I am trying to ensure that I only instantiate a class once. In my function I have a static variable. When $_POST receives a value, it calls the function with the value received. Why is this static variable overwritten each time? $aClass is always NULL. Is the $_POST call via HTML resetting everything?
function RunFunctions($inputStr)
{
static $aClass;
var_dump($aClass);
if (!isset($aClass))
{
$aClass = new CreateNewClass();
$aClass->SetNumber($inputStr);
}
}
You didn't give us full details on your PHP setup, but most PHP environments are start-from-scratch on each request. What this means is that the entire program is initialized from scratch including your static variables each time.
If you're not using an optimizer, the PHP code itself can be compiled from scratch for each request as well.
A lot of PHP requests are handled by separate system processes, meaning that even if data could be shared between requests, it would only work for requests handled by the same process.
If you want to share data between requests, consider storing it in a Cookie that the user's browser automatically provides on each request, or store it in a local database.
Related
I have a struct that abstracts MongoDB for specific objects in my system, and during the factory function for it I set a few variables like hostname and other connection information. At the moment in each of the UserService's methods* it creates a new session, does what it needs to, then closes the session when it's done.
The system itself is the backend of a web application, so the lifetime of each UserService struct is usually only a few seconds at most, but more than one operation might be performed for each request that comes in. So I'm wondering whether to make session a member of the struct, initialise it when I create my UserService, and then ensure the request handler function that creates it calls a close function once it's done all the operations it needs to. I haven't been able to find anything that encourages or discourages this behaviour so I'm not really sure if the mgo package I'm using is designed that way.
This is my proposed code:
type UserService struct {
callingUserId id.ID //The ID of the user calling this service.
host string //The host name.
session mgo.Session //The active session.
}
func NewUserService(userId id.ID) *UserService {
nus := new(UserService)
nus.callingUserId = userId
nus.host = "localhost" //TODO change this to read from file or buffer.
nus.session, sessionErr = mgo.Dial(nos.host)
if sessionErr != nil {
//TODO log error.
}
return nus
}
func (us UserService) GetById(usrId id.ID) *users.User {
//TODO get a user from the database with the matching ID using the existing session.
}
There will also be a function called UserService.CloseSession, which as I mentioned, will be called after all the required operations are done by the handler function that creates the service.
Does anyone know if this is a sensible idea or should I just call mgo.Dial in every function on UserService?
Opening a connection to MongoDB or any other DB is an expensive task that should be done once and kept operative as much as possible inside your service.
You have three options:
A local package level MongoDB instance.
Using Contexts and Composing Handlers.
A method receiver which holds the MongoDB Instance.
This is a very informative blog post for handling DBs connections.
Take a look to this example, especially for MongoDB
I am attempting to call out to parallels.js via JSNI. Parallels provides a nice API around web workers, and I wrote some lightweight wrapper code which provides a more convenient interface to workers from GWT than Elemental. However I'm getting an error which has me stumped:
com.google.gwt.core.client.JavaScriptException: (DataCloneError) #io.mywrapper.workers.Parallel::runParallel([Ljava/lang/String;Lcom/google/gwt/core/client/JavaScriptObject;Lcom/google/gwt/core/client/JavaScriptObject;)([Java object: [Ljava.lang.String;#1922352522, JavaScript object(3006), JavaScript object(3008)]): An object could not be cloned.
This comes from, in hosted mode:
at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:249) at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136) at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571) at com.google.gwt.dev.shell.ModuleSpace.invokeNativeVoid(ModuleSpace.java:299) at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeVoid(JavaScriptHost.java:107) at io.mywrapper.workers.Parallel.runParallel(Parallel.java)
Here's my code:
Example client call to create a worker:
Workers.spawnWorker(new String[]{"hello"}, new Worker() {
#Override
public String[] work(String[] data) {
return data;
}
#Override
public void done(String[] data) {
int i = data.length;
}
});
The API that provides a general interface:
public class Workers {
public static void spawnWorker(String[] data, Worker worker) {
Parallel.runParallel(data, workFunction(worker), callbackFunction(worker));
}
/**
* Create a reference to the work function.
*/
public static native JavaScriptObject workFunction(Worker worker) /*-{
return worker == null ? null : $entry(function(x) {
worker.#io.mywrapper.workers.Worker::work([Ljava/lang/String;)(x);
});
}-*/;
/**
* Create a reference to the done function.
*/
public static native JavaScriptObject callbackFunction(Worker worker) /*-{
return worker == null ? null : $entry(function(x) {
worker.#io.mywrapper.workers.Worker::done([Ljava/lang/String;)(x);
});
}-*/;
}
Worker:
public interface Worker extends Serializable {
/**
* Called to perform the work.
