In my ClojureScript programs running in FireFox 5.0 on Ubuntu 10.04.1 LTS, I get a single cryptic line when an exception is thrown.
'Error: No protocol method ISeqable.-seq defined for type object: [object Object]' when calling method: [nsIDOMEventListener::handleEvent]
The "-seq" bit seems strange to me and I have searched the generated javascript files for it and not found it.
I hope I am not missing something entirely obvious, but how do I get a stack trace of the exception thrown? How are you debugging your scripts?
Unfortunately stack traces from errors rely on browser support. Most (all?) browsers will allow you to access a canned version of the stack trace (usually the top 10 elements, iirc) as a string by dereferencing the 'stack' field, so you could do something like this:
(try ...throws...
(catch js/Error e
(.log js/console (.-stack e))))
However, string stack traces aren't much fun, you can't click them to take you to the source. Better is printing the exception directory to the javascript console (if it's available) to print stack traces with clickable links. E.g.
(try ...throws...
(catch js/Error e
(.log js/console e)))
At least in chrome, this only works if the javascript console was open when the error was thrown. This is great for debugging, but less useful when the error was unexpected.
The javascript console objects provided by most browsers have lots of useful functions that you can use from clojurescript. If you want to get helpful line numbers though, you probably want to write a couple of macros to inject the code to print to the console, otherwise all your line numbers will point to your print function.
Looks like you are passing a Javascript object to a Clojurescript function which expects a Clojure sequence. Try (my-function (js->clj my-thing)) edit: or, I'm guessing you're using (.strobj) where you don't need to
Related
As indicated by Tom Browder in this issue, the $*ARGFILES dynamic variable might contain invalid filehandles if any of the files mentioned in the command line is not present.
for $*ARGFILES.handles -> $fh {
say $fh;
}
will fail with and X::AdHoc exception (this should probably be improved too):
Failed to open file /home/jmerelo/Code/perl6/my-perl6-examples/args/no-file: No such file or directory
The problem will occur as soon as the invalid filehandle is used for anything. Would there be a way of checking if the filehandle is valid before incurring in an exception?
You can check if something is a Failure by checking for truthiness or definedness without the Failure throwing:
for $*ARGFILES.handles -> $fh {
say $fh if $fh; # check truthiness
.say with $fh; # check definedness + topicalization
}
If you still want to throw the Exception that the Failure encompasses, then you can just .throw it.
TL;DR I thought Liz had it nailed but it seems like there's a bug or perhaps Ugh.
A bug?
It looks like whenever the IO::CatHandle class's .handles method reaches a handle that ought by rights produce a Failure (delaying any exception throw) it instead immediately throws an exception (perhaps the very one that would work if it were just delayed or perhaps something broken).
This seems either wrong or very wrong.
Ugh
See the exchange between Zoffix and Brad Gilbert and Zoffix's answer to the question How should I handle Perl 6 $*ARGFILES that can't be read by lines()?
Also:
https://github.com/rakudo/rakudo/issues/1313
https://github.com/rakudo/rakudo/search?q=argfiles&type=Issues
https://github.com/rakudo/rakudo/search?q=cathandle&type=Issues
A potential workaround is currently another bug?
In discussing "Implement handler for failed open on IO::CatHandle" Zoffix++ closed it with this code as a solution:
.say for ($*ARGFILES but role {
method next-handle {
loop {try return self.IO::CatHandle::next-handle}
}
})
I see that tbrowder has reopened this issue as part of the related issue this SO is about saying:
If this works, it would at least be a usable example for the $*ARGFILES var in the docs.
But when I run it in 6.d (and see similar results for a 6.c), with or without valid input, I get:
say not yet implemented
(similar if I .put or whatever).
This is nuts and suggests something gutsy is getting messed up.
I've searched rt and gh/rakudo issues for "not yet implemented" and see no relevant matches.
Another workaround?
Zoffix clearly intended their code as a permanent solution, not merely a workaround. But it unfortunately doesn't seem to work at all for now.
The best I've come up with so far:
try {$*ARGFILES} andthen say $_ # $_ is a defined ArgFiles instance
orelse say $!; # $! is an error encountered inside the `try`
Perhaps this works as a black-and-white it either all works or none of it does solution. (Though I'm not convinced it's even that.)
What the doc has to say about $*ARGFILES
$*ARGFILES says it is an instance of
IO::ArgFiles which is doc'd as a class which
exists for backwards compatibility reasons and provides no methods.
And
All the functionality is inherited from
IO::CatHandle which is subtitled as
Use multiple IO handles as if they were one
and doc'd as a class that is
IO::Handle which is subtitled as
Opened file or stream
and doc'd as a class that doesn't inherit from any other class (so defaults to inheriting from Any) or do any role.
