audio: Add a helper class to simplify legacy HALs migration am: 43a85cfb2b

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/2674340

Change-Id: Id2572acb414548928dc3ee086d569d6882313254
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

audio/aidl/default/Android.bp

@@ -76,6 +76,7 @@ cc_library {
         "ModulePrimary.cpp",
         "SoundDose.cpp",
         "Stream.cpp",
+        "StreamSwitcher.cpp",
         "Telephony.cpp",
         "alsa/Mixer.cpp",
         "alsa/ModuleAlsa.cpp",

audio/aidl/default/Stream.cpp

@@ -670,8 +670,7 @@ ndk::ScopedAStatus StreamCommonImpl::close() {
         LOG(DEBUG) << __func__ << ": joining the worker thread...";
         mWorker->stop();
         LOG(DEBUG) << __func__ << ": worker thread joined";
-        onClose();
-        mWorker->setClosed();
+        onClose(mWorker->setClosed());
         return ndk::ScopedAStatus::ok();
     } else {
         LOG(ERROR) << __func__ << ": stream was already closed";

audio/aidl/default/StreamSwitcher.cpp

@@ -0,0 +1,230 @@
+/*
+ * Copyright (C) 2023 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.
+ */
+
+#include <limits>
+
+#define LOG_TAG "AHAL_StreamSwitcher"
+
+#include <Utils.h>
+#include <android-base/logging.h>
+#include <error/expected_utils.h>
+
+#include "core-impl/StreamStub.h"
+#include "core-impl/StreamSwitcher.h"
+
+using aidl::android::hardware::audio::effect::IEffect;
+using aidl::android::media::audio::common::AudioDevice;
+
+namespace aidl::android::hardware::audio::core {
+
+StreamSwitcher::StreamSwitcher(StreamContext* context, const Metadata& metadata)
+    : mMetadata(metadata), mStream(new InnerStreamWrapper<StreamStub>(context, mMetadata)) {}
+
+ndk::ScopedAStatus StreamSwitcher::closeCurrentStream(bool validateStreamState) {
+    if (!mStream) return ndk::ScopedAStatus::ok();
+    RETURN_STATUS_IF_ERROR(mStream->prepareToClose());
+    RETURN_STATUS_IF_ERROR(mStream->close());
+    if (validateStreamState && !isValidClosingStreamState(mStream->getStatePriorToClosing())) {
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    mStream.reset();
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::close() {
+    if (mStream != nullptr) {
+        auto status = closeCurrentStream(false /*validateStreamState*/);
+        // The actual state is irrelevant since only StreamSwitcher cares about it.
+        onClose(StreamDescriptor::State::STANDBY);
+        return status;
+    }
+    LOG(ERROR) << __func__ << ": stream was already closed";
+    return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+}
+
+ndk::ScopedAStatus StreamSwitcher::prepareToClose() {
+    if (mStream != nullptr) {
+        return mStream->prepareToClose();
+    }
+    LOG(ERROR) << __func__ << ": stream was closed";
+    return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+}
+
+ndk::ScopedAStatus StreamSwitcher::updateHwAvSyncId(int32_t in_hwAvSyncId) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    RETURN_STATUS_IF_ERROR(mStream->updateHwAvSyncId(in_hwAvSyncId));
+    mHwAvSyncId = in_hwAvSyncId;
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::getVendorParameters(const std::vector<std::string>& in_ids,
+                                                       std::vector<VendorParameter>* _aidl_return) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    if (mIsStubStream) {
+        LOG(ERROR) << __func__ << ": the stream is not connected";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    return mStream->getVendorParameters(in_ids, _aidl_return);
+}
+
+ndk::ScopedAStatus StreamSwitcher::setVendorParameters(
+        const std::vector<VendorParameter>& in_parameters, bool in_async) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    if (mIsStubStream) {
+        mMissedParameters.emplace_back(in_parameters, in_async);
+        return ndk::ScopedAStatus::ok();
+    }
+    return mStream->setVendorParameters(in_parameters, in_async);
+}
+
+ndk::ScopedAStatus StreamSwitcher::addEffect(const std::shared_ptr<IEffect>& in_effect) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    if (!mIsStubStream) {
+        RETURN_STATUS_IF_ERROR(mStream->addEffect(in_effect));
+    }
+    mEffects.push_back(in_effect);
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::removeEffect(const std::shared_ptr<IEffect>& in_effect) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    for (auto it = mEffects.begin(); it != mEffects.end();) {
+        if ((*it)->asBinder() == in_effect->asBinder()) {
+            it = mEffects.erase(it);
+        } else {
+            ++it;
+        }
+    }
+    return !mIsStubStream ? mStream->removeEffect(in_effect) : ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::getStreamCommonCommon(
+        std::shared_ptr<IStreamCommon>* _aidl_return) {
