runtime/VersionedInterfaces.h

/*
 * Copyright (C) 2018 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.
 */

#ifndef ANDROID_ML_NN_RUNTIME_VERSIONED_INTERFACES_H
#define ANDROID_ML_NN_RUNTIME_VERSIONED_INTERFACES_H

#include "HalInterfaces.h"

#include <android-base/macros.h>
#include <memory>
#include <string>
#include <tuple>
#include "Callbacks.h"

namespace android {
namespace nn {

// forward declarations
class ExecutionBurstController;
class IDeviceDeathHandler;
class IPreparedModelDeathHandler;
class VersionedIPreparedModel;

/**
 * Each class (VersionedIDevice, VersionedIPreparedModel) wraps a HIDL interface
 * of any version to abstract away version differences. It allows the remainder
 * of the runtime to always use the most up-to-date version of all HIDL types.
 * As such, any reference to a HIDL type in the rest of the runtime
 * will--by default--be the latest HIDL version.
 *
 * Each class will attempt to call the latest version of each interface method
 * if possible. If the latest method is unavailable, the versioned class
 * will attempt to upcast the type (e.g., V1_1::Model to V1_0::Model), and
 * invoke the latest interface method possible. If the versioned class
 * fails to find a matching applicable function, it will return an error.
 */

/** This class wraps an IDevice object of any version. */
class VersionedIDevice {
    DISALLOW_IMPLICIT_CONSTRUCTORS(VersionedIDevice);

   public:
    /**
     * Create a VersionedIDevice object.
     *
     * Prefer using this function over the constructor, as it adds more
     * protections.
     *
     * This call linksToDeath a hidl_death_recipient that can
     * proactively handle the case when the service containing the IDevice
     * object crashes.
     *
     * @param device A device object that is at least version 1.0 of the IDevice
     *               interface.
     * @return A valid VersionedIDevice object, otherwise nullptr.
     */
    static std::shared_ptr<VersionedIDevice> create(sp<V1_0::IDevice> device);

    /**
     * Constructor for the VersionedIDevice object.
     *
     * VersionedIDevice is constructed with the V1_0::IDevice object, which
     * represents a device that is at least v1.0 of the interface. The
     * constructor downcasts to the latest version of the IDevice interface, and
     * will default to using the latest version of all IDevice interface
     * methods automatically.
     *
     * @param device A device object that is at least version 1.0 of the IDevice
     *               interface.
     * @param deathHandler A hidl_death_recipient that will proactively handle
     *                     the case when the service containing the IDevice
     *                     object crashes.
     */
    VersionedIDevice(sp<V1_0::IDevice> device, sp<IDeviceDeathHandler> deathHandler);

    /**
     * Destructor for the VersionedIDevice object.
     *
     * This destructor unlinksToDeath this object's hidl_death_recipient as it
     * no longer needs to handle the case where the IDevice's service crashes.
     */
    ~VersionedIDevice();

    /**
     * Gets the capabilities of a driver.
     *
     * @return status Error status of the call, must be:
     *                - NONE if successful
     *                - DEVICE_UNAVAILABLE if driver is offline or busy
     *                - GENERAL_FAILURE if there is an unspecified error
     * @return capabilities Capabilities of the driver.
     */
    std::pair<ErrorStatus, Capabilities> getCapabilities();

    /**
     * Gets information about extensions supported by the driver implementation.
     *
     * Extensions of category ExtensionCategory::BASE must not appear
     * in the list.
     *
     * All extension operations and operands must be fully supported for the
     * extension to appear in the list of supported extensions.
     *
     * @return status Error status of the call, must be:
     *     - NONE if successful
     *     - DEVICE_UNAVAILABLE if driver is offline or busy
     *     - GENERAL_FAILURE if there is an unspecified error
     * @return extensions A list of supported extensions.
     */
    std::pair<ErrorStatus, hidl_vec<Extension>> getSupportedExtensions();