So, $*ARGFILES is (exactly functionally the same as) a IO::CatHandle object which is (a superset of the functionality of) an IO::Handle object, specifically:
The IO::CatHandle class provides a means to create an IO::Handle that seamlessly gathers input from multiple IO::Handle and IO::Pipe sources. All of IO::Handle's methods are implemented, and while attempt to use write methods will (currently) throw an exception, an IO::CatHandle is usable anywhere a read-only IO::Handle can be used.
Exploring the code for IO::CatHandle
(To be filled in later?)
I am using reagent and am connected to the browser using weasel (tenzing template using boot). In my browser (chrome) console I am able to call clear() and it works.
However when I type (js/clear) in my cider repl, it throws an error -
ReferenceError: clear is not defined
I am however able to run (js/alert "Hello") without any problems. Any ideas what is wrong ?
When you're typing clear() into the console you're not using the Console API, but the Command Line API.
It's not possible to call this function from javascript:
This API complements the Console API, the Command Line API is only
available from within the console itself.
Note that: Some are available in both. Such as console.dir or console.clear which you can call with (.clear js/console).
Try this:
(.clear js/console)
(.log js/console "asdasd")
Worked in my Figwheel REPL. You should try Figwheel, btw: https://github.com/bhauman/lein-figwheel
In case you ask "why" but not "how", this question should clear the situation: clear javascript console in Google Chrome
In Lablgtk, whenever there is an exception in a callback, the exception is automatically caught and an error message is printed in the console, such as:
(prog:12345) LablGTK-CRITICAL **: gtk_tree_model_foreach_func:
callback raised an exception
This gives no stack trace and no details about the exception, and because it is caught I cannot retrieve this information myself.
Can I enable more detailed logging information for this case? Or prevent the exception from being caught automatically?
I guess the best way to do so is to catch your exception manually and handle it yourself.
let callback_print_exn f () =
try f () with
e -> my_exn_printer e
Assuming val my_exn_printer : exn -> unit is your custom exception printer, you can simply print your callbacks exceptions by replacing ~callback:f by ~callback:(callback_print_exn f) in your code.
Of course, you can also with that method send that exception to another
thread, register a "callback id" that would be passed along with your exception...
About the stack trace, I'm not sure you can retrieve it easily. As it's launched as a callback, you probably want to know the signal used and that can be stored in your callback handler.
I had another similar issue, but this time it was harder to find where to put the calls to intercept the exception.
Fortunately, this time there was a very specific error message coming from the Glib C code:
GLib-CRITICAL **: Source ID ... was not found when attempting to remove it`
Stack Overflow + grep led me to the actual C function, but I could not find which of the several Lablgtk functions bound to this code was the culprit.
So I downloaded the Glib source, added an explicit segmentation fault to the code, compiled it and used LD_LIBRARY_PATH to force my modified Glib version to be loaded.
Then I ran the OCaml binary with gdb, and I got my stack trace, with the precise line number where the Lablgtk function was being called. And from there it was a quick 3-line patch.
Hacks like this one (which was still faster than trying to find where to intercept the call) could be avoided by having a "strict mode" preventing exceptions from being automatically caught. I still believe such a switch should be available for Lablgtk users, and hope it will eventually be available.
I'm really struggling to resolve a stack underflow that I'm getting. The traceback I get at runtime is:
VerifyError: Error #1024: Stack underflow occurred.
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at flash.net::URLLoader/onComplete()
This is particularly difficult to debug because when I run in debug mode it does not happen at all. It only happens when compiled as a release.
Does anyone have any tips on how to debug a Stack Underflow? Are have a clean explanation of what that means for Flash?
In case it helps, this error is occurring when I click a button whose handler makes an RPC call, which uses a URLLoader, an AsyncToken, and then invokes the set of AsyncResponder instances associated with the AsyncToken. With some server-side logging as well as some logging hacked into the swf, I know that the UrlLoader is successfully doing and GET'ing a crossdomain.xml file, is correctly processing it (ie: if I wreck it, I get a security error), and is also successfully completing the "load" request (the server sends the data). The underflow seems to be happening in the Event.COMPLETE listening/handling process (as is, of course, implied by the traceback as well).
mxmlc used = from flex_sdk_4.5.0.20967
Example player (I've tried a few) = 10.2.153.1
UPDATE: My specific problem is solved... but I'm leaving the question as-is since I would like to know how to generally debug such a problem, rather than just getting my specific solution.
In my code I had the following Application definition:
<s:Application height="100%" width="100%"
xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx"
initialize="InitData();">
Note that the code is/was attached to the initialize event.
InitData() and relevant defintions are/were:
import classes.RpcServerProxy;
public var SP:RpcServerProxy;
public function InitData():void {
SP = new RpcServerProxy("http://192.168.1.102:1234");
}
When I switched the InitData() call to be on the onCompletion event instead of initialize (thanks J_A_X!), the problem goes away entirely. What seems to have been happening was that the Event.COMPLETE event handler (onComplete in the stack trace) was using the global SP object. Something about the release (vs debug) compilation must have been affecting the startup timing of the SP variable initialization. Moving the handler later to the onCompletion event resolved all issues.
