Capturing Ctrl-C in MINGW-Bash shell #1248

mrkita · 2017-07-28T16:55:55Z

I was not able to find an open or closed issue matching what I'm seeing

Setup

git version 2.13.3.windows.1
built from commit: faaf232
sizeof-long: 4
machine: x86_64

This is specific to MINGW64

NOTE: This problem does NOT occur with the MINGW32 package.

Which version of Windows are you running? Vista, 7, 8, 10? Is it 32-bit or 64-bit?

Microsoft Windows [Version 6.1.7601]

What options did you set as part of the installation? Or did you choose the
defaults?

Path Option: Cmd
SSH Option: OpenSSH
CURL Option: OpenSSL
CRLF Option: CRLFAlways
Bash Terminal Option: MinTTY
Performance Tweaks FSCache: Enabled
Use Credential Manager: Enabled
Enable Symlinks: Enabled

Any other interesting things about your environment that might be related
to the issue you're seeing?

Details

Which terminal/shell are you running Git from? e.g Bash/CMD/PowerShell/other

BASH

What commands did you run to trigger this issue?

This is not specific to GIT, but rather for the GIT for windows installation and MSYS.

I am running a self created C# program, which attempts to capture a Ctrl-C event and cancel using an event handler like so:

    protected static void CheckForConsoleCancel(object sender, ConsoleCancelEventArgs args)
    {
        //Do cleanup here
    }

Main program flow:

Console.CancelKeyPress += new ConsoleCancelEventHandler(CheckForConsoleCancel);

What did you expect to occur after running these commands?

I expected the program to reach my event handler allowing me to clean up my program before exit.

What actually happened instead?

The program exits without calling my handler.

This problem DOES NOT happen with a windows CMD prompt, nor SH.exe provided with the installation.

I remember reading before that this was a problem with an older version of MSYS's BASH shell, but I can't find the link anymore... to my knowledge it was fixed there awhile ago.

The text was updated successfully, but these errors were encountered:

dscho · 2017-08-22T12:44:37Z

If you want to intercept Ctrl+C in Git Bash, I fear that is possible only in MSYS2 programs... Maybe there's some stty option you can use before starting your application, but that's sub-optimal.

PhilWim · 2017-10-03T18:27:26Z

I kind of had the same problem where commands weren't killed when i hit CRTL+C.

This is how it came and how i solved it:

On my fresh windows installation i installed Git-2.14.2-64-bit. Then i faces the issue that commands (docker logs etc) keep on sending to console after i killed them through CRTL+C.

I reinstalled the older version which i know was working (Git-2.10.2-64-bit) on my old windows installation. Still same problem.

Then i found in an issue in mintty tacker a comment which leaded to a probably wrong cygwin dependency.

And exactly this is the case here. Uninstalling of Git-2.14.2-64-bit didn't wipe C:/Program Files/Git completely. Cygwin libs stayed.

So probably these broken libs were used also with the working version Git-2.10.2-64-bit.

Then i did manually clean git folder and reinstalled Git-2.10.2-64-bit and voila no issues anymore.

I guess also for updating to newer versions, old cygwin files stay and some users never face this problem. Obviously fresh installation leads into problems.

worc · 2017-12-07T01:19:36Z

I'm was running 2.14.2.windows.1 and in the whole MINGW64 Git Bash MinTTY shell on Windows 10 and running into the same or similar issue where CTRL+C didn't seem to be sending the correct signal.

In my case I'm starting up an http server using Node and closing it with CTRL+C. If I start the server using just node index.js, one process is spawned and can be closed with CTRL+C and the used port will be released.

If I start the same server using npm run demo (which itself is actually calling node index.js) two processes are spawned and CTRL+C will only close one of them, orphaning the server process and causing an EADDRINUSE error the next time I try to run npm run demo.

This bug doesn't show up on a Windows 7 box or on a Linux Mint box running Git 2.7.4. In both cases, two processes are spawned, but CTRL+C from the command line will close both and free up the port.

Installing 2.15.1.windows.2 didn't solve the problem. My installation of Git was in C:/Users/<username>/AppData/Local/Programs/Git originally. After uninstalling all of those files were removed and there was no C:/Program Files/Git folder to manually clear out. After reinstalling, Git is now installed at C:/Program Files/Git, but I'm still encountering the bug and still digging for a solution.