    /**
     * Gets the supported operations in a model.
     *
     * getSupportedSubgraph indicates which operations of a model are fully
     * supported by the vendor driver. If an operation may not be supported for
     * any reason, getSupportedOperations must return false for that operation.
     *
     * @param model A model whose operations--and their corresponding
     *              operands--are to be verified by the driver.
     * @return status Error status of the call, must be:
     *                - NONE if successful
     *                - DEVICE_UNAVAILABLE if driver is offline or busy
     *                - GENERAL_FAILURE if there is an unspecified error
     *                - INVALID_ARGUMENT if provided model is invalid
     * @return supportedOperations A list of supported operations, where true
     *                             indicates the operation is supported and
     *                             false indicates the operation is not
     *                             supported. The index of "supported"
     *                             corresponds with the index of the operation
     *                             it is describing.
     */
    std::pair<ErrorStatus, hidl_vec<bool>> getSupportedOperations(const Model& model);

    /**
     * Synchronously creates a prepared model for execution and optionally saves it
     * into cache files.
     *
     * prepareModel is used to make any necessary transformations or alternative
     * representations to a model for execution, possibly including
     * transformations on the constant data, optimization on the model's graph,
     * or compilation into the device's native binary format. The model itself
     * is not changed.
     *
     * Optionally, caching information may be provided for the driver to save
     * the prepared model to cache files for faster model compilation time
     * when the same model preparation is requested in the future. There are
     * two types of cache file handles provided to the driver: model cache
     * and data cache. For more information on the two types of cache handles,
     * refer to getNumberOfCacheFilesNeeded.
     *
     * The file descriptors must be opened with read and write permission. A file may
     * have any size, and the corresponding file descriptor may have any offset. The
     * driver must truncate a file to zero size before writing to that file. The file
     * descriptors may be closed by the client once the asynchronous preparation has
     * finished. The driver must dup a file descriptor if it wants to get access to
     * the cache file later.
     *
     * The model is prepared synchronously with respect to the caller. The
     * prepareModel function must verify the inputs to the preparedModel
     * function related to preparing the model (as opposed to saving the
     * prepared model to cache) are correct. If there is an error, prepareModel
     * must immediately return the appropriate ErrorStatus value and nullptr for
     * the VersionedIPreparedModel. If the inputs to the prepareModel function
     * that are related to preparing the model are valid and there is no error,
     * prepareModel must prepare the model.
     *
     * If the model was prepared successfully, prepareModel must return
     * ErrorStatus::NONE and the produced VersionedIPreparedModel object. If an
     * error occurred preparing the model, prepareModel must return the
     * appropriate ErrorStatus value and nullptr for the
     * VersionedIPreparedModel.
     *
     * Optionally, the driver may save the prepared model to cache during
     * preparation. Any error that occurs when saving to cache must not affect
     * the status of preparing the model. Even if the input arguments related to
     * the cache may be invalid, or the driver may fail to save to cache, the
     * prepareModel function must finish preparing the model. The driver may
     * choose not to save to cache even if the caching information is provided
     * and valid.
     *
     * The only information that may be unknown to the model at this stage is
     * the shape of the tensors, which may only be known at execution time. As
     * such, some driver services may return partially prepared models, where
     * the prepared model may only be finished when it is paired with a set of
     * inputs to the model. Note that the same prepared model object may be
     * used with different shapes of inputs on different (possibly concurrent)
     * executions.
     *
     * Multiple threads may call prepareModel on the same model concurrently.
     *
     * @param model The model to be prepared for execution.
     * @param preference Indicates the intended execution behavior of a prepared
     *     model.
     * @param modelCache A vector of handles with each entry holding exactly one
     *     cache file descriptor for the security-sensitive cache. The length of
     *     the vector must either be 0 indicating that caching information is not provided,
     *     or match the numModelCache returned from getNumberOfCacheFilesNeeded. The cache
     *     handles will be provided in the same order when retrieving the
     *     preparedModel from cache files with prepareModelFromCache.
     * @param dataCache A vector of handles with each entry holding exactly one
     *     cache file descriptor for the constants' cache. The length of
     *     the vector must either be 0 indicating that caching information is not provided,
     *     or match the numDataCache returned from getNumberOfCacheFilesNeeded. The cache
     *     handles will be provided in the same order when retrieving the
     *     preparedModel from cache files with prepareModelFromCache.
     * @param token A caching token of length Constant::BYTE_SIZE_OF_CACHE_TOKEN
     *     identifying the prepared model. The same token will be provided when retrieving
     *     the prepared model from the cache files with prepareModelFromCache.
     *     Tokens should be chosen to have a low rate of collision for a particular
     *     application. The driver cannot detect a collision; a collision will result
     *     in a failed execution or in a successful execution that produces incorrect
     *     output values. If both modelCache and dataCache are empty indicating that
     *     caching information is not provided, this token must be ignored.
     * @return A pair of:
     *     - status Error status of preparing the model; must be:
     *         - NONE if preparation succeeded
     *         - DEVICE_UNAVAILABLE if driver is offline or busy
     *         - GENERAL_FAILURE if there is an unspecified error
     *         - INVALID_ARGUMENT if one of the input arguments related to
     *             preparing the model is invalid
     *     - preparedModel A VersionedIPreparedModel object representing a model
     *         that has been prepared for execution, else nullptr.
     */
    std::pair<ErrorStatus, std::shared_ptr<VersionedIPreparedModel>> prepareModel(
            const Model& model, ExecutionPreference preference,
            const hidl_vec<hidl_handle>& modelCache, const hidl_vec<hidl_handle>& dataCache,
            const hidl_array<uint8_t, static_cast<uint32_t>(Constant::BYTE_SIZE_OF_CACHE_TOKEN)>&
                    token);

