This is xnu-8019. See this file in:
/* test that the header doesn't implicitly depend on others */
#include <sys/work_interval.h>

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <err.h>
#include <string.h>
#include <pthread.h>

#include <mach/mach.h>

#include <darwintest.h>

T_GLOBAL_META(T_META_NAMESPACE("xnu.scheduler"),
    T_META_RUN_CONCURRENTLY(true));

static mach_port_t port = MACH_PORT_NULL;

static void *
joining_thread_fn(__unused void *arg)
{
	int ret = 0;
	kern_return_t kr = KERN_SUCCESS;

	ret = work_interval_join_port(port);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_join_port, another thread");

	kr = mach_port_deallocate(mach_task_self(), port);
	T_ASSERT_MACH_SUCCESS(kr, "mach_port_deallocate of port, another thread");

	/* deliberately exit with joined work interval */
	return NULL;
}

T_DECL(work_interval, "work interval interface")
{
	int ret = 0;
	work_interval_t handle = NULL;
	uint64_t now = mach_absolute_time();
	kern_return_t kr = KERN_SUCCESS;

	ret = work_interval_create(NULL, 0);
	T_ASSERT_EQ(errno, EINVAL, "create with null errno EINVAL");
	T_ASSERT_EQ(ret, -1, "create with null returns -1");

	/* Binary must be entitled for this to succeed */
	ret = work_interval_create(&handle, 0);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_create, no flags");

	ret = work_interval_copy_port(handle, &port);
	T_ASSERT_EQ(errno, EINVAL, "work_interval_copy_port on non-joinable interval errno EINVAL");
	T_ASSERT_EQ(ret, -1, "work_interval_copy_port on non-joinable interval returns -1");

	ret = work_interval_notify(handle, now - 1000, now, now + 1000, now + 2000, 0);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_notify, no flags");

	ret = work_interval_destroy(handle);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_destroy, no flags");

	uint32_t flags[] = {
		WORK_INTERVAL_FLAG_JOINABLE,
		WORK_INTERVAL_FLAG_JOINABLE | WORK_INTERVAL_FLAG_GROUP,
	};

	for (uint32_t i = 0; i < sizeof(flags) / sizeof(flags[0]); i++) {
		ret = work_interval_create(&handle, flags[i]);
		T_ASSERT_POSIX_SUCCESS(ret, "work_interval_create, joinable");

		ret = work_interval_copy_port(handle, &port);
		T_ASSERT_POSIX_SUCCESS(ret, "work_interval_copy_port, joinable");

		ret = work_interval_notify(handle, now - 1000, now, now + 1000, now + 2000, 0);
		T_ASSERT_EQ(ret, -1, "work_interval_notify on non-joined thread returns -1");
		T_ASSERT_EQ(errno, EINVAL, "work_interval_copy_port on non-joined thread errno EINVAL");

		ret = work_interval_join_port(port);
		T_ASSERT_POSIX_SUCCESS(ret, "work_interval_join_port, joinable");

		ret = work_interval_notify(handle, now - 1000, now, now + 1000, now + 2000, 0);
		T_ASSERT_POSIX_SUCCESS(ret, "work_interval_notify, on joined thread");

		ret = work_interval_join_port(port);
		T_ASSERT_POSIX_SUCCESS(ret, "work_interval_join_port, join the same interval after destroy");

		kr = mach_port_deallocate(mach_task_self(), port);
		T_ASSERT_MACH_SUCCESS(kr, "mach_port_deallocate of port");

		ret = work_interval_notify(handle, now - 1000, now, now + 1000, now + 2000, 0);
		T_ASSERT_POSIX_SUCCESS(ret, "work_interval_notify, on joined thread after destroy");

		ret = work_interval_destroy(handle);
		T_ASSERT_POSIX_SUCCESS(ret, "work_interval_destroy, joinable, on joined thread");

		ret = work_interval_leave();
		T_ASSERT_POSIX_SUCCESS(ret, "work_interval_leave, on destroyed work interval");
	}

	ret = work_interval_create(&handle, WORK_INTERVAL_FLAG_JOINABLE | WORK_INTERVAL_FLAG_GROUP);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_create, joinable");

	ret = work_interval_copy_port(handle, &port);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_copy_port, joinable");

	ret = work_interval_join_port(port);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_join_port, join before handing to another thread");

	pthread_t joining_thread;

	T_ASSERT_POSIX_ZERO(pthread_create(&joining_thread, NULL, joining_thread_fn, NULL), "pthread_create");

