTS delete_read_write_lock_parent_before_trigger ON worker_read_write_locks; |
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DROP FUNCTION IF EXISTS delete_read_write_lock_parent_before; |
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-- Ensure that we keep `worker_read_write_locks_mode` up to date whenever a lock |
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-- is released (i.e. a row deleted from `worker_read_write_locks`). Either we |
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-- update the `worker_read_write_locks_mode.token` to match another instance |
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-- that has currently acquired the lock, or we delete the row if nobody has |
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-- currently acquired a lock. |
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CREATE OR REPLACE FUNCTION delete_read_write_lock_parent() RETURNS trigger AS $$ |
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DECLARE |
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new_token TEXT; |
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mode_row_token TEXT; |
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BEGIN |
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-- Only update the token in `_mode` if its our token. This prevents |
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-- deadlocks. |
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-- |
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-- We shove the token into `mode_row_token`, as otherwise postgres complains |
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-- we're not using the returned data. |
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SELECT token INTO mode_row_token FROM worker_read_write_locks_mode |
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WHERE |
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lock_name = OLD.lock_name |
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AND lock_key = OLD.lock_key |
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AND token = OLD.token |
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FOR UPDATE; |
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IF NOT FOUND THEN |
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RETURN NEW; |
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END IF; |
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SELECT token INTO new_token FROM worker_read_write_locks |
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WHERE |
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lock_name = OLD.lock_name |
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AND lock_key = OLD.lock_key |
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LIMIT 1 FOR UPDATE SKIP LOCKED; |
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IF NOT FOUND THEN |
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DELETE FROM worker_read_write_locks_mode |
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WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key AND token = OLD.token; |
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ELSE |
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UPDATE worker_read_write_locks_mode |
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SET token = new_token |
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WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key; |
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END IF; |
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RETURN NEW; |
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END |
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$$ |
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LANGUAGE plpgsql; |
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DROP TRIGGER IF EXISTS delete_read_write_lock_parent_trigger ON worker_read_write_locks; |
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CREATE TRIGGER delete_read_write_lock_parent_trigger AFTER DELETE ON worker_read_write_locks |
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FOR EACH ROW |
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EXECUTE PROCEDURE delete_read_write_lock_parent(); |