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65 lines
1.9 KiB
Go
65 lines
1.9 KiB
Go
package callbacks
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import (
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"sync"
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)
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// The logic of this file is largely adapted from:
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// https://github.com/golang/go/wiki/cgo#function-variables
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//
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// Also helpful:
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// https://eli.thegreenplace.net/2019/passing-callbacks-and-pointers-to-cgo/
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// Callbacks provides a tracker for data that is to be passed between Go
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// and C callback functions. The Go callback/object may not be passed
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// by a pointer to C code and so instead integer indexes into an internal
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// map are used.
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// Typically the item being added will either be a callback function or
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// a data structure containing a callback function. It is up to the caller
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// to control and validate what "callbacks" get used.
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type Callbacks struct {
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mutex sync.RWMutex
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cmap map[uintptr]interface{}
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}
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// New returns a new callbacks tracker.
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func New() *Callbacks {
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return &Callbacks{cmap: make(map[uintptr]interface{})}
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}
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// Add a callback/object to the tracker and return a new index
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// for the object.
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func (cb *Callbacks) Add(v interface{}) uintptr {
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cb.mutex.Lock()
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defer cb.mutex.Unlock()
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// this approach assumes that there are typically very few callbacks
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// in play at once and can just use the length of the map as our
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// index. But in case of collisions we fall back to simply incrementing
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// until we find a free key like in the cgo wiki page.
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// If this code ever becomes a hot path there's surely plenty of room
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// for optimization in the future :-)
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index := uintptr(len(cb.cmap) + 1)
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for {
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if _, found := cb.cmap[index]; !found {
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break
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}
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index++
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}
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cb.cmap[index] = v
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return index
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}
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// Remove a callback/object given it's index.
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func (cb *Callbacks) Remove(index uintptr) {
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cb.mutex.Lock()
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defer cb.mutex.Unlock()
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delete(cb.cmap, index)
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}
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// Lookup returns a mapped callback/object given an index.
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func (cb *Callbacks) Lookup(index uintptr) interface{} {
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cb.mutex.RLock()
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defer cb.mutex.RUnlock()
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return cb.cmap[index]
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}
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