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60 lines
2.8 KiB
60 lines
2.8 KiB
// Copyright 2024 The Gitea Authors. All rights reserved.
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// SPDX-License-Identifier: MIT
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package globallock
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import (
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"context"
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"fmt"
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)
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type Locker interface {
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// Lock tries to acquire a lock for the given key, it blocks until the lock is acquired or the context is canceled.
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//
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// Lock returns a new context which should be used in the following code.
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// The new context will be canceled when the lock is released or lost - yes, it's possible to lose a lock.
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// For example, it lost the connection to the redis server while holding the lock.
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// If it fails to acquire the lock, the returned context will be the same as the input context.
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//
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// Lock returns a ReleaseFunc to release the lock, it cannot be nil.
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// It's always safe to call this function even if it fails to acquire the lock, and it will do nothing in that case.
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// And it's also safe to call it multiple times, but it will only release the lock once.
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// That's why it's called ReleaseFunc, not UnlockFunc.
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// But be aware that it's not safe to not call it at all; it could lead to a memory leak.
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// So a recommended pattern is to use defer to call it:
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// ctx, release, err := locker.Lock(ctx, "key")
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// if err != nil {
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// return err
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// }
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// defer release()
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// The ReleaseFunc will return the original context which was used to acquire the lock.
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// It's useful when you want to continue to do something after releasing the lock.
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// At that time, the ctx will be canceled, and you can use the returned context by the ReleaseFunc to continue:
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// ctx, release, err := locker.Lock(ctx, "key")
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// if err != nil {
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// return err
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// }
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// defer release()
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// doSomething(ctx)
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// ctx = release()
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// doSomethingElse(ctx)
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// Please ignore it and use `defer release()` instead if you don't need this, to avoid forgetting to release the lock.
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//
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// Lock returns an error if failed to acquire the lock.
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// Be aware that even the context is not canceled, it's still possible to fail to acquire the lock.
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// For example, redis is down, or it reached the maximum number of tries.
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Lock(ctx context.Context, key string) (context.Context, ReleaseFunc, error)
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// TryLock tries to acquire a lock for the given key, it returns immediately.
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// It follows the same pattern as Lock, but it doesn't block.
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// And if it fails to acquire the lock because it's already locked, not other reasons like redis is down,
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// it will return false without any error.
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TryLock(ctx context.Context, key string) (bool, context.Context, ReleaseFunc, error)
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}
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// ReleaseFunc is a function that releases a lock.
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// It returns the original context which was used to acquire the lock.
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type ReleaseFunc func() context.Context
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// ErrLockReleased is used as context cause when a lock is released
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var ErrLockReleased = fmt.Errorf("lock released")
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