forked from cerc-io/ipld-eth-server
73 lines
1.3 KiB
Go
73 lines
1.3 KiB
Go
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package repo
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import (
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"sync"
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)
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// OnlyOne tracks open Repos by arbitrary key and returns the already
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// open one.
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type OnlyOne struct {
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mu sync.Mutex
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active map[interface{}]*ref
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}
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// Open a Repo identified by key. If Repo is not already open, the
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// open function is called, and the result is remember for further
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// use.
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//
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// Key must be comparable, or Open will panic. Make sure to pick keys
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// that are unique across different concrete Repo implementations,
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// e.g. by creating a local type:
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//
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// type repoKey string
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// r, err := o.Open(repoKey(path), open)
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//
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// Call Repo.Close when done.
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func (o *OnlyOne) Open(key interface{}, open func() (Repo, error)) (Repo, error) {
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o.mu.Lock()
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defer o.mu.Unlock()
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if o.active == nil {
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o.active = make(map[interface{}]*ref)
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}
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item, found := o.active[key]
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if !found {
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repo, err := open()
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if err != nil {
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return nil, err
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}
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item = &ref{
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parent: o,
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key: key,
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Repo: repo,
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}
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o.active[key] = item
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}
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item.refs++
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return item, nil
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}
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type ref struct {
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parent *OnlyOne
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key interface{}
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refs uint32
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Repo
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}
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var _ Repo = (*ref)(nil)
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func (r *ref) Close() error {
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r.parent.mu.Lock()
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defer r.parent.mu.Unlock()
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r.refs--
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if r.refs > 0 {
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// others are holding it open
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return nil
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}
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// last one
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delete(r.parent.active, r.key)
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return r.Repo.Close()
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}
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