Add a buffer queue for Android Downloader to prevent out of memory

When the AssetManagerEx start downloading, it used to create all the
download tasks all at once. When the app has a large number of asset
files, it is likely to crash due to out of memory when creating
threads for each of the download tasks. This commit adds a buffer
queue to the downloader to use the `countOfMaxProcessingTasks`
property from hints, preventing all the tasks from starting all at once.

cocos/network/CCDownloader-android.cpp

@@ -70,7 +70,7 @@ namespace cocos2d { namespace network {
             if (JniHelper::getStaticMethodInfo(methodInfo,
                                                JCLS_DOWNLOADER,
                                                "createDownloader",
-                                               "(II" JARG_STR ")" JARG_DOWNLOADER))
+                                               "(II" JARG_STR "I)" JARG_DOWNLOADER))
             {
                 jobject jStr = methodInfo.env->NewStringUTF(hints.tempFileNameSuffix.c_str());
                 jobject jObj = methodInfo.env->CallStaticObjectMethod(
@@ -78,7 +78,8 @@ namespace cocos2d { namespace network {
                         methodInfo.methodID,
                         _id,
                         hints.timeoutInSeconds,
-                        jStr
+                        jStr,
+                        hints.countOfMaxProcessingTasks
                 );
                 _impl = methodInfo.env->NewGlobalRef(jObj);
                 DLLOG("android downloader: jObj: %p, _impl: %p", jObj, _impl);

cocos/platform/android/java/src/org/cocos2dx/lib/Cocos2dxDownloader.java

@@ -99,6 +99,10 @@ class FileTaskHandler extends FileAsyncHttpResponseHandler {
     @Override
     public void onFinish() {
         // onFinish called after onSuccess/onFailure
+        Runnable taskRunnable = _downloader.dequeue();
+        if (taskRunnable != null) {
+            Cocos2dxHelper.getActivity().runOnUiThread(taskRunnable);
+        }
     }
 
     @Override
@@ -166,7 +170,9 @@ public class Cocos2dxDownloader {
     private int _id;
     private AsyncHttpClient _httpClient = new AsyncHttpClient();
     private String _tempFileNameSufix;
+    private int _countOfMaxProcessingTasks;
     private HashMap _taskMap = new HashMap();
+    private Queue<Runnable> _taskQueue = new LinkedList<Runnable>();
 
     void onProgress(final int id, final long downloadBytes, final long downloadNow, final long downloadTotal) {
         DownloadTask task = (DownloadTask)_taskMap.get(id);
@@ -202,7 +208,7 @@ public class Cocos2dxDownloader {
         });
     }
 
-    public static Cocos2dxDownloader createDownloader(int id, int timeoutInSeconds, String tempFileNameSufix) {
+    public static Cocos2dxDownloader createDownloader(int id, int timeoutInSeconds, String tempFileNameSufix, int countOfMaxProcessingTasks) {
         Cocos2dxDownloader downloader = new Cocos2dxDownloader();
         downloader._id = id;
 
@@ -214,6 +220,7 @@ public class Cocos2dxDownloader {
         downloader._httpClient.allowRetryExceptionClass(javax.net.ssl.SSLException.class);
 
         downloader._tempFileNameSufix = tempFileNameSufix;
+        downloader._countOfMaxProcessingTasks = countOfMaxProcessingTasks;
         return downloader;
     }
 
@@ -222,7 +229,7 @@ public class Cocos2dxDownloader {
         final String url = url_;
         final String path = path_;
 
-        Cocos2dxHelper.getActivity().runOnUiThread(new Runnable() {
+        Runnable taskRunnable = new Runnable() {
             @Override
             public void run() {
                 DownloadTask task = new DownloadTask();
@@ -269,7 +276,13 @@ public class Cocos2dxDownloader {
                     downloader._taskMap.put(id, task);
                 }
             }
-        });
+        };
+        if (downloader._taskQueue.size() < downloader._countOfMaxProcessingTasks) {
+            Cocos2dxHelper.getActivity().runOnUiThread(taskRunnable);
+            downloader._taskQueue.add(null);
+        } else {
+            downloader._taskQueue.add(taskRunnable);
+        }
     }
 
     public static void cancelAllRequests(final Cocos2dxDownloader downloader) {
@@ -291,6 +304,16 @@ public class Cocos2dxDownloader {
         });
     }
 
+    public Runnable dequeue() {
+        if (!_taskQueue.isEmpty() && _taskQueue.element() == null) {
+            _taskQueue.remove();
+        }
+        if (!_taskQueue.isEmpty()) {
+            return _taskQueue.remove();
+        }
+        return null;
+    }
+
     native void nativeOnProgress(int id, int taskId, long dl, long dlnow, long dltotal);
     native void nativeOnFinish(int id, int taskId, int errCode, String errStr, final byte[] data);
 }