    /**
     * Creates a prepared model from cache files for execution.
     *
     * prepareModelFromCache is used to retrieve a prepared model directly from
     * cache files to avoid slow model compilation time. There are
     * two types of cache file handles provided to the driver: model cache
     * and data cache. For more information on the two types of cache handles,
     * refer to getNumberOfCacheFilesNeeded.
     *
     * The file descriptors must be opened with read and write permission. A file may
     * have any size, and the corresponding file descriptor may have any offset. The
     * driver must truncate a file to zero size before writing to that file. The file
     * descriptors may be closed by the client once the asynchronous preparation has
     * finished. The driver must dup a file descriptor if it wants to get access to
     * the cache file later.
     *
     * The model is prepared synchronously with respect to the caller. The
     * prepareModelFromCache function must verify the inputs to the
     * prepareModelFromCache function are correct, and that the
     * security-sensitive cache has not been modified since it was last written
     * by the driver. If there is an error, or if compilation caching is not
     * supported, or if the security-sensitive cache has been modified,
     * prepareModelFromCache must return the appropriate ErrorStatus value and
     * nullptr for the VersionedIPreparedModel. If the inputs to the
     * prepareModelFromCache function are valid, the security-sensitive cache is
     * not modified, and there is no error, prepareModelFromCache must prepare
     * the model.
     *
     * If the model was prepared successfully, prepareModelFromCache must return
     * ErrorStatus::NONE and the produced VersionedIPreparedModel object. If an
     * error occurred preparing the model, prepareModelFromCache must return the
     * appropriate ErrorStatus value and nullptr for the
     * VersionedIPreparedModel.
     *
     * The only information that may be unknown to the model at this stage is
     * the shape of the tensors, which may only be known at execution time. As
     * such, some driver services may return partially prepared models, where
     * the prepared model may only be finished when it is paired with a set of
     * inputs to the model. Note that the same prepared model object may be
     * used with different shapes of inputs on different (possibly concurrent)
     * executions.
     *
     * @param modelCache A vector of handles with each entry holding exactly one
     *     cache file descriptor for the security-sensitive cache. The length of
     *     the vector must match the numModelCache returned from getNumberOfCacheFilesNeeded.
     *     The cache handles will be provided in the same order as with prepareModel_1_2.
     * @param dataCache A vector of handles with each entry holding exactly one
     *     cache file descriptor for the constants' cache. The length of the vector
     *     must match the numDataCache returned from getNumberOfCacheFilesNeeded.
     *     The cache handles will be provided in the same order as with prepareModel_1_2.
     * @param token A caching token of length Constant::BYTE_SIZE_OF_CACHE_TOKEN
     *     identifying the prepared model. It is the same token provided when saving
     *     the cache files with prepareModel_1_2. Tokens should be chosen
     *     to have a low rate of collision for a particular application. The driver
     *     cannot detect a collision; a collision will result in a failed execution
     *     or in a successful execution that produces incorrect output values.
     * @return A pair of:
     *     - status Error status of preparing the model; must be:
     *         - NONE if preparation succeeded
     *         - DEVICE_UNAVAILABLE if driver is offline or busy
     *         - GENERAL_FAILURE if caching is not supported or if there is an
     *             unspecified error
     *         - INVALID_ARGUMENT if one of the input arguments is invalid
     *     - preparedModel A VersionedIPreparedModel object representing a model
     *        that has been prepared for execution, else nullptr.
     */
    std::pair<ErrorStatus, std::shared_ptr<VersionedIPreparedModel>> prepareModelFromCache(
            const hidl_vec<hidl_handle>& modelCache, const hidl_vec<hidl_handle>& dataCache,
            const hidl_array<uint8_t, static_cast<uint32_t>(Constant::BYTE_SIZE_OF_CACHE_TOKEN)>&
                    token);