+    if (!mCommon) {
+        LOG(FATAL) << __func__ << ": the common interface was not created";
+    }
+    *_aidl_return = mCommon.getInstance();
+    LOG(DEBUG) << __func__ << ": returning " << _aidl_return->get()->asBinder().get();
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::updateMetadataCommon(const Metadata& metadata) {
+    if (mStream == nullptr) {
+        LOG(ERROR) << __func__ << ": stream was closed";
+        return ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
+    }
+    mMetadata = metadata;
+    return !mIsStubStream ? mStream->updateMetadataCommon(metadata) : ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus StreamSwitcher::initInstance(
+        const std::shared_ptr<StreamCommonInterface>& delegate) {
+    mCommon = ndk::SharedRefBase::make<StreamCommonDelegator>(delegate);
+    // The delegate is null because StreamSwitcher handles IStreamCommon methods by itself.
+    return mStream->initInstance(nullptr);
+}
+
+const StreamContext& StreamSwitcher::getContext() const {
+    return *mContext;
+}
+
+bool StreamSwitcher::isClosed() const {
+    return mStream == nullptr || mStream->isClosed();
+}
+
+const StreamCommonInterface::ConnectedDevices& StreamSwitcher::getConnectedDevices() const {
+    return mStream->getConnectedDevices();
+}
+
+ndk::ScopedAStatus StreamSwitcher::setConnectedDevices(const std::vector<AudioDevice>& devices) {
+    LOG(DEBUG) << __func__ << ": " << ::android::internal::ToString(devices);
+    if (mStream->getConnectedDevices() == devices) return ndk::ScopedAStatus::ok();
+    const DeviceSwitchBehavior behavior = switchCurrentStream(devices);
+    if (behavior == DeviceSwitchBehavior::UNSUPPORTED_DEVICES) {
+        return ndk::ScopedAStatus::fromExceptionCode(EX_UNSUPPORTED_OPERATION);
+    } else if (behavior == DeviceSwitchBehavior::SWITCH_TO_STUB_STREAM && !devices.empty()) {
+        // This is an error in the extending class.
+        LOG(FATAL) << __func__
+                   << ": switching to stub stream with connected devices is not allowed";
+    }
+    if (behavior == USE_CURRENT_STREAM) {
+        mIsStubStream = false;
+    } else {
+        LOG(DEBUG) << __func__ << ": connected devices changed, switching stream";
+        // Two streams can't be opened for the same context, thus we always need to close
+        // the current one before creating a new one.
+        RETURN_STATUS_IF_ERROR(closeCurrentStream(true /*validateStreamState*/));
+        if (behavior == CREATE_NEW_STREAM) {
+            mStream = createNewStream(devices, mContext, mMetadata);
+            mIsStubStream = false;
+        } else {  // SWITCH_TO_STUB_STREAM
+            mStream.reset(new InnerStreamWrapper<StreamStub>(mContext, mMetadata));
+            mIsStubStream = true;
+        }
+        // The delegate is null because StreamSwitcher handles IStreamCommon methods by itself.
+        if (ndk::ScopedAStatus status = mStream->initInstance(nullptr); !status.isOk()) {
+            // Need to close the current failed stream, and report an error.
+            // Since we can't operate without a stream implementation, put a stub in.
+            RETURN_STATUS_IF_ERROR(closeCurrentStream(false /*validateStreamState*/));
+            mStream.reset(new InnerStreamWrapper<StreamStub>(mContext, mMetadata));
+            (void)mStream->initInstance(nullptr);
+            (void)mStream->setConnectedDevices(devices);
+            return status;
+        }
+    }
+    RETURN_STATUS_IF_ERROR(mStream->setConnectedDevices(devices));
+    if (behavior == CREATE_NEW_STREAM) {
+        // These updates are less critical, only log warning on failure.
+        if (mHwAvSyncId.has_value()) {
+            if (auto status = mStream->updateHwAvSyncId(*mHwAvSyncId); !status.isOk()) {
+                LOG(WARNING) << __func__ << ": could not update HW AV Sync for a new stream: "
+                             << status.getDescription();
+            }
+        }
+        for (const auto& vndParam : mMissedParameters) {
+            if (auto status = mStream->setVendorParameters(vndParam.first, vndParam.second);
+                !status.isOk()) {
+                LOG(WARNING) << __func__ << ": error while setting parameters for a new stream: "
+                             << status.getDescription();
+            }
+        }
+        mMissedParameters.clear();
+        for (const auto& effect : mEffects) {
+            if (auto status = mStream->addEffect(effect); !status.isOk()) {
+                LOG(WARNING) << __func__ << ": error while adding effect for a new stream: "
+                             << status.getDescription();
+            }
+        }
+    }
+    return ndk::ScopedAStatus::ok();
+}
+
+}  // namespace aidl::android::hardware::audio::core

