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sequential.go
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sequential.go
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package callbacks
import (
"sync"
"sync/atomic"
"unsafe"
)
const autoTrimThreshold = 10
type SequentialCallbackManager struct {
callbacksMutex sync.Mutex // this mutex only protects the `callbacks` pointer itself.
callbacks *[]callbackState
pendingRemovalCount uint64
reverse bool
}
type callbackState struct {
cb Callback
pendingRemoval uint32
}
func NewSequentialCallbackManager() *SequentialCallbackManager {
callbacks := make([]callbackState, 0)
return &SequentialCallbackManager{
reverse: false,
callbacks: &callbacks,
}
}
func (m *SequentialCallbackManager) pushCallback(cb Callback) {
callbacks := m.loadCallbacks()
if len(callbacks) == cap(callbacks) {
newCallbacks := make([]callbackState, len(callbacks), len(callbacks)*2+1)
for i := 0; i < len(callbacks); i++ {
oldCb := &callbacks[i]
newCallbacks[i].cb = oldCb.cb
newCallbacks[i].pendingRemoval = atomic.LoadUint32(&oldCb.pendingRemoval)
}
callbacks = newCallbacks
}
callbacks = append(callbacks, callbackState{
cb: cb,
})
m.storeCallbacks(callbacks)
}
func (m *SequentialCallbackManager) UnsafelySetReverse() *SequentialCallbackManager {
m.reverse = true
return m
}
func (m *SequentialCallbackManager) loadCallbacks() []callbackState {
return *(*[]callbackState)(atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&m.callbacks))))
}
func (m *SequentialCallbackManager) storeCallbacks(callbacks []callbackState) {
atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&m.callbacks)), unsafe.Pointer(&callbacks))
}
func (m *SequentialCallbackManager) Trim() {
atomic.StoreUint64(&m.pendingRemovalCount, 0)
m.callbacksMutex.Lock()
newCallbacks := make([]callbackState, 0)
oldCallbacks := m.loadCallbacks()
for i := 0; i < len(oldCallbacks); i++ {
cb := &oldCallbacks[i]
if atomic.LoadUint32(&cb.pendingRemoval) == 0 {
newCallbacks = append(newCallbacks, callbackState{
cb: cb.cb,
pendingRemoval: 0,
})
}
}
m.storeCallbacks(newCallbacks)
m.callbacksMutex.Unlock()
}
// RegisterCallback atomically registers all callbacks passed in.
func (m *SequentialCallbackManager) RegisterCallback(callbacks ...Callback) {
//log.Debug().Str("callbacks", fmt.Sprintf("%+v", callbacks)).Msg("Registering callbacks")
m.callbacksMutex.Lock()
for _, c := range callbacks {
m.pushCallback(c)
}
m.callbacksMutex.Unlock()
}
// RunCallbacks runs all callbacks on a variadic parameter list, and de-registers callbacks
// that throw an error.
func (m *SequentialCallbackManager) RunCallbacks(params ...interface{}) []error {
callbacks := m.loadCallbacks()
//log.Debug().Str("callbacks", fmt.Sprintf("%+v", callbacks)).Msg("Running callbacks")
if m.reverse {
for i := len(callbacks) - 1; i >= 0; i-- {
c := &callbacks[i]
if err := m.doRunCallback(c, params...); err != nil {
return []error{err}
}
}
} else {
for i := 0; i < len(callbacks); i++ {
c := &callbacks[i]
if err := m.doRunCallback(c, params...); err != nil {
return []error{err}
}
}
}
if atomic.LoadUint64(&m.pendingRemovalCount) >= autoTrimThreshold {
m.Trim()
}
return nil
}
func (m *SequentialCallbackManager) doRunCallback(c *callbackState, params ...interface{}) error {
if atomic.LoadUint32(&c.pendingRemoval) == 0 {
err := c.cb(params...)
if err != nil {
atomic.StoreUint32(&c.pendingRemoval, 1)
atomic.AddUint64(&m.pendingRemovalCount, 1)
if err != Deregister {
return err
}
}
}
return nil
}