Very often I have a function that causes an issue but not a crash, so I want to disable code that causes that issue but I don't know exactly what piece of code causes it.
So I have the function return at various points until I find the issue, for example by injecting code like
if (1) return;
at various places of the function.
The problem with this is that I have to constantly stop and recompile the application.
Is there a runtime VC++ debugger feature that would instruct the debugger to exit the function as If executing a return statement? I could drag the 'next statement to be executed' at the end of the function but this is cumbersome for big functions.
Assembly-wise it's possible by changing RIP to the point just before destructors are to be called.
Eclipse has such a feature for Java.
Related
I recently completed making an asynchronous version for all the functions in a pure C API, wrapped with N-API to work with JS/TS as a nodejs addon.
The last problem I had to fix was making sure that C POSIX-style errors (ie, returned integer codes) were transferred correctly to the JS at the end of a worker's execution (with the corresponding string, for which we have both an enum of exceptions, and a list of error messages).
When thrown with napi_throw_error (as I did for the synchronous version of all our calls), within the napi_async_complete_callback, these exceptions were never caught at the JS level (I suppose it was because it was within a different async context; I saw online people having a similar problem with ajax). Instead, I opted to just construct my errors as napi_value types, and return these via napi_reject_deferred. This seemed to have the desired effect, of being caught properly when doing a try { await My_NapiWrapper_XYZ() } catch (ex) { ... }.
So I don't really have a problem to fix, but I AM intrigued. These napi_throw_error thrown errors do probably go somewhere. Though I have no idea where. Where should one look to catch an error thrown with napi_throw_error from a napi_async_complete_callback ? Can you give a code example ?
No, they don't go anywhere. It is a bug that I just opened with them:
https://github.com/nodejs/node/issues/41377
There is a general problem with handling exceptions in asynchronous callbacks. Normally, they cannot be catched and should lead to program termination but Node's developers have decided to try to keep it running when they can.
I have created a plugin for the OpenCPN marine navigation program that incorporates Duktape to provide a scripting capability. OpenCPN uses wxWidgets.
Basically, the plugin presents the user with a console comprising a script window, an output window and various buttons. The user enters their script (or loads it from a .js file) and clicks on Run. The script is run using duk_peval. On return I display the result, destroy the context and wait for the user to run again, perhaps after modifying the script. All this works well. However, consider the following test script:
add(2, 3);
function add(a, b){
if (a == b) throw("args match");
return(a + b);
}
If the two arguments in the call to add are equal. The script throws an error and the user can try again. This all works.
Now I can implement add as a c++ function thus:
static duk_ret_t add(duk_context *ctx){
int a, b;
a = duk_get_int(ctx, 0);
b = duk_get_int(ctx, 1);
if (a == b){
duk_error(ctx, DUK_ERR_TYPE_ERROR, "args match");
}
duk_pop_2(ctx);
duk_push_int(ctx, a+b);
return (1);
}
As written, this passes the error to the fatal error handler. I know I must not try and use Duktape further but I can display the error OK. However, I have no way back to the plugin.
The prescribed action is to exit or abort but these both terminate the hosting application, which is absolutely unacceptable. Ideally, I need to be able to return from the duk_peval call with the error.
I have tried running the add function using duk_pcall from an outer C++ function. This catches the error and I can display it from that outer function. But when I return from that outer function, the script carries on when it should not and the eventual return from the duk_peval call has no knowledge of the error.
I know I could use try/catch in the script but with maybe dozens of calls to the OpenCPN APIs this is unrealistic. Percolating an error return code all the way back, maybe through several C++ functions and then to the top-level script would also be very cumbersome as the scripts and functions can be quite complex.
Can anyone please suggest a way of passing control back to my invoking plugin - preferably by returning from the duk_peval?
I have cracked this at last.
Firstly, I use the following in error situations:
if (a == b){
duk_push_error_object(ctx, DUK_ERR_ERROR, "args match");
duk_thow(ctx);
}
If an error has been thrown, the returned values from duk_peval and duk_pcall are non-zero and the error object is on the stack - as documented
It is all working nicely for me now.
enter image description here
No idea whats going with these errors code, i dont understand why is it saying anonymous and its giving me security concerns
Strictly speaking, those are warnings (not errors). Nothing is broken, but some things may be running sub-optimally. The alerts are noting that the code on your site is preloading a number of assets but not using them right away. This may indicate that your site is unnecessarily using priority resources to bring those resources in.
Beneath the warning message, you are seeing what is known as a "call stack" - it's the chain of functions that have been called to get to the point that resulted in that warning message. There are two kinds of functions in Javascript: named functions and anonymous functions.
Named functions are what you might normally think of as a function. You declare it with something like:
function doSomething(parameter){
// Some awesome code here
}
And later call it as:
doSomething(some_input);
However, in Javascript we can also create un-named, aka anonymous, functions in-line. This is often done for 'callback' functions, or functions that serve as a part B to the main function's part A, especially when part A does something asynchronously.
