diff --git a/services/audioflinger/AudioFlinger.cpp b/services/audioflinger/AudioFlinger.cpp
index f71ba0a..1c19057 100644
--- a/services/audioflinger/AudioFlinger.cpp
+++ b/services/audioflinger/AudioFlinger.cpp
@@ -809,9 +809,8 @@
             }
         }
     }
-    if (thread != NULL) {
-        result = thread->setParameters(keyValuePairs);
-        return result;
+    if (thread != 0) {
+        return thread->setParameters(keyValuePairs);
     }
     return BAD_VALUE;
 }
@@ -3206,7 +3205,7 @@
     mWaitTimeMs = UINT_MAX;
     for (size_t i = 0; i < mOutputTracks.size(); i++) {
         sp<ThreadBase> strong = mOutputTracks[i]->thread().promote();
-        if (strong != NULL) {
+        if (strong != 0) {
             uint32_t waitTimeMs = (strong->frameCount() * 2 * 1000) / strong->sampleRate();
             if (waitTimeMs < mWaitTimeMs) {
                 mWaitTimeMs = waitTimeMs;
@@ -3330,9 +3329,12 @@
         }
     }
     mCblkMemory.clear();            // and free the shared memory
-    if (mClient != NULL) {
+    if (mClient != 0) {
         // Client destructor must run with AudioFlinger mutex locked
         Mutex::Autolock _l(mClient->audioFlinger()->mLock);
+        // If the client's reference count drops to zero, the associated destructor
+        // must run with AudioFlinger lock held. Thus the explicit clear() rather than
+        // relying on the automatic clear() at end of scope.
         mClient.clear();
     }
 }
@@ -3486,7 +3488,7 @@
     uint32_t vlr = mCblk->getVolumeLR();
     snprintf(buffer, size, "   %05d %05d %03u %03u 0x%08x %05u   %04u %1d %1d %1d %05u %05u %05u  0x%08x 0x%08x 0x%08x 0x%08x\n",
             mName - AudioMixer::TRACK0,
-            (mClient == NULL) ? getpid() : mClient->pid(),
+            (mClient == 0) ? getpid() : mClient->pid(),
             mStreamType,
             mFormat,
             mChannelMask,
@@ -3813,7 +3815,7 @@
 void AudioFlinger::RecordThread::RecordTrack::dump(char* buffer, size_t size)
 {
     snprintf(buffer, size, "   %05d %03u 0x%08x %05d   %04u %01d %05u  %08x %08x\n",
-            (mClient == NULL) ? getpid() : mClient->pid(),
+            (mClient == 0) ? getpid() : mClient->pid(),
             mFormat,
             mChannelMask,
             mSessionId,
@@ -4528,7 +4530,7 @@
         track = new RecordTrack(this, client, sampleRate,
                       format, channelMask, frameCount, flags, sessionId);
 
-        if (track->getCblk() == NULL) {
+        if (track->getCblk() == 0) {
             lStatus = NO_MEMORY;
             goto Exit;
         }
@@ -7102,7 +7104,7 @@
     bool locked = mCblk != NULL && tryLock(mCblk->lock);
 
     snprintf(buffer, size, "\t\t\t%05d %05d    %01u    %01u      %05u  %05u\n",
-            (mClient == NULL) ? getpid() : mClient->pid(),
+            (mClient == 0) ? getpid() : mClient->pid(),
             mPriority,
             mHasControl,
             !locked,