I am wondering, are there any languages allows you to add/delete/update any class on the fly without reloading whole application? (Provided that I can accept some inconveniences like making sure that there is no methods running at the moment + some extra effort to 'migrate' class data members). Web applications where you replace 1 file and it is used on the next client request is not what I need (like Perl, PHP). Application must be continuously running, and it have some internal state. Other requirements are No GIL or similar issues preventing from utilizing SMP Preferably - existence of JIT-like VM (i.e. where performance is close to native code). Ideal solution would be to be able to reload module in CLang or any other LLVM-based language. It would be just perfect. About the answers already made: .NET/Java is not suitable - they both have too bulky VM's, and significant part of app will be running on Linux. Erlang - looks like it's possible, but it's terrible for my naked eye, I just cannot look calm at it's if's, case's and strings. Also, I would prefer to avoid transfering bare sources to clients, compiled bytecode would be much better.

Reputation: 6585

Which programming language allows to update any class on-the-fly?

I am wondering, are there any languages allows you to add/delete/update any class on the fly without reloading whole application? (Provided that I can accept some inconveniences like making sure that there is no methods running at the moment + some extra effort to 'migrate' class data members).

Web applications where you replace 1 file and it is used on the next client request is not what I need (like Perl, PHP). Application must be continuously running, and it have some internal state.

Other requirements are

No GIL or similar issues preventing from utilizing SMP
Preferably - existence of JIT-like VM (i.e. where performance is close to native code). Ideal solution would be to be able to reload module in CLang or any other LLVM-based language. It would be just perfect.

About the answers already made:

.NET/Java is not suitable - they both have too bulky VM's, and significant part of app will be running on Linux.
Erlang - looks like it's possible, but it's terrible for my naked eye, I just cannot look calm at it's if's, case's and strings. Also, I would prefer to avoid transfering bare sources to clients, compiled bytecode would be much better.

Upvotes: 15

Answers (15)

Günter Zöchbauer

Reputation: 657038

The Dart VM has great hot code reload support which greatly improves the Flutter development experience.

https://github.com/dart-lang/sdk/wiki/Hot-reload

Upvotes: 2

Bartosz Hernas

Reputation: 1128

Objective-C allows you to hot swap code, and there is a plugin which allows that. I answered similar question about Objective-C here

Upvotes: 0

Trevor Rudolph

Reputation: 1063

you should use php for this, i too have a linux server, it is very good with permission to change files like i have this php code to open a text box with an editable on site file,

<?php 
$fn = "test.txt"; //the path to any file

if (isset($_POST['content'])) 
{ 
    $content = stripslashes($_POST['content']); 
    $fp = fopen($fn,"w") or die ("Error opening file in write mode!"); 
    fputs($fp,$content); 
    fclose($fp) or die ("Error closing file!"); 
} 
?> 
<h4>You are editing <?php echo $fn ?> </h4>
<form action="<?php echo $_SERVER["PHP_SELF"] ?>" method="post"> 
    <textarea rows="25" cols="40" name="content"><?php readfile($fn); ?></textarea>
    <br/>
    <input type="submit" value="Save">  
</form>

Upvotes: 0

Andrei Andrushkevich

Reputation: 9973

The following are generally considered dynamic languages:

Some of these languages are supported in the .NET Framework by the Microsoft Dynamic Language Runtime.

Upvotes: 5

Stephan Eggermont

Reputation: 15907

We do this with a Seaside smalltalk webapplication running on the free version of Gemstone. Gemstone has been doing this for the past 20 years or so, so they have everything you need. Some of the high-availability features are not free.

Open source smalltalks don't have the extensive class version/migration gemstone has. The simple 'load a new version and migrate all instances' works with all smalltalks.

Upvotes: 3

Billy Moon

Reputation: 58521

Depending on the specifics of your project - Javascript might be the answer via Node.js (nodejs.com) which allows you to program an event based server using javascript that is interpreted by the V8 engine.

This approach can be ver efficient compared to traditional web-servers in circumstances where there are many connections at one time, and especially if there is a lot of idling around for the server. This is due to the event based nature of Javascript where the cost of idling is very low.

There are several methods for hot-swapping code using node.js - this should get you started: Node.Js in Erlang style? and https://github.com/kriszyp/nodules

Upvotes: 1

Andy

Reputation: 4866

You could look through the list at http://en.wikipedia.org/wiki/List_of_programming_languages_by_category#Reflective_languages. One that I don't see mentioned here yet is Lua, which has a reputation as being fast compared to other dynamic languages.

Another strategy might be to look at the academic research. A possible starting point is http://scholar.google.com/scholar?q=ksplice, which is about patching a running linux kernel.

I'm not sure what degree of automation you're looking for. Obviously the general case of seamlessly replacing a running instance of program A with A' is difficult, even with some guarantees on what is allowed to change in A'.

Depending on how the pieces of the program that need to be updated can be grouped and isolated, you could put them in a shared library, and (re-)load the shared library at run time (using e.g. the dlopen family of functions if you're on unix).

Upvotes: 0

Fang-Pen Lin

Reputation: 14406

I have did some research on zero downtime service migration recently. And my solution is not a language-relative one. Here is the idea, we can dump the state of current service, create another process, transfer the connection state description to the new process, finally terminate the old process. As shown in following diagram:

enter image description here

With a well defined abstract service description format and migration protocol, you can migrate any kind of services from one process to another, which means, you could write a server in C++, and migrate the service to the new process written in Python without any disconnection. Of curse, you can migrate your service from the old version to the new version. Adding/Deleting/Updating classes won't be a problem. For more detail, you can reference to my article

Zero-downtime service migration

The difficulty of this kind of technique is that you have to dump the all state of the running service and load them on another process. For most libraries out there you could find, it is hard to get internal state of those classes, which means you may have to do some hack on them, or write your own library. It would be a nightmare to transfer service state for complex services, but for simple services, that's not a big deal.

Upvotes: 3

user541686

Reputation: 210352

Take a look at Scheme. You can do object-oriented programming in Scheme using very simple extensions, such as the Berkeley extensions. Just extend the code to allow for replacing methods (should be very easy) and you can hot-swap them however you want -- the syntax would still stay simple because, well... it's Scheme. :)

Right now, the code for the classlooks something like:

(define-class (person name)
  (method (greet) (print `Hello!))
  ...)

where person is a lambda. It should be pretty easy to change the define-class macro to make person a list, for example, so that you can add to or remove from it dynamically.

Upvotes: 2

Matt Joiner

Reputation: 118470

Python can do this. Note the following:

The multiprocessing module.
The GIL is specific to CPython it's not inherent to Python.
The GIL is not the problem you think it is. It won't effect heavy IO use, and doesn't apply to C code, or C libraries (if wrapped correctly). If you are doing anything computationally intensive, it should be in C anyway (those parts anyway).

Upvotes: 3

Anomie

Reputation: 94794

Objective-C might fit the bill. You can use the functions documented here to add new classes and swap method implementations at runtime, and you can load new NSBundles with additional classes or categories on existing classes if additional implementations are required. GNUStep, while not implementing all of the recent Apple additions to the language, does claim to implement these features (see [1] and [2]).

Upvotes: 5