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// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package les
import "sync"
// execQueue implements a queue that executes function calls in a single thread,
// in the same order as they have been queued.
type execQueue struct {
mu sync.Mutex
cond *sync.Cond
funcs []func()
closeWait chan struct{}
}
// newExecQueue creates a new execution queue.
func newExecQueue(capacity int) *execQueue {
q := &execQueue{funcs: make([]func(), 0, capacity)}
q.cond = sync.NewCond(&q.mu)
go q.loop()
return q
}
func (q *execQueue) loop() {
for f := q.waitNext(false); f != nil; f = q.waitNext(true) {
f()
}
close(q.closeWait)
}
func (q *execQueue) waitNext(drop bool) (f func()) {
q.mu.Lock()
if drop {
// Remove the function that just executed. We do this here instead of when
// dequeuing so len(q.funcs) includes the function that is running.
q.funcs = append(q.funcs[:0], q.funcs[1:]...)
}
for !q.isClosed() {
if len(q.funcs) > 0 {
f = q.funcs[0]
break
}
q.cond.Wait()
}
q.mu.Unlock()
return f
}
func (q *execQueue) isClosed() bool {
return q.closeWait != nil
}
// canQueue returns true if more function calls can be added to the execution queue.
func (q *execQueue) canQueue() bool {
q.mu.Lock()
ok := !q.isClosed() && len(q.funcs) < cap(q.funcs)
q.mu.Unlock()
return ok
}
// queue adds a function call to the execution queue. Returns true if successful.
func (q *execQueue) queue(f func()) bool {
q.mu.Lock()
ok := !q.isClosed() && len(q.funcs) < cap(q.funcs)
if ok {
q.funcs = append(q.funcs, f)
q.cond.Signal()
}
q.mu.Unlock()
return ok
}
// quit stops the exec queue.
// quit waits for the current execution to finish before returning.
func (q *execQueue) quit() {
q.mu.Lock()
if !q.isClosed() {
q.closeWait = make(chan struct{})
q.cond.Signal()
}
q.mu.Unlock()
<-q.closeWait
}
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