    /**
     * Returns the current status of a driver.
     *
     * @return status Status of the driver, one of:
     *                - DeviceStatus::AVAILABLE
     *                - DeviceStatus::BUSY
     *                - DeviceStatus::OFFLINE
     *                - DeviceStatus::UNKNOWN
     */
    DeviceStatus getStatus();

    /**
     * Returns the feature level of a driver.
     *
     * @return featureLevel The API level of the most advanced feature this driver implements.
     *                      For example, if the driver implements the features introduced in
     *                      Android P, the value would be 28.
     *                      Return -1 if the driver is offline or busy, or the query resulted in
     *                      an unspecified error.
     */
    int64_t getFeatureLevel();

    /**
     * Returns the device type of a driver.
     *
     * @return deviceType The type of a given device, which can help application developers
     *                    developers to distribute Machine Learning workloads and other workloads
     *                    such as graphical rendering. E.g., for an app which renders AR scenes
     *                    based on real time object detection results, the developer could choose
     *                    an ACCELERATOR type device for ML workloads, and reserve GPU for
     *                    graphical rendering.
     *                    Return -1 if the driver is offline or busy, or the query resulted in
     *                    an unspecified error.
     */
    int32_t getType() const;

    /**
     * Get the version string of the driver implementation.
     *
     * The version string must be a unique token among the set of version strings of
     * drivers of a specific device. The token identifies the device driver's
     * implementation. The token must not be confused with the feature level which is solely
     * defined by the interface version. This API is opaque to the Android framework, but the
     * Android framework may use the information for debugging or to pass on to NNAPI applications.
     *
     * Application developers sometimes have specific requirements to ensure good user experiences,
     * and they need more information to make intelligent decisions when the Android framework
     * cannot. For example, combined with the device name and other information, the token can help
     * NNAPI applications filter devices based on their needs:
     *     - An application demands a certain level of performance, but a specific version of
     *       the driver cannot meet that requirement because of a performance regression.
     *       The application can blacklist the driver based on the version provided.
     *     - An application has a minimum precision requirement, but certain versions of
     *       the driver cannot meet that requirement because of bugs or certain optimizations.
     *       The application can filter out versions of these drivers.
     *
     * @return status Error status returned from querying the version string. Must be:
     *     - NONE if the query was successful
     *     - DEVICE_UNAVAILABLE if driver is offline or busy
     *     - GENERAL_FAILURE if the query resulted in an
     *       unspecified error
     * @return version The version string of the device implementation.
     *     Must have nonzero length if the query is successful, and must be an empty string if not.
     */
    std::pair<ErrorStatus, hidl_string> getVersionString();