audio/aidl/default/include/core-impl/Stream.h

@@ -66,7 +66,8 @@ class StreamContext {
             DataMQ;
 
     // Ensure that this value is not used by any of StreamDescriptor.State enums
-    static constexpr int32_t STATE_CLOSED = -1;
+    static constexpr StreamDescriptor::State STATE_CLOSED =
+            static_cast<StreamDescriptor::State>(-1);
 
     struct DebugParameters {
         // An extra delay for transient states, in ms.
@@ -205,10 +206,14 @@ struct DriverInterface {
 
 class StreamWorkerCommonLogic : public ::android::hardware::audio::common::StreamLogic {
   public:
-    bool isClosed() const {
-        return static_cast<int32_t>(mState.load()) == StreamContext::STATE_CLOSED;
+    bool isClosed() const { return mState == StreamContext::STATE_CLOSED; }
+    StreamDescriptor::State setClosed() {
+        auto prevState = mState.exchange(StreamContext::STATE_CLOSED);
+        if (prevState != StreamContext::STATE_CLOSED) {
+            mStatePriorToClosing = prevState;
+        }
+        return mStatePriorToClosing;
     }
-    void setClosed() { mState = static_cast<StreamDescriptor::State>(StreamContext::STATE_CLOSED); }
     void setIsConnected(bool connected) { mIsConnected = connected; }
 
   protected:
@@ -231,6 +236,9 @@ class StreamWorkerCommonLogic : public ::android::hardware::audio::common::Strea
     // which happens on the worker thread only.
     StreamContext* const mContext;
     DriverInterface* const mDriver;
+    // This is the state the stream was in before being closed. It is retrieved by the main
+    // thread after joining the worker thread.
+    StreamDescriptor::State mStatePriorToClosing = StreamDescriptor::State::STANDBY;
     // Atomic fields are used both by the main and worker threads.
     std::atomic<bool> mIsConnected = false;
     static_assert(std::atomic<StreamDescriptor::State>::is_always_lock_free);
@@ -252,7 +260,7 @@ struct StreamWorkerInterface {
     virtual ~StreamWorkerInterface() = default;
     virtual bool isClosed() const = 0;
     virtual void setIsConnected(bool isConnected) = 0;
-    virtual void setClosed() = 0;
+    virtual StreamDescriptor::State setClosed() = 0;
     virtual bool start() = 0;
     virtual void stop() = 0;
 };
@@ -267,7 +275,7 @@ class StreamWorkerImpl : public StreamWorkerInterface,
         : WorkerImpl(context, driver) {}
     bool isClosed() const override { return WorkerImpl::isClosed(); }
     void setIsConnected(bool isConnected) override { WorkerImpl::setIsConnected(isConnected); }
-    void setClosed() override { WorkerImpl::setClosed(); }
+    StreamDescriptor::State setClosed() override { return WorkerImpl::setClosed(); }
     bool start() override {
         return WorkerImpl::start(WorkerImpl::kThreadName, ANDROID_PRIORITY_AUDIO);
     }
@@ -459,7 +467,7 @@ class StreamCommonImpl : virtual public StreamCommonInterface, virtual public Dr
         };
     }
 
