I have a web application, using Spring-Boot. There is now a need for this application to use a custom dll (in house build dll file). There is nothing wrong with this dll, as we use it on our other applications, and have no problems with it.
To load the library in this new web application I'm writing, I have added the dll file to the procrun directory. This directory is on the library path, so that makes sense.
During startup I put in code to immediately load the dll, and also test some of its functionality. This works fine.
However, I have a timer, that schedules the execution of some functions, which may or may not include function calls to the dll.
At some point, about 10 minutes or so into execution, the service unexpected and seemingly without any valid reason, stops.
Although I try/catch exceptions at the appropriate logical places in code, there are no relevant log entries printed.
The Event Log shows something that reminds me of a null pointer exception:
Another bread crumb is that the event log will print something about the dll_unload. (see picture)
I need some help figuring out why the service is failing/stopping.
Kind Regards.
EDIT: After about three days of debugging and scratching my head, I came upon a forum thread that explained that this problem has something to do with the manner in which the system releases the memory during garbage collection. It seems that the dll in question was being unloaded by the garbage collector, even though it could still be called at some time later - which of course was the cause of the service falling over.
To solve the problem, I put in a timer that would call a method in the dll at three minute intervals (on my system this would not impact performance). I know this solution is a hack, but it works for me.
Related
in my project i injected a DLL(64-bit Windows 10) in to a external process with Manual-map & Thread-hijacking and i do some stuff in there.
In current state i use "RtlCreateUserThread" to create a new thread and do some extra workload in there to distribute it for better performance.
My question is now... Is it possible to access other threads from the current process (hijack it) and add your own workload/code there. Without creating a new thread?
I didn't found anything helpful yet in the internet and the code i used and modified for Thread-hijacking seems to only work for a DLL file. Because i am pretty new to C++ i am still learning i am already thankful for any help.
(If you want to see the source for injector Google GHInjector your find the library on github.)
It is possible, but so complicated and may not work in all cases.
You need to splice existing thread's machine codes, so you will need write access to code page memory.
Logic:
find thread id and thread handle, then suspend thread with SuspendThread WINAPI call
suspended thread can be in wait state or in system DLL call now, so you need to analyze current execution stack, backtrace it and find execution address from application space. You need API functions StackWalk, and PDB files in some cases. Also it depends on running architecture (x86, amd64, ...). Walk through stack until your EIP/RIP will not be in application memory address space
decode machine instruction (it will be 'call') and splice next instructions to your function call. You need to use __declspec(naked) declared function or ASM implemented one for execute your code and replaced instructions.
ResumeThread
This method may work only once because no guarantees that application code is executed in loop.
My firm's Access database has been having some serious problems recently. The errors we're getting seem like they indicate corruption -- here are the most common:
Error accessing file. Network connection may have been lost.
There was an error compiling this function.
No error, Access just crashes completely.
I've noticed that these errors only happen with a compiled database. If I decompile it, it works fine. If I take an uncompiled database and compile it, it works fine -- until the next time I try to open it. It appears that compiling the database into a .ACCDE file solves the problem, which is what I've been doing, but one person has reported that the issue returned for her, which has me very nervous.
I've tried exporting all of the objects in the database to text, starting with a brand new database, and importing them all again, but that doesn't solve the problem. Once I import all of the objects into the clean database, the problem comes back.
One last point that seems be related, but I don't understand how. The problem started right around the time that I added some class modules to the database. These class modules use the VBA Implements keyword, in an effort to clean up my code by introducing some polymorphism. I don't know why this would cause the problem, but the timing seems to indicate a relationship.
I've been searching for an explanation, but haven't found one yet. Does anyone have any suggestions?
EDIT: The database includes a few references in addition to the standard ones:
Microsoft ActiveX Data Objects 2.8
Microsoft Office 12.0
Microsoft Scripting Runtime
Microsoft VBScript Regular Expressions 5.5
Some of the things I do and use when debugging Access:
Test my app in a number of VM. You can use HyperV on Win8, VMWare or VirtualBox to set up various controlled test environments, like testing on WinXP, Win7, Win8, 32bit or 64 bits, just anything that matches the range of OS and bitness of your users.
I use vbWatchDog, a clever utility that only adds a few classes to your application (no external dependency) and allows you to trap errors at high level, and show you exactly where they happen. This is invaluable to catch and record strange errors, especially in the field.
If the issue appears isolated to one or a few users only, I would try to find out what is special about their config. If nothing seems out of place, I would completely unsintall all Office component and re-install it after scrubbing the registry for dangling keys and removing all traces of folders from the old install.
If your users do not need a complete version of Access, just use the free Access Runtime on their machine.
Make sure that you are using consistent versions of Access throughout: if you are using Access 2007, make sure your dev machine is also using that version and that all other users are also only using that version and that no components from Access 2010/2013 are present.
