juce/source/src/threads/juce_ReadWriteLock.h

   1 /*
   2   ==============================================================================
   3
   4    This file is part of the JUCE library - "Jules' Utility Class Extensions"
   5    Copyright 2004-11 by Raw Material Software Ltd.
   6
   7   ------------------------------------------------------------------------------
   8
   9    JUCE can be redistributed and/or modified under the terms of the GNU General
  10    Public License (Version 2), as published by the Free Software Foundation.
  11    A copy of the license is included in the JUCE distribution, or can be found
  12    online at www.gnu.org/licenses.
  13
  14    JUCE is distributed in the hope that it will be useful, but WITHOUT ANY
  15    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  16    A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
  17
  18   ------------------------------------------------------------------------------
  19
  20    To release a closed-source product which uses JUCE, commercial licenses are
  21    available: visit www.rawmaterialsoftware.com/juce for more information.
  22
  23   ==============================================================================
  24 */
  25
  26 #ifndef __JUCE_READWRITELOCK_JUCEHEADER__
  27 #define __JUCE_READWRITELOCK_JUCEHEADER__
  28
  29 #include "juce_CriticalSection.h"
  30 #include "juce_SpinLock.h"
  31 #include "juce_WaitableEvent.h"
  32 #include "juce_Thread.h"
  33 #include "../containers/juce_Array.h"
  34
  35
  36 //==============================================================================
  37 /**
  38     A critical section that allows multiple simultaneous readers.
  39
  40     Features of this type of lock are:
  41
  42     - Multiple readers can hold the lock at the same time, but only one writer
  43       can hold it at once.
  44     - Writers trying to gain the lock will be blocked until all readers and writers
  45       have released it
  46     - Readers trying to gain the lock while a writer is waiting to acquire it will be
  47       blocked until the writer has obtained and released it
  48     - If a thread already has a read lock and tries to obtain a write lock, it will succeed if
  49       there are no other readers
  50     - If a thread already has the write lock and tries to obtain a read lock, this will succeed.
  51     - Recursive locking is supported.
  52
  53     @see ScopedReadLock, ScopedWriteLock, CriticalSection
  54 */
  55 class JUCE_API  ReadWriteLock
  56 {
  57 public:
  58     //==============================================================================
  59     /**
  60         Creates a ReadWriteLock object.
  61     */
  62     ReadWriteLock() noexcept;
  63
  64     /** Destructor.
  65
  66         If the object is deleted whilst locked, any subsequent behaviour
  67         is unpredictable.
  68     */
  69     ~ReadWriteLock() noexcept;
  70
  71     //==============================================================================
  72     /** Locks this object for reading.
  73
  74         Multiple threads can simulaneously lock the object for reading, but if another
  75         thread has it locked for writing, then this will block until it releases the
  76         lock.
  77
  78         @see exitRead, ScopedReadLock
  79     */
  80     void enterRead() const noexcept;
  81
  82     /** Releases the read-lock.
  83
  84         If the caller thread hasn't got the lock, this can have unpredictable results.
  85
  86         If the enterRead() method has been called multiple times by the thread, each
  87         call must be matched by a call to exitRead() before other threads will be allowed
  88         to take over the lock.
  89
  90         @see enterRead, ScopedReadLock
  91     */
  92     void exitRead() const noexcept;
  93
  94     //==============================================================================
  95     /** Locks this object for writing.
  96
  97         This will block until any other threads that have it locked for reading or
  98         writing have released their lock.
  99
 100         @see exitWrite, ScopedWriteLock
 101     */
 102     void enterWrite() const noexcept;
 103
 104     /** Tries to lock this object for writing.
 105
 106         This is like enterWrite(), but doesn't block - it returns true if it manages
 107         to obtain the lock.
 108
 109         @see enterWrite
 110     */
 111     bool tryEnterWrite() const noexcept;
 112
 113     /** Releases the write-lock.
 114
 115         If the caller thread hasn't got the lock, this can have unpredictable results.
 116
 117         If the enterWrite() method has been called multiple times by the thread, each
 118         call must be matched by a call to exit() before other threads will be allowed
 119         to take over the lock.
 120
 121         @see enterWrite, ScopedWriteLock
 122     */
 123     void exitWrite() const noexcept;
 124
 125
 126 private:
 127     //==============================================================================
 128     SpinLock accessLock;
 129     WaitableEvent waitEvent;
 130     mutable int numWaitingWriters, numWriters;
 131     mutable Thread::ThreadID writerThreadId;
 132     mutable Array <Thread::ThreadID> readerThreads;
 133
 134     JUCE_DECLARE_NON_COPYABLE (ReadWriteLock);
 135 };
 136
 137
 138 #endif   // __JUCE_READWRITELOCK_JUCEHEADER__