oboe: refactor waitForStateChange for OpenSL ES

Do not return ErrorTimeout is user passed timeout==0.

Related to #406

src/opensles/AudioStreamOpenSLES.cpp

@@ -311,23 +311,30 @@ int64_t AudioStreamOpenSLES::getFramesProcessedByServer() const {
 Result AudioStreamOpenSLES::waitForStateChange(StreamState currentState,
                                                      StreamState *nextState,
                                                      int64_t timeoutNanoseconds) {
-    LOGD("AudioStreamOpenSLES::waitForStateChange()");
-
+    Result oboeResult = (timeoutNanoseconds <= 0) ? Result::OK : Result::ErrorTimeout;
     int64_t durationNanos = 20 * kNanosPerMillisecond; // arbitrary
-    StreamState state = getState();
 
-    while (state == currentState && timeoutNanoseconds > 0){
+    while (true) {
+        const StreamState state = getState(); // this does not require a lock
+        if (nextState != nullptr) {
+            *nextState = state;
+        }
+        if (currentState != state) { // state changed?
+            oboeResult = Result::OK;
+            break;
+        }
+
+        // Did we timeout or did user ask for non-blocking?
+        if (timeoutNanoseconds <= 0) {
+            break;
+        }
+
         if (durationNanos > timeoutNanoseconds){
             durationNanos = timeoutNanoseconds;
         }
         AudioClock::sleepForNanos(durationNanos);
         timeoutNanoseconds -= durationNanos;
-
-        state = getState();
-    }
-    if (nextState != nullptr) {
-        *nextState = state;
     }
 
-    return (state == currentState) ? Result::ErrorTimeout : Result::OK;
+    return oboeResult;
 }

src/opensles/AudioStreamOpenSLES.h

@@ -112,7 +112,7 @@ class AudioStreamOpenSLES : public AudioStreamBuffered {
 
     uint8_t              *mCallbackBuffer = nullptr;
     int32_t               mBytesPerCallback = oboe::kUnspecified;
-    StreamState           mState = StreamState::Uninitialized;
+    std::atomic<StreamState>           mState{StreamState::Uninitialized};
 
     MonotonicCounter      mPositionMillis; // for tracking OpenSL ES service position
 };