Try to ascertain if the crash is always happening around the same user-actions. I use a simple log file that I write to when a debugging flag is set. The log file is a simple text file that I open/write to/close everytime I log something (I don't keep it open to make sure the data is flushed to the file, otherwise when Access crashes, you may only have old data in the log file as the new one may still be in the buffer). Things I log are, for instance, sensitive function entry/exit, SQL queries that I execute from code, form open/close, etc.
As a generality, make sure your app compiles without issue (I mean when doing Debug > Compile from the IDE). Any issue at this stage must be solved.
Make absolutely sure you close all open recordsets, preferrably followed by setting their variables to Nothing. VBA is not as sensitive as it used to be about dangling references, but I found it good practice, especially when you cannot be absolutely sure that these references will be freed (especially when doing stuff at Module-level or Class-level for instance, where the scope may be longer-lived than expected).
Similarly, make sure you properly destroy any COM object you create in your classes (and subs/functions. The Class_Terminate destructor must explicitly clean up all. This is also valid when closing forms if you created COM objects (you mentioned using ADOX, scripting objects and regex). In general keeping track of created objects is paramount: make sure you explicitly free all your objects by resetting them (for instance using RemoveAll on a dictionary, then assigning their reference to Nothing.
Do not over-use On Error Resume or On Error Goto. I almost never use these except when absolutely necessary to recover from otherwise undetectable errors. Using these error trapping constructs can hide a lot of errors that would otherwise show you that something is wrong with your code. I prefer to program defensively than having to handle exceptions.
For testing, disable your error trapping to see if it isn't hiding the cause of your crashes.
Make sure that the front-end is local to the user machine, You mention they get their individual front-end from the network but I'm not sure if they run it from there or if it it copied on their local machine. At any rate, it should be local not on a remote folder.
You mention using SQL Server as a backend. Try to trace all the queries being executed. It's possible that the issue comes from communication with SQL Server, a corrupt driver, a security issue that prevents some queries from being run, a query returning unexpected data, etc. Watch the log files and event log on the server closely for strange errors, especially if they involve security.
Speaking of event log, look for the trace of the crash in the event log of your users. There may be information there, however cryptic.
If you use custom ribbon actions, make sure thy are not causing issues. I had strange problems over time with the ribbon. Log all all function calls made by the ribbon.
I'm developing a DirectShow CSource capture filter. It works fine, but when I close the program that is using the filter (in this case I'm testing with VLC, but the same happens with other programs), the program crashes (if I'm debugging it in Visual Studio then a breakpoint is triggered).
I've been hunting down this problem for some time now and found that both, my source filter and my source stream are not being released; this is, their reference counter is 1 at the end of the program, DllCanUnloadNow() function reports that there are 2 objects still in use, and, when CoUninitialize() is invoked, the program crashes.
I'm pretty sure that the reference counters are being handled correctly since I'm using the base classes implementation. The only unusual thing in my software that I can think of is that I'm using my own version of DllGetClassObject(): I configured the .DEF file to have MyDllGetClassObject() exported instead of DllGetClassObject() so I could insert some code before invoking the default implementation. I don't think this is a problem since I've checked that the reference counter of all objects I return at the end of MyDllGetClassObject() is 1.
I guess I'm missing something about the lifecycle of the filter, but can't figure out what (this is the very first capture filter I'm developing). Any suggestion?
Thank you in advance,
Guillermo
I finally figured out what was going on. The static method InitializeInstance in my source filter is invoked with bLoading == false and rclsid == <the GUID of my filter> at process shutdown. That seems to be the appropriate place to release that remaining reference counter from the filter instance.
I got the key idea of how important is to release all COM objects before CoUninitialize some time ago from another post on StackOverflow entitled DirectShow code crashes after exit (PushSourceDesktop sample). All I needed was just a little bit more knowledge on DirectShow filters lifecycle.
Anyway, thank you for your efforts, Roman, I know how vague this thread sounded from the beginning :)
From what experience I have programming whenever a program has a problem it crashes, whether it is from an unhanded exception or a piece of code that should have been checked for errors, but was not and threw one. What would cause a program to completely freeze a system to the point of requiring a restart.
Edit: Thanks for the answers. As for the language and OS this question was inspired by me playing Fallout and the game freezing twice in an hour causing me to have to restart the xbox, so I am guessing c++.
A million different things. The most common that come to mind are:
Spawning too many threads or processes, which drowns the OS scheduler.
Gobbling too much RAM, which puts the memory manager into page-fault hell.
In a Dotnet/Java type environment its quite difficult to seize a system up, because the Runtime keeps you code at a distance from the OS.
Closer to the metal say C or C++, Assembly etc you have to play fair with the rest of the system - If you dont have it already grab a copy of Petzold and observe/experiment yourself with the amount of 'boilerplate' code to get a single Window running...
Even closer, down at the driver level all sorts of things can happen...