-    virtual void onClose() = 0;
+    virtual void onClose(StreamDescriptor::State statePriorToClosing) = 0;
     void stopWorker();
 
     const StreamContext& mContext;

audio/aidl/default/include/core-impl/StreamRemoteSubmix.h

@@ -81,7 +81,7 @@ class StreamInRemoteSubmix final : public StreamIn, public StreamRemoteSubmix {
             const std::vector<::aidl::android::media::audio::common::MicrophoneInfo>& microphones);
 
   private:
-    void onClose() override { defaultOnClose(); }
+    void onClose(StreamDescriptor::State) override { defaultOnClose(); }
     ndk::ScopedAStatus getActiveMicrophones(
             std::vector<::aidl::android::media::audio::common::MicrophoneDynamicInfo>* _aidl_return)
             override;
@@ -97,7 +97,7 @@ class StreamOutRemoteSubmix final : public StreamOut, public StreamRemoteSubmix
                     offloadInfo);
 
   private:
-    void onClose() override { defaultOnClose(); }
+    void onClose(StreamDescriptor::State) override { defaultOnClose(); }
 };
 
 }  // namespace aidl::android::hardware::audio::core

audio/aidl/default/include/core-impl/StreamStub.h

@@ -52,7 +52,7 @@ class StreamInStub final : public StreamIn, public StreamStub {
             const std::vector<::aidl::android::media::audio::common::MicrophoneInfo>& microphones);
 
   private:
-    void onClose() override { defaultOnClose(); }
+    void onClose(StreamDescriptor::State) override { defaultOnClose(); }
 };
 
 class StreamOutStub final : public StreamOut, public StreamStub {
@@ -64,7 +64,7 @@ class StreamOutStub final : public StreamOut, public StreamStub {
                           offloadInfo);
 
   private:
-    void onClose() override { defaultOnClose(); }
+    void onClose(StreamDescriptor::State) override { defaultOnClose(); }
 };
 
