forked from TrueCloudLab/distribution
111 lines
2.3 KiB
Go
111 lines
2.3 KiB
Go
package events
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import (
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"container/list"
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"sync"
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"github.com/sirupsen/logrus"
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)
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// Queue accepts all messages into a queue for asynchronous consumption
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// by a sink. It is unbounded and thread safe but the sink must be reliable or
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// events will be dropped.
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type Queue struct {
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dst Sink
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events *list.List
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cond *sync.Cond
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mu sync.Mutex
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closed bool
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}
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// NewQueue returns a queue to the provided Sink dst.
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func NewQueue(dst Sink) *Queue {
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eq := Queue{
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dst: dst,
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events: list.New(),
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}
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eq.cond = sync.NewCond(&eq.mu)
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go eq.run()
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return &eq
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}
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// Write accepts the events into the queue, only failing if the queue has
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// been closed.
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func (eq *Queue) Write(event Event) error {
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eq.mu.Lock()
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defer eq.mu.Unlock()
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if eq.closed {
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return ErrSinkClosed
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}
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eq.events.PushBack(event)
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eq.cond.Signal() // signal waiters
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return nil
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}
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// Close shutsdown the event queue, flushing
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func (eq *Queue) Close() error {
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eq.mu.Lock()
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defer eq.mu.Unlock()
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if eq.closed {
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return nil
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}
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// set closed flag
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eq.closed = true
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eq.cond.Signal() // signal flushes queue
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eq.cond.Wait() // wait for signal from last flush
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return eq.dst.Close()
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}
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// run is the main goroutine to flush events to the target sink.
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func (eq *Queue) run() {
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for {
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event := eq.next()
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if event == nil {
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return // nil block means event queue is closed.
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}
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if err := eq.dst.Write(event); err != nil {
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// TODO(aaronl): Dropping events could be bad depending
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// on the application. We should have a way of
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// communicating this condition. However, logging
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// at a log level above debug may not be appropriate.
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// Eventually, go-events should not use logrus at all,
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// and should bubble up conditions like this through
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// error values.
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logrus.WithFields(logrus.Fields{
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"event": event,
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"sink": eq.dst,
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}).WithError(err).Debug("eventqueue: dropped event")
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}
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}
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}
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// next encompasses the critical section of the run loop. When the queue is
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// empty, it will block on the condition. If new data arrives, it will wake
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// and return a block. When closed, a nil slice will be returned.
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func (eq *Queue) next() Event {
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eq.mu.Lock()
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defer eq.mu.Unlock()
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for eq.events.Len() < 1 {
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if eq.closed {
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eq.cond.Broadcast()
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return nil
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}
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eq.cond.Wait()
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}
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front := eq.events.Front()
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block := front.Value.(Event)
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eq.events.Remove(front)
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return block
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}
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