libs/binder/IServiceManager.cpp - platform/frameworks/native - Gitiles

 /*
  * Copyright (C) 2005 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #define LOG_TAG "ServiceManager"

 #include <binder/IServiceManager.h>

 #include <inttypes.h>
 #include <unistd.h>

 #include <android/os/BnServiceCallback.h>
 #include <android/os/IServiceManager.h>
 #include <binder/IPCThreadState.h>
 #include <binder/Parcel.h>
 #include <utils/Log.h>
 #include <utils/String8.h>
 #include <utils/SystemClock.h>

 #ifndef __ANDROID_VNDK__
 #include <binder/IPermissionController.h>
 #endif

 #ifdef __ANDROID__
 #include <cutils/properties.h>
 #endif

 #include "Static.h"

 namespace android {

 using AidlServiceManager = android::os::IServiceManager;
 using android::binder::Status;

 // libbinder's IServiceManager.h can't rely on the values generated by AIDL
 // because many places use its headers via include_dirs (meaning, without
 // declaring the dependency in the build system). So, for now, we can just check
 // the values here.
 static_assert(AidlServiceManager::DUMP_FLAG_PRIORITY_CRITICAL == IServiceManager::DUMP_FLAG_PRIORITY_CRITICAL);
 static_assert(AidlServiceManager::DUMP_FLAG_PRIORITY_HIGH == IServiceManager::DUMP_FLAG_PRIORITY_HIGH);
 static_assert(AidlServiceManager::DUMP_FLAG_PRIORITY_NORMAL == IServiceManager::DUMP_FLAG_PRIORITY_NORMAL);
 static_assert(AidlServiceManager::DUMP_FLAG_PRIORITY_DEFAULT == IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT);
 static_assert(AidlServiceManager::DUMP_FLAG_PRIORITY_ALL == IServiceManager::DUMP_FLAG_PRIORITY_ALL);
 static_assert(AidlServiceManager::DUMP_FLAG_PROTO == IServiceManager::DUMP_FLAG_PROTO);

 const String16& IServiceManager::getInterfaceDescriptor() const {
     return AidlServiceManager::descriptor;
 }
 IServiceManager::IServiceManager() {}
 IServiceManager::~IServiceManager() {}

 // From the old libbinder IServiceManager interface to IServiceManager.
 class ServiceManagerShim : public IServiceManager
 {
 public:
     explicit ServiceManagerShim (const sp<AidlServiceManager>& impl);

     sp<IBinder> getService(const String16& name) const override;
     sp<IBinder> checkService(const String16& name) const override;
     status_t addService(const String16& name, const sp<IBinder>& service,
                         bool allowIsolated, int dumpsysPriority) override;
     Vector<String16> listServices(int dumpsysPriority) override;
     sp<IBinder> waitForService(const String16& name16) override;
     bool isDeclared(const String16& name) override;
     Vector<String16> getDeclaredInstances(const String16& interface) override;
     std::optional<String16> updatableViaApex(const String16& name) override;

     // for legacy ABI
     const String16& getInterfaceDescriptor() const override {
         return mTheRealServiceManager->getInterfaceDescriptor();
     }
     IBinder* onAsBinder() override {
         return IInterface::asBinder(mTheRealServiceManager).get();
     }
 private:
     sp<AidlServiceManager> mTheRealServiceManager;
 };

 [[clang::no_destroy]] static std::once_flag gSmOnce;
 [[clang::no_destroy]] static sp<IServiceManager> gDefaultServiceManager;

 sp<IServiceManager> defaultServiceManager()
 {
     std::call_once(gSmOnce, []() {
         sp<AidlServiceManager> sm = nullptr;
         while (sm == nullptr) {
             sm = interface_cast<AidlServiceManager>(ProcessState::self()->getContextObject(nullptr));
             if (sm == nullptr) {
                 ALOGE("Waiting 1s on context object on %s.", ProcessState::self()->getDriverName().c_str());
                 sleep(1);
             }
         }

         gDefaultServiceManager = sp<ServiceManagerShim>::make(sm);
     });

     return gDefaultServiceManager;
 }

 void setDefaultServiceManager(const sp<IServiceManager>& sm) {
     bool called = false;
     std::call_once(gSmOnce, [&]() {
         gDefaultServiceManager = sm;
         called = true;
     });

     if (!called) {
         LOG_ALWAYS_FATAL("setDefaultServiceManager() called after defaultServiceManager().");
     }
 }

