My app makes use of a shared library, say, mylib.so
This mylib.iso would like to use API from either lib1.so or lib2.so depending on some condition.
Both lib1.so and lib2.so provide the exact same set of API.
I can only calculate the condition once mylib.iso has been loaded. It does not depend on APIs from lib1.so or lib2.so but I can not do from java:
static {
if(nativeHasCondition()) System.loadLibrary("lib1");
else System.loadLibrary("lib2");
}
System.loadLibrary("mylib");
}
because nativeHasCondition() is in mylib.so.
So, I think I shall somehow load either lib1.so or lib2.iso from my native code depending on some calculation in my native code.
How do I do that?
If nativeHasCondition() is the method of mylib.so, then you have to load mylib.so first.
Then you can follow the condition.
Perhaps you should make that code into a separate library and load it first. If you need to test cpu caps, probably you should just do it from java and then load appropriate libs (as long as you manage to load your mylib.so which should reference lib1.so or lib2.so in its import section).
Related
What is the difference between toBeInTheDocument() and toBeDefined() when testing with Jest and React Testing Library? When should they be used?
The #testing-library/jest-dom library provides a set of custom jest matchers that you can use to extend jest. These will make your tests more declarative, clear to read and to maintain.
It solve the below problem:
You want to use jest to write tests that assert various things about the state of a DOM. As part of that goal, you want to avoid all the repetitive patterns that arise in doing so. Checking for an element's attributes, its text content, its css classes, you name it.
From the source code of toBeInTheDocument(), it uses several DOM APIs such as Node.getRootNode() and Node.cloneNode(). You don't need to check if the element is present in the document on your own. This is very convenient and readable.
toBeDefined has nothing to do with DOM API, it's a basic matcher uses const pass = received !== void 0; to check if the value is defined or not.
I'd like to add an important functionality that I can use at work without using require() every time. So, I thought modifying built-in objects can make this happen but I could not locate the locations of those objects to do the modification.
Are those objects in NodeJS binary? Would that mean I have to fork the whole NodeJS repo to make this happen?
Please, I don't want to use prototype editing etc which are same as require. I need to have native feeling.
First off, I agree with an earlier comment that this sounds like a bit of an XY problem where we could better help you if you describe what problem you're really trying to solve. Portable node.js programs that work anywhere or work with any future versions of node.js don't rely on some sort of custom configured environment in order to run. They use the built-in capabilities of node.js and they require/import in external things they want to add to the environment.
Are those objects in NodeJS binary?
Yes, they are in the executable.
Would that mean I have to fork the whole NodeJS repo to make this happen?
Yes.
Please, I don't want to use prototype editing etc which are same as require. I need to have native feeling.
"Native feeling"? This sounds like you haven't really bought into the node.js module architecture. It is different than many other environments. It's easy to get used to over time. IMO, it would really be better to go with the flow and architecture of the platform rather than make some custom version of node.js just to save one line of typing in your startup code.
And, the whole concept of adding a number of globals you can use anywhere pretty much shows that you haven't fully understood the design, architectural, code reuse and testability advantages of the module design baked into node.js. If you had, you wouldn't be trying to write a lot of code that can't be reused in other ways that you don't anticipate now.
That said, in searching through the node.js source code on Github, I found this source file node.js which is where lots of things are added to the node.js global object such as setTimeout(), clearTimeout(), setImmediate(), clearImmediate() and so on. So, that source file seems to be where node.js is setting up the global object. If you wanted to add your own things there, that's one place where it would be done.
To provide a sample of that code (you can see the link above for the complete code):
if (!config.noBrowserGlobals) {
// Override global console from the one provided by the VM
// to the one implemented by Node.js
// https://console.spec.whatwg.org/#console-namespace
exposeNamespace(global, 'console', createGlobalConsole(global.console));
const { URL, URLSearchParams } = require('internal/url');
// https://url.spec.whatwg.org/#url
exposeInterface(global, 'URL', URL);
// https://url.spec.whatwg.org/#urlsearchparams
exposeInterface(global, 'URLSearchParams', URLSearchParams);
const {
TextEncoder, TextDecoder
} = require('internal/encoding');
// https://encoding.spec.whatwg.org/#textencoder
exposeInterface(global, 'TextEncoder', TextEncoder);
// https://encoding.spec.whatwg.org/#textdecoder
exposeInterface(global, 'TextDecoder', TextDecoder);
// https://html.spec.whatwg.org/multipage/webappapis.html#windoworworkerglobalscope
const timers = require('timers');
defineOperation(global, 'clearInterval', timers.clearInterval);
defineOperation(global, 'clearTimeout', timers.clearTimeout);
defineOperation(global, 'setInterval', timers.setInterval);
defineOperation(global, 'setTimeout', timers.setTimeout);
defineOperation(global, 'queueMicrotask', queueMicrotask);
// Non-standard extensions:
defineOperation(global, 'clearImmediate', timers.clearImmediate);
defineOperation(global, 'setImmediate', timers.setImmediate);
}
This code is built into the node.js executable so the only way I know of to directly modify it (without hackish patching of the executable itself) would be to modify the file and then rebuild node.js for your platform into a custom build.
On a little more practical note, you can also use the -r module command line argument to tell node.js to run require(module) before starting your main script. So, you could make a different way of starting node.js from a shell file that always passes the -r fullPathToYourModule argument to node.js so it will always run your startup module that adds things to the global object.
Again, you'd be doing this just to save one line of typing in your startup file. It is really worth doing that?
