diff --git a/services/oboeservice/AAudioServiceStreamBase.cpp b/services/oboeservice/AAudioServiceStreamBase.cpp
index dba9fb9..e750e81 100644
--- a/services/oboeservice/AAudioServiceStreamBase.cpp
+++ b/services/oboeservice/AAudioServiceStreamBase.cpp
@@ -24,6 +24,7 @@
 
 #include <media/MediaMetricsItem.h>
 #include <media/TypeConverter.h>
+#include <mediautils/SchedulingPolicyService.h>
 
 #include "binding/IAAudioService.h"
 #include "binding/AAudioServiceMessage.h"
@@ -169,11 +170,16 @@
 }
 
 aaudio_result_t AAudioServiceStreamBase::close() {
+    std::lock_guard<std::mutex> lock(mLock);
+    return close_l();
+}
+
+aaudio_result_t AAudioServiceStreamBase::close_l() {
     if (getState() == AAUDIO_STREAM_STATE_CLOSED) {
         return AAUDIO_OK;
     }
 
-    stop();
+    stop_l();
 
     aaudio_result_t result = AAUDIO_OK;
     sp<AAudioServiceEndpoint> endpoint = mServiceEndpointWeak.promote();
@@ -185,7 +191,7 @@
         endpointManager.closeEndpoint(endpoint);
 
         // AAudioService::closeStream() prevents two threads from closing at the same time.
-        mServiceEndpoint.clear(); // endpoint will hold the pointer until this method returns.
+        mServiceEndpoint.clear(); // endpoint will hold the pointer after this method returns.
     }
 
     {
@@ -219,9 +225,18 @@
  * An AAUDIO_SERVICE_EVENT_STARTED will be sent to the client when complete.
  */
 aaudio_result_t AAudioServiceStreamBase::start() {
+    std::lock_guard<std::mutex> lock(mLock);
+
     const int64_t beginNs = AudioClock::getNanoseconds();
     aaudio_result_t result = AAUDIO_OK;
 
+    if (auto state = getState();
+        state == AAUDIO_STREAM_STATE_CLOSED || state == AAUDIO_STREAM_STATE_DISCONNECTED) {
+        ALOGW("%s() already CLOSED, returns INVALID_STATE, handle = %d",
+                __func__, getHandle());
+        return AAUDIO_ERROR_INVALID_STATE;
+    }
+
     mediametrics::Defer defer([&] {
         mediametrics::LogItem(mMetricsId)
             .set(AMEDIAMETRICS_PROP_EVENT, AMEDIAMETRICS_PROP_EVENT_VALUE_START)
@@ -231,7 +246,7 @@
             .record(); });
 
     if (isRunning()) {
-        return AAUDIO_OK;
+        return result;
     }
 
     setFlowing(false);
@@ -254,16 +269,21 @@
     return result;
 
 error:
-    disconnect();
+    disconnect_l();
     return result;
 }
 
 aaudio_result_t AAudioServiceStreamBase::pause() {
-    const int64_t beginNs = AudioClock::getNanoseconds();
+    std::lock_guard<std::mutex> lock(mLock);
+    return pause_l();
+}
+
+aaudio_result_t AAudioServiceStreamBase::pause_l() {
     aaudio_result_t result = AAUDIO_OK;
     if (!isRunning()) {
         return result;
     }
+    const int64_t beginNs = AudioClock::getNanoseconds();
 
     mediametrics::Defer defer([&] {
         mediametrics::LogItem(mMetricsId)
@@ -279,7 +299,7 @@
 
     result = stopTimestampThread();
     if (result != AAUDIO_OK) {
-        disconnect();
+        disconnect_l();
         return result;
     }
 
@@ -292,7 +312,7 @@
     result = endpoint->stopStream(this, mClientHandle);
     if (result != AAUDIO_OK) {
         ALOGE("%s() mServiceEndpoint returned %d, %s", __func__, result, getTypeText());
-        disconnect(); // TODO should we return or pause Base first?
+        disconnect_l(); // TODO should we return or pause Base first?
     }
 
     sendServiceEvent(AAUDIO_SERVICE_EVENT_PAUSED);
@@ -301,11 +321,16 @@
 }
 
 aaudio_result_t AAudioServiceStreamBase::stop() {
-    const int64_t beginNs = AudioClock::getNanoseconds();
+    std::lock_guard<std::mutex> lock(mLock);
+    return stop_l();
+}
+
+aaudio_result_t AAudioServiceStreamBase::stop_l() {
     aaudio_result_t result = AAUDIO_OK;
     if (!isRunning()) {
         return result;
     }
+    const int64_t beginNs = AudioClock::getNanoseconds();
 
     mediametrics::Defer defer([&] {
         mediametrics::LogItem(mMetricsId)
@@ -322,7 +347,7 @@
     sendCurrentTimestamp(); // warning - this calls a virtual function
     result = stopTimestampThread();
     if (result != AAUDIO_OK) {
-        disconnect();
+        disconnect_l();
         return result;
     }
 