 #if !defined(__ANDROID_VNDK__) && defined(__ANDROID__)
 // IPermissionController is not accessible to vendors

 bool checkCallingPermission(const String16& permission)
 {
     return checkCallingPermission(permission, nullptr, nullptr);
 }

 static String16 _permission("permission");


 bool checkCallingPermission(const String16& permission, int32_t* outPid, int32_t* outUid)
 {
     IPCThreadState* ipcState = IPCThreadState::self();
     pid_t pid = ipcState->getCallingPid();
     uid_t uid = ipcState->getCallingUid();
     if (outPid) *outPid = pid;
     if (outUid) *outUid = uid;
     return checkPermission(permission, pid, uid);
 }

 bool checkPermission(const String16& permission, pid_t pid, uid_t uid)
 {
     static Mutex gPermissionControllerLock;
     static sp<IPermissionController> gPermissionController;

     sp<IPermissionController> pc;
     gPermissionControllerLock.lock();
     pc = gPermissionController;
     gPermissionControllerLock.unlock();

     int64_t startTime = 0;

     while (true) {
         if (pc != nullptr) {
             bool res = pc->checkPermission(permission, pid, uid);
             if (res) {
                 if (startTime != 0) {
                     ALOGI("Check passed after %d seconds for %s from uid=%d pid=%d",
                             (int)((uptimeMillis()-startTime)/1000),
                             String8(permission).string(), uid, pid);
                 }
                 return res;
             }

             // Is this a permission failure, or did the controller go away?
             if (IInterface::asBinder(pc)->isBinderAlive()) {
                 ALOGW("Permission failure: %s from uid=%d pid=%d",
                         String8(permission).string(), uid, pid);
                 return false;
             }

             // Object is dead!
             gPermissionControllerLock.lock();
             if (gPermissionController == pc) {
                 gPermissionController = nullptr;
             }
             gPermissionControllerLock.unlock();
         }

         // Need to retrieve the permission controller.
         sp<IBinder> binder = defaultServiceManager()->checkService(_permission);
         if (binder == nullptr) {
             // Wait for the permission controller to come back...
             if (startTime == 0) {
                 startTime = uptimeMillis();
                 ALOGI("Waiting to check permission %s from uid=%d pid=%d",
                         String8(permission).string(), uid, pid);
             }
             sleep(1);
         } else {
             pc = interface_cast<IPermissionController>(binder);
             // Install the new permission controller, and try again.
             gPermissionControllerLock.lock();
             gPermissionController = pc;
             gPermissionControllerLock.unlock();
         }
     }
 }

 #endif //__ANDROID_VNDK__

 // ----------------------------------------------------------------------

 ServiceManagerShim::ServiceManagerShim(const sp<AidlServiceManager>& impl)
  : mTheRealServiceManager(impl)
 {}

 // This implementation could be simplified and made more efficient by delegating
 // to waitForService. However, this changes the threading structure in some
 // cases and could potentially break prebuilts. Once we have higher logistical
 // complexity, this could be attempted.
 sp<IBinder> ServiceManagerShim::getService(const String16& name) const
 {
     static bool gSystemBootCompleted = false;

     sp<IBinder> svc = checkService(name);
     if (svc != nullptr) return svc;