    /**
     * Gets the caching requirements of the driver implementation.
     *
     * There are two types of cache file descriptors provided to the driver: model cache
     * and data cache.
     *
     * The data cache is for caching constant data, possibly including preprocessed
     * and transformed tensor buffers. Any modification to the data cache should
     * have no worse effect than generating bad output values at execution time.
     *
     * The model cache is for caching security-sensitive data such as compiled
     * executable machine code in the device's native binary format. A modification
     * to the model cache may affect the driver's execution behavior, and a malicious
     * client could make use of this to execute beyond the granted permission. Thus,
     * the driver must always check whether the model cache is corrupted before
     * preparing the model from cache.
     *
     * getNumberOfCacheFilesNeeded returns how many of each type of cache files the driver
     * implementation needs to cache a single prepared model. Returning 0 for both types
     * indicates compilation caching is not supported by this driver. The driver may
     * still choose not to cache certain compiled models even if it reports that caching
     * is supported.
     *
     * If the device reports that caching is not supported, the user may avoid calling
     * IDevice::prepareModelFromCache or providing cache file descriptors to
     * IDevice::prepareModel_1_2.
     *
     * @return status Error status of the call, must be:
     *     - NONE if successful
     *     - DEVICE_UNAVAILABLE if driver is offline or busy
     *     - GENERAL_FAILURE if there is an unspecified error
     * @return numModelCache An unsigned integer indicating how many files for model cache
     *                       the driver needs to cache a single prepared model. It must
     *                       be less than or equal to Constant::MAX_NUMBER_OF_CACHE_FILES.
     * @return numDataCache An unsigned integer indicating how many files for data cache
     *                      the driver needs to cache a single prepared model. It must
     *                      be less than or equal to Constant::MAX_NUMBER_OF_CACHE_FILES.
     */
    std::tuple<ErrorStatus, uint32_t, uint32_t> getNumberOfCacheFilesNeeded();

    /**
     * Returns whether this handle to an IDevice object is valid or not.
     *
     * @return bool true if V1_0::IDevice (which could be V1_1::IDevice) is
     *              valid, false otherwise.
     */
    bool operator!=(nullptr_t) const;

    /**
     * Returns whether this handle to an IDevice object is valid or not.
     *
     * @return bool true if V1_0::IDevice (which could be V1_1::IDevice) is
     *              invalid, false otherwise.
     */
    bool operator==(nullptr_t) const;

   private:
    /**
     * All versions of IDevice are necessary because the driver could be v1.0,
     * v1.1, or a later version. All these pointers logically represent the same
     * object.
     *
     * The general strategy is: HIDL returns a V1_0 device object, which
     * (if not nullptr) could be v1.0, v1.1, or a greater version. The V1_0
     * object is then "dynamically cast" to a V1_1 object. If successful,
     * mDeviceV1_1 will point to the same object as mDeviceV1_0; otherwise,
     * mDeviceV1_1 will be nullptr.
     *
     * In general:
     * * If the device is truly v1.0, mDeviceV1_0 will point to a valid object
     *   and mDeviceV1_1 will be nullptr.
     * * If the device is truly v1.1 or later, both mDeviceV1_0 and mDeviceV1_1
     *   will point to the same valid object.
     *
     * Idiomatic usage: if mDeviceV1_1 is non-null, do V1_1 dispatch; otherwise,
     * do V1_0 dispatch.
     */
    sp<V1_0::IDevice> mDeviceV1_0;
    sp<V1_1::IDevice> mDeviceV1_1;
    sp<V1_2::IDevice> mDeviceV1_2;

    /**
     * HIDL callback to be invoked if the service for mDeviceV1_0 crashes.
     */
    const sp<IDeviceDeathHandler> mDeathHandler;
};

