This is xnu-4903.221.2. See this file in:
/*
 * Copyright (c) 2017 Apple Inc. All rights reserved.
 */

#include <IOKit/perfcontrol/IOPerfControl.h>

#include <stdatomic.h>

#include <kern/thread_group.h>

#undef super
#define super OSObject
OSDefineMetaClassAndStructors(IOPerfControlClient, OSObject);

bool IOPerfControlClient::init(IOService *driver, uint64_t maxWorkCapacity)
{
    if (!super::init())
        return false;

    interface = PerfControllerInterface{
        .version = 0,
        .registerDevice =
            [](IOService *device) {
                return kIOReturnSuccess;
            },
        .unregisterDevice =
            [](IOService *device) {
                return kIOReturnSuccess;
            },
        .workCanSubmit =
            [](IOService *device, PerfControllerInterface::WorkState *state, WorkSubmitArgs *args) {
                return false;
            },
        .workSubmit =
            [](IOService *device, uint64_t token, PerfControllerInterface::WorkState *state, WorkSubmitArgs *args) {
            },
        .workBegin =
            [](IOService *device, uint64_t token, PerfControllerInterface::WorkState *state, WorkBeginArgs *args) {
            },
        .workEnd =
            [](IOService *device, uint64_t token, PerfControllerInterface::WorkState *state, WorkEndArgs *args, bool done) {
            },
    };

    interfaceLock = IOLockAlloc();
    if (!interfaceLock)
        goto error;

    deviceRegistrationList = OSSet::withCapacity(4);
    if (!deviceRegistrationList)
        goto error;

    bzero(workTable, sizeof(workTable));
    memset(&workTable[kIOPerfControlClientWorkUntracked], ~0, sizeof(WorkTableEntry));
    workTableNextIndex = kIOPerfControlClientWorkUntracked + 1;

    workTableLock = IOSimpleLockAlloc();
    if (!workTableLock)
        goto error;

    // TODO: check sum(maxWorkCapacities) < table size

    return true;

error:
    if (interfaceLock)
        IOLockFree(interfaceLock);
    if (deviceRegistrationList)
        deviceRegistrationList->release();
    if (workTableLock)
        IOSimpleLockFree(workTableLock);
    return false;
}

IOPerfControlClient *_Atomic gSharedClient = nullptr;

IOPerfControlClient *IOPerfControlClient::copyClient(IOService *driver, uint64_t maxWorkCapacity)
{
    IOPerfControlClient *client = atomic_load_explicit(&gSharedClient, memory_order_acquire);
    if (client == nullptr) {
        IOPerfControlClient *expected = client;
        client = new IOPerfControlClient;
        if (!client || !client->init(driver, maxWorkCapacity))
            panic("could not create IOPerfControlClient");
        if (!atomic_compare_exchange_strong_explicit(&gSharedClient, &expected, client, memory_order_acq_rel,
                                                     memory_order_acquire)) {
            client->release();
            client = expected;
        }
    }
    // TODO: add maxWorkCapacity to existing client
    client->retain();
    return client;
}

uint64_t IOPerfControlClient::allocateToken(thread_group *thread_group)
{
    uint64_t token = kIOPerfControlClientWorkUntracked;


    return token;
}

void IOPerfControlClient::deallocateToken(uint64_t token)
{
}

bool IOPerfControlClient::getEntryForToken(uint64_t token, IOPerfControlClient::WorkTableEntry &entry)
{
    if (token == kIOPerfControlClientWorkUntracked)
        return false;

    if (token >= kWorkTableNumEntries)
        panic("Invalid work token (%llu): index out of bounds.", token);

    entry = workTable[token];
    auto *thread_group = entry.thread_group;
    assertf(thread_group, "Invalid work token: %llu", token);
    return thread_group != nullptr;
}

void IOPerfControlClient::markEntryStarted(uint64_t token, bool started)
{
    if (token == kIOPerfControlClientWorkUntracked)
        return;

    if (token >= kWorkTableNumEntries)
        panic("Invalid work token (%llu): index out of bounds.", token);

    workTable[token].started = started;
}

IOReturn IOPerfControlClient::registerDevice(__unused IOService *driver, IOService *device)
{
    IOReturn ret = kIOReturnSuccess;

    IOLockLock(interfaceLock);

    if (interface.version > 0)
        ret = interface.registerDevice(device);
    else
        deviceRegistrationList->setObject(device);

    IOLockUnlock(interfaceLock);

    return ret;
}

void IOPerfControlClient::unregisterDevice(__unused IOService *driver, IOService *device)
{
    IOLockLock(interfaceLock);

    if (interface.version > 0)
        interface.unregisterDevice(device);
    else
        deviceRegistrationList->removeObject(device);

    IOLockUnlock(interfaceLock);
}

uint64_t IOPerfControlClient::workSubmit(IOService *device, WorkSubmitArgs *args)
{
    return kIOPerfControlClientWorkUntracked;
}

uint64_t IOPerfControlClient::workSubmitAndBegin(IOService *device, WorkSubmitArgs *submitArgs, WorkBeginArgs *beginArgs)
{
    return kIOPerfControlClientWorkUntracked;
}

void IOPerfControlClient::workBegin(IOService *device, uint64_t token, WorkBeginArgs *args)
{
}

void IOPerfControlClient::workEnd(IOService *device, uint64_t token, WorkEndArgs *args, bool done)
{
}

IOReturn IOPerfControlClient::registerPerformanceController(PerfControllerInterface pci)
{
    IOReturn result = kIOReturnError;

    IOLockLock(interfaceLock);

    if (interface.version == 0 && pci.version > 0) {
        assert(pci.registerDevice && pci.unregisterDevice && pci.workCanSubmit && pci.workSubmit && pci.workBegin && pci.workEnd);
        result = kIOReturnSuccess;

        OSObject *obj;
        while ((obj = deviceRegistrationList->getAnyObject())) {
            IOService *device = OSDynamicCast(IOService, obj);
            if (device)
                pci.registerDevice(device);
            deviceRegistrationList->removeObject(obj);
        }

        interface = pci;
    }

    IOLockUnlock(interfaceLock);

    return result;
}