     const bool isVendorService =
         strcmp(ProcessState::self()->getDriverName().c_str(), "/dev/vndbinder") == 0;
     constexpr int64_t timeout = 5000;
     int64_t startTime = uptimeMillis();
     // Vendor code can't access system properties
     if (!gSystemBootCompleted && !isVendorService) {
 #ifdef __ANDROID__
         char bootCompleted[PROPERTY_VALUE_MAX];
         property_get("sys.boot_completed", bootCompleted, "0");
         gSystemBootCompleted = strcmp(bootCompleted, "1") == 0 ? true : false;
 #else
         gSystemBootCompleted = true;
 #endif
     }
     // retry interval in millisecond; note that vendor services stay at 100ms
     const useconds_t sleepTime = gSystemBootCompleted ? 1000 : 100;

     ALOGI("Waiting for service '%s' on '%s'...", String8(name).string(),
           ProcessState::self()->getDriverName().c_str());

     int n = 0;
     while (uptimeMillis() - startTime < timeout) {
         n++;
         usleep(1000*sleepTime);

         sp<IBinder> svc = checkService(name);
         if (svc != nullptr) {
             ALOGI("Waiting for service '%s' on '%s' successful after waiting %" PRIi64 "ms",
                   String8(name).string(), ProcessState::self()->getDriverName().c_str(),
                   uptimeMillis() - startTime);
             return svc;
         }
     }
     ALOGW("Service %s didn't start. Returning NULL", String8(name).string());
     return nullptr;
 }

 sp<IBinder> ServiceManagerShim::checkService(const String16& name) const
 {
     sp<IBinder> ret;
     if (!mTheRealServiceManager->checkService(String8(name).c_str(), &ret).isOk()) {
         return nullptr;
     }
     return ret;
 }

 status_t ServiceManagerShim::addService(const String16& name, const sp<IBinder>& service,
                                         bool allowIsolated, int dumpsysPriority)
 {
     Status status = mTheRealServiceManager->addService(
         String8(name).c_str(), service, allowIsolated, dumpsysPriority);
     return status.exceptionCode();
 }

 Vector<String16> ServiceManagerShim::listServices(int dumpsysPriority)
 {
     std::vector<std::string> ret;
     if (!mTheRealServiceManager->listServices(dumpsysPriority, &ret).isOk()) {
         return {};
     }

     Vector<String16> res;
     res.setCapacity(ret.size());
     for (const std::string& name : ret) {
         res.push(String16(name.c_str()));
     }
     return res;
 }

 sp<IBinder> ServiceManagerShim::waitForService(const String16& name16)
 {
     class Waiter : public android::os::BnServiceCallback {
         Status onRegistration(const std::string& /*name*/,
                               const sp<IBinder>& binder) override {
             std::unique_lock<std::mutex> lock(mMutex);
             mBinder = binder;
             lock.unlock();
             // Flushing here helps ensure the service's ref count remains accurate
             IPCThreadState::self()->flushCommands();
             mCv.notify_one();
             return Status::ok();
         }
     public:
         sp<IBinder> mBinder;
         std::mutex mMutex;
         std::condition_variable mCv;
     };

     // Simple RAII object to ensure a function call immediately before going out of scope
     class Defer {
     public:
         explicit Defer(std::function<void()>&& f) : mF(std::move(f)) {}
         ~Defer() { mF(); }
     private:
         std::function<void()> mF;
     };

     const std::string name = String8(name16).c_str();

     sp<IBinder> out;
     if (!mTheRealServiceManager->getService(name, &out).isOk()) {
         return nullptr;
     }
     if (out != nullptr) return out;

     sp<Waiter> waiter = sp<Waiter>::make();
     if (!mTheRealServiceManager->registerForNotifications(
             name, waiter).isOk()) {
         return nullptr;
     }
     Defer unregister ([&] {
         mTheRealServiceManager->unregisterForNotifications(name, waiter);
     });

     while(true) {
         {
             // It would be really nice if we could read binder commands on this
             // thread instead of needing a threadpool to be started, but for
             // instance, if we call getAndExecuteCommand, it might be the case
             // that another thread serves the callback, and we never get a
             // command, so we hang indefinitely.
             std::unique_lock<std::mutex> lock(waiter->mMutex);
             using std::literals::chrono_literals::operator""s;
             waiter->mCv.wait_for(lock, 1s, [&] {
                 return waiter->mBinder != nullptr;
             });
             if (waiter->mBinder != nullptr) return waiter->mBinder;
         }

