github.com/dubbogo/gost@v1.14.0/container/gxsync/semaphore.go (about)

     1  /*
     2  Copyright 2019 The Vitess Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  /*
    18   * Licensed to the Apache Software Foundation (ASF) under one or more
    19   * contributor license agreements.  See the NOTICE file distributed with
    20   * this work for additional information regarding copyright ownership.
    21   * The ASF licenses this file to You under the Apache License, Version 2.0
    22   * (the "License"); you may not use this file except in compliance with
    23   * the License.  You may obtain a copy of the License at
    24   *
    25   *     http://www.apache.org/licenses/LICENSE-2.0
    26   *
    27   * Unless required by applicable law or agreed to in writing, software
    28   * distributed under the License is distributed on an "AS IS" BASIS,
    29   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    30   * See the License for the specific language governing permissions and
    31   * limitations under the License.
    32   */
    33  
    34  package gxsync
    35  
    36  // What's in a name? Channels have all you need to emulate a counting
    37  // semaphore with a boatload of extra functionality. However, in some
    38  // cases, you just want a familiar API.
    39  
    40  import (
    41  	"time"
    42  )
    43  
    44  // Semaphore is a counting semaphore with the option to
    45  // specify a timeout.
    46  type Semaphore struct {
    47  	slots   chan struct{}
    48  	timeout time.Duration
    49  }
    50  
    51  // NewSemaphore creates a Semaphore. The count parameter must be a positive
    52  // number. A timeout of zero means that there is no timeout.
    53  func NewSemaphore(count int, timeout time.Duration) *Semaphore {
    54  	sem := &Semaphore{
    55  		slots:   make(chan struct{}, count),
    56  		timeout: timeout,
    57  	}
    58  	for i := 0; i < count; i++ {
    59  		sem.slots <- struct{}{}
    60  	}
    61  	return sem
    62  }
    63  
    64  // Acquire returns true on successful acquisition, and
    65  // false on a timeout.
    66  func (sem *Semaphore) Acquire() bool {
    67  	if sem.timeout == 0 {
    68  		<-sem.slots
    69  		return true
    70  	}
    71  	tm := time.NewTimer(sem.timeout)
    72  	defer tm.Stop()
    73  	select {
    74  	case <-sem.slots:
    75  		return true
    76  	case <-tm.C:
    77  		return false
    78  	}
    79  }
    80  
    81  // TryAcquire acquires a semaphore if it's immediately available.
    82  // It returns false otherwise.
    83  func (sem *Semaphore) TryAcquire() bool {
    84  	select {
    85  	case <-sem.slots:
    86  		return true
    87  	default:
    88  		return false
    89  	}
    90  }
    91  
    92  // Release releases the acquired semaphore. You must
    93  // not release more than the number of semaphores you've
    94  // acquired.
    95  func (sem *Semaphore) Release() {
    96  	sem.slots <- struct{}{}
    97  }
    98  
    99  // Size returns the current number of available slots.
   100  func (sem *Semaphore) Size() int {
   101  	return len(sem.slots)
   102  }