I have been working on something that checks an MySQL Database to check something - however the program stops responding because it is constantly checking the database. Is it possible to have it wait a few seconds to recheck the database? I have tried sleep() but it is giving a strange error:
A call to PInvoke function
'Game!WindowsApplication1.Form1::Sleep' has unbalanced the
stack. This is likely because the managed PInvoke signature
does not match the
unmanaged target signature. Check that the calling convention
and parameters of the
PInvoke signature match the target unmanaged signature.
I have been looking into this for quite a while and i am in a predicament. I do need the MySQL databases to be checked very often. I tried making a web browser refresh before checking it again - but it started to lag the application.
Code:
function updateit()
' SQL Code goes here, it succeeds.
updateit() ' Update it again.
return true
end
updateit()
Your code example shows a recursive function with no base case. The result of that is always a stack overflow (an uncatchable exception in .Net).
Don't call your updateit() function from within the function itself. Instead, just write a loop to call it over and over.
Try doing your checks from a separate thread. Try dragging a BackgroundWorker onto your form and putting your check in that to make your program more responsive. I've never seen that error before though. Is it System.Threading.Thread.Sleep() or something specific to VB?
Looking at your code it looks like you've got infinite recursion. That will cause a stackoverflow... try
while(true)
'SQL code
end
Related
I have used many discord API wrappers, but as an experienced python developer, unfortunately I somehow still do not understand how a command gets called!
#client.command()
async demo(ctx):
channel = ctx.channel
await channel.send(f'Demonstration')
Above a command has been created (function) and it is placed after its decorator #client.command()
To my understanding, the decorator is in a way, a "check" performed before running the function (demo) but I do not understand how the discord.py library seemingly "calls" the demo function.....?? Is there some form of short/long polling system in the local imported discord.py library which polls the discord API and receives a list of jobs/messages and checks these against the functions the user has created?
I would love to know how this works as I dont understand what "calls" the functions that the user makes, and this would allow me to make my own wrapper for another similar social media platform! Many thanks in advance.
I am trying to work out how functions created by the user are seemingly "called" by the discord.py library. I have worked with the discord.py wrapper and other API wrappers before.
(See source code attached at the bottom of the answer)
The #bot.command() decorator adds a command to the internal lists/mappings of commands stored in the Bot instance.
Whenever a message is received, this runs through Bot.process_commands. It can then look through every command stored to check if the message starts with one of them (prefix is checked beforehand). If it finds a match, then it can invoke it (the underlying callback is stored in the Command instance).
If you've ever overridden an on_message event and your commands stopped working, then this is why: that method is no longer being called, so it no longer tries to look through your commands to find a match.
This uses a dictionary to make it far more efficient - instead of having to iterate over every single command & alias available, it only has to check if the first letters of the message match anything at all.
The commands.Command() decorator used in Cogs works slightly different. This turns your function into a Command instance, and when adding a cog (using Bot.add_cog()) the library checks every attribute to see if any of them are Command instances.
References to source code
GroupMixin.command() (called when you use #client.command()): https://github.com/Rapptz/discord.py/blob/24bdb44d54686448a336ea6d72b1bf8600ef7220/discord/ext/commands/core.py#L1493
As you can see, it calls add_command() internally to add it to the list of commands.
Adding commands (GroupMixin.add_command()): https://github.com/Rapptz/discord.py/blob/24bdb44d54686448a336ea6d72b1bf8600ef7220/discord/ext/commands/core.py#L1315
Bot.process_commands(): https://github.com/Rapptz/discord.py/blob/master/discord/ext/commands/bot.py#L1360
You'll have to follow the chain - most of the processing actually happens in get_context which tries to create a Context instance out of the message: https://github.com/Rapptz/discord.py/blob/24bdb44d54686448a336ea6d72b1bf8600ef7220/discord/ext/commands/bot.py#L1231
commands.Command(): https://github.com/Rapptz/discord.py/blob/master/discord/ext/commands/core.py#L1745
When working on a SolidJS project you might start seeing the following warning message in your JS console:
computations created outside a `createRoot` or `render` will never be disposed
There are some information available on this in SolidJS' Github repository issues. But after reading them I was still not quite sure what this was all about and whether my code was really doing something wrong.