         ALOGW("Waited one second for %s (is service started? are binder threads started and available?)", name.c_str());

         // Handle race condition for lazy services. Here is what can happen:
         // - the service dies (not processed by init yet).
         // - sm processes death notification.
         // - sm gets getService and calls init to start service.
         // - init gets the start signal, but the service already appears
         //   started, so it does nothing.
         // - init gets death signal, but doesn't know it needs to restart
         //   the service
         // - we need to request service again to get it to start
         if (!mTheRealServiceManager->getService(name, &out).isOk()) {
             return nullptr;
         }
         if (out != nullptr) return out;
     }
 }

 bool ServiceManagerShim::isDeclared(const String16& name) {
     bool declared;
     if (!mTheRealServiceManager->isDeclared(String8(name).c_str(), &declared).isOk()) {
         return false;
     }
     return declared;
 }

 Vector<String16> ServiceManagerShim::getDeclaredInstances(const String16& interface) {
     std::vector<std::string> out;
     if (!mTheRealServiceManager->getDeclaredInstances(String8(interface).c_str(), &out).isOk()) {
         return {};
     }

     Vector<String16> res;
     res.setCapacity(out.size());
     for (const std::string& instance : out) {
         res.push(String16(instance.c_str()));
     }
     return res;
 }

 std::optional<String16> ServiceManagerShim::updatableViaApex(const String16& name) {
     std::optional<std::string> declared;
     if (!mTheRealServiceManager->updatableViaApex(String8(name).c_str(), &declared).isOk()) {
         return std::nullopt;
     }
     return declared ? std::optional<String16>(String16(declared.value().c_str())) : std::nullopt;
 }

 } // namespace android
	/*
	* Copyright (C) 2005 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#define LOG_TAG "ServiceManager"

	#include <binder/IServiceManager.h>

	#include <inttypes.h>
	#include <unistd.h>

	#include <android/os/BnServiceCallback.h>
	#include <android/os/IServiceManager.h>
	#include <binder/IPCThreadState.h>
	#include <binder/Parcel.h>
	#include <utils/Log.h>
	#include <utils/String8.h>
	#include <utils/SystemClock.h>

	#ifndef __ANDROID_VNDK__
	#include <binder/IPermissionController.h>
	#endif

	#ifdef __ANDROID__
	#include <cutils/properties.h>
	#endif

	#include "Static.h"

	namespace android {

	using AidlServiceManager = android::os::IServiceManager;
	using android::binder::Status;

	// libbinder's IServiceManager.h can't rely on the values generated by AIDL
	// because many places use its headers via include_dirs (meaning, without
	// declaring the dependency in the build system). So, for now, we can just check
	// the values here.
	static_assert(AidlServiceManager::DUMP_FLAG_PRIORITY_CRITICAL == IServiceManager::DUMP_FLAG_PRIORITY_CRITICAL);
	static_assert(AidlServiceManager::DUMP_FLAG_PRIORITY_HIGH == IServiceManager::DUMP_FLAG_PRIORITY_HIGH);
	static_assert(AidlServiceManager::DUMP_FLAG_PRIORITY_NORMAL == IServiceManager::DUMP_FLAG_PRIORITY_NORMAL);
	static_assert(AidlServiceManager::DUMP_FLAG_PRIORITY_DEFAULT == IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT);
	static_assert(AidlServiceManager::DUMP_FLAG_PRIORITY_ALL == IServiceManager::DUMP_FLAG_PRIORITY_ALL);
	static_assert(AidlServiceManager::DUMP_FLAG_PROTO == IServiceManager::DUMP_FLAG_PROTO);

	const String16& IServiceManager::getInterfaceDescriptor() const {
	return AidlServiceManager::descriptor;
	}
	IServiceManager::IServiceManager() {}
	IServiceManager::~IServiceManager() {}

