88 lines
2.1 KiB
Go
88 lines
2.1 KiB
Go
package tasklifecycle
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const (
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gateClosed = false
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gateOpened = true
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)
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// Gate is used by the Coordinator to block or allow tasks from running.
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//
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// It provides a channel that taskRunners listens on to determine when they are
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// allowed to run. The Gate has an infinite loop that is either feeding this
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// channel (therefore allowing listeners to proceed) or not doing anything
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// (causing listeners to block an wait).
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//
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// The Coordinator uses the Gate Open() and Close() methods to control this
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// producer loop.
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type Gate struct {
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sendCh chan struct{}
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updateCh chan bool
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shutdownCh <-chan struct{}
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}
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// NewGate returns a new Gate that is initially closed. The Gate should not be
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// used after the shutdownCh is closed.
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func NewGate(shutdownCh <-chan struct{}) *Gate {
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g := &Gate{
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sendCh: make(chan struct{}),
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updateCh: make(chan bool),
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shutdownCh: shutdownCh,
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}
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go g.run(gateClosed)
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return g
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}
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// WaitCh returns a channel that the listener must block on before starting its
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// task.
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//
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// Callers must also check the state of the shutdownCh used to create the Gate
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// to avoid blocking indefinitely.
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func (g *Gate) WaitCh() <-chan struct{} {
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return g.sendCh
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}
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// Open is used to allow listeners to proceed.
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// If the gate shutdownCh channel is closed, this method is a no-op so callers
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// should check its state.
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func (g *Gate) Open() {
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select {
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case <-g.shutdownCh:
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case g.updateCh <- gateOpened:
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}
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}
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// Close is used to block listeners from proceeding.
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// if the gate shutdownch channel is closed, this method is a no-op so callers
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// should check its state.
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func (g *Gate) Close() {
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select {
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case <-g.shutdownCh:
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case g.updateCh <- gateClosed:
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}
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}
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// run starts the infinite loop that feeds the channel if the Gate is opened.
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func (g *Gate) run(initState bool) {
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isOpen := initState
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for {
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if isOpen {
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select {
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// Feed channel if the gate is open.
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case g.sendCh <- struct{}{}:
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case <-g.shutdownCh:
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return
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case isOpen = <-g.updateCh:
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continue
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}
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} else {
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select {
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case <-g.shutdownCh:
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return
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case isOpen = <-g.updateCh:
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continue
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}
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}
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}
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}
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