/** This class wraps an IPreparedModel object of any version. */
class VersionedIPreparedModel {
    DISALLOW_IMPLICIT_CONSTRUCTORS(VersionedIPreparedModel);

   public:
    /**
     * Constructor for the VersionedIPreparedModel object.
     *
     * This constructor should not be used directly. Instead,
     * VersionedIPreparedModel should be created via
     * VersionedIDevice::prepareModel*.
     *
     * VersionedIPreparedModel is constructed with the V1_0::IPreparedModel object, which
     * represents a device that is at least v1.0 of the interface. The constructor downcasts
     * to the latest version of the IPreparedModel interface, and will default to using the
     * latest version of all IPreparedModel interface methods automatically.
     *
     * @param preparedModel A prepared model object that is least version 1.0 of the
     *                      IPreparedModel interface.
     * @param deathHandler A hidl_death_recipient that will proactively handle
     *                     the case when the service containing the IDevice
     *                     object crashes.
     */
    VersionedIPreparedModel(sp<V1_0::IPreparedModel> preparedModel,
                            sp<IPreparedModelDeathHandler> deathHandler);

    /**
     * Destructor for the VersionedIPreparedModel object.
     *
     * This destructor unlinksToDeath this object's hidl_death_recipient as it
     * no longer needs to handle the case where the IPreparedModel's service
     * crashes.
     */
    ~VersionedIPreparedModel();

    /**
     * Launches an asynchronous execution on a prepared model.
     *
     * The execution is performed asynchronously with respect to the caller.
     * execute must verify the inputs to the function are correct. If there is
     * an error, execute must immediately invoke the callback with the
     * appropriate ErrorStatus value, then return with the same ErrorStatus. If
     * the inputs to the function are valid and there is no error, execute must
     * launch an asynchronous task to perform the execution in the background,
     * and immediately return with ErrorStatus::NONE. If the asynchronous task
     * fails to launch, execute must immediately invoke the callback with
     * ErrorStatus::GENERAL_FAILURE, then return with
     * ErrorStatus::GENERAL_FAILURE.
     *
     * When the asynchronous task has finished its execution, it must
     * immediately invoke the callback object provided as an input to the
     * execute function. This callback must be provided with the ErrorStatus of
     * the execution.
     *
     * If the prepared model was prepared from a model wherein all
     * tensor operands have fully specified dimensions, and the inputs
     * to the function are valid, then the execution should launch
     * and complete successfully (ErrorStatus::NONE). There must be
     * no failure unless the device itself is in a bad state.
     *
     * Multiple threads can call the execute and ExecuteSynchronously functions
     * on the same VersionedIPreparedModel object concurrently with different
     * requests.
     *
     * @param request The input and output information on which the prepared
     *                model is to be executed.
     * @param measure Specifies whether or not to measure duration of the execution.
     * @param callback A callback object used to return the error status of
     *                 the execution. The callback object's notify function must
     *                 be called exactly once, even if the execution was
     *                 unsuccessful.
     * @return status Error status of the call, must be:
     *                - NONE if task is successfully launched
     *                - DEVICE_UNAVAILABLE if driver is offline or busy
     *                - GENERAL_FAILURE if there is an unspecified error
     *                - OUTPUT_INSUFFICIENT_SIZE if provided output buffer is
     *                  not large enough to store the resultant values
     *                - INVALID_ARGUMENT if one of the input arguments is
     *                  invalid
     */
    ErrorStatus execute(const Request& request, MeasureTiming timing,
                        const sp<ExecutionCallback>& callback);