	// From the old libbinder IServiceManager interface to IServiceManager.
	class ServiceManagerShim : public IServiceManager
	{
	public:
	explicit ServiceManagerShim (const sp<AidlServiceManager>& impl);

	sp<IBinder> getService(const String16& name) const override;
	sp<IBinder> checkService(const String16& name) const override;
	status_t addService(const String16& name, const sp<IBinder>& service,
	bool allowIsolated, int dumpsysPriority) override;
	Vector<String16> listServices(int dumpsysPriority) override;
	sp<IBinder> waitForService(const String16& name16) override;
	bool isDeclared(const String16& name) override;
	Vector<String16> getDeclaredInstances(const String16& interface) override;
	std::optional<String16> updatableViaApex(const String16& name) override;

	// for legacy ABI
	const String16& getInterfaceDescriptor() const override {
	return mTheRealServiceManager->getInterfaceDescriptor();
	}
	IBinder* onAsBinder() override {
	return IInterface::asBinder(mTheRealServiceManager).get();
	}
	private:
	sp<AidlServiceManager> mTheRealServiceManager;
	};

	[[clang::no_destroy]] static std::once_flag gSmOnce;
	[[clang::no_destroy]] static sp<IServiceManager> gDefaultServiceManager;

	sp<IServiceManager> defaultServiceManager()
	{
	std::call_once(gSmOnce, []() {
	sp<AidlServiceManager> sm = nullptr;
	while (sm == nullptr) {
	sm = interface_cast<AidlServiceManager>(ProcessState::self()->getContextObject(nullptr));
	if (sm == nullptr) {
	ALOGE("Waiting 1s on context object on %s.", ProcessState::self()->getDriverName().c_str());
	sleep(1);
	}
	}

	gDefaultServiceManager = sp<ServiceManagerShim>::make(sm);
	});

	return gDefaultServiceManager;
	}

	void setDefaultServiceManager(const sp<IServiceManager>& sm) {
	bool called = false;
	std::call_once(gSmOnce, [&]() {
	gDefaultServiceManager = sm;
	called = true;
	});

	if (!called) {
	LOG_ALWAYS_FATAL("setDefaultServiceManager() called after defaultServiceManager().");
	}
	}

	#if !defined(__ANDROID_VNDK__) && defined(__ANDROID__)
	// IPermissionController is not accessible to vendors

	bool checkCallingPermission(const String16& permission)
	{
	return checkCallingPermission(permission, nullptr, nullptr);
	}

	static String16 _permission("permission");


	bool checkCallingPermission(const String16& permission, int32_t* outPid, int32_t* outUid)
	{
	IPCThreadState* ipcState = IPCThreadState::self();
	pid_t pid = ipcState->getCallingPid();
	uid_t uid = ipcState->getCallingUid();
	if (outPid) *outPid = pid;
	if (outUid) *outUid = uid;
	return checkPermission(permission, pid, uid);
	}

	bool checkPermission(const String16& permission, pid_t pid, uid_t uid)
	{
	static Mutex gPermissionControllerLock;
	static sp<IPermissionController> gPermissionController;

	sp<IPermissionController> pc;
	gPermissionControllerLock.lock();
	pc = gPermissionController;
	gPermissionControllerLock.unlock();

	int64_t startTime = 0;

	while (true) {
	if (pc != nullptr) {
	bool res = pc->checkPermission(permission, pid, uid);
	if (res) {
	if (startTime != 0) {
	ALOGI("Check passed after %d seconds for %s from uid=%d pid=%d",
	(int)((uptimeMillis()-startTime)/1000),
	String8(permission).string(), uid, pid);
	}
	return res;
	}