@PhilWim Do you have a link to that comment in the mintty tracker?

jakubnavratil · 2017-12-28T17:15:33Z

Thanks @PhilWim Uninstalling, wiping Program Files/Git folder and installing version 2.10.2-64 helped.
https://github.com/git-for-windows/git/releases/tag/v2.10.2.windows.1

Broutard · 2018-02-27T15:19:22Z

+1
Please provide a fix :(

dwjohnston · 2018-02-28T00:18:29Z

@Broutard - I suggest this:

I have a script called portkill.sh

#!/usr/bin/env bash
echo killing process on port $1
taskkill //PID `netstat -aon | grep $1 | grep -P '(?=LISTENING).*' -o -m1 | grep -P '\d*' -o` //F

Add it to your path, then run with portkill.sh 8000 or whatever.

huyong007 · 2018-03-10T10:42:23Z

how to use your script?my solution is netstat -ano|findstr 3000 in cmd，and then taskkill /pid 3000 /F,pardon me my poor english.as a newer do you have a video to teach how to use the script ?

dwjohnston · 2018-03-11T23:08:33Z

@huyong007 -

Put the script in a file called portkill.sh
Add that folder to your PATH variable
run with portkill.sh 8000

dscho · 2018-03-13T16:12:08Z

Uninstalling, wiping Program Files/Git folder and installing version 2.10.2-64 helped.
https://github.com/git-for-windows/git/releases/tag/v2.10.2.windows.1

Sadly, this introduces regressions for fixes we made in the meantime.

Please provide a fix :(

Oh wow. This elicits quite a negative reaction here. Probably not what you expected.

If you want anybody to work for you, to solve your problem, you might want to take a different approach.

As to the original report: this should be addressed by our recent change in how processes are killed when the user presses Ctrl+C.

If it still does not work for you in Git for Windows v2.16.2, you may want to consider selecting the "ConHost" option rather than the "MinTTY" option as terminal for the Git Bash. That should fix the issue, too.

dscho · 2018-04-23T06:49:50Z

I cannot say that I am happy about the enthusiasm to leave all the hard work to me. Nevertheless, I think I have a fix for this now. It should hit https://wingit.blob.core.windows.net/files/index.html within 24h.

This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was git-for-windows/msys2-runtime@c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: git-for-windows/msys2-runtime@e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: git-for-windows/msys2-runtime@53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: git-for-windows/msys2-runtime@ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

dscho · 2018-04-23T12:48:28Z

The newest snapshot at https://wingit.blob.core.windows.net/files/index.html should fix this. Please test.

AnthonyPaulO · 2018-04-25T16:13:58Z

Wow... I've been trying to figure out why ctrl-C was taking forever to register in my git bash for windows when running webpack-dev-server (a problem I've had for the past year) and found this issue, and as luck would have it find that it was fixed two days ago! I'll have to wait for it to get to a 'maintained' release state but I'm glad it's been fixed. I've been going through the comments as well as the author's (Johannes) summary of the history of this issue and want to thank him for taking this challenge and fixing it when others in the community would not. @dscho, perhaps an alternative perspective on this would help... perhaps nobody else was up to the task, and you are the only one in this community with the technical expertise to fix it; the Linus Torvalds or Richard Stallman of Git for Windows, so to speak. Whatever the reason, you are indeed the man... thank you!

This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was git-for-windows/msys2-runtime@c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: git-for-windows/msys2-runtime@e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: git-for-windows/msys2-runtime@53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: git-for-windows/msys2-runtime@ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

raycashmore mentioned this issue Aug 16, 2017

http server doesn't shut down with Ctrl-C in Windows Git Bash webpack/webpack-dev-server#1041

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dscho added the question label Aug 22, 2017

dwjohnston mentioned this issue Aug 31, 2017

Dev server continues to run after aborting npm run dev (Ctrl+C) vuejs-templates/webpack#802

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dscho self-assigned this Apr 23, 2018

dscho added this to the v2.17.0(2) milestone Apr 23, 2018

dscho closed this as completed Apr 23, 2018

naveen521kk mentioned this issue Mar 15, 2021

Handle Ctrl+C interupts for Mingw Executables msys2/msys2-runtime#29

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Capturing Ctrl-C in MINGW-Bash shell #1248

Capturing Ctrl-C in MINGW-Bash shell #1248

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Capturing Ctrl-C in MINGW-Bash shell #1248

Capturing Ctrl-C in MINGW-Bash shell #1248

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