This is xnu-8019. See this file in:
/*
 * Copyright (c) 1998-2019 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
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 *
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 */
/* Copyright (c) 1999 Apple Computer, Inc.  All rights reserved.
 * Copyright (c) 1994-1996 NeXT Software, Inc.  All rights reserved.
 */

#ifndef _IOKIT_IOCONDITIONLOCK_H
#define _IOKIT_IOCONDITIONLOCK_H

#include <libkern/c++/OSPtr.h>
#include <libkern/c++/OSObject.h>
#include <IOKit/IOLib.h>
#include <IOKit/system.h>

#include <IOKit/IOLocks.h>

class IOConditionLock : public OSObject
{
	OSDeclareDefaultStructors(IOConditionLock);

private:
	IOLock *            cond_interlock;     // condition var Simple lock
	volatile int        condition;

	IOLock *            sleep_interlock;    // sleep lock Simple lock
	unsigned char       interruptible;
	volatile bool       want_lock;
	volatile bool       waiting;

public:
	static OSPtr<IOConditionLock> withCondition(int condition, bool inIntr = true);
	virtual bool initWithCondition(int condition, bool inIntr = true);
	virtual void free() APPLE_KEXT_OVERRIDE;

	virtual bool tryLock(); // acquire lock, no waiting
	virtual int  lock();    // acquire lock (enter critical section)
	virtual void unlock();  // release lock (leave critical section)

	virtual bool getInterruptible() const;
	virtual int  getCondition() const;
	virtual int  setCondition(int condition);

	virtual int  lockWhen(int condition);// acquire lock when condition
	virtual void unlockWith(int condition); // set condition & release lock
};

#endif /* _IOKIT_IOCONDITIONLOCK_H */