	// Is this a permission failure, or did the controller go away?
	if (IInterface::asBinder(pc)->isBinderAlive()) {
	ALOGW("Permission failure: %s from uid=%d pid=%d",
	String8(permission).string(), uid, pid);
	return false;
	}

	// Object is dead!
	gPermissionControllerLock.lock();
	if (gPermissionController == pc) {
	gPermissionController = nullptr;
	}
	gPermissionControllerLock.unlock();
	}

	// Need to retrieve the permission controller.
	sp<IBinder> binder = defaultServiceManager()->checkService(_permission);
	if (binder == nullptr) {
	// Wait for the permission controller to come back...
	if (startTime == 0) {
	startTime = uptimeMillis();
	ALOGI("Waiting to check permission %s from uid=%d pid=%d",
	String8(permission).string(), uid, pid);
	}
	sleep(1);
	} else {
	pc = interface_cast<IPermissionController>(binder);
	// Install the new permission controller, and try again.
	gPermissionControllerLock.lock();
	gPermissionController = pc;
	gPermissionControllerLock.unlock();
	}
	}
	}

	#endif //__ANDROID_VNDK__

	// ----------------------------------------------------------------------

	ServiceManagerShim::ServiceManagerShim(const sp<AidlServiceManager>& impl)
	: mTheRealServiceManager(impl)
	{}

	// This implementation could be simplified and made more efficient by delegating
	// to waitForService. However, this changes the threading structure in some
	// cases and could potentially break prebuilts. Once we have higher logistical
	// complexity, this could be attempted.
	sp<IBinder> ServiceManagerShim::getService(const String16& name) const
	{
	static bool gSystemBootCompleted = false;

	sp<IBinder> svc = checkService(name);
	if (svc != nullptr) return svc;

	const bool isVendorService =
	strcmp(ProcessState::self()->getDriverName().c_str(), "/dev/vndbinder") == 0;
	constexpr int64_t timeout = 5000;
	int64_t startTime = uptimeMillis();
	// Vendor code can't access system properties
	if (!gSystemBootCompleted && !isVendorService) {
	#ifdef __ANDROID__
	char bootCompleted[PROPERTY_VALUE_MAX];
	property_get("sys.boot_completed", bootCompleted, "0");
	gSystemBootCompleted = strcmp(bootCompleted, "1") == 0 ? true : false;
	#else
	gSystemBootCompleted = true;
	#endif
	}
	// retry interval in millisecond; note that vendor services stay at 100ms
	const useconds_t sleepTime = gSystemBootCompleted ? 1000 : 100;

	ALOGI("Waiting for service '%s' on '%s'...", String8(name).string(),
	ProcessState::self()->getDriverName().c_str());

	int n = 0;
	while (uptimeMillis() - startTime < timeout) {
	n++;
	usleep(1000*sleepTime);

	sp<IBinder> svc = checkService(name);
	if (svc != nullptr) {
	ALOGI("Waiting for service '%s' on '%s' successful after waiting %" PRIi64 "ms",
	String8(name).string(), ProcessState::self()->getDriverName().c_str(),
	uptimeMillis() - startTime);
	return svc;
	}
	}
	ALOGW("Service %s didn't start. Returning NULL", String8(name).string());
	return nullptr;
	}

	sp<IBinder> ServiceManagerShim::checkService(const String16& name) const
	{
	sp<IBinder> ret;
	if (!mTheRealServiceManager->checkService(String8(name).c_str(), &ret).isOk()) {
	return nullptr;
	}
	return ret;
	}

	status_t ServiceManagerShim::addService(const String16& name, const sp<IBinder>& service,
	bool allowIsolated, int dumpsysPriority)
	{
	Status status = mTheRealServiceManager->addService(
	String8(name).c_str(), service, allowIsolated, dumpsysPriority);
	return status.exceptionCode();
	}

	Vector<String16> ServiceManagerShim::listServices(int dumpsysPriority)
	{
	std::vector<std::string> ret;
	if (!mTheRealServiceManager->listServices(dumpsysPriority, &ret).isOk()) {
	return {};
	}

