I'm maintaining a number of console applications at work and one thing I've been noticing in a number of them is that they call Environment.Exit(0).
A sample program would look like this:
public class Program
{
public static void Main(string[] args)
{
DoStuff();
Environment.Exit(0);
}
}
I don't understand what the intent of the original programmer was in doing this? In my mind even without the Environment.Exit statement the program should exit just fine. That said, for one of these programs, it's console window has been remaining even after it was supposed to have closed so I'm really not sure what's going on there....
Am I missing something here? Or is there a reason why Environment.Exit should be called in this instance?
The only reason for calling Exit() as the last line of the Main method is if there might be other foreground threads running. They would stay running if execution just fell off the end of Main. Even in this case, it would usually be a better idea either to put in some explicit graceful termination into the other threads - or make them background threads to start with.
If you ever want to return a different exit code from Main, the simpler way to achieve that is to declare it to return int.
In short, I don't think you need Environment.Exit() here, and it's worth asking your colleagues exactly why they're using it - chances are they won't be able to give you a good reason, and it's another bit of fluff you can cut out.
Basically, the statement Environment.Exit(0) tells the operating system that this is a "clean" exit. There are other numbers as well, each with a different meaning like, Environment.Exit(1).
However, one thing to note is that the "Main" has been declared as returning nothing "void", so the exit code will really not have a meaning to it.
Just in case you wanted to know more about the different exit codes, have a look here:
System Error Codes (0-499)
This is (compatibility) for command-line programs to indicate success or failure to an underlying shell, and is inherited from older C-style main loops where the prototype of the main function was
int main(void);
int main(int argc, char *argv[]);
The return value of 0 traditionally meant success, while non-zero meant failure or something else, depending on what the programmer decided.
References
Wikipedia for more information on the main function.
MSDN documentation on Environment.Exit()
In .NET Core, as of right now, one must use Environment.Exit to terminate their program on Mac. Purely returning from main doesn't stop the process and it keeps running until the user aborts it. Patterns like:
public class Program
{
public static void Main(string[] args)
{
Environment.Exit(TryRun(args));
}
}
are common in my work place because we want to ship for both Windows and Mac.
I'm currently using Environment.Exit() in a console application where I don't want to throw ugly exception text back to the console. Instead, I just notice the condition, write a user-friendly message to the screen about what happened and then call Environment.Exit().
Otherwise, you shouldn't need to call it from Main() in a basic console application.
In SSIS, when you have an Execute Process Task and you want to know if process is failure, this method is useful.
This is really used when other applications are waiting on the result of your console application. For example, SQL Server Reporting Services (SSRS) (tool) can launch a console application and waits to get back a success of failure response. The Environment.Exit(0) sends back a successful execution message.
Related
In my C# MVC4 ASP.NET code (in a method on a controller) I call a function that I know has the possibility that it may never return. It is a call to a Microsoft object that does not raise and error, does not time out, just hangs (and hangs and hangs).
I think I have found the cause of the specific incidents of why this has happened, but the general problem worries me and I want to guard against it (as it causes general problems on the server, rather than just isolated problems to the individual user). I want to know the most graceful way of handling this sort of problem.
The method I am calling is LocalReport.Render and this Google search shows a number of people with a number of problems where this method never seems to return.
Maybe try calling the method on a different Thread ? and abort the thread after a timeout ?
Although not a neat solution at all, but not a lot of options available in case there is no misconception about why the method hangs.
Having looked at this answer to a similar question I think the least worse solution is to wrap the offending call (to LocalReport.Render) into a separate Process and app domain. I will then kill the process if it starts behaving erratically.
I'm creating a memory modifying program for my own learning purposes. A friend of mine pointed out a function in another program that I want to trigger.
The function is at 0x004B459C in the other program. I know how to read and write memory, but how can I trigger this function from my program. I do not have the source to this other program.
My question is do I need to inject the function if I know this hex code, or do I just write something to memory to trigger this?
Think a bit about what you really want. You want the other process to execute this function. Processes don't execute code, it's threads that execute code. If you want the other process to call this function as a part of it's normal operations, you will have to figure out inputs etc. which will make one of the other process's threads call it. Generally speaking, any other way you will be running the risk of corrupting the other process. It is possible to inject a thread into another process and have it call the function you're interested in (see CreateRemoteThread). If this function is intended to be called on the message pump thread, you could inject a message hook into the other process, send it a special message and call it from your hook. There are a few more ways (APC) but these are still more complicated for little gain.
you are missing some basic architecture fundamentals :-) you cannot simply call a function knowing its address from another process! think of it, this means that your program can get the memory of any program and execute code! this will be a mess and a complete insecure environment. first some basics:
1) windows guarantees that you only see the memory of your own process, one of the most important principles of an OS (even Windows) is to isolate processes including their memory of course.