Does the node interpreter look for core modules (let's say "fs") within the node binary? If yes, are these modules packaged as js files. Are the core modules that are referenced within our code converted to c/c++ code first and then executed? For example, I see a method in the _tls_common.js (https://github.com/nodejs/node/blob/master/lib/_tls_common.js) file called "loadPKCS12" and the only place that I see this method being referenced/defined is within the "node_crypto.cc" file (https://github.com/nodejs/node/blob/master/src/node_crypto.cc). So how does node link a method in javascript with the one defined in the c/c++ file?
here is the extract from the _tls_common.js file that makes use of the "loadPKCS12" method:
if (passphrase) {
c.context.loadPKCS12(buf, toBuf(passphrase));
} else {
c.context.loadPKCS12(buf);
}
}
} else {
const buf = toBuf(options.pfx);
const passphrase = options.passphrase;
if (passphrase) {
c.context.loadPKCS12(buf, toBuf(passphrase));
} else {
c.context.loadPKCS12(buf);
There are two different (but seemingly related) questions asked here. The first one is: "How the core modules work?". Second one being "How does NodeJS let c++ code get referenced and executed in JavaScript?". Let's take them one by one.
How the core modules work?
The core modules are packaged with NodeJS binary. And, while they are packaged with the binary, they are not converted to c++ code before packaging. The internal modules are loaded into memory during bootstrap of the node process. When a program executes, lets say require('fs'), the require function simply returns the already loaded module from cache. The actual loading of the internal module obviously happens in c++ code.
How does NodeJS let c++ code get referenced in JS?
This ability comes partly from V8 engine which exposes the ability to create and manage JS constructs in C++, and partly from NodeJS / LibUV which create a wrapper on top of V8 to provide the execution environment. The documentation about such node modules can be accessed here. As the documentation states, these c++ modules can be used in JS file by requiring them, like any other ordinary JS module.
Your example for use of c++ function in JS (loadPKCS12), however, is more special case of internal c++ functionality of NodeJS. loadPKCS12 is called on a object of SecureContext imported from crypto c++ module. If you follow the link to SecureContext import in _tls_common.js above, you will see that the crypto is not loaded using require(), instead a special (global) method internalBinding is used to obtain the reference. At the last line in node_crypto.cc file, initializer for internal module crypto is registered. Following the chain of initialization, node::crypto::Initialize calls node::crypto::SecureContext::Initialize which creates a function template, assigns the appropriate prototype methods and exports it on target. Eventually these exported functionalities from C++ world are imported and used in JS-World using internalBinding.
I got to the point that I'd like to have a factory to manage all my dependencies for the modules in a single place instead of having a lot of statements using require all over the place in my code.
I've looked at some approaches that rely on AMD, but I'd like to know how to do it by using node.js / express combination with the OOB module loader which I think it uses common.js.
I've been thinking of doing something like this:
module.exports = {
lib:[],
load:function(name){
if(this.lib[name]!==undefined && this.lib[name]!==null){
return this.lib[name];
}
switch(name)
{
case 'express':
this.lib[name] = require('express');
break;
case 'morgan':
this.lib[name] = require('morgan');
break;
case 'body-parser':
this.lib[name] = require('body-parser');
break;
}
console.log(this.lib);
return this.lib[name];
}
};
Some people say that's more than a factory its a mediator pattern, so either way I just wanted to illustrate my point.
my basic requirement is to handle all the dependencies from a single place in the system if I need to change a dependency I just change it on this file and automatically updates through the whole system.
so is there a better way to handle this? any Implementation that already have done this approach?
thanks!
Technically this is what require() does internally.
require('foo'); require('foo')
guarantees that it will load and run foo only once. The second call will return a cached copy from its internal array.
You can achieve the same naming indirection (and an API adapter if you'll ever decide to change the implementation without changing callers) by requiring JS files or your node modules that re-export modules you actually use (e.g. require('./my-express-wrapper') instead of require('express')).
if I need to change a dependency I just change it on this file and automatically updates through the whole system.
I'd be concerned that it will cause code to be surprising:
require('factory').load('body-parser'); // loads Formidable!?
I see little benefit in having such layer of indirection:
Even in the best case of drop-in-replacement it saves very little work, because project-global find'n'replace of require('foo') with require('bar') is an easy task in most text editors.
The hard part of replacing module (which is unlikely to be 100% compatible) is getting existing code to correctly work with it. This is not avoided by use of the factory pattern. You'll need to write an adapter either way, and sometimes it may even be better to actually change uses of the module everywhere than to write an emulation layer for an API that probably wasn't good anyway.
I want to set up include paths (and other paths, like view script paths) based on the module being accessed. Is this safe? If not, how could I safely set up include paths dynamically? I'm doing something like the code below (this is from a controller plugin.)
public function dispatchLoopStartup(Zend_Controller_Request_Abstract $request) {
$modName = $request->getModuleName();
$modulePath = APP_PATH.'/modules/'.$modName.'/classes';
set_include_path(get_include_path().PATH_SEPARATOR.$modulePath);
}
I'm not sure whether it is safe or not, but it doesn't sound like the best practice. What if someone entered a module name like ../admin/? You should sanitize the module name before using it.
It's fine as long as you sanitize your variables before using them, but it won't be very performant. Fiddling with include paths at runtime causes a serious impact performance.
You're trying to load models/helpers per module? You should look at Zend_Application:
Zend_Application provides a bootstrapping facility for applications which provides reusable resources, common- and module-based bootstrap classes and dependency checking. It also takes care of setting up the PHP environment and introduces autoloading by default.
Emphasis by me