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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
/* ----------------------------------------------------------------------------
---------------------------------------------------------------------------- */
#ifndef __UTSEM_H__
#define __UTSEM_H__
// -------------------------------------------------------------
// INCLUDES
// -------------------------------------------------------------
#include "utilcode.h"
/* ----------------------------------------------------------------------------
@class UTSemReadWrite
An instance of class UTSemReadWrite provides multi-read XOR single-write
(a.k.a. shared vs. exclusive) lock capabilities, with protection against
writer starvation.
A thread MUST NOT call any of the Lock methods if it already holds a Lock.
(Doing so may result in a deadlock.)
---------------------------------------------------------------------------- */
class UTSemReadWrite
{
public:
UTSemReadWrite(); // Constructor
~UTSemReadWrite(); // Destructor
HRESULT Init();
HRESULT LockRead(); // Lock the object for reading
HRESULT LockWrite(); // Lock the object for writing
void UnlockRead(); // Unlock the object for reading
void UnlockWrite(); // Unlock the object for writing
#ifdef _DEBUG
BOOL Debug_IsLockedForRead();
BOOL Debug_IsLockedForWrite();
#endif //_DEBUG
private:
Semaphore * GetReadWaiterSemaphore()
{
return m_pReadWaiterSemaphore;
}
Event * GetWriteWaiterEvent()
{
return m_pWriteWaiterEvent;
}
Volatile<ULONG> m_dwFlag; // internal state, see implementation
Semaphore * m_pReadWaiterSemaphore; // semaphore for awakening read waiters
Event * m_pWriteWaiterEvent; // event for awakening write waiters
}; // class UTSemReadWrite
#endif // __UTSEM_H__
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