source/modules/juce_core/threads/juce_ScopedWriteLock.h

   1 /*
   2   ==============================================================================
   3
   4    This file is part of the JUCE library.
   5    Copyright (c) 2022 - Raw Material Software Limited
   6
   7    JUCE is an open source library subject to commercial or open-source
   8    licensing.
   9
  10    The code included in this file is provided under the terms of the ISC license
  11    http://www.isc.org/downloads/software-support-policy/isc-license. Permission
  12    To use, copy, modify, and/or distribute this software for any purpose with or
  13    without fee is hereby granted provided that the above copyright notice and
  14    this permission notice appear in all copies.
  15
  16    JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
  17    EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
  18    DISCLAIMED.
  19
  20   ==============================================================================
  21 */
  22
  23 namespace juce
  24 {
  25
  26 //==============================================================================
  27 /**
  28     Automatically locks and unlocks a ReadWriteLock object.
  29
  30     Use one of these as a local variable to control access to a ReadWriteLock.
  31
  32     e.g. @code
  33
  34     ReadWriteLock myLock;
  35
  36     for (;;)
  37     {
  38         const ScopedWriteLock myScopedLock (myLock);
  39         // myLock is now locked
  40
  41         ...do some stuff...
  42
  43         // myLock gets unlocked here.
  44     }
  45     @endcode
  46
  47     @see ReadWriteLock, ScopedReadLock
  48
  49     @tags{Core}
  50 */
  51 class JUCE_API  ScopedWriteLock
  52 {
  53 public:
  54     //==============================================================================
  55     /** Creates a ScopedWriteLock.
  56
  57         As soon as it is created, this will call ReadWriteLock::enterWrite(), and
  58         when the ScopedWriteLock object is deleted, the ReadWriteLock will
  59         be unlocked.
  60
  61         Make sure this object is created and deleted by the same thread,
  62         otherwise there are no guarantees what will happen! Best just to use it
  63         as a local stack object, rather than creating one with the new() operator.
  64     */
  65     inline explicit ScopedWriteLock (const ReadWriteLock& lock) noexcept : lock_ (lock) { lock.enterWrite(); }
  66
  67     /** Destructor.
  68
  69         The ReadWriteLock's exitWrite() method will be called when the destructor is called.
  70
  71         Make sure this object is created and deleted by the same thread,
  72         otherwise there are no guarantees what will happen!
  73     */
  74     inline ~ScopedWriteLock() noexcept                                   { lock_.exitWrite(); }
  75
  76
  77 private:
  78     //==============================================================================
  79     const ReadWriteLock& lock_;
  80
  81     JUCE_DECLARE_NON_COPYABLE (ScopedWriteLock)
  82 };
  83
  84 //==============================================================================
  85 /**
  86     Automatically locks and unlocks a ReadWriteLock object.
  87
  88     Use one of these as a local variable to control access to a ReadWriteLock.
  89
  90     e.g. @code
  91
  92     ReadWriteLock myLock;
  93
  94     for (;;)
  95     {
  96         const ScopedTryWriteLock myScopedTryLock (myLock);
  97
  98         // Unlike using a ScopedWriteLock, this may fail to actually get the lock, so you
  99         // should test this with the isLocked() method before doing your thread-unsafe
 100         // action.
 101
 102         if (myScopedTryLock.isLocked())
 103         {
 104             ...do some stuff...
 105         }
 106         else
 107         {
 108             ..our attempt at locking failed because some other thread has already locked the object..
 109         }
 110
 111         // myLock gets unlocked here (if it was locked).
 112     }
 113     @endcode
 114
 115     @see ReadWriteLock, ScopedTryWriteLock
 116
 117     @tags{Core}
 118 */
 119 class JUCE_API  ScopedTryWriteLock
 120 {
 121 public:
 122     //==============================================================================
 123     /** Creates a ScopedTryWriteLock and calls ReadWriteLock::tryEnterWrite() immediately.
 124         When the ScopedTryWriteLock object is destructed, the ReadWriteLock will be unlocked
 125         (if it was successfully acquired).
 126
 127         Make sure this object is created and destructed by the same thread, otherwise there are no
 128         guarantees what will happen! Best just to use it as a local stack object, rather than creating
 129         one with the new() operator.
 130     */
 131     ScopedTryWriteLock (ReadWriteLock& lockIn) noexcept
 132             : ScopedTryWriteLock (lockIn, true) {}
 133
 134     /** Creates a ScopedTryWriteLock.
 135
 136         If acquireLockOnInitialisation is true then as soon as it is created, this will call
 137         ReadWriteLock::tryEnterWrite(), and when the ScopedTryWriteLock object is destructed, the
 138         ReadWriteLock will be unlocked (if it was successfully acquired).
 139
 140         Make sure this object is created and destructed by the same thread, otherwise there are no
 141         guarantees what will happen! Best just to use it as a local stack object, rather than creating
 142         one with the new() operator.
 143     */
 144     ScopedTryWriteLock (ReadWriteLock& lockIn, bool acquireLockOnInitialisation) noexcept
 145         : lock (lockIn), lockWasSuccessful (acquireLockOnInitialisation && lock.tryEnterWrite()) {}
 146
 147     /** Destructor.
 148
 149         The ReadWriteLock's exitWrite() method will be called when the destructor is called.
 150
 151         Make sure this object is created and destructed by the same thread,
 152         otherwise there are no guarantees what will happen!
 153     */
 154     ~ScopedTryWriteLock() noexcept                  { if (lockWasSuccessful) lock.exitWrite(); }
 155
 156     /** Returns true if the mutex was successfully locked. */
 157     bool isLocked() const noexcept                  { return lockWasSuccessful; }
 158
 159     /** Retry gaining the lock by calling tryEnter on the underlying lock. */
 160     bool retryLock() noexcept                       { return lockWasSuccessful = lock.tryEnterWrite(); }
 161
 162 private:
 163     //==============================================================================
 164     ReadWriteLock& lock;
 165     bool lockWasSuccessful;
 166
 167     JUCE_DECLARE_NON_COPYABLE (ScopedTryWriteLock)
 168 };
 169
 170 }