Potential crash when sorting files in a directory

[joelim-work]

When a directory is loaded but the settings for displaying files are modified, the following code is run:

lf/nav.go

Lines 473 to 477 in 83af3e1

	go func() {
	dir.sort()
	dir.loading = false
	nav.dirChan <- dir
	}()

This code looks very suspicious to me because it accesses and sorts dir.files in a different goroutine, when normally this is manipulated by the main thread. I suspect this is what causes lf to crash as reported in #502, and I have also experienced crashing when I was playing around with the dironly option.

I was thinking that this could be solved by simply creating a copy for the goroutine like below:

--- a/nav.go
+++ b/nav.go
@@ -470,10 +470,11 @@ func (nav *nav) checkDir(dir *dir) {
                dir.ignorecase != gOpts.ignorecase ||
                dir.ignoredia != gOpts.ignoredia:
                dir.loading = true
+               sd := *dir
                go func() {
-                       dir.sort()
-                       dir.loading = false
-                       nav.dirChan <- dir
+                       sd.sort()
+                       sd.loading = false
+                       nav.dirChan <- &sd
                }()
        }
 }

But since this is hard to prove and I'm not 100% certain, I'm raising this as an issue first.

[joelim-work]

I managed to produce the crash again on version r28, below is the stack trace:

panic: runtime error: index out of range [61] with length 60

goroutine 82 [running]:
main.(*dir).sort.func11(0x3b?, 0x3a?)
	github.com/gokcehan/lf/nav.go:283 +0x12f
sort.insertionSort_func({0xc000718f88?, 0xc0008068a0?}, 0x3c, 0x50)
	sort/zsortfunc.go:12 +0xb1
sort.stable_func({0xc000718f88?, 0xc0008068a0?}, 0x53)
	sort/zsortfunc.go:339 +0x4a
sort.SliceStable({0x55a91a5f98a0, 0xc000012600}, 0x53?)
	sort/slice.go:35 +0x85
main.(*dir).sort(0xc0000c65b0)
	github.com/gokcehan/lf/nav.go:282 +0x47c
main.(*nav).checkDir.func2()
	github.com/gokcehan/lf/nav.go:469 +0x2b
created by main.(*nav).checkDir
	github.com/gokcehan/lf/nav.go:468 +0x1ef

BTW I have found that it's convenient to redirect stderr to a file so that the stack trace can be viewed easily:

lf 2> ~/lf.log

[joelim-work]

I believe this was detected and fixed in #759, but the commit was later reverted in 8954e9f. I'm not sure why but possibly the commit contained a bunch of other changes which might have caused other issues.

[gokcehan]

@joelim-work Your proposed change sounds reasonable to me. We can change it and try it for a while if you want. Is there a way to reproduce the crash in a consistent manner?

[joelim-work]

@gokcehan I first noticed this crashing behaviour when I was using the dironly option to improve upon the move in parent directory operation (I have now added this to the wiki):

map J :updir; set dironly true; down; set dironly false; open
map K :updir; set dironly true; up; set dironly false; open

I can consistently reproduce this crash on my machine by using it to select a very large directory, but because the crashing behaviour depends on goroutine scheduling and the filesystem, I don't know how easy it is for others to reproduce. I have created a pull request #1204, which fixes the issue for me, and hopefully others as well.