71 lines
2.3 KiB
Go
71 lines
2.3 KiB
Go
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/*
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GoToSocial
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Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU Affero General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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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 Affero General Public License for more details.
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You should have received a copy of the GNU Affero General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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package federatingdb
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import (
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"context"
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"errors"
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"net/url"
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"sync"
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)
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// Lock takes a lock for the object at the specified id. If an error
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// is returned, the lock must not have been taken.
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//
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// The lock must be able to succeed for an id that does not exist in
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// the database. This means acquiring the lock does not guarantee the
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// entry exists in the database.
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//
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// Locks are encouraged to be lightweight and in the Go layer, as some
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// processes require tight loops acquiring and releasing locks.
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//
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// Used to ensure race conditions in multiple requests do not occur.
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func (f *federatingDB) Lock(c context.Context, id *url.URL) error {
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// Before any other Database methods are called, the relevant `id`
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// entries are locked to allow for fine-grained concurrency.
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// Strategy: create a new lock, if stored, continue. Otherwise, lock the
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// existing mutex.
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mu := &sync.Mutex{}
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mu.Lock() // Optimistically lock if we do store it.
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i, loaded := f.locks.LoadOrStore(id.String(), mu)
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if loaded {
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mu = i.(*sync.Mutex)
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mu.Lock()
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}
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return nil
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}
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// Unlock makes the lock for the object at the specified id available.
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// If an error is returned, the lock must have still been freed.
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//
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// Used to ensure race conditions in multiple requests do not occur.
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func (f *federatingDB) Unlock(c context.Context, id *url.URL) error {
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// Once Go-Fed is done calling Database methods, the relevant `id`
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// entries are unlocked.
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i, ok := f.locks.Load(id.String())
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if !ok {
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return errors.New("missing an id in unlock")
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}
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mu := i.(*sync.Mutex)
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mu.Unlock()
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return nil
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}
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