forked from apache/mynewt-newtmgr
/
sres.go
137 lines (110 loc) · 2.73 KB
/
sres.go
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/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package nmxutil
import (
"sync"
)
type SRWaiter struct {
c chan error
token interface{}
}
type SingleResource struct {
acquired bool
waitQueue []SRWaiter
mtx sync.Mutex
}
func NewSingleResource() SingleResource {
return SingleResource{}
}
// Appends an entry to the wait queue and returns a channel for the caller to
// block on. The caller must either read from the channel or call
// StopWaiting().
func (s *SingleResource) Acquire(token interface{}) <-chan error {
s.mtx.Lock()
if !s.acquired {
s.acquired = true
s.mtx.Unlock()
// Indicate immediate acquisition.
ch := make(chan error)
close(ch)
return ch
}
// XXX: Verify no duplicates.
w := SRWaiter{
c: make(chan error),
token: token,
}
s.waitQueue = append(s.waitQueue, w)
s.mtx.Unlock()
return w.c
}
// @return true if a pending waiter acquired the resource;
// false if the resource is now free.
func (s *SingleResource) Release() bool {
initiate := func() *SRWaiter {
s.mtx.Lock()
defer s.mtx.Unlock()
if !s.acquired {
panic("SingleResource release without acquire")
return nil
}
if len(s.waitQueue) == 0 {
s.acquired = false
return nil
}
w := s.waitQueue[0]
s.waitQueue = s.waitQueue[1:]
return &w
}
w := initiate()
if w == nil {
return false
}
w.c <- nil
return true
}
func (s *SingleResource) StopWaiting(token interface{}, err error) {
getw := func() *SRWaiter {
s.mtx.Lock()
defer s.mtx.Unlock()
for i, w := range s.waitQueue {
if w.token == token {
s.waitQueue = append(s.waitQueue[:i], s.waitQueue[i+1:]...)
return &w
}
}
return nil
}
if w := getw(); w != nil {
w.c <- err
}
}
func (s *SingleResource) Abort(err error) {
s.mtx.Lock()
defer s.mtx.Unlock()
for _, w := range s.waitQueue {
w.c <- err
}
s.waitQueue = nil
}
func (s *SingleResource) Acquired() bool {
s.mtx.Lock()
defer s.mtx.Unlock()
return s.acquired
}