Fixes ContextExt referencing itself and not deallocating

Also alleviates NIO direct buffers deallocation slowness

Signed-off-by: ncordon <[email protected]>

Author: ncordon

src/main/native/org_bblfsh_client_v2_libuast_Libuast.cc

@@ -144,7 +144,7 @@ class ContextExt {
     delete (ctx);
 
     if (jCtxExt)
-      getJNIEnv()->DeleteGlobalRef(jCtxExt);
+      getJNIEnv()->DeleteWeakGlobalRef(jCtxExt);
   }
 
   // lookup searches for a specific node handle.
@@ -159,7 +159,7 @@ class ContextExt {
   // We need this because a NodeExt from Scala side includes
   // a Scala ContextExt and a handle to the native C node
   void setJavaContext(jobject ctx) {
-    jCtxExt = getJNIEnv()->NewGlobalRef(ctx);
+    jCtxExt = getJNIEnv()->NewWeakGlobalRef(ctx);
   }
 
   // Iterate returns iterator over an external UAST tree.

src/main/scala/org/bblfsh/client/v2/BblfshClient.scala

@@ -149,7 +149,16 @@ object BblfshClient {
     def decode(): ContextExt = {
       val bufDirectCopy = ByteBuffer.allocateDirect(buf.size)
       buf.copyTo(bufDirectCopy)
-      BblfshClient.decode(bufDirectCopy)
+      val result = BblfshClient.decode(bufDirectCopy)
+      // Sometimes the direct buffer can take a lot to deallocate,
+      // causing Out of Memory, because it is not allocated in
+      // in the JVM heap and will only be deallocated them when
+      // JVM does not have more space in its heap
+      // This line alleviates the problem
+      // Problem can be tested if we remove it and do a
+      // loop decoding a file
+      System.gc()
+      result
     }
   }