2) did think about permissions, usually any code that runs must run under a user account, another process might mean another process account.
the answer is simple, if your program is .NET/C# then check what the .NET framework provides you for inter process communication, this is the thing you must search for, every platform, Java, windows native, .NET provides an offical way how process communicate with each other, it is called interprocess communication, check it in .NET framework
I realise this might be hard to explain, so let me start by using an example from Windows; keBugCheckEx().
How would I go about making a method that is contained within one program but, when executed from another, affect the program it is in. For example, in the main program, you could have:
public static void Panic(uint errCode)
{
System.Windows.MessageBox.Show("Function Panic() was called with error code: "
+ errCode);
Application.Exit();
}
And then, in the second program, you could call that method, e.g.
public static void Main(string[] args)
{
Foo.Panic(0x3C);
}
How would I go about making it so that, instead of the MessageBox showing in the second program, it appears in the first program? Sorry if this is not very well explained.
You mention two separate "programs". Do you mean two separate executables? I think what you mean is you would have a project that is more of a class library that encapsulates certain functions / validations. You refer to "Foo" but no other declaration... is it a second project within your overall application "Solution" and included as part of the main with #using. Secondary class libraries SHOULD be able to do a simple messagebox as long as its called from within the overall main UI thread.
You might need to elaborate a bit more / update your question.
I guess the final solution was the feedback comment to have the class just have a method within the class that does nothing but pass a string message BACK to the calling source. From that, any application calling it can get the message and display it within their own UI thread.
The ability of one process to affect another process is, for very good reason, tightly controlled by most OSes. A program that can make another program execute instructions that don't follow the normal logic path of that program can induce undesirable behavior, and such actions are a hallmark of viruses.
That being said, there are ways to structure these two processes to allow for inter-process communication; processes often have to talk to each other, and often one program can "tell" another program to execute code, but the actual decision to do so is made by the program. For two programs that could also stand alone, something like a named pipe would allow for one process to input data into another process which could be interpreted as a command.
If both of these processes are .NET, or the libraries containing the code are COM-compatible, you can simply execute the code from the other program in the calling process. You simply reference the external library, and if Foo as a class is visible to external consumers, you can instantiate one and call its methods. This would be the normal way to execute behavior from a different process within your own; but, you can't tell a different process with a Foo to call Panic(), but not execute absolutely everything in it (which includes showing the dialog in the context of the owning process's UI thread)
I'm not sure if there is a proper term for what I want to because any I've tried in google haven't bought anything up.
Basically, on an application crash I would like to perform a final action to clean up database record locking.
I would also like to catch this when debugging is stopped using the stop button, as I understand it using the stop button is very different to exiting your application by a normal process in your application.
Is there a normal way for achieving what I'm trying to do? The application is a C#, .NET 3.5 Windows Forms Application written in VS2008.
Cheers
You can't do anything within a process after it's killed.
Your only way to achieve what you want would be to have a second process that watched for the first one dying, and then did the cleanup on its behalf.
You have to worry about the second process crashing, or being killed, and so on. Not easy to make it work in all conceivable cases, but a lot better than nothing.
Check if any of the solution on Handling end process of a windows app helps you.
I don't think its possible to catch when the user stops the process via the debugger, however, you can override the OnUnhandledException event to catch when any exceptions are raised and not caught by your application.
The answer to your first requirement is to have (at it's most basic):
try
{
// Main application
}
catch // Though you might not want this
{
}
finally
{
// This code always executed even if application crashes.
}
However there are other considerations when dealing with Windows applications as RichardOD indicates in his comments here - http://msdn.microsoft.com/en-us/library/system.appdomain.unhandledexception.aspx and here http://msdn.microsoft.com/en-us/library/system.windows.forms.application.threadexception.aspx
The answer to your second requirement is no you can't trap the application being stopped in the debugger (or at least there's not a way I've come across). It just kills the process.
For instance if you have stopped at a break point and then press stop the code doesn't carry on executing to termination - it just exits.
The same is true if the application stops due to some external factor like the power being turned off. In scenarios like this there's no way that the program can execute any code whether it's in a finally block or not!