I managed to track down where it came from and find a fix for it based on the documentation. So I'm providing the explanation and the solution for those Googling this warning message.
In essence this is a warning about a possibility of a memory leak due to a reactive computation being created without the proper context which would dispose of it when no longer needed.
A proper context is created a couple of different ways. Here are the ones I know about:
By using the render function.
By using the createRoot function. Under the hood render uses this.
By using the createContext function.
The first is by far the most common way, because each app has at least one render function call to get the whole show started.
So what makes the code go "out of context"?
Probably the most common way is via async calls. The context creation with its dependency tree happens only when the synchronous portion of the code finishes running. This includes all the export default function in your modules and the main app function.
But code that runs at a later time because of a setTimeout or by being in an async function will be outside of this context and any reactive computations created will not be tracked and might stick around without being garbage collected.
An example
Let's say you have a data input screen and have a Save button on it that makes an API call to your server to save the data. And you want to provide a feedback to the user whether the operation succeeded or not, with a nice HTML formatted message.
[msg,setMsg] = createSignal(<></>)
async function saveForm(){
...
setMsg(<p>Saving your data.<i>Please stand by...</i></p>)
const result=await callApi('updateUser',formData)
if(result.ok){
setMsg(<p>Your changes were <b>successfully</b> saved!</p> )
} else {
setMsg(<p>There was a problem saving your data! <br>Error: </p><pre>{result.error}</pre> )
}
}
...
<div>
...
<button onClick={saveForm} >Save</button>
{msg()}
</div>
This will produce the above mentioned warning when the API call returns an error, but not the other times. Why?
The reason for this is that SolidJS considers the code inserts inside JSX to be reactive, ie: need to be watched and re-evaluated. So inserting the error message from the API call creates a reactive computation.
The solution
I found the solution at the very end of the SolidJS doc. It's a special JSX modifier: /*#once*/
It can be used at the beginning of a curly brace expression and it tells the SolidJS compiler to explicitly not to make this a reactive expression. In other words: it will evaluated once and only once when the DOM nodes are created from the JSX.
In the above example here's how to use it:
setMsg(<p>There was a problem saving your data! <br>Error: </p><pre>{/*#once*/ result.error}</pre> )
After this there will be no more warning messages :)
In my case, I had an input and when that input changed I re-created an SVG drawing. Because the SVG creation was an expensive operation, I added a debounce in the createEffect function which ran when the input changed. debounce is a technique to defer the processing until the input stops changing for at least X amount of time. It involved running the SVG generation code inside the setTimeout function, thus being outside of the main context. Using the /*#once*/ modifier everywhere where I inserted an expression in the generated JSX has fixed the problem.
when I reverse the binary with IDA gui, all the functions get decompiled without a problem.
but when I am running an automatic script on ida without gui, there is always the same function, that refuses to be decompiled. (when I am openning the same IDB that the automation script worked on, the function get decompiled without a problem)
I am using bip. and using BipFunc.can_decompile to check if a function can get decompiled.
EDIT:
according to an answer bellow, I have tried to add the following:
if not func.can_decompile:
print(f"can't decompile function 0x{func.ea:04x}, trying again")
decomp_all()
if not func.can_decompile:
print(f"can't decompile function 0x{func.ea:04x}, trying again")
decomp_all_twice_cacheclear()
if not func.can_decompile:
print(f"can't decompile function 0x{func.ea:04x}, skipping...")
return
sadly it did not work, I get all 3 prints every time, even on different binaries
it seems to be fixed on IDA Pro 7.6
There is several reason you can get an error on the decompilation from IDA. If it works on some case and other it does not it is probably because of the call analysis. When decompiling a function IDA will try to gather information on the function called by this one and in some case fail to get those information which will make the decompilation fail. But once that function has been decompiled, the information fetched by IDA will be updated, and so the decompilation of the caller function might now work. So basically it means you have to decompile the function in an order, which is a pain, for fixing that the simplest way is to just decompile everything twice, but it can take quite some time if you do it on "big" binaries.