As said above, I would still like to know what tricks/tools are available for debugging initialization issues like this.
UPDATE 2:
applicationComplete seems to be an even better event than creationComplete to put application initialization code. See this blog entry for some explanation, and and this video (around 4:25) by an Adobe Tech Evangelist for an example of simple "start of application" data initialization.
I got rid of this error by adding compiler argument:
-omit-trace-statements=false
Stack underflow basically means the compiler messed up.
You can use SWFWire Inspector to look at the bytecode of the event handler, if you want to know exactly how it messed up. You can also use SWFWire Debugger to see which methods were called, but in this case, you already knew where it was happening.
If you post the broken swf, I can give you more info.
Sean is right that to debug it you can look at the byte code, but that didn't sound appealing to me.
Based on my experience and research, it is often due to the presence of a trace statement that incorrectly gets compiled out in release mode, and generates invalid byte code. So, I would say to "debug" it, "Look for places where you are using trace. Try commenting them all out in the offending function and see if the issue goes away."
In my case, it was a trace statement as the first line of a catch block:
catch (e:TypeError) {
trace(e.getStackTrace()); //This line is the problem
throw new Error("Unexpected type encountered");
}
I found someone else with this exact issue here.
This code also leads to stack underflow only in release mode (flag -debug=false):
true && trace('123');
mxlmc flex sdk version 4.5.0.20967, flashplayer version 10.3.181.14 (linux).
Check your code for similar expressions.
This code caused me issues when I compiled a release candidate from flash builder 4.5
public function set configVO( value:PopupConfigVO ):void
{trace("CHANGING")
Resolved by inserting a space between the the trace and curly brace
public function set configVO( value:PopupConfigVO ):void
{ trace("CHANGING")
Hope this helps.
For people looking for the same problem, I just got this caused by a trace statement in the 'default' case of a switch statement. Commented out the trace, stack underflow resolved.
Interesting... I was getting this error with a SWF that I'd pulled off the web, an Away3D based graphics demo. At the time I was running this on the Tamarin VM rather than the actual Flash/AIR runtimes, so could stick a breakpoint on the "verifyFailed(kStackUnderflowError)" line and see what was happening.
The -Dverbose flag also helped find the culprit:
typecheck MethodInfo-1480()
outer-scope = [global]
[Object~ Object] {} ()
0:pop
VERIFY FAILED: Error #1024: Stack underflow occurred.
And looking at the ABC using SWFInvestigator, I found this:
var function(Object):void /* disp_id=0 method_id=1480 nameIndex = 0 */
{
// local_count=2 max_scope=0 max_stack=0 code_len=2
// method position=52968 code position=155063
0 pop
1 returnvoid
}
So there is an obvious issue where the 'trace' has been removed but the compiler has put a 'pop' in there: I wouldn't have thought this was needed as a trace call should presumably have been made via 'callpropvoid'?
Quite why this doesn't fail on AIR/Flash I don't know..
Anyway: looks to me like an ASC compiler problem i.e perhaps one of the ActionScript3 compilers had a fault with this - hence the workarounds that have been mentioned so far.
It's quite simple, and it doesn't have anything to do with spaces before or after brackets, trace commands or whatever else: it's just 1 really simple thingy:
DO NOT LOOP EMPTY!
Meaning, while developing, we all //comment some lines sometimes, and when that results in
for (...) {
// skip for now
}
the compiler gets :
for(...){}
and that my good friends, is something the compiler doesn't like!
so, NO empty loops, and you're on your way again...
Happy hunting,
P.
I had the exact same problem, but in my case the cause of the problem was a trace statement in a place where the compiler didn't expect it to find it, right after a package declaration at the beginning of the class:
package utils
{
trace ("trace something here");
And that's why compiling in debug mode removed the problem.
I have a DLL with some COM objects. Sometimes, this objects crashes and register an error event in the Windows Event Log with lots of hexadecimal informations. I have no clue why this crashes happens.
So, How can I trace those COM objects exceptions?
The first step is to lookup the Fail code's hex value (E.G. E_FAIL 0x80004005). I've had really good luck with posting that value in Google to get a sense of what the error code means.
Then, I just use trial and error to try to isolate the location in code that's failing, and the root cause of the failure.
If you just want a really quick way to find out what the error code means, you could use the "Error Lookup" tool packaged with Visual Studio (details here). Enter the hex value, and it will give you the string describing that error code.
Of course, once you know that, you've still got to figure out why it's happening.
A good way to look up error (hresult) codes is HResult Plus or welt.exe (Windows Error Lookup Tool).
I use logging internally in the COM-classes to see what is going on. Also, once the COM-class is loaded by the executable, you can attach the VS debugger to it and debug the COM code with breakpoints, watches, and all that fun stuff.
COM objects don't throw exceptions. They return HRESULTs, most of which indicate a failure. So if you're looking for the equivalent of an exception stack trace, you're out of luck. You're going to have to walk through the code by hand and figure out what's going on.