| /** |
| * 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 |
| } |