les: fix goroutine leak in execQueue (#14480)

execQueue used an atomic counter to track whether the queue had been
closed, but the checking the counter didn't happen because the queue was
blocked on its channel.

Fix it by using a condition variable instead of sync/atomic. I tried an
implementation based on channels first, but it was hard to make it
reliable.

quit now waits for the queue loop to exit.
This commit is contained in:
Felix Lange 2017-05-16 20:56:02 +02:00 committed by GitHub
parent ef7b9fb7d0
commit e20158176d
2 changed files with 118 additions and 30 deletions

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@ -16,56 +16,82 @@
package les package les
import ( import "sync"
"sync/atomic"
)
// ExecQueue implements a queue that executes function calls in a single thread, // execQueue implements a queue that executes function calls in a single thread,
// in the same order as they have been queued. // in the same order as they have been queued.
type execQueue struct { type execQueue struct {
chn chan func() mu sync.Mutex
cnt, stop, capacity int32 cond *sync.Cond
funcs []func()
closeWait chan struct{}
} }
// NewExecQueue creates a new execution queue. // newExecQueue creates a new execution queue.
func newExecQueue(capacity int32) *execQueue { func newExecQueue(capacity int) *execQueue {
q := &execQueue{ q := &execQueue{funcs: make([]func(), 0, capacity)}
chn: make(chan func(), capacity), q.cond = sync.NewCond(&q.mu)
capacity: capacity,
}
go q.loop() go q.loop()
return q return q
} }
func (q *execQueue) loop() { func (q *execQueue) loop() {
for f := range q.chn { for f := q.waitNext(false); f != nil; f = q.waitNext(true) {
atomic.AddInt32(&q.cnt, -1)
if atomic.LoadInt32(&q.stop) != 0 {
return
}
f() f()
} }
close(q.closeWait)
} }
// CanQueue returns true if more function calls can be added to the execution queue. 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 { func (q *execQueue) canQueue() bool {
return atomic.LoadInt32(&q.stop) == 0 && atomic.LoadInt32(&q.cnt) < q.capacity 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. // queue adds a function call to the execution queue. Returns true if successful.
func (q *execQueue) queue(f func()) bool { func (q *execQueue) queue(f func()) bool {
if atomic.LoadInt32(&q.stop) != 0 { q.mu.Lock()
return false ok := !q.isClosed() && len(q.funcs) < cap(q.funcs)
if ok {
q.funcs = append(q.funcs, f)
q.cond.Signal()
} }
if atomic.AddInt32(&q.cnt, 1) > q.capacity { q.mu.Unlock()
atomic.AddInt32(&q.cnt, -1) return ok
return false
}
q.chn <- f
return true
} }
// Stop stops the exec queue. // quit stops the exec queue.
// quit waits for the current execution to finish before returning.
func (q *execQueue) quit() { func (q *execQueue) quit() {
atomic.StoreInt32(&q.stop, 1) q.mu.Lock()
if !q.isClosed() {
q.closeWait = make(chan struct{})
q.cond.Signal()
}
q.mu.Unlock()
<-q.closeWait
} }

62
les/execqueue_test.go Normal file
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@ -0,0 +1,62 @@
// 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 (
"testing"
)
func TestExecQueue(t *testing.T) {
var (
N = 10000
q = newExecQueue(N)
counter int
execd = make(chan int)
testexit = make(chan struct{})
)
defer q.quit()
defer close(testexit)
check := func(state string, wantOK bool) {
c := counter
counter++
qf := func() {
select {
case execd <- c:
case <-testexit:
}
}
if q.canQueue() != wantOK {
t.Fatalf("canQueue() == %t for %s", !wantOK, state)
}
if q.queue(qf) != wantOK {
t.Fatalf("canQueue() == %t for %s", !wantOK, state)
}
}
for i := 0; i < N; i++ {
check("queue below cap", true)
}
check("full queue", false)
for i := 0; i < N; i++ {
if c := <-execd; c != i {
t.Fatal("execution out of order")
}
}
q.quit()
check("closed queue", false)
}