For example, if we want to fetch a file and then do something with it once it loads, we would make an asynchronous file call and then run our callback function once it loads. If we're using a library like jQuery as a helper to make that call, our code might look something like this:
function getPageAndDoStuff(url, callback){
jQuery.get(url, callback)
}
// We can declare a named function to do our stuff...
function justLogIt(html){
console.log(html);
}
getPageAndDoStuff('/cart', justLogIt);
Alternatively:
// We can just declare an inline anonymous function to do that
getPageAndDoStuff('/cart', function(html){
console.log(html);
})
The latter is a common design pattern for many types of tasks, but you'll note that the function we pass around doesn't have a name. When something happens and we look at the call stack to see the order of functions that have been called to get us to that point, what name would we print? Each unnamed function in our chain is simply called "(anonymous)"
Going back to your posted image, there is nothing in what you're showing that indicates a cause for serious concern. The script file 'rocket-loader' is possibly pre-loading a few assets that it doesn't need to, so you may be able to boost your site's performance by tweaking whatever parameters 'rocket-loader' uses to be more selective in what you are pre-loading.
I notice Debug.Assert does not trigger in Metro apps, however, if the project is a traditional one like Console or WinForm, it does trigger. And yes, I am in Debug mode.
Is it a setting not properly set in Visual Studio (11 Beta)? Or Debug.Assert is intended to be disabled in metro apps?
I know many exceptions are swallowed during the execution of Metro apps, but Debug.Assert is so handy that I can't think of a reason why it should be disabled.
Seems like a bug. I would roll out my own assert method. Something like:
[Conditional("DEBUG")]
public static void Assert(bool condition)
{
if (!condition)
System.Diagnostics.Debugger.Break();
}
It does trigger, look in the Output window. It just doesn't automatically prompt you to ask if you want a debugger break and thus just keeps motoring.
The DefaultTraceListener.AssertUIEnabled property is false. That's an implementation problem, can't display a message box on top of Metro UI. Which does actually work but the monitor switches to the desktop, pretty undesirable when you would have liked to click No. Hard to solve and no doubt on the todo list. You can't easily get to the property to set it to true, it is inaccessible from the metadata. Filip's workaround sounds half-decent.
There is the same problem with F# in WinRT, in VS2013. The assert statement, which is an alias for System.Diagnostics.Debug.Assert, does not raise an exception, so unless you are watching the Output window then your assertions can fail without being noticed. Even if you are watching, it is hard to find the spot where the assertion was raised.
I followed Filip's suggestion and wrote a short utility, as follows:
namespace MyProj.Infrastructure
module Diagnostics =
let Assert condition = if not condition then
System.Diagnostics.Debugger.Break()
I chose Debugger.Break over raising an exception because it stops the debugger at the place the assertion fails. However, raising an exception is an acceptable alternative.
I didn't have any suitable global projects or modules already in my solution, so I had to create them just for this, which was quite annoying.
I am developing a Windows forms application which connects to a piece of hardware, acquires a lot of data (~1 GSample/sec), processes it, and spits it out to the screen upon a button click. I am now trying to automate the process in a loop that can be started/stopped at any time so I can monitor it whilst tweaking the input to the acquisition hardware. I thinks it's clear that I need to do this on a separate thread, but I'm having a heck of a time trying to do this in c++/cli - I have found a number of good examples using MFC, which is not supported by Express.
Specifically: My task is to press a button which is handled in Form1.h, to call a function in my main file Acquisition.cpp which contains the following code (currently an infinite loop)
void Form1::realTimeUpdate()
{
// live is a boolean variable set by a button on the form
while(live)
{
displayVariance(getVar(getQuadratures(100),nbrSamples));
}
}
I wish to execute this code in a separate thread so that the main program can listen for the user request to stop the operation. Without threading, I currently have to forcefully quit the program (or set it to run a fixed number of times) to stop it.
Is there any suggestions how I might go about running this code on a separate thread?
I've (unsuccessfully) tried a few things already:
Modifying the example given in This Microsoft Example. Problem: requires /clr:oldSyntax option which is incompatible with the other 1300 lines of code in the program.
Trying to do what I'd do in Java (Declare a global thread and start/stop it from any point in the code. Problem: Compiler won't let me declare a global System::Threading.Thread
this beautiful example. Problem: Requires MFC.
Any suggestions would be greatly appreciated!
You can use a BackgroundWorker or a Thread to handle this. You'll need to make sure that the portion of your work that updates the UI is marshaled back to the UI thread, however.
Here is a tutorial on threading in C++/CLI.
For the record, upon Reed's suggestion about using a BackgroundWorker, I sifted through the code at the bottom of this page and modified my code so that:
It created a new backgroundWorker BGWorker in which BGWorker->DoWork() called my realTimeUpdate() function.
A button on the main Form calls either RunWorkerAsync() or CancelAsync() depending on whether or not the process is running (checked by a boolean flag in my main program).
The realTimeUpdate() function is now passed a BackgroundWorker - realTimeUpdate(BackgroundWorker^ worker, DoWorkEventArgs ^ e) After each calculation is complete within the internal loop, it calls worker->ReportProgress(result) function. In the BGWorker->ProgressChanged() function a separate function, upDataUI(int) draws the result on the main form.
Thanks again for the help.