Can I send a ctrl-C (SIGINT) to an application on Windows?

Question

I have (in the past) written cross-platform (Windows/Unix) applications which, when started from the command line, handled a user-typed Ctrl-C combinat

Answer 1

I guess I'm a bit late on this question but I'll write something anyway for anyone having the same problem. This is the same answer as I gave to this question.

My problem was that I'd like my application to be a GUI application but the processes executed should be run in the background without any interactive console window attached. I think this solution should also work when the parent process is a console process. You may have to remove the "CREATE_NO_WINDOW" flag though.

I managed to solve this using GenerateConsoleCtrlEvent() with a wrapper app. The tricky part is just that the documentation is not really clear on exactly how it can be used and the pitfalls with it.

My solution is based on what is described here. But that didn't really explain all the details either and with an error, so here is the details on how to get it working.

Create a new helper application "Helper.exe". This application will sit between your application (parent) and the child process you want to be able to close. It will also create the actual child process. You must have this "middle man" process or GenerateConsoleCtrlEvent() will fail.

Use some kind of IPC mechanism to communicate from the parent to the helper process that the helper should close the child process. When the helper get this event it calls "GenerateConsoleCtrlEvent(CTRL_BREAK, 0)" which closes down itself and the child process. I used an event object for this myself which the parent completes when it wants to cancel the child process.

To create your Helper.exe create it with CREATE_NO_WINDOW and CREATE_NEW_PROCESS_GROUP. And when creating the child process create it with no flags (0) meaning it will derive the console from its parent. Failing to do this will cause it to ignore the event.

It is very important that each step is done like this. I've been trying all different kinds of combinations but this combination is the only one that works. You can't send a CTRL_C event. It will return success but will be ignored by the process. CTRL_BREAK is the only one that works. Doesn't really matter since they will both call ExitProcess() in the end.

You also can't call GenerateConsoleCtrlEvent() with a process groupd id of the child process id directly allowing the helper process to continue living. This will fail as well.

I spent a whole day trying to get this working. This solution works for me but if anyone has anything else to add please do. I went all over the net finding lots of people with similar problems but no definite solution to the problem. How GenerateConsoleCtrlEvent() works is also a bit weird so if anyone knows more details on it please share.

Answer 2

In Java, using JNA with the Kernel32.dll library, similar to a C++ solution. Runs the CtrlCSender main method as a Process which just gets the console of the process to send the Ctrl+C event to and generates the event. As it runs separately without a console the Ctrl+C event does not need to be disabled and enabled again.

CtrlCSender.java - Based on Nemo1024's and KindDragon's answers.

Given a known process ID, this consoless application will attach the console of targeted process and generate a CTRL+C Event on it.

import com.sun.jna.platform.win32.Kernel32;    

public class CtrlCSender {

    public static void main(String args[]) {
        int processId = Integer.parseInt(args[0]);
        Kernel32.INSTANCE.AttachConsole(processId);
        Kernel32.INSTANCE.GenerateConsoleCtrlEvent(Kernel32.CTRL_C_EVENT, 0);
    }
}

Main Application - Runs CtrlCSender as a separate consoless process

ProcessBuilder pb = new ProcessBuilder();
pb.command("javaw", "-cp", System.getProperty("java.class.path", "."), CtrlCSender.class.getName(), processId);
pb.redirectErrorStream();
pb.redirectOutput(ProcessBuilder.Redirect.INHERIT);
pb.redirectError(ProcessBuilder.Redirect.INHERIT);
Process ctrlCProcess = pb.start();
ctrlCProcess.waitFor();

Answer 3

// Send [CTRL-C] to interrupt a batch file running in a Command Prompt window, even if the Command Prompt window is not visible,
// without bringing the Command Prompt window into focus.
// [CTRL-C] will have an effect on the batch file, but not on the Command Prompt  window itself -- in other words,
// [CTRL-C] will not have the same visible effect on a Command Prompt window that isn't running a batch file at the moment
// as bringing a Command Prompt window that isn't running a batch file into focus and pressing [CTRL-C] on the keyboard.
ulong ulProcessId = 0UL;
// hwC = Find Command Prompt window HWND
GetWindowThreadProcessId (hwC, (LPDWORD) &ulProcessId);
AttachConsole ((DWORD) ulProcessId);
SetConsoleCtrlHandler (NULL, TRUE);
GenerateConsoleCtrlEvent (CTRL_C_EVENT, 0UL);
SetConsoleCtrlHandler (NULL, FALSE);
FreeConsole ();

Answer 4

Here is the code I use in my C++ app.

Positive points :

• Works from console app
• Works from Windows service
• No delay required
• Does not close the current app

Negative points :

• The main console is lost and a new one is created (see FreeConsole)
• The console switching give strange results...

---

// Inspired from http://stackoverflow.com/a/15281070/1529139
// and http://stackoverflow.com/q/40059902/1529139
bool signalCtrl(DWORD dwProcessId, DWORD dwCtrlEvent)
{
    bool success = false;
    DWORD thisConsoleId = GetCurrentProcessId();
    // Leave current console if it exists
    // (otherwise AttachConsole will return ERROR_ACCESS_DENIED)
    bool consoleDetached = (FreeConsole() != FALSE);

    if (AttachConsole(dwProcessId) != FALSE)
    {
        // Add a fake Ctrl-C handler for avoid instant kill is this console
        // WARNING: do not revert it or current program will be also killed
        SetConsoleCtrlHandler(nullptr, true);
        success = (GenerateConsoleCtrlEvent(dwCtrlEvent, 0) != FALSE);
        FreeConsole();
    }

    if (consoleDetached)
    {
        // Create a new console if previous was deleted by OS
        if (AttachConsole(thisConsoleId) == FALSE)
        {
            int errorCode = GetLastError();
            if (errorCode == 31) // 31=ERROR_GEN_FAILURE
            {
                AllocConsole();
            }
        }
    }
    return success;
}

Usage example :

DWORD dwProcessId = ...;
if (signalCtrl(dwProcessId, CTRL_C_EVENT))
{
    cout << "Signal sent" << endl;
}

Answer 5

Thanks to jimhark's answer and other answers here, I found a way to do it in PowerShell:

$ProcessID = 1234
$MemberDefinition = '
    [DllImport("kernel32.dll")]public static extern bool FreeConsole();
    [DllImport("kernel32.dll")]public static extern bool AttachConsole(uint p);
    [DllImport("kernel32.dll")]public static extern bool GenerateConsoleCtrlEvent(uint e, uint p);
    public static void SendCtrlC(uint p) {
        FreeConsole();
        if (AttachConsole(p)) {
            GenerateConsoleCtrlEvent(0, p);
            FreeConsole();
        }
        AttachConsole(uint.MaxValue);
    }'
Add-Type -Name 'dummyName' -Namespace 'dummyNamespace' -MemberDefinition $MemberDefinition
[dummyNamespace.dummyName]::SendCtrlC($ProcessID) }

What made things work was sending the GenerateConsoleCtrlEvent to the desired process group instead of all processes that share the console of the calling process and AttachConsole back to the console of the parent of the current process.