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From: | Ken Brown |
Subject: | bug#17510: 24.3.91; Problem with `emacs --daemon' in cygw32 build |
Date: | Sat, 24 May 2014 18:18:47 -0400 |
User-agent: | Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 |
On 5/24/2014 3:28 PM, Daniel Colascione wrote:
On 05/24/2014 05:38 AM, Ken Brown wrote:On 5/19/2014 3:25 PM, Ken Brown wrote:On 5/19/2014 12:46 PM, Eli Zaretskii wrote:I guess it's OK for the branch, thanks. But it strikes me that simply replacing the car of dpyinfo->name_list_element by something like "!!!DELETED DISPLAY!!!", or even just an empty string, would serve the same purpose, and save us the nuisance of an additional list in cygw32_display_name_list. After all, all you need is to mark a display deleted without actually deleting it, right? IOW, the main problem is in x_delete_display, and all the rest is just the overhead you needed to fix that, correct?I think that's correct, and I agree that there should be a much simpler fix. I'll have to look into the code and try to understand better exactly what happens when emacs is started as a daemon and then a client frame is opened and closed.My guess as to the cause of this bug was completely wrong. What happens in my recipe is that the pointer dpyinfo->w32_id_name is freed twice. (This is done in x_delete_display each time the only existing client frame is deleted.) An attempt to create a client frame for the third time then leads to a crash because of malloc corruption.Thanks for finding that. I wonder whether this double-free also has something to do with random crashes people have been seeing in 64-bit Cygwin cygw32 Emacs builds.
I doubt it, because this double-free occurs in both 64-bit and 32-bit Cygwin. Also, I think it can only be triggered by running emacs as a daemon, and none of the people reporting crashes mentioned doing that.
Ken
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