* #param data
* #return
*/
public String[] work(String[] data);
/**
* Called with the result of the work.
* #param data
*/
public void done(String[] data);
}
And finally the Parallels wrapper:
public class Parallel {
/**
* #param data Data to be passed to the function
* #param work Function to perform the work, given the data
* #param callback Function to be called with result
* #return
*/
public static native void runParallel(String[] data, JavaScriptObject work, JavaScriptObject callback) /*-{
var p = new $wnd.Parallel(data);
p.spawn(work).then(callback);
}-*/;
}
What's causing this?
The JSNI docs say, regarding arrays:
opaque value that can only be passed back into Java code
This is quite terse, but ultimately my arrays are passed back into Java code, so I assume these are OK.
EDIT - ok, bad assumption. The arrays, despite only ostensibly being passed back to Java code, are causing the error (which is strange, because there's very little googleability on DataCloneError.) Changing them to String works; however, String isn't sufficient for my needs here. Looks like objects face the same kinds of issues as arrays do; I saw Thomas' reference to JSArrayUtils in another StackOverflow thread, but I can't figure out how to call it with an array of strings (it wants an array of JavaScriptObjects as input for non-primitive types, which does me no good.) Is there a neat way out of this?
EDIT 2 - Changed to use JSArrayString wherever I was using String[]. New issue; no stacktrace this time, but in the console I get the error: Uncaught ReferenceError: __gwt_makeJavaInvoke is not defined. When I click on the url to the generated script in developer tools, I get this snippet:
self.onmessage = function(e) {self.postMessage((function (){
try {
return __gwt_makeJavaInvoke(3)(null, 65626, jsFunction, this, arguments);
}
catch (e) {
throw e;
}
})(e.data))}
I see that _gwt_makeJavaInvoke is part of the JSNI class; so why would it not be found?
You can find working example of GWT and WebWorkers here: https://github.com/tomekziel/gwtwwlinker/
This is a preliminary work, but using this pattern I was able to pass GWT objects to and from webworker using serialization provided by AutoBeanFactory.
If you never use dev mode it is currently safe to pretend that a Java String[] is a JS array with strings in it. This will break in dev mode since arrays have to be usable in Java and Strings are treated specially, and may break in the future if the compiler optimizes arrays differently.
Cases where this could go wrong in the future:
The semantics of Java arrays and JavaScript arrays are different - Java arrays cannot be resized, and are initialized with specific values based on the component type (the data in the array). Since you are writing Java code, the compiler could conceivable make assumptions based on details about how you create and use that array that could be broken by JS code that doesn't know to never modify the array.
Some arrays of primitive types could be optimized into TypedArrays in JavaScript, more closely following Java semantics in terms of resizing and Java behavior in terms of allocation. This would be a performance boost as well, but could break any use of int[], double[], etc.
Instead, you should copy your data into a JsArrayString, or just use the js array to hold the data rather than going back and forth, depending on your use case. The various JsArray types can be resized and already exist as JavaScript objects that outside JS can understand and work with.
Reply to EDIT 2:
At a guess, the parallel.js script is trying to run your code from another scope such a in the webworker (that's the point of the code, right) where your GWT code isn't present. As such, it can't call the makeJavaInvoke which is the bridge back into dev mode (would be a different failure with compiled JS). According to http://adambom.github.io/parallel.js/ there are specific requirements that a passed callback must meet to be passed in to spawn and perhaps then - your anonymous functions definitely do not meet them, and it may not be possible to maintain java semantics.
Before I get much deeper, check out this answer I did a while ago addressing the basic issues with webworkers and gwt/java: https://stackoverflow.com/a/11376059/860630
As noted there, WebWorkers are effectively new processes, with no shared code or shared state with the original process. The Parallel.js code attempts to paper over this with a little bit of trickery - shared state is only available in the form of the contents passed in to the original Parallel constructor, but you are attempting to pass in instances of 'java' objects and calling methods on them. Those Java instances come with their own state, and potentially can link back to the rest of the Java app by fields in the Worker instance. If I were implementing Worker and doing something that referenced other data than what was passed in, then I would be seeing further bizarre failures.
So the functions you pass in must be completely standalone - they must not refer to external code in any way, since then the function can't be passed off to the webworker, or to several webworkers, each unaware of each other's existence. See https://github.com/adambom/parallel.js/issues/32 for example:
That's not possible since it would
require a shared state across workers
require us to transmit all scope variables (I don't think there's even a possibility to read the available scopes)
The only thing which might be possible would be cache variables, but these can already be defined in the function itself with spawn() and don't make any sense in map (because there's no shared state).