 }  // namespace aidl::android::hardware::audio::core

audio/aidl/default/include/core-impl/StreamSwitcher.h

@@ -0,0 +1,191 @@
+/*
+ * Copyright (C) 2023 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.
+ */
+
+#pragma once
+
+#include "Stream.h"
+
+namespace aidl::android::hardware::audio::core {
+
+// 'StreamSwitcher' is implementation of 'StreamCommonInterface' which allows
+// dynamically switching the underlying stream implementation based on currently
+// connected devices. This is achieved by replacing inheritance from
+// 'StreamCommonImpl' with owning an instance of it. StreamSwitcher must be
+// extended in order to supply the logic for choosing the stream
+// implementation. When there are no connected devices, for instance, upon the
+// creation, the StreamSwitcher engages an instance of a stub stream in order to
+// keep serving requests coming via 'StreamDescriptor'.
+//
+// StreamSwitcher implements the 'IStreamCommon' interface directly, with
+// necessary delegation to the current stream implementation. While the stub
+// stream is engaged, any requests made via 'IStreamCommon' (parameters, effects
+// setting, etc) are postponed and only delivered on device connection change
+// to the "real" stream implementation provided by the extending class. This is why
+// the behavior of StreamSwitcher in the "stub" state is not identical to behavior
+// of 'StreamStub'. It can become a full substitute for 'StreamStub' once
+// device connection change event occurs and the extending class returns
+// 'LEAVE_CURRENT_STREAM' from 'switchCurrentStream' method.
+//
+// There is a natural limitation that the current stream implementation may only
+// be switched when the stream is in the 'STANDBY' state. Thus, when the event
+// to switch the stream occurs, the current stream is stopped and joined, and
+// its last state is validated. Since the change of the set of connected devices
+// normally occurs on patch updates, if the stream was not in standby, this is
+// reported to the caller of 'IModule.setAudioPatch' as the 'EX_ILLEGAL_STATE'
+// error.
+//
+// The simplest use case, when the implementor just needs to emulate the legacy HAL API
+// behavior of receiving the connected devices upon stream creation, the implementation
+// of the extending class can look as follows. We assume that 'StreamLegacy' implementation
+// is the one requiring to know connected devices on creation:
+//
+//   class StreamLegacy : public StreamCommonImpl {
+//     public:
+//       StreamLegacy(StreamContext* context, const Metadata& metadata,
+//                    const std::vector<AudioDevice>& devices);
+//   };
+//
+//   class StreamOutLegacy final : public StreamOut, public StreamSwitcher {
+//     public:
+//       StreamOutLegacy(StreamContext&& context, metatadata etc.)
+//     private:
+//       DeviceSwitchBehavior switchCurrentStream(const std::vector<AudioDevice>&) override {
+//           // This implementation effectively postpones stream creation until
+//           // receiving the first call to 'setConnectedDevices' with a non-empty list.
+//           return isStubStream() ? DeviceSwitchBehavior::CREATE_NEW_STREAM :
+//               DeviceSwitchBehavior::USE_CURRENT_STREAM;
+//       }
+//       std::unique_ptr<StreamCommonInterfaceEx> createNewStream(
+//               const std::vector<AudioDevice>& devices,
+//               StreamContext* context, const Metadata& metadata) override {
+//           return std::unique_ptr<StreamCommonInterfaceEx>(new InnerStreamWrapper<StreamLegacy>(
+//               context, metadata, devices));
+//       }
+//       void onClose(StreamDescriptor::State) override { defaultOnClose(); }
+//   }
+//
+
+class StreamCommonInterfaceEx : virtual public StreamCommonInterface {
+  public:
+    virtual StreamDescriptor::State getStatePriorToClosing() const = 0;
+};
+
+template <typename T>
+class InnerStreamWrapper : public T, public StreamCommonInterfaceEx {
+  public:
+    InnerStreamWrapper(StreamContext* context, const Metadata& metadata) : T(context, metadata) {}
+    StreamDescriptor::State getStatePriorToClosing() const override { return mStatePriorToClosing; }
+
+  private:
+    // Do not need to do anything on close notification from the inner stream
+    // because StreamSwitcher handles IStreamCommon::close by itself.
+    void onClose(StreamDescriptor::State statePriorToClosing) override {
+        mStatePriorToClosing = statePriorToClosing;
+    }
+
+    StreamDescriptor::State mStatePriorToClosing = StreamDescriptor::State::STANDBY;
+};
+
+class StreamSwitcher : virtual public StreamCommonInterface {
+  public:
+    StreamSwitcher(StreamContext* context, const Metadata& metadata);
+
+    ndk::ScopedAStatus close() override;
+    ndk::ScopedAStatus prepareToClose() override;
+    ndk::ScopedAStatus updateHwAvSyncId(int32_t in_hwAvSyncId) override;
+    ndk::ScopedAStatus getVendorParameters(const std::vector<std::string>& in_ids,
+                                           std::vector<VendorParameter>* _aidl_return) override;
+    ndk::ScopedAStatus setVendorParameters(const std::vector<VendorParameter>& in_parameters,
+                                           bool in_async) override;