@@ -336,7 +361,7 @@
     result = endpoint->stopStream(this, mClientHandle);
     if (result != AAUDIO_OK) {
         ALOGE("%s() stopStream returned %d, %s", __func__, result, getTypeText());
-        disconnect();
+        disconnect_l();
         // TODO what to do with result here?
     }
 
@@ -355,11 +380,12 @@
 }
 
 aaudio_result_t AAudioServiceStreamBase::flush() {
-    const int64_t beginNs = AudioClock::getNanoseconds();
+    std::lock_guard<std::mutex> lock(mLock);
     aaudio_result_t result = AAudio_isFlushAllowed(getState());
     if (result != AAUDIO_OK) {
         return result;
     }
+    const int64_t beginNs = AudioClock::getNanoseconds();
 
     mediametrics::Defer defer([&] {
         mediametrics::LogItem(mMetricsId)
@@ -404,16 +430,66 @@
 }
 
 void AAudioServiceStreamBase::disconnect() {
-    if (getState() != AAUDIO_STREAM_STATE_DISCONNECTED) {
+    std::lock_guard<std::mutex> lock(mLock);
+    disconnect_l();
+}
+
+void AAudioServiceStreamBase::disconnect_l() {
+    if (getState() != AAUDIO_STREAM_STATE_DISCONNECTED
+        && getState() != AAUDIO_STREAM_STATE_CLOSED) {
+
         mediametrics::LogItem(mMetricsId)
             .set(AMEDIAMETRICS_PROP_EVENT, AMEDIAMETRICS_PROP_EVENT_VALUE_DISCONNECT)
             .set(AMEDIAMETRICS_PROP_STATE, AudioGlobal_convertStreamStateToText(getState()))
             .record();
+
         sendServiceEvent(AAUDIO_SERVICE_EVENT_DISCONNECTED);
         setState(AAUDIO_STREAM_STATE_DISCONNECTED);
     }
 }
 
+aaudio_result_t AAudioServiceStreamBase::registerAudioThread(pid_t clientThreadId,
+        int priority) {
+    std::lock_guard<std::mutex> lock(mLock);
+    aaudio_result_t result = AAUDIO_OK;
+    if (getRegisteredThread() != AAudioServiceStreamBase::ILLEGAL_THREAD_ID) {
+        ALOGE("AAudioService::registerAudioThread(), thread already registered");
+        result = AAUDIO_ERROR_INVALID_STATE;
+    } else {
+        const pid_t ownerPid = IPCThreadState::self()->getCallingPid(); // TODO review
+        setRegisteredThread(clientThreadId);
+        int err = android::requestPriority(ownerPid, clientThreadId,
+                                           priority, true /* isForApp */);
+        if (err != 0) {
+            ALOGE("AAudioService::registerAudioThread(%d) failed, errno = %d, priority = %d",
+                  clientThreadId, errno, priority);
+            result = AAUDIO_ERROR_INTERNAL;
+        }
+    }
+    return result;
+}
+
+aaudio_result_t AAudioServiceStreamBase::unregisterAudioThread(pid_t clientThreadId) {
+    std::lock_guard<std::mutex> lock(mLock);
+    aaudio_result_t result = AAUDIO_OK;
+    if (getRegisteredThread() != clientThreadId) {
+        ALOGE("%s(), wrong thread", __func__);
+        result = AAUDIO_ERROR_ILLEGAL_ARGUMENT;
+    } else {
+        setRegisteredThread(0);
+    }
+    return result;
+}
+
+void AAudioServiceStreamBase::setState(aaudio_stream_state_t state) {
+    // CLOSED is a final state.
+    if (mState != AAUDIO_STREAM_STATE_CLOSED) {
+        mState = state;
+    } else {
+        ALOGW_IF(mState != state, "%s(%d) when already CLOSED", __func__, state);
+    }
+}
+
 aaudio_result_t AAudioServiceStreamBase::sendServiceEvent(aaudio_service_event_t event,
                                                           double  dataDouble) {
     AAudioServiceMessage command;
@@ -511,6 +587,7 @@
  * used to communicate with the underlying HAL or Service.
  */
 aaudio_result_t AAudioServiceStreamBase::getDescription(AudioEndpointParcelable &parcelable) {
+    std::lock_guard<std::mutex> lock(mLock);
     {
         std::lock_guard<std::mutex> lock(mUpMessageQueueLock);
         if (mUpMessageQueue == nullptr) {