Without being actually familiar with how parallel.js is implemented (all of this answer so far is reading the docs and a quick google search for "parallel.js shared state", plus having experiemented with WebWorkers for a day or so and deciding that my present problem wasn't yet worth the bother), I would guess that then is unrestricted, and you can you pass it whatever you like, but spawn, map, and reduce must be written in such a way that their JS can be passed off to the new JS process and completely stand alone there.
This may be possible from your normal Java code when compiled, provided you have just one implementation of Worker and that impl never uses state other than what is directly passed in. In that case the compiler should rewrite your methods to be static so that they are safe to use in this context. However, that doesn't make for a very useful library, as it seems you are trying to achieve. With that in mind, you could keep your worker code in JSNI to ensure that you follow the parallel.js rules.
Finally, and against the normal GWT rules, avoid $entry for calls you expect to happen in other contexts, since those workers have no access to the normal exception handling and scheduling that $entry enables.
(and finally finally, this is probably still possible if you are very careful at writing Worker implementations and write a Generator that invokes each worker implementation in very specific ways to make sure that com.google.gwt.dev.jjs.impl.MakeCallsStatic and com.google.gwt.dev.jjs.impl.Pruner can correctly act to knock out the this in those instance methods once they've been rewritten as JS functions. I think the cleanest way to do this is to emit the JSNI in the generator itself, call a static method written in real Java, and from that static method call the specific instance method that does the heavy lifting for spawn, etc.)
I am currently active PlayFramework learner who came from world of PHP.
For example I have a Head block object in my app, which should hold title, charset encoding, meta information, etc. Something similar to Magento blocks, but without XML declaration
package blocks.Page
object Head {
var title: String = "";
}
In Application.index() method I have
blocks.Page.Head.title
Ok(views.html.application.index());
And finally in html template
#import blocks.Page.Head
<title>#Head.title</title>
However, blocks.Page.Head object is defined for entire application scope, not for single request. This object is the same for each request.
What is the right way to do, what I am trying to do? I can create container with all blocks and instantiate it with each request, then just pass to all templates. But I have a feeling that this is wrong way.
Just use usual class instead of object and pass instance to template as parameter.
Like this:
package blocks.Page
case class Head(title: String = "")
Controller:
val head = Head("Blah")
Ok(views.html.application.index(head))
And template will looks like:
#(head: blocks.Page.Head)
...
<title>#head.title</title>
I know the feeling when coming from a request-oriented language like PHP :). However, consider application-wide access as a gift of a VM (in PHP we need to go the extra mile of using some bytecode and data caching tool like APC or eAccellerator).
I would probably create a blockManager class which gives you static access to blocks by name/tag/id from the template: Block.get("MyBlock"). Then you can define and later modify your caching / storing strategy (holding in memory vs. loading from storage) without affecting your templates.
Does anyone have or know of an example which demonstrates loading data via a GWT RPC call into a ListStore using Sencha GXT 3.0? I know there are numerous examples of using the ModelData and BeanModel interfaces used in the 2.x versions but 3.0 does away with the need to use these interfaces and supposedly allows for POJO objects to be loaded in using classes which implement the ValueProperty interface.
I have seen the RequestFactoryBinding example and the RequestFactory Grid example in the 3.0 Explorer but those appear to demonstrate the use of a custom Data Proxy and a Receiver. I assume from reviewing the code in those examples that these techniques/classes may be required but that is not made apparent anywhere. It's possible that there is more documentation forthcoming but so far I haven't been able to find much of anything beyond that javadocs and the Explorer which lacks some of the source classes used in the example methods.
Links to both examples below.
The RequestFactoryBinding Example:
http://www.sencha.com/examples/#ExamplePlace:requestfactorybinding
RequestFactory Grid example:
http://www.sencha.com/examples/#ExamplePlace:requestfactorygrid
DataProxy and Loader are used mostly to facilitate a) relying on the server for filtering/paging/sorting, or b) reuse between parts of the application for getting access to the same pieces of data. They are not required (as in 2.x) in cases where the client only loads data once, or where manual store management is done.
The various store loading classes (ListStoreBinding, LoadResultListStoreBinding) demonstrate internally how the ListStore can be fed items. This first way allows you to replace the existing items in the store from the onSuccess method in your RPC callback or RequestFactory receiver:
List<MyData> newItems = ...;//response from server
ListStore<MyData> store = ...;//current store to replace/update
store.replaceAll(newItems);
If only loading once, or only appending, not replacing, the other method should be used:
store.addAll(newItems);
Items can be added one by one using store.add, however this will result in an event per item, and should be avoided.