However, I've just come across this question Visual Studio : executing clean up code when debugging stops which has an answer that states:
You can use the DTE (VisualStudio
Automation Model) to write a macro
that will be invoked when a stop debug
happens, below is a snippet of the
idea.
Private Sub DebuggerEvents_OnEnterDesignMode(ByVal Reason As EnvDTE.dbgEventReason, ByRef ExecutionAction As EnvDTE.dbgExecutionAction) Handles DebuggerEvents.OnEnterDesignMode
If (Reason = dbgEventReason.dbgEventReasonStopDebugging) Then
// DO YOUR CLEAN UP CODE HERE
End If
End Sub
So while you can't trap the stopping of the execution in your application you can do something about it in Visual Studio.
NOTE: Answer provided by Shay Erlichmen not me!
You could subscribe to the Application.ThreadException event when your program starts up, before you call Application.Run. This will give you a chance to do something if your application throws and exception. It will not do anything, however, for catching the debugger when you hit stop.
<SecurityPermission(SecurityAction.Demand, Flags:=SecurityPermissionFlag.ControlAppDomain)> _
Public Shared Sub Main()
AddHandler Application.ThreadException, AddressOf ErrorHandlerForm.Form1_UIThreadException
Application.SetUnhandledExceptionMode(UnhandledExceptionMode.CatchException)
' Run the application.
Application.Run(New Form1())
End Sub
Private Shared Sub Form1_UIThreadException(ByVal sender As Object, ByVal t As ThreadExceptionEventArgs)
' Handle exception
End Sub
Your other option is to just surround your Application.Run in a Try...Catch block, which should give you similar results.
If you're targeting Windows Vista (or above) you might be interested in the RegisterApplicationRecoveryCallback API...
http://msdn.microsoft.com/en-us/library/aa373345.aspx
It doesn't address the debugging scenario, but it does allow you to do something when your app is about to crash.
You can p/invoke to this API from C# (I have done it), but bear in mind that when your callback is invoked your app is already in a very bad state, and you can make very few assumptions about the state of your memory. If you have any in-memory data that you want to use in this routine, I would put it in a static at a very general scope so that you have the best possible chance of it not having been "tidied up" when your callback routine runs.
There are some other interesting APIs, related to this one, that allow you automatically restart your app after a failure, etc.
A "normal way for achieving what you're trying" is to make sure your application never crashes.
You can also provide a standalone application which will let system administrator to release any file locks which might be left for whatever reason (power outage, ...). Such application could be used to fix this as well.
I have a seemingly very simple case where I'm using System.Threading.ReaderWriterLockSlim in the 3.5 version of the .NET Framework. I first declare one, as shown here:
Lock Declaration http://odeh.temp.s3.amazonaws.com/lock_declaration.bmp
I put a break point right before the lock is acquired and took a screen shot so you can see (in the watch window) that there are currently no locks held:
pre lock acquisition http://odeh.temp.s3.amazonaws.com/prelock.bmp
Then, after calling EnterWriteLock, as you can see I am holding a Read Lock.
post lock acquisition http://odeh.temp.s3.amazonaws.com/postlock.bmp
This seems like truly unexpected behavior and I can't find it documented anywhere. Does anyone else know why this happens? In other places in my code (earlier), this exact same line of code correctly obtains a write lock. Consistently, however, across multiple systems it instead obtains a read lock at this place in the call stack. Hope I've made this clear and thanks for taking the time to look at this.
--- EDIT---
For those mentioning asserts... this just confuses me further:
post assert http://odeh.temp.s3.amazonaws.com/assert.bmp
I really can't say how it got past this assertion except that perhaps the Watch Window and the Immediate window are wrong (perhaps the value is stored thread locally, as another poster mentioned). This seems like an obvious case for a volatile variable and a Happens Before relationship to be established. Either way, several lines later there is code that asserts for a write lock and does not have one. I have set a break point on the only line of code in the entire program that releases this lock, and it doesn't get called after the acquisition shown here so that must mean it was never actually acquired... right?
This could be a debugger side-effect. The ReaderWriterLockSlim class is very sensitive to the current thread ID (Thread.ManagedThreadId). I can't state for a fact that the debugger will always use the current active thread to evaluate the watch expressions. It usually does, but there might be different behavior, say, if you entered the debugger with a hard break.
Trust what the code does first of all, your Debug.Assert proves the point.