On Fri, Jun 7, 2013 at 2:19 PM, Johannes Sixt <[email protected]> wrote:
> Am 6/7/2013 14:00, schrieb Erik Faye-Lund:
>> On Fri, Jun 7, 2013 at 12:24 PM, Johannes Sixt <[email protected]> wrote:
>>> Am 6/7/2013 12:12, schrieb Erik Faye-Lund:
>>>> On Thu, Jun 6, 2013 at 7:40 PM, Jeff King <[email protected]> wrote:
>>>>> On Thu, Jun 06, 2013 at 10:21:47AM -0700, Junio C Hamano wrote:
>>>>>
>>>>>>> The particular deficiency is that when a signal is raise()d whose
>>>>>>> SIG_DFL
>>>>>>> action will cause process death (SIGTERM in this case), the
>>>>>>> implementation of raise() just calls exit(3).
>>>>>>
>>>>>> After a bit of web searching, it seems to me that this behaviour of
>>>>>> raise() is in msvcrt, and compat/mingw.c::mingw_raise() just calls
>>>>>> that. In other words, "the implementation of raise()" is at an even
>>>>>> lower level than mingw/msys, and I would agree that it is a platform
>>>>>> issue.
>>>>>
>>>>> Yeah, if it were mingw_raise responsible for this, I would suggest using
>>>>> the POSIX shell "128+sig" instead. We could potentially check for
>>>>> SIG_DFL[1] mingw_raise and intercept and exit there. I don't know if
>>>>> that would create headaches or confusion for other msys programs,
>>>>> though. I'd leave that up to the msysgit people to decide whether it is
>>>>> worth the trouble.
>>>>>
>>>>
>>>> ...and here's the code to do just that:
>>>>
>>>> diff --git a/compat/mingw.c b/compat/mingw.c
>>>> index b295e2f..8b3c1b4 100644
>>>> --- a/compat/mingw.c
>>>> +++ b/compat/mingw.c
>>>> @@ -1573,7 +1573,8 @@ static HANDLE timer_event;
>>>> static HANDLE timer_thread;
>>>> static int timer_interval;
>>>> static int one_shot;
>>>> -static sig_handler_t timer_fn = SIG_DFL, sigint_fn = SIG_DFL;
>>>> +static sig_handler_t timer_fn = SIG_DFL, sigint_fn = SIG_DFL,
>>>> + sigterm_fn = SIG_DFL;
>>>>
>>>> /* The timer works like this:
>>>> * The thread, ticktack(), is a trivial routine that most of the time
>>>> @@ -1688,6 +1689,10 @@ sig_handler_t mingw_signal(int sig,
>>>> sig_handler_t handler)
>>>> sigint_fn = handler;
>>>> break;
>>>>
>>>> + case SIGTERM:
>>>> + sigterm_fn = handler;
>>>> + break;
>>>> +
>>>> default:
>>>> return signal(sig, handler);
>>>> }
>>>> @@ -1715,6 +1720,13 @@ int mingw_raise(int sig)
>>>> sigint_fn(SIGINT);
>>>> return 0;
>>>>
>>>> + case SIGTERM:
>>>> + if (sigterm_fn == SIG_DFL)
>>>> + exit(128 + SIGTERM);
>>>> + else if (sigterm_fn != SIG_IGN)
>>>> + sigterm_fn(SIGTERM);
>>>> + return 0;
>>>> +
>>>> default:
>>>> return raise(sig);
>>>> }
>>>
>>> That's pointless and does not work. The handler would only be called when
>>> raise() is called, but not when a SIGTERM is received, e.g., via Ctrl-C
>>> from the command line, because that route ends up in MSVCRT, which does
>>> not know about this handler.
>>
>> That's not entirely true. On Windows, there's only *one* way to
>> generate SIGTERM; "signal(SIGTERM)". Ctrl+C does not generate SIGTERM.
>> We generate SIGINT on Ctrl+C in mingw_fgetc, but the default Control+C
>> handler routine calls ExitProcess():
>> http://msdn.microsoft.com/en-us/library/windows/desktop/ms683242(v=vs.85).aspx
>
> But a call to signal(SIGTERM, my_handler) should divert Ctrl+C to
> my_handler. The unpatched version does, because MSVCRT now knows about
> my_handler and sets things up so that the event handler calls my_handler.
No, it does not:
--->8---
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
void my_handler(int signum)
{
printf("signal: %d\n", signum);
exit(1);
}
int main()
{
signal(SIGTERM, my_handler);
while (1);
return 0;
}
--->8---
This quietly kills the process on Windows with MSVCRT's
signal-implementation. In fact SIGTERM isn't raised on Linux either.
Ctrl+C raises SIGINT, not SIGTERM.
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