This is xnu-4903.221.2. See this file in:
/*
 * Copyright (c) 2018 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
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 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
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#ifndef _KERN_CPU_QUIESCE_H_
#define _KERN_CPU_QUIESCE_H_

#ifdef XNU_KERNEL_PRIVATE

#include <sys/cdefs.h>

/* State field kept on each CPU to track participation */
typedef enum {
	/* Processor that never participated */
	CPU_QUIESCE_COUNTER_NONE = 0,
	/* Processor ready to participate, waiting for return to user */
	CPU_QUIESCE_COUNTER_PENDING_JOIN = 1,
	/* Processor currently participating in counter */
	CPU_QUIESCE_COUNTER_JOINED = 2,
	/* Processor currently not participating in counter */
	CPU_QUIESCE_COUNTER_LEFT = 3,
} cpu_quiescent_state_t;

#if CONFIG_QUIESCE_COUNTER

extern void cpu_quiescent_counter_join(uint64_t ctime);
extern void cpu_quiescent_counter_leave(uint64_t ctime);
extern void cpu_quiescent_counter_checkin(uint64_t ctime);
extern void cpu_quiescent_counter_ast(void);
extern void cpu_quiescent_counter_init(void);

/* use of these is guarded by the config */
extern uint32_t cpu_checkin_min_interval_us;
extern void cpu_quiescent_counter_set_min_interval_us(uint32_t new_value);

#else /* CONFIG_QUIESCE_COUNTER */

/* stub routines for platforms without the counter */

static inline void cpu_quiescent_counter_join(__unused uint64_t ctime) { }
static inline void cpu_quiescent_counter_leave(__unused uint64_t ctime) { }
static inline void cpu_quiescent_counter_checkin(__unused uint64_t ctime) { }
static inline void cpu_quiescent_counter_ast(void) { }
static inline void cpu_quiescent_counter_init(void) { }

#endif /* CONFIG_QUIESCE_COUNTER */

#if MACH_ASSERT && CONFIG_QUIESCE_COUNTER
extern void cpu_quiescent_counter_assert_ast(void);
#else
static inline void cpu_quiescent_counter_assert_ast(void) { }
#endif

#endif /* XNU_KERNEL_PRIVATE */

#endif /* _KERN_CPU_QUIESCE_H_ */