Error: createEngine() has already been called

vaduganathan

I am using following code to connect my JAVA web application to Light Streamer

public native static void init(String username, String password)
	/*-{
		$wnd.user_name = username;		
		var divTag = document.createElement("div");
		divTag.id = "list";

		divTag.setAttribute("class","ClassName");
		divTag.setAttribute("source","lightstreamer");
		divTag.setAttribute("table","TableName");
		divTag.setAttribute("item",username+"#TableName");
		divTag.setAttribute("field","FieldName");
		divTag.style.display = 'none'; 
		document.body.appendChild(divTag);

		$wnd.page = new $wnd.PushPage();
		$wnd.page.context.setDomain("chellasoftapp.com"); 
		$wnd.page.onEngineCreation = function(engine) {
			$wnd.lsEngine = engine;

			engine.connection.setLSHost("domainName.com"); 
			engine.connection.setLSPort("port"); 
			
			engine.connection.setAdapterName("AdapterName");						

			engine.connection.setUserName(username);
			engine.connection.setPassword(password);

			engine.changeStatus("STREAMING");
		}

		$wnd.page.bind();		
		$wnd.page.createEngine("AdapterName", "LS", "SHARE_SESSION", true);

		var itemName = username+"#iTableName";
		$wnd.pushtable = new $wnd.NonVisualTable(itemName, new Array("TableName"), "DISTINCT");
		$wnd.chellaSoft = this;
		$wnd.pushtable.onItemUpdate = function (item, updateInfo) {
			$wnd.jsonUpdatedStaticJS(updateInfo.getNewValue("FieldName"));
		}

		$wnd.page.addTable($wnd.pushtable, "TableName");
	}-*/;

I had called this method, once the user submit his/her user name and password.
On first time suppose user type mistype his password. And this methord will called and create the engine without any issue. But, then he type the correct password and submit the details it throws the following error.

“3: 18:0:18,438 ER createEngine createEngine() has already been called” .

please advise me how to overcome to this error? Or give me any other suggestions.

Dario Crivelli

In fact, the Engine can only be created once.
Your init function creates the Engine, supplies the credentials, starts streaming and subscribes to a table altogether.
If you have to change the password afterwards, then you should do it separately, by acting on the Engine pointer you have saved, and by just

disconnecting (although the previous STREAMING attempt with the wrong credentials probably failed);
setting the new password on the Engine object
requesting STREAMING again

Note that the table subscription is also kept by the library, so you don't need to repeat it when requesting STREAMING the second time.

vaduganathan

Hi

Thank you very much for your reply,
Following are my queries as a newbie on here (it may very simple one),

How to disconnect the engine? I tried to access the engine object out side of this method. But all of my effort lead me on wrong path (I think).

Yes, as you said, creates the Engine, supplies the credentials, starts streaming and subscribes to a table altogether. Due to I have no idea about, how to access the engine object out side this function I keep all the effort in one place. Kindly advice me, how to split this method too. Thank you.

Dario Crivelli

A pointer to the Engine is received when your onEngineCreation callback is invoked by Lightstreamer library.
I see that the callback saves the pointer to $wnd.lsEngine;
this is the pointer you can use afterwards to invoke all methods targeted to the Engine,
like: $wnd.lsEngine.changeStatus("DISCONNECTED") to disconnect.
If you did that, it should have worked.

Note that the general way of managing the lifecycle of the Engine pointer is slightly different and has to be followed in case you have multiple pages sharing the Engine; it consists of:

implementing the onEngineReadycallback and saving the pointer there (onEngineReady is similar to onEngineCreation, but it is invoked also when the page already finds an Engine and just shares it).
implementing the onEngineLost callback to just clear the pointer (in fact, if a different page holds the shared Engine and gets closed, the Engine may be temporarily unavailable to the other pages).

I didn't really mean that your init method had better be split.
In general, the PushPage and Engine initialization code is separated from the table creation and subscription code. After creating and configuring the PushPage object, you can save the pointer (as you do, in $wnd.page) and use it later when you generate the cells on the page and create the Table object.