There are number of reasons, being internal or external that leads to deadlocked application, more general case is when something is being asked for by a program but is not given that leads to infinite waiting, the practical example to this is, a program writes some text to a file, but when it is about to open a file for writing, same file is opened by any other application, so the requesting app will wait (freeze in some cases if not coded properly) until it gets exclusive control of the file.
And a critical freeze that leads to restarting the system is when the file which is asked for is something which very important for the OS. However, you may not need to restart the system in order to get it back to normal, unless the program which was frozen is written in a language that produces native binary, i.e. C/C++ to be precise. So if application is written in a language which works with the concept of managed code, like any .NET language, it will not need a system restart to get things back to normal.
page faults, trying to access inaccessible data or memory(acces violation), incompatible data types etc.
I have an old VW3/ENVY image with a parcel loaded as unmanaged code (exactly the situation Mastering ENVY/DEVELOPER warns against). Unfortunately, this problem happened a long time ago and it's too late to just "go back" to an image without the parcel loaded.
Apparently, there is a way to solve this problem (we have one development image where this has been solved, and there are normal configuration maps that contain the exact same code as the unmanaged parcel but they can't be loaded), but the exact way has long since been forgotten (and there are some problems with taking that particular dev image as the base for a new runtime image, so I need to find out how how to do it again).
In theory, it should be possible to remove the parcel and reload the code from a configuration map. In practice, all normal ways (using the ParcelBrowser or directly calling UnmanagedCode>>remove) fail. I even tried manually removing the offending selectors from the method dictionary, but past a certain point (involving a call to #primBecome:) the whole image hangs completely (I can't even drop into the debugger). I started hacking the instances of the classes and methods, hoping I'd trick ENVY into thinking that these particular methods are normal versioned code, but without any success yet.
Are there any smalltalk/envy gurus around that still remember enough of VW 3 to provide me with any pointers?
Status update
After a week of trying to solve the problem I finally made it, at least partially, so in case anyone's interested...
First, I had to fix file pointers for the umnanaged code (otherwise, all everything that tried to touch the methods would throw an exception). It looks like ENVY extends Parcel so that, in theory, all integer file pointers are changed to ENVY's void filepointer when loaded, but in my case, I had to do it manually (a Parcel provides enumeration for all selectors it defines). Another way would be to tweak the filePointer code, but that can't easily be done automatically on every image where it's needed.
Then, the parcel can be discarded, which drops the parcel information, but keeps the code. The official "Discard" mechanism needs to have a valid changes file (which envy doesn't use so it has to be set manually, and reset afterwards) and the parcel source (which we fortunately had).
To be able to make any changes to the methods (either manually, or via loading an application or class from ENVY), they need to get rid of their unmanaged status. This can be done by manually tweaking TheClass>>applicationAssocs (I also got rid of all references to the classes in UnmanagedCode sich as timestamps, and removed the reference to the discarded parcel). I actually had some info on how to get to this point from my boss, but I haven't been able to understand the instructions until I almost figured it out by myself.
This finally allowed me to load and reload all the Applications that contained the classes. In theory. In practice, the image still hung completely whenever I tried to load a newer version of the Application (that contained the code formerly in the parcel).
It turned out that the crashes had absolutely nothing to do with the code being unmanaged, but with the fact that the parcel in question modified InputState>>process:, where it caused an exception due to a missing and/or uninitialized class variable (the InputState>>initialize method wasn't called until after the new process: method was in place). I had to modify the Notifier class to dump all exceptions to a file to find out what was going on. Adding the class variable to the source of the class (instead of adding it via reflection), suspending the input processing thread via toBeLoadedCode and starting it again in the loaded method and creating a new version of the application solved even this problem.
Now everything works, in theory. In practice it's still unusable, because reloading the WindowSystem or VisualworksBase applications causes their initialization blocks to run, and a whole lot of settings are reset to their defaults - fonts and font sizes, window colors, UI settings... And there doesn't seem to be any way to just save the settings to a file and load them later on, or just to see what all the settings are (either the official Settings menu doesn't show everything, or we have a heavily tweaked image... so much for reconstructing it from scratch). But that's a completely different question.
Well, normally the recommendation would be that you should be able to rebuild your development image from scratch by loading your code from the repository. But if you had that, then the answer would be simple, just discard that image and reload. I think it's been long enough that I've lost whatever knowledge I've had about how to mess with the internal structures to get it back, and it sounds like you've tried a lot of things. So, although it might be painful, figuring out the recipe to rebuild your development image by loading stuff from the repository sounds like it may be your best bet. It probably isn't all that horrible, there just might be a few dependencies on the image state, or special doits that need to be executed.
You also probably need to validate what's in the repository against what's in the image you're working from. If there was unmanaged code loaded and then someone modified it and saved it, it's not clear to me that it would have been saved to ENVY. So you probably want to audit everything that was unmanaged code and if it's been changed, save that to a repository edition.
Sorry I don't have any better answers.