	T_ASSERT_POSIX_ZERO(pthread_join(joining_thread, NULL), "pthread_join");

	ret = work_interval_leave();
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_leave");

	ret = work_interval_destroy(handle);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_destroy");
}

static mach_timebase_info_data_t timebase_info;

static uint64_t
nanos_to_abs(uint64_t nanos)
{
	mach_timebase_info(&timebase_info);
	return nanos * timebase_info.denom / timebase_info.numer;
}

static void
set_realtime(pthread_t thread)
{
	kern_return_t kr;
	thread_time_constraint_policy_data_t pol;

	mach_port_t target_thread = pthread_mach_thread_np(thread);
	T_ASSERT_NOTNULL(target_thread, "pthread_mach_thread_np");

	/* 1s 100ms 10ms */
	pol.period      = (uint32_t)nanos_to_abs(1000000000);
	pol.constraint  = (uint32_t)nanos_to_abs(100000000);
	pol.computation = (uint32_t)nanos_to_abs(10000000);

	pol.preemptible = 0; /* Ignored by OS */
	kr = thread_policy_set(target_thread, THREAD_TIME_CONSTRAINT_POLICY, (thread_policy_t) &pol,
	    THREAD_TIME_CONSTRAINT_POLICY_COUNT);
	T_ASSERT_MACH_SUCCESS(kr, "thread_policy_set(THREAD_TIME_CONSTRAINT_POLICY)");
}

static void
set_nonrealtime(pthread_t thread)
{
	kern_return_t kr;
	thread_standard_policy_data_t pol = {0};

	mach_port_t target_thread = pthread_mach_thread_np(thread);
	T_ASSERT_NOTNULL(target_thread, "pthread_mach_thread_np");

	kr = thread_policy_set(target_thread, THREAD_STANDARD_POLICY, (thread_policy_t) &pol,
	    THREAD_STANDARD_POLICY_COUNT);
	T_ASSERT_MACH_SUCCESS(kr, "thread_policy_set(THREAD_STANDARD_POLICY)");
}

T_DECL(work_interval_audio_realtime_only, "joining RT threads to audio work interval", T_META_ASROOT(YES))
{
	int ret = 0;
	work_interval_t handle = NULL;
	kern_return_t kr = KERN_SUCCESS;

	uint32_t flags = WORK_INTERVAL_FLAG_GROUP | WORK_INTERVAL_FLAG_JOINABLE | WORK_INTERVAL_TYPE_COREAUDIO;

	ret = work_interval_create(&handle, flags);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_create, joinable");

	ret = work_interval_copy_port(handle, &port);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_copy_port, joinable");

	ret = work_interval_join_port(port);
	T_EXPECT_POSIX_FAILURE(ret, EINVAL, "work_interval_join_port for audio on non-RT thread");

	set_realtime(pthread_self());

	ret = work_interval_join_port(port);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_join_port for audio on RT thread");

	ret = work_interval_leave();
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_leave");

	ret = work_interval_destroy(handle);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_destroy");

	kr = mach_port_deallocate(mach_task_self(), port);
	T_ASSERT_MACH_SUCCESS(kr, "mach_port_deallocate of port");

	set_nonrealtime(pthread_self());
}

T_DECL(work_interval_get_flags, "querying a port for create flags")
{
	int ret = 0;
	work_interval_t handle = NULL;
	uint32_t flags = WORK_INTERVAL_FLAG_JOINABLE | WORK_INTERVAL_FLAG_GROUP | WORK_INTERVAL_TYPE_COREAUDIO;

	ret = work_interval_create(&handle, flags);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_create(AUDIO)");

	ret = work_interval_copy_port(handle, &port);
	T_ASSERT_POSIX_SUCCESS(ret, "work_interval_copy_port");
	T_ASSERT_TRUE(MACH_PORT_VALID(port), "port from copy port is a valid port");

	uint32_t expected_flags = 0;

	ret = work_interval_get_flags_from_port(port, &expected_flags);
	T_ASSERT_EQ(ret, 0, "work_interval_get_flags_from_port");

	T_ASSERT_EQ(expected_flags, flags, "Flags match with what work interval was created with");

	mach_port_mod_refs(mach_task_self(), port, MACH_PORT_RIGHT_SEND, -1);
	work_interval_destroy(handle);

	// Negative test

	mach_port_t fake_port = MACH_PORT_NULL;
	ret = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &fake_port);
	T_ASSERT_EQ(ret, 0, "successfully allocated a port");
	T_ASSERT_TRUE(MACH_PORT_VALID(fake_port), "allocated port is valid");

	ret = mach_port_insert_right(mach_task_self(), fake_port, fake_port, MACH_MSG_TYPE_MAKE_SEND);
	T_ASSERT_EQ(ret, 0, "successfully inserted a send right");

	ret = work_interval_get_flags_from_port(fake_port, &expected_flags);
	T_ASSERT_EQ(ret, -1, "query port failed as expected");

	mach_port_mod_refs(mach_task_self(), fake_port, MACH_PORT_RIGHT_SEND, -1);
	mach_port_mod_refs(mach_task_self(), fake_port, MACH_PORT_RIGHT_RECEIVE, -1);
}