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89 lines
4.0 KiB
89 lines
4.0 KiB
#-- encoding: UTF-8
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#-- copyright
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# OpenProject is an open source project management software.
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# Copyright (C) 2012-2020 the OpenProject GmbH
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#
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# This program is free software; you can redistribute it and/or
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# modify it under the terms of the GNU General Public License version 3.
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#
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# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
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# Copyright (C) 2006-2017 Jean-Philippe Lang
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# Copyright (C) 2010-2013 the ChiliProject Team
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#
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# This program is free software; you can redistribute it and/or
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# modify it under the terms of the GNU General Public License
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# as published by the Free Software Foundation; either version 2
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# of the License, or (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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#
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# See docs/COPYRIGHT.rdoc for more details.
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#++
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module OpenProject
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module Mutex
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module_function
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# Adds a mutex on database level via advisory locks:
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# https://www.postgresql.org/docs/12/explicit-locking.html
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# employing the with_advisory_lock gem.
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# This leads to requests received in parallel by two different workers, which might be in different OS processes
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# on different hosts, to be executed sequentially.
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# The locks are, from an abstract perspective, on row level as the entry's id is taken to create the lock.
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# Other entries of the same class can still be created/updated.
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# Relying on explicit row level locking (e.g. ROW EXCLUSIVE FOR UPDATE) would not work, I believe, as it would still
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# allow reading. Allowing reading is desirable in some cases, e.g. when fetching for the work package list, but would not
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# prevent the creation of journals. The journals transaction could not be committed, but the faulty view of the entries
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# current state could be committed anyway afterwards. See below for details.
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#
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# We in particular have to wait until the transaction is complete.
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# Otherwise the following is e.g. possible:
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# Action 1 writes an attachment and releases the lock.
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# Action 2, running in parallel, writes an attachment and releases the lock.
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# Action 3 updates something, some time later.
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# Both have not yet committed their transaction so, given that we have the "READ COMMITTED" transaction level,
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# the two actions cannot yet see the attachment added by the respective other action.
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# Both actions now proceed to write their journals, which will create attachable journals based on the attachments
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# at that time. But given that both do not see the attachment added by the other action yet, they only add
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# attachable journals for the attachment added by themselves. To the user this will look as if one of the actions
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# deleted the other attachment. The next action, Action 3, will then seem to have readded the attachment,
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# seemingly removed before.
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def with_advisory_lock_transaction(entry, &block)
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ActiveRecord::Base.transaction do
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with_advisory_lock(entry, &block)
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end
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end
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def with_advisory_lock(entry)
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lock_name = "mutex_on_#{entry.class.name}_#{entry.id}"
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debug_log("Attempting to fetched advisory lock", lock_name)
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result = entry.class.with_advisory_lock(lock_name, transaction: true) do
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debug_log("Fetched advisory lock", lock_name)
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yield
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end
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debug_log("Released advisory lock", lock_name)
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result
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end
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def debug_log(action, lock_name)
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message = <<~MESSAGE
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#{action}:
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* lockname: #{lock_name}
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* thread: #{Thread.current.object_id}
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* held locks: #{WithAdvisoryLock::Base.lock_stack.map(&:name).join(', ')}
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MESSAGE
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Rails.logger.debug { message }
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end
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end
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end
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