	Vector<String16> res;
	res.setCapacity(ret.size());
	for (const std::string& name : ret) {
	res.push(String16(name.c_str()));
	}
	return res;
	}

	sp<IBinder> ServiceManagerShim::waitForService(const String16& name16)
	{
	class Waiter : public android::os::BnServiceCallback {
	Status onRegistration(const std::string& /name/,
	const sp<IBinder>& binder) override {
	std::unique_lock<std::mutex> lock(mMutex);
	mBinder = binder;
	lock.unlock();
	// Flushing here helps ensure the service's ref count remains accurate
	IPCThreadState::self()->flushCommands();
	mCv.notify_one();
	return Status::ok();
	}
	public:
	sp<IBinder> mBinder;
	std::mutex mMutex;
	std::condition_variable mCv;
	};

	// Simple RAII object to ensure a function call immediately before going out of scope
	class Defer {
	public:
	explicit Defer(std::function<void()>&& f) : mF(std::move(f)) {}
	~Defer() { mF(); }
	private:
	std::function<void()> mF;
	};

	const std::string name = String8(name16).c_str();

	sp<IBinder> out;
	if (!mTheRealServiceManager->getService(name, &out).isOk()) {
	return nullptr;
	}
	if (out != nullptr) return out;

	sp<Waiter> waiter = sp<Waiter>::make();
	if (!mTheRealServiceManager->registerForNotifications(
	name, waiter).isOk()) {
	return nullptr;
	}
	Defer unregister ([&] {
	mTheRealServiceManager->unregisterForNotifications(name, waiter);
	});

	while(true) {
	{
	// It would be really nice if we could read binder commands on this
	// thread instead of needing a threadpool to be started, but for
	// instance, if we call getAndExecuteCommand, it might be the case
	// that another thread serves the callback, and we never get a
	// command, so we hang indefinitely.
	std::unique_lock<std::mutex> lock(waiter->mMutex);
	using std::literals::chrono_literals::operator""s;
	waiter->mCv.wait_for(lock, 1s, [&] {
	return waiter->mBinder != nullptr;
	});
	if (waiter->mBinder != nullptr) return waiter->mBinder;
	}

	ALOGW("Waited one second for %s (is service started? are binder threads started and available?)", name.c_str());

	// Handle race condition for lazy services. Here is what can happen:
	// - the service dies (not processed by init yet).
	// - sm processes death notification.
	// - sm gets getService and calls init to start service.
	// - init gets the start signal, but the service already appears
	// started, so it does nothing.
	// - init gets death signal, but doesn't know it needs to restart
	// the service
	// - we need to request service again to get it to start
	if (!mTheRealServiceManager->getService(name, &out).isOk()) {
	return nullptr;
	}
	if (out != nullptr) return out;
	}
	}

	bool ServiceManagerShim::isDeclared(const String16& name) {
	bool declared;
	if (!mTheRealServiceManager->isDeclared(String8(name).c_str(), &declared).isOk()) {
	return false;
	}
	return declared;
	}

	Vector<String16> ServiceManagerShim::getDeclaredInstances(const String16& interface) {
	std::vector<std::string> out;
	if (!mTheRealServiceManager->getDeclaredInstances(String8(interface).c_str(), &out).isOk()) {
	return {};
	}

	Vector<String16> res;
	res.setCapacity(out.size());
	for (const std::string& instance : out) {
	res.push(String16(instance.c_str()));
	}
	return res;
	}

	std::optional<String16> ServiceManagerShim::updatableViaApex(const String16& name) {
	std::optional<std::string> declared;
	if (!mTheRealServiceManager->updatableViaApex(String8(name).c_str(), &declared).isOk()) {
	return std::nullopt;
	}
	return declared ? std::optional<String16>(String16(declared.value().c_str())) : std::nullopt;
	}

	} // namespace android