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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 utils
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 && len(q.funcs) > 0 {
// 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
}
// Clear drops all queued functions.
func (q *ExecQueue) Clear() {
q.mu.Lock()
q.funcs = q.funcs[:0]
q.mu.Unlock()
}
// 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
}