PR feedback.

Remove busywait

usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/util/SerialInputOutputManager.java

@@ -152,7 +152,16 @@ public class SerialInputOutputManager {
      */
     public void writeAsync(byte[] data) {
         synchronized (mWriteBufferLock) {
+            while (mWriteBuffer.remaining() < data.length) {
+                try {
+                    wait(); // Block until space is available in the buffer
+                } catch (InterruptedException e) {
+                    Thread.currentThread().interrupt(); // Restore the interrupt flag
+                    return; // Exit gracefully
+                }
+            }
             mWriteBuffer.put(data);
+            notifyAll(); // Notify waiting threads
         }
     }
 
@@ -184,6 +193,9 @@ public class SerialInputOutputManager {
      */
     public void stop() {
         if(mState.compareAndSet(State.RUNNING, State.STOPPING)) {
+            synchronized (mWriteBufferLock) {
+                notifyAll(); // Wake up any waiting thread to check the stop condition
+            }
             Log.i(TAG, "Stop requested");
         }
     }
@@ -231,7 +243,7 @@ public class SerialInputOutputManager {
      * Continuously services the read buffers until {@link #stop()} is called, or until a driver exception is
      * raised.
      */
-    private void runRead() {
+    void runRead() {
         Log.i(TAG, "runRead running ...");
         try {
             setThreadPriority();
@@ -263,7 +275,7 @@ public class SerialInputOutputManager {
      * Continuously services the write buffers until {@link #stop()} is called, or until a driver exception is
      * raised.
      */
-    private void runWrite() {
+    void runWrite() {
         Log.i(TAG, "runWrite running ...");
         try {
             setThreadPriority();
@@ -311,7 +323,7 @@ public class SerialInputOutputManager {
         }
     }
 
-    private void stepWrite() throws IOException {
+    private void stepWrite() throws IOException, InterruptedException {
         // Handle outgoing data.
         byte[] buffer = null;
         synchronized (mWriteBufferLock) {
@@ -321,12 +333,15 @@ public class SerialInputOutputManager {
                 mWriteBuffer.rewind();
                 mWriteBuffer.get(buffer, 0, len);
                 mWriteBuffer.clear();
+            } else {
+                wait();
             }
         }
         if (buffer != null) {
             if (DEBUG) {
                 Log.d(TAG, "Writing data len=" + buffer.length);
             }
+            notifyAll(); // Notify writeAsync that there is space in the buffer
             mSerialPort.write(buffer, mWriteTimeout);
         }
     }