    /**
     * Performs a synchronous execution on a prepared model.
     *
     * The execution is performed synchronously with respect to the caller.
     * executeSynchronously must verify the inputs to the function are
     * correct. If there is an error, executeSynchronously must immediately
     * return with the appropriate ErrorStatus value. If the inputs to the
     * function are valid and there is no error, executeSynchronously must
     * perform the execution, and must not return until the execution is
     * complete.
     *
     * If the prepared model was prepared from a model wherein all tensor
     * operands have fully specified dimensions, and the inputs to the function
     * are valid, then the execution should complete successfully
     * (ErrorStatus::NONE). There must be no failure unless the device itself is
     * in a bad state.
     *
     * Any number of calls to the execute and executeSynchronously
     * functions, in any combination, may be made concurrently, even on the same
     * VersionedIPreparedModel object.
     *
     * @param request The input and output information on which the prepared
     *                model is to be executed.
     * @param measure Specifies whether or not to measure duration of the execution.
     * @return status Error status of the execution, must be:
     *                - NONE if execution is performed successfully
     *                - DEVICE_UNAVAILABLE if driver is offline or busy
     *                - GENERAL_FAILURE if there is an unspecified error
     *                - OUTPUT_INSUFFICIENT_SIZE if at least one output
     *                  operand buffer is not large enough to store the
     *                  corresponding output
     *                - INVALID_ARGUMENT if one of the input arguments is
     *                  invalid
     * @return outputShapes A list of shape information of model output operands.
     *                      The index into "outputShapes" corresponds with the index
     *                      of the output operand in the Request outputs vector.
     *                      outputShapes nust be empty unless the status is either
     *                      NONE or OUTPUT_INSUFFICIENT_SIZE. outputShaps may be
     *                      empty if the status is NONE and all model output operands
     *                      are fully-specified at execution time. outputShapes must
     *                      have the same number of elements as the number of model
     *                      output operands if the status is OUTPUT_INSUFFICIENT_SIZE,
     *                      or if the status is NONE and the model has at least one
     *                      output operand that is not fully-specified.
     * @return Timing Duration of execution. Unless measure is YES and status is
     *                NONE, all times must be reported as UINT64_MAX. A driver may
     *                choose to report any time as UINT64_MAX, indicating that
     *                measurement is not available.
     */
    std::tuple<ErrorStatus, hidl_vec<OutputShape>, Timing> executeSynchronously(
            const Request& request, MeasureTiming measure);

    /**
     * Creates a burst controller on a prepared model.
     *
     * @param blocking 'true' if the FMQ should block until data is available.
     * @return ExecutionBurstController Execution burst controller object.
     *                                  nullptr is returned if the burst cannot
     *                                  be configured for any reason.
     */
    std::shared_ptr<ExecutionBurstController> configureExecutionBurst(bool blocking) const;

    /**
     * Returns whether this handle to an IPreparedModel object is valid or not.
     *
     * @return bool true if V1_0::IPreparedModel (which could be V1_2::IPreparedModel) is
     *              valid, false otherwise.
     */
    bool operator!=(nullptr_t) const;

    /**
     * Returns whether this handle to an IPreparedModel object is valid or not.
     *
     * @return bool true if V1_0::IPreparedModel (which could be V1_2::IPreparedModel) is
     *              invalid, false otherwise.
     */
    bool operator==(nullptr_t) const;

   private:
    /**
     * All versions of IPreparedModel are necessary because the preparedModel could be v1.0,
     * v1.2, or a later version. All these pointers logically represent the same object.
     *
     * The general strategy is: HIDL returns a V1_0 prepared model object, which
     * (if not nullptr) could be v1.0, v1.2, or a greater version. The V1_0
     * object is then "dynamically cast" to a V1_2 object. If successful,
     * mPreparedModelV1_2 will point to the same object as mPreparedModelV1_0; otherwise,
     * mPreparedModelV1_2 will be nullptr.
     *
     * In general:
     * * If the prepared model is truly v1.0, mPreparedModelV1_0 will point to a valid object
     *   and mPreparedModelV1_2 will be nullptr.
     * * If the prepared model is truly v1.2 or later, both mPreparedModelV1_0 and
     *   mPreparedModelV1_2 will point to the same valid object.
     *
     * Idiomatic usage: if mPreparedModelV1_2 is non-null, do V1_2 dispatch; otherwise,
     * do V1_0 dispatch.
     */
    sp<V1_0::IPreparedModel> mPreparedModelV1_0;
    sp<V1_2::IPreparedModel> mPreparedModelV1_2;

    /**
     * HIDL callback to be invoked if the service for mPreparedModelV1_0 crashes.
     */
    const sp<IPreparedModelDeathHandler> mDeathHandler;
};

}  // namespace nn
}  // namespace android

#endif  // ANDROID_ML_NN_RUNTIME_VERSIONED_INTERFACES_H