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
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 *  Copyright (c) 1998 Apple Computer, Inc.  All rights reserved.
 *
 *  HISTORY
 *   1998-7-13	Godfrey van der Linden(gvdl)
 *       Created.
 *   1998-10-30	Godfrey van der Linden(gvdl)
 *       Converted to C++
 *   1999-9-22	Godfrey van der Linden(gvdl)
 *       Deprecated
 *  ]*/
#ifndef _IOKIT_IOCOMMANDQUEUE_H
#define _IOKIT_IOCOMMANDQUEUE_H

#include <IOKit/IOEventSource.h>
#include <libkern/c++/OSPtr.h>

class IOCommandQueue;

typedef void (*IOCommandQueueAction)
(OSObject *, void *field0, void *field1, void *field2, void *field3);

class IOCommandQueue : public IOEventSource
{
	OSDeclareDefaultStructors(IOCommandQueue);

protected:
	static const int kIOCQDefaultSize = 128;

	void *queue;
	IOLock *producerLock;
	semaphore_port_t producerSema;
	int producerIndex, consumerIndex;
	int size;

	virtual void free() APPLE_KEXT_OVERRIDE;

	virtual bool checkForWork() APPLE_KEXT_OVERRIDE;

public:
	static OSPtr<IOCommandQueue> commandQueue(OSObject *inOwner,
	    IOCommandQueueAction inAction = NULL,
	    int inSize = kIOCQDefaultSize)
	APPLE_KEXT_DEPRECATED;
	virtual bool init(OSObject *inOwner,
	    IOCommandQueueAction inAction = NULL,
	    int inSize = kIOCQDefaultSize)
	APPLE_KEXT_DEPRECATED;

	virtual kern_return_t enqueueCommand(bool gotoSleep = true,
	    void *field0 = NULL, void *field1 = NULL,
	    void *field2 = NULL, void *field3 = NULL)
	APPLE_KEXT_DEPRECATED;

// WARNING:  This function can only be safely called from the appropriate
// work loop context.  You should check IOWorkLoop::onThread is true.
//
// For each entry in the commandQueue call the target/action.
// Lockout all new entries to the queue while iterating.
// If the input fields are zero then the queue's owner/action will be used.
	virtual int performAndFlush(OSObject *target = NULL,
	    IOCommandQueueAction inAction = NULL)
	APPLE_KEXT_DEPRECATED;
};

#endif /* !_IOKIT_IOCOMMANDQUEUE_H */