Edit: Also, and this may not totally be clear coming from 2.x, but no superclass/interface is required for data itself. ValueProvider is only used as an external abstraction for how models are manipulated - how values are generically read or set from any kind of model. The PropertyAccess interface allows ValueProvider (and other) instances to be generated by just the property name that the values will be get/set from using bean accessors. ValueProvider types/instances are not required for loading data, merely for the data widgets themselves to extract the data they are displaying, and to make modifications after the user edits the values.
Knowing these pieces, the loader/proxy mechanism will be loading data in the same basic way. The Loader is responsible for being told what settings (paging, filtering, and/or sorting) to use when loading, then triggering the load - different subclasses have different responsibilities, accept different load config types, and return different results. The DataProxy then is the mechanism that actually talks to whatever holds the data, asynchronously if on a server, and informs the loader when the results are available via a callback.
The examples listed in the question both use RequestFactory, but there are several examples as well that use RPC, and a few loading from just JSON or XML. In http://www.sencha.com/examples/#ExamplePlace:paginggrid the main data loading parts are as follows:
// The rpc async instance
final ExampleServiceAsync service = GWT.create(ExampleService.class);
// As in Ext GWT 2, there is a convenience proxy for RPC to just pass the callback
// directly to the RPC call. If you need a custom callback, just be sure to invoke
// `callback.onSuccess` with the final result.
RpcProxy<PagingLoadConfig, PagingLoadResult<Post>> proxy = new RpcProxy<PagingLoadConfig, PagingLoadResult<Post>>() {
#Override
public void load(PagingLoadConfig loadConfig, AsyncCallback<PagingLoadResult<Post>> callback) {
service.getPosts(loadConfig, callback);
}
};
// ...
// The loader itself has a reference to the proxy so that loader.load() results
// in a round trip to the server, as outlined above.
final PagingLoader<PagingLoadConfig, PagingLoadResult<Post>> loader = new PagingLoader<PagingLoadConfig, PagingLoadResult<Post>>(
proxy);
loader.setRemoteSort(true);
// This last piece - instead of 2.x where the loader is a parameter to the store,
// in 3 you directly wire the results of the loader to add the items into the
// store, as discussed in the first half of this answer
loader.addLoadHandler(new LoadResultListStoreBinding<PagingLoadConfig, Post, PagingLoadResult<Post>>(store));
FWIW I spiked a GWTP Dispatch version of a remotely paged and sorted grid. Which is GWT RPC with a command pattern twist.
Assuming you're familiar with grids, you'll require an instance of:
RpcProxy
PagingLoader
LoadResultListStoreBinding
And the methods that need to be invoked:
PagingLoader.setRemoteSort(true)
PagingLoader.addLoadHandler()
Grid.setLoader()
PagingToolBar.bind()
"core" refers to the initial piece of the application that is loaded.
In order to bind url to places, GWT uses PlaceTokenizer<P extends Place>. When loading the application from the url, it calls the method P getPlace(String token) to retrieve a new instance of the place to call.
due to the asynchronous nature of code splitting, I can't create the place inside a runAsync in this method. So I have to put all the places of my app in the core.
To link places to activity, GWT callsActivity getActivity(Place place) (from com.google.gwt.activity.shared.ActivityMapper) to retrieve a new instance of the activity.
Once again, i have to put all my activities in the core.
Here's what I want to try: Write a custom com.google.gwt.place.shared.Delegate that
bind itself on PlaceChangeRequestEvent. If the AppPiece corresponding to the requestedPlace isn't loaded, it calls event.setWarning(NEED_TO_LOAD_MODULE)
in the confirm(String message) method, always return false when the message equals NEED_TO_LOAD_MODULE (so it doesn't bother the user), and load the module via RunAsync.
Once the module is loaded, call goTo(requestedPlace)
Each AppPiece of my application contains a bunch of activies and the corresponding views. Since the mappers are only called when PlaceChangeEventis fired, i could generate a new instance of my activity via AppPiece.getSomeActivityInstance().
I'm pretty sure this will work, but what bother me is that
Finding wich AppPiece to load depending on the requestedPlace will force me to write code that will be very similar to my mappers
I would like to have my places inside the corresponding AppPiece
Overriding Delegate for this purpose is tricky, and I'm looking for a better solution
You don't have to put all your activities in the core (as you call it): while an Activity instance is retrieved synchronously, it's allowed to start asynchronously. This is where you'd put your GWT.runAsync call.
See http://code.google.com/p/google-web-toolkit/issues/detail?id=5129 and https://groups.google.com/d/topic/google-web-toolkit/8_P_d4aT-0E/discussion