mirror of
https://github.com/superseriousbusiness/gotosocial
synced 2024-12-23 19:23:12 +00:00
70 lines
2.3 KiB
Go
70 lines
2.3 KiB
Go
/*
|
|
GoToSocial
|
|
Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org
|
|
|
|
This program is free software: you can redistribute it and/or modify
|
|
it under the terms of the GNU Affero General Public License as published by
|
|
the Free Software Foundation, either version 3 of the License, or
|
|
(at your option) any later version.
|
|
|
|
This program is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
GNU Affero General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Affero General Public License
|
|
along with this program. If not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
package federatingdb
|
|
|
|
import (
|
|
"context"
|
|
"errors"
|
|
"net/url"
|
|
"sync"
|
|
)
|
|
|
|
// Lock takes a lock for the object at the specified id. If an error
|
|
// is returned, the lock must not have been taken.
|
|
//
|
|
// The lock must be able to succeed for an id that does not exist in
|
|
// the database. This means acquiring the lock does not guarantee the
|
|
// entry exists in the database.
|
|
//
|
|
// Locks are encouraged to be lightweight and in the Go layer, as some
|
|
// processes require tight loops acquiring and releasing locks.
|
|
//
|
|
// Used to ensure race conditions in multiple requests do not occur.
|
|
func (f *federatingDB) Lock(c context.Context, id *url.URL) error {
|
|
// Before any other Database methods are called, the relevant `id`
|
|
// entries are locked to allow for fine-grained concurrency.
|
|
|
|
// Strategy: create a new lock, if stored, continue. Otherwise, lock the
|
|
// existing mutex.
|
|
mu := &sync.Mutex{}
|
|
mu.Lock() // Optimistically lock if we do store it.
|
|
i, loaded := f.locks.LoadOrStore(id.String(), mu)
|
|
if loaded {
|
|
mu = i.(*sync.Mutex)
|
|
mu.Lock()
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// Unlock makes the lock for the object at the specified id available.
|
|
// If an error is returned, the lock must have still been freed.
|
|
//
|
|
// Used to ensure race conditions in multiple requests do not occur.
|
|
func (f *federatingDB) Unlock(c context.Context, id *url.URL) error {
|
|
// Once Go-Fed is done calling Database methods, the relevant `id`
|
|
// entries are unlocked.
|
|
|
|
i, ok := f.locks.Load(id.String())
|
|
if !ok {
|
|
return errors.New("missing an id in unlock")
|
|
}
|
|
mu := i.(*sync.Mutex)
|
|
mu.Unlock()
|
|
return nil
|
|
}
|