How to debug slow respond or halt?

Question

I try to comments 1.4K+ lines in a C++ function by using M-; or rectangle insert string //.

Wait for several minutes, Emacs still no respond. I have to kill Emacs.

In this case, how could I locate what cause the Emacs use 100% CPU and looks like do nothing?

Emacs: 25.0

OS: Ubuntu 14.04

Do you see the same slow response if you use `M-x comment-region` (after activating the region) instead of `M-;`? If not, then use it. — Drew, Aug 11 '15 at 14:31

score 4 · Accepted Answer · answered Aug 11 '15 at 02:29

4

Little-known trick... You can send an interrupting debug signal to Emacs with kill/killall/pkill.

pkill -USR2 emacs

When sent to Emacs, the USR2 kill signal will interrupt whatever Emacs is doing and drop you to a debugger. From there, you can likely tell what is causing the hang from the stack trace.

answered Aug 11 '15 at 02:29

Archenoth

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It always stop at `magit-pre-command-hook`. – Enze Chi Dec 20 '15 at 23:15

How to debug slow respond or halt?

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