+    ndk::ScopedAStatus addEffect(
+            const std::shared_ptr<::aidl::android::hardware::audio::effect::IEffect>& in_effect)
+            override;
+    ndk::ScopedAStatus removeEffect(
+            const std::shared_ptr<::aidl::android::hardware::audio::effect::IEffect>& in_effect)
+            override;
+
+    ndk::ScopedAStatus getStreamCommonCommon(std::shared_ptr<IStreamCommon>* _aidl_return) override;
+    ndk::ScopedAStatus updateMetadataCommon(const Metadata& metadata) override;
+
+    ndk::ScopedAStatus initInstance(
+            const std::shared_ptr<StreamCommonInterface>& delegate) override;
+    const StreamContext& getContext() const override;
+    bool isClosed() const override;
+    const ConnectedDevices& getConnectedDevices() const override;
+    ndk::ScopedAStatus setConnectedDevices(
+            const std::vector<::aidl::android::media::audio::common::AudioDevice>& devices)
+            override;
+
+  protected:
+    // Since switching a stream requires closing down the current stream, StreamSwitcher
+    // asks the extending class its intent on the connected devices change.
+    enum DeviceSwitchBehavior {
+        // Continue using the current stream implementation. If it's the stub implementation,
+        // StreamSwitcher starts treating the stub stream as a "real" implementation,
+        // without effectively closing it and starting again.
+        USE_CURRENT_STREAM,
+        // This is the normal case when the extending class provides a "real" implementation
+        // which is not a stub implementation.
+        CREATE_NEW_STREAM,
+        // This is the case when the extending class wants to revert back to the initial
+        // condition of using a stub stream provided by the StreamSwitcher. This behavior
+        // is only allowed when the list of connected devices is empty.
+        SWITCH_TO_STUB_STREAM,
+        // Use when the set of devices is not supported by the extending class. This returns
+        // 'EX_UNSUPPORTED_OPERATION' from 'setConnectedDevices'.
+        UNSUPPORTED_DEVICES,
+    };
+    // StreamSwitcher will call these methods from 'setConnectedDevices'. If the switch behavior
+    // is 'CREATE_NEW_STREAM', the 'createwNewStream' function will be called (with the same
+    // device vector) for obtaining a new stream implementation, assuming that closing
+    // the current stream was a success.
+    virtual DeviceSwitchBehavior switchCurrentStream(
+            const std::vector<::aidl::android::media::audio::common::AudioDevice>& devices) = 0;
+    virtual std::unique_ptr<StreamCommonInterfaceEx> createNewStream(
+            const std::vector<::aidl::android::media::audio::common::AudioDevice>& devices,
+            StreamContext* context, const Metadata& metadata) = 0;
+    virtual void onClose(StreamDescriptor::State streamPriorToClosing) = 0;
+
+    bool isStubStream() const { return mIsStubStream; }
+    StreamCommonInterfaceEx* getCurrentStream() const { return mStream.get(); }
+
+  private:
+    using VndParam = std::pair<std::vector<VendorParameter>, bool /*isAsync*/>;
+
+    static constexpr bool isValidClosingStreamState(StreamDescriptor::State state) {
+        return state == StreamDescriptor::State::STANDBY || state == StreamDescriptor::State::ERROR;
+    }
+
+    ndk::ScopedAStatus closeCurrentStream(bool validateStreamState);
+
+    // StreamSwitcher does not own the context.
+    StreamContext* mContext;
+    Metadata mMetadata;
+    ChildInterface<StreamCommonDelegator> mCommon;
+    // The current stream.
+    std::unique_ptr<StreamCommonInterfaceEx> mStream;
+    // Indicates whether 'mCurrentStream' is a stub stream implementation
+    // maintained by StreamSwitcher until the extending class provides a "real"
+    // implementation. The invariant of this state is that there are no connected
+    // devices.
+    bool mIsStubStream = true;
+    // Storage for the data from commands received via 'IStreamCommon'.
+    std::optional<int32_t> mHwAvSyncId;
+    std::vector<VndParam> mMissedParameters;
+    std::vector<std::shared_ptr<::aidl::android::hardware::audio::effect::IEffect>> mEffects;
+};
+
+}  // namespace aidl::android::hardware::audio::core

audio/aidl/default/include/core-impl/StreamUsb.h

@@ -53,7 +53,7 @@ class StreamInUsb final : public StreamIn, public StreamUsb {
             const std::vector<::aidl::android::media::audio::common::MicrophoneInfo>& microphones);
 
   private:
-    void onClose() override { defaultOnClose(); }
+    void onClose(StreamDescriptor::State) override { defaultOnClose(); }
     ndk::ScopedAStatus getActiveMicrophones(
             std::vector<::aidl::android::media::audio::common::MicrophoneDynamicInfo>* _aidl_return)
             override;
@@ -68,7 +68,7 @@ class StreamOutUsb final : public StreamOut, public StreamUsb {
                          offloadInfo);
 
   private:
-    void onClose() override { defaultOnClose(); }
+    void onClose(StreamDescriptor::State) override { defaultOnClose(); }
     ndk::ScopedAStatus getHwVolume(std::vector<float>* _aidl_return) override;
     ndk::ScopedAStatus setHwVolume(const std::vector<float>& in_channelVolumes) override;