I though I put that in the Bip repository somewhere but I can't find it, so here is a small plugin/code which should allows to do that:
from bip import *
class DecompileAll(BipPlugin):
"""
Plugin for decompiling all the function in the binary.
"""
#menu("Bip/DecompileAll/", "Invalidate hexrays caches")
def clear_hxcCache(self):
HxCFunc.invalidate_all_caches()
#menu("Bip/DecompileAll/", "Decompile all func")
def decomp_all(self):
count = 0
for f in HxCFunc.iter_all():
count += 1
print("0x{:X} functions decompiled".format(count))
#menu("Bip/DecompileAll/", "Decompile twice with cache clear")
def decomp_all_twice_cacheclear(self):
HxCFunc.invalidate_all_caches()
self.decomp_all()
self.decomp_all()
Just for information the basic reason for decompilation error, is that it is not able to make a correct translation of some piece of code because it does not understand the assembly, this is typically true if there is a problem during the analysis and the code is not correctly detected (also happens a lot if you are dealing with obfuscation). You can typically view this case by an error telling you "failed analysis at ADDR" in the IDAPython console, and then look at the problem. Probably not your case but might still help.
Glad to hear you are using bip. So about the BipFunc.can_decompile function: like indicated in the documentation (https://synacktiv.github.io/bip/build/html/base/func.html#bip.base.BipFunction.can_decompile) it will just try to decompile the function and see if an error occurs. The code is pretty straight forward (https://github.com/synacktiv/bip/blob/master/bip/base/func.py#L372), this is mostly written for being done while using one-liner, its the same thing as catching the exception when trying to decompile.
I'm new to access and am working with a database someone else wrote.
I'm trying to understand the code by tracing it, but surprisingly I'm having trouble here.
There's a form, let's call it form 1, such that if you click it's "go" button it will execute a procedure. The first command in that procedure is:
DoCmd.OpenForm "Frm2", acNormal
When this line executes it goes to some module, "module X", where two functions are executed. These
functions are in a stand-alone module and I don't see how they are related to Frm2.
After these two functions are executed, control goes to Frm2, specifically this line in Frm2's code:
Form.Load
So, my question, as I alluded to earlier, is why are the two functions in module X called before
control is handed to Frm2?
When the first of the two mystery functions are being executed, I do a stack trace and I see this:
function1()
<non-basic code>
Frm1_Btn_click()
This doesn't tell me what's calling function1, and its throwing me off.
If I comment out function1, I get a run-time error 3085 "Undefined Function
function 1 in Expression". This begs the question, what "expression" is the error referring to?
I believe this is the missing link, but I can't find it.
Thanks for your help
I solved it. The issue was a dependency that was caused by the form having a record source linked to a query. The was due to this.
I'm glad I was able to solve this!
The problem that I am facing is primarily on Exception Handling! When an exception occurs I want to put that data in another log table with the error message. However, in DB2 I am not able to figure out a way to retrieve the corresponding error message for the raised SQLSTATE.
PS: I have a stored procedure for this migration and I am not using any other language to call it.
We could do this through SQLERRM in oracle; probably it should be a small thing, still for some strange reasons I have not been able to find it yet!
Hopefully you would have an idea on this, ;-). I just need a pointer on this.
Thanks,
Harveer Uppal
DB2 has an SQLERRM function too. All you need to to is capture all of the tokens from the error and feed them into the function for the equivalent message you'd get from the CLP.
http://publib.boulder.ibm.com/infocenter/db2luw/v9r5/topic/com.ibm.db2.luw.sql.rtn.doc/doc/r0022027.html
You should be able to get in the front-end code using DB2Exception.Message property.