@Override
            public void run() {
              subscriber.onProgressUpdate(AbstractDataSource.this);
            }
Subclasses should invoke this method to set the progress.

<p>This method will return {@code true} if the progress was successfully set, or {@code false}
if the data source has already been set, failed or closed.

<p>This will also notify the subscribers if the progress was successfully set.

<p>Do NOT call this method from a synchronized block as it invokes external code of the
subscribers.

@param progress the progress in range [0, 1] to be set.
@return true if the progress was successfully set.
fbcore/src/main/java/com/facebook/datasource/AbstractDataSource.java