105 lines
1.9 KiB
Go
105 lines
1.9 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package execqueue implements an ordered asynchronous queue for executing functions.
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package execqueue
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import (
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"context"
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"errors"
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"sync"
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)
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type ExecQueue struct {
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mu sync.Mutex
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closed bool
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inFlight bool // whether a goroutine is running q.run
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doneWaiter chan struct{} // non-nil if waiter is waiting, then closed
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queue []func()
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}
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func (q *ExecQueue) Add(f func()) {
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q.mu.Lock()
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defer q.mu.Unlock()
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if q.closed {
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return
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}
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if q.inFlight {
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q.queue = append(q.queue, f)
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} else {
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q.inFlight = true
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go q.run(f)
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}
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}
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// RunSync waits for the queue to be drained and then synchronously runs f.
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// It returns an error if the queue is closed before f is run or ctx expires.
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func (q *ExecQueue) RunSync(ctx context.Context, f func()) error {
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for {
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if err := q.Wait(ctx); err != nil {
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return err
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}
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q.mu.Lock()
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if q.inFlight {
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q.mu.Unlock()
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continue
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}
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defer q.mu.Unlock()
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if q.closed {
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return errors.New("closed")
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}
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f()
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return nil
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}
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}
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func (q *ExecQueue) run(f func()) {
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f()
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q.mu.Lock()
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for len(q.queue) > 0 && !q.closed {
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f := q.queue[0]
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q.queue[0] = nil
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q.queue = q.queue[1:]
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q.mu.Unlock()
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f()
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q.mu.Lock()
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}
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q.inFlight = false
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q.queue = nil
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if q.doneWaiter != nil {
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close(q.doneWaiter)
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q.doneWaiter = nil
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}
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q.mu.Unlock()
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}
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// Shutdown asynchronously signals the queue to stop.
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func (q *ExecQueue) Shutdown() {
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q.mu.Lock()
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defer q.mu.Unlock()
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q.closed = true
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}
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// Wait waits for the queue to be empty.
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func (q *ExecQueue) Wait(ctx context.Context) error {
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q.mu.Lock()
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waitCh := q.doneWaiter
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if q.inFlight && waitCh == nil {
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waitCh = make(chan struct{})
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q.doneWaiter = waitCh
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}
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q.mu.Unlock()
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if waitCh == nil {
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return nil
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}
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select {
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case <-waitCh:
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return nil
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case <-ctx.Done():
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return ctx.Err()
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}
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}
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