Re: graphicsmagick signal handler problem

Hi, 
I write to confirm whether GraphicsMagick can officially disable establishing signal handlers for library users in InitializeMagick. ImageMagick already disable it in MagickWandGenesis. See https://github.com/ImageMagick/ImageMagick/blob/93b707b4a5882ab3d7f8904984684846fe178a97/MagickWand/magick-wand.c



-----邮件原件-----
发件人: yzh杨振宏 
发送时间: 2018年3月5日 10:01
收件人: Requests for help with GraphicsMagick <[email protected]>
主题: 答复: [GM-help] graphicsmagick signal handler problem

Yes, it can work. Since Go set up its signal handlers and flags (contain SA_ONSTACK) before InitializeMagick, so I try to set back both signal handlers and flags when signal handlers != default in InitializeMagickSignalHandlers (GM default set handlers back but flags is ignored), than program will not crash.

On the other hand, I note that ImageMagick already use a variable establish_signal_handlers to enable/disable own signal handlers and default is set to false for proper reason, i.e., 

MagickCoreGenesis(const char *path, const MagickBooleanType establish_signal_handlers) WandExport void MagickWandGenesis(void) {
  if (IsMagickCoreInstantiated() == MagickFalse)
    MagickCoreGenesis((char *) NULL,MagickFalse); }

So, I believe GM can take the same action for library/application user

-----邮件原件-----
发件人: Bob Friesenhahn [mailto:[email protected]]
发送时间: 2018年3月1日 22:11
收件人: Requests for help with GraphicsMagick <[email protected]>
主题: Re: [GM-help] graphicsmagick signal handler problem

On Thu, 1 Mar 2018, yzh杨振宏 wrote:

> hi,
>
> I'm a GM API user. I use GM in Go lang. Since Golang require that
>
> "If the non-Go code installs any signal handlers, it must use the 
> SA_ONSTACK flag with sigaction. Failing to do so is likely to cause 
> the program to crash if the signal is received."
> (https://golang.org/pkg/os/signal/)
>
> So could GM let user determine whether or not set signal handlers (i.e., use a bool variable) in InitializeMagick?

Would it work if GM was to specify SA_ONSTACK when the feature is available?  What harm might result from making this the default?

Otherwise, the using library/application will need to (re)-establish its own signal handlers with sigaction after invoking InitializeMagick().

Bob
--
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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