Ilia Denisov
44 lines
1.3 KiB
Go
44 lines
1.3 KiB
Go
package push
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import (
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pushv1 "galaxy/backend/proto/push/v1"
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)
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// subscription is the per-gateway-instance delivery queue. Each
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// subscription owns a buffered channel; the publisher writes into it
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// without blocking by dropping the oldest queued event when the buffer
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// is full. The done channel is closed by the Service when the
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// subscription is replaced (a new connection arrived for the same
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// gateway_client_id) or when the Service is shutting down.
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type subscription struct {
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clientID string
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ch chan *pushv1.PushEvent
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done chan struct{}
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dropped uint64
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}
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// deliver enqueues ev into the subscription's buffer. When the buffer
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// is full, the oldest queued event is dropped to make room and the
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// dropped counter increments. The bool reports whether a drop occurred,
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// so the publisher can update its drop metric.
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//
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// The Service holds its mutex while calling deliver, which means at
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// most one publisher writes to ch at a time. The reader goroutine runs
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// independently and only consumes from ch, so the second send below is
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// guaranteed not to block: after evicting the head, the channel has at
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// least one free slot which no other publisher can fill.
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func (s *subscription) deliver(ev *pushv1.PushEvent) bool {
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select {
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case s.ch <- ev:
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return false
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default:
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}
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select {
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case <-s.ch:
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default:
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}
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s.ch <- ev
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s.dropped++
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return true
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}
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