github.com/unigraph-dev/dgraph@v1.1.1-0.20200923154953-8b52b426f765/x/lock.go (about)

     1  /*
     2   * Copyright 2016-2018 Dgraph Labs, Inc. and Contributors
     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  package x
    18  
    19  import (
    20  	"sync"
    21  	"sync/atomic"
    22  )
    23  
    24  // SafeMutex can be used in place of sync.RWMutex. It allows code to assert
    25  // whether the mutex is locked.
    26  type SafeMutex struct {
    27  	m sync.RWMutex
    28  	// m deadlock.RWMutex // Useful during debugging and testing for detecting locking issues.
    29  	writer  int32
    30  	readers int32
    31  }
    32  
    33  // AlreadyLocked returns true if safe mutex is already being held.
    34  func (s *SafeMutex) AlreadyLocked() bool {
    35  	return atomic.LoadInt32(&s.writer) > 0
    36  }
    37  
    38  // Lock locks the safe mutex.
    39  func (s *SafeMutex) Lock() {
    40  	s.m.Lock()
    41  	AssertTrue(atomic.AddInt32(&s.writer, 1) == 1)
    42  }
    43  
    44  // Unlock unlocks the safe mutex.
    45  func (s *SafeMutex) Unlock() {
    46  	AssertTrue(atomic.AddInt32(&s.writer, -1) == 0)
    47  	s.m.Unlock()
    48  }
    49  
    50  // AssertLock asserts whether the lock is being held.
    51  func (s *SafeMutex) AssertLock() {
    52  	AssertTrue(s.AlreadyLocked())
    53  }
    54  
    55  // RLock holds the reader lock.
    56  func (s *SafeMutex) RLock() {
    57  	s.m.RLock()
    58  	atomic.AddInt32(&s.readers, 1)
    59  }
    60  
    61  // RUnlock releases the reader lock.
    62  func (s *SafeMutex) RUnlock() {
    63  	atomic.AddInt32(&s.readers, -1)
    64  	s.m.RUnlock()
    65  }
    66  
    67  // AssertRLock asserts whether the reader lock is being held.
    68  func (s *SafeMutex) AssertRLock() {
    69  	AssertTrue(atomic.LoadInt32(&s.readers) > 0 ||
    70  		atomic.LoadInt32(&s.writer) == 1)
    71  }