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/*
==============================================================================
This file is part of the JUCE framework.
Copyright (c) Raw Material Software Limited
JUCE is an open source framework subject to commercial or open source
licensing.
By downloading, installing, or using the JUCE framework, or combining the
JUCE framework with any other source code, object code, content or any other
copyrightable work, you agree to the terms of the JUCE End User Licence
Agreement, and all incorporated terms including the JUCE Privacy Policy and
the JUCE Website Terms of Service, as applicable, which will bind you. If you
do not agree to the terms of these agreements, we will not license the JUCE
framework to you, and you must discontinue the installation or download
process and cease use of the JUCE framework.
JUCE End User Licence Agreement: https://juce.com/legal/juce-8-licence/
JUCE Privacy Policy: https://juce.com/juce-privacy-policy
JUCE Website Terms of Service: https://juce.com/juce-website-terms-of-service/
Or:
You may also use this code under the terms of the AGPLv3:
https://www.gnu.org/licenses/agpl-3.0.en.html
THE JUCE FRAMEWORK IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL
WARRANTIES, WHETHER EXPRESSED OR IMPLIED, INCLUDING WARRANTY OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE DISCLAIMED.
==============================================================================
*/
namespace juce
{
//==============================================================================
/**
A critical section that allows multiple simultaneous readers.
Features of this type of lock are:
- Multiple readers can hold the lock at the same time, but only one writer
can hold it at once.
- Writers trying to gain the lock will be blocked until all readers and writers
have released it
- Readers trying to gain the lock while a writer is waiting to acquire it will be
blocked until the writer has obtained and released it
- If a thread already has a read lock and tries to obtain a write lock, it will succeed if
there are no other readers
- If a thread already has the write lock and tries to obtain a read lock, this will succeed.
- Recursive locking is supported.
@see ScopedReadLock, ScopedWriteLock, CriticalSection
@tags{Core}
*/
class JUCE_API ReadWriteLock
{
public:
//==============================================================================
/**
Creates a ReadWriteLock object.
*/
ReadWriteLock() noexcept;
/** Destructor.
If the object is deleted whilst locked, any subsequent behaviour is undefined.
*/
~ReadWriteLock() noexcept;
//==============================================================================
/** Locks this object for reading.
Multiple threads can simultaneously lock the object for reading, but if another
thread has it locked for writing, then this will block until it releases the lock.
@see exitRead, ScopedReadLock
*/
void enterRead() const noexcept;
/** Tries to lock this object for reading.
Multiple threads can simultaneously lock the object for reading, but if another
thread has it locked for writing, then this will fail and return false.
@returns true if the lock is successfully gained.
@see exitRead, ScopedTryReadLock
*/
bool tryEnterRead() const noexcept;
/** Releases the read-lock.
If the caller thread hasn't got the lock, this can have unpredictable results.
If the enterRead() method has been called multiple times by the thread, each
call must be matched by a call to exitRead() before other threads will be allowed
to take over the lock.
@see enterRead, ScopedReadLock
*/
void exitRead() const noexcept;
//==============================================================================
/** Locks this object for writing.
This will block until any other threads that have it locked for reading or
writing have released their lock.
@see exitWrite, ScopedWriteLock
*/
void enterWrite() const noexcept;
/** Tries to lock this object for writing.
This is like enterWrite(), but doesn't block - it returns true if it manages
to obtain the lock.
@returns true if the lock is successfully gained.
@see enterWrite, ScopedTryWriteLock
*/
bool tryEnterWrite() const noexcept;
/** Releases the write-lock.
If the caller thread hasn't got the lock, this can have unpredictable results.
If the enterWrite() method has been called multiple times by the thread, each
call must be matched by a call to exit() before other threads will be allowed
to take over the lock.
@see enterWrite, ScopedWriteLock
*/
void exitWrite() const noexcept;
private:
//==============================================================================
SpinLock accessLock;
WaitableEvent readWaitEvent, writeWaitEvent;
mutable int numWaitingWriters = 0, numWriters = 0;
mutable Thread::ThreadID writerThreadId = {};
struct ThreadRecursionCount
{
Thread::ThreadID threadID;
int count;
};
mutable Array <ThreadRecursionCount> readerThreads;
bool tryEnterWriteInternal (Thread::ThreadID) const noexcept;
JUCE_DECLARE_NON_COPYABLE (ReadWriteLock)
};
} // namespace juce
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