Hot reloading invalid memory access on Windows

[CodeOptimist]

Describe the bug

Hot reloading example seems to fail with RUNTIME ERROR: invalid memory access

Reproduction Steps

v -live run examples/hot_reload/message.v
on a fresh V installation; Windows 11

Current Behavior

PS C:\Dropbox\vlang\examples\hot_reload> v -live run message.v
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
Unhandled Exception 0xC0000005
C:/Users/Chris/AppData/Local/Temp/v_0/message.01JFGGEH73ZXN1SG5KJGJEW3G1.tmp.c:5222: at print_backtrace_skipping_top_frames_tcc: Backtrace
C:/Users/Chris/AppData/Local/Temp/v_0/message.01JFGGEH73ZXN1SG5KJGJEW3G1.tmp.c:5208: by print_backtrace_skipping_top_frames
C:/Users/Chris/AppData/Local/Temp/v_0/message.01JFGGEH73ZXN1SG5KJGJEW3G1.tmp.c:5778: by unhandled_exception_handler
7fffb76ded36 : by ???
C:/Users/Chris/AppData/Local/Temp/v_0/tmp.1.message.01JFGGEHKS30AVVRA0GZ9PPZJR.tmp.so.c:4996: at strconv__format_dec_sb: RUNTIME ERROR: invalid memory access
C:/Users/Chris/AppData/Local/Temp/v_0/tmp.1.message.01JFGGEHKS30AVVRA0GZ9PPZJR.tmp.so.c:12319: by StrIntpData_process_str_intp_data
C:/Users/Chris/AppData/Local/Temp/v_0/tmp.1.message.01JFGGEHKS30AVVRA0GZ9PPZJR.tmp.so.c:12721: by str_intp
C:/Users/Chris/AppData/Local/Temp/v_0/tmp.1.message.01JFGGEHKS30AVVRA0GZ9PPZJR.tmp.so.c:15383: by impl_live_main__print_message
C:/Users/Chris/AppData/Local/Temp/v_0/message.01JFGGEH73ZXN1SG5KJGJEW3G1.tmp.c:2883: by main__print_message
C:/Users/Chris/AppData/Local/Temp/v_0/message.01JFGGEH73ZXN1SG5KJGJEW3G1.tmp.c:9676: by main__main
C:/Users/Chris/AppData/Local/Temp/v_0/message.01JFGGEH73ZXN1SG5KJGJEW3G1.tmp.c:9795: by wmain
0044da88 : by ???
0044dbeb : by ???
7fffb63de8d7 : by ???
PS C:\Dropbox\vlang\examples\hot_reload>

Additional Information/Context

I was able to run other examples without hot reloading fine, like examples/gg/polygons.v.

V version

V 0.4.8 30ececc

Environment details (OS name and version, etc.)

V full version: V 0.4.8 30ececc
OS: windows, Microsoft Windows 11 Pro v26100 64-bit
Processor: 24 cpus, 64bit, little endian,

getwd: C:\Dropbox\vlang\examples\hot_reload
vexe: C:\Dropbox\vlang\v.exe
vexe mtime: 2024-12-19 21:25:10

vroot: OK, value: C:\Dropbox\vlang
VMODULES: OK, value: C:\Users\Chris.vmodules
VTMP: OK, value: C:\Users\Chris\AppData\Local\Temp\v_0

Git version: git version 2.45.1.windows.1
Git vroot status: weekly.2024.51-23-g30ececc2
.git/config present: true

CC version: Error: 'cc' is not recognized as an internal or external command,
operable program or batch file.

emcc version: Error: 'emcc' is not recognized as an internal or external command,
operable program or batch file.

thirdparty/tcc status: thirdparty-windows-amd64 b425ac82

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[kbkpbot]

I think it maybe a TCC compiler bug, because I use msvc can run the program:

v -live -cc msvc run examples\hot_reload\message.v
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.
OK reloads:    0 | Total reloads:    0 | Hello! Modify this message while the program is running.

[CodeOptimist]

Apparently I'm a little blind, thanks @JalonSolov for pointing out that there are open issues on this. 😅
It looks like @KevinDaSilvaS already discovered the solution a cold-reloading alternative in #16256

Succeeds:
v watch run message.v
Fails:
v -live run message.v

So this might be a documentation issue. I'll change the title and/or submit a fix for this myself shortly.

[CodeOptimist]

I believe I figured it out; I'll leave the history of my stupidity here for posterity. 😅
Edit: Nope, this is all wrong, watch is helpful but it's not hot reloading.

v -live run is not related to watching,
it's just compile for live (to watch separately?), and run.
v watch will continually watch/rebuild (I think), and v watch run will continually watch/rebuild/rerun.

---

investigation

I had found vwatch.v created in 2021 c698fa1
I saw v -live run in docs.md in 2022 43d6b97

Grepping for (\blive\b.*?\brun\b|\brun\b.*?\blive\b) (whole-words "live" and "run" in either order) I found -live run mentioned in just doc/docs.md and vlib/v/gen/c/consts_and_globals.v.

I saw -live run mentioned in a couple of commit messages: 48d4228 and e9fac05

Noting that those commit messages were by the author of vwatch.v themselves and thus unlikely to be a mistake, my brain finally kicked-in and I recognized -live run as its own thing not related to watching (they aren't a pair, just separate things).

run is simply an option of the separate program watch just like it's an option of the compiler.

v/cmd/tools/vwatch.v

Line 33 in 74f0ce6

// Implements `v watch file.v` , `v watch run file.v` etc.

---

So I think the docs need updated. I need a break for now!
Though perhaps v -live run crashing still needs sorted somehow? A suggestion to run it with watch run instead??? 🤔

[KevinDaSilvaS]

Awesome investigation work!

[CodeOptimist]

I was wrong. I finally finished reading all of the V documentation today, and it's very plain that the program should continue running. (The @[live] functions go in a shared library, recompiled and reloaded via a separate thread.)
https://docs.vlang.io/other-v-features.html#hot-code-reloading

So I guess it's just broken.
Using watch is a workaround... but more like "cold" reloading than "hot" reloading.

@kbkpbot is probably right

I think it maybe a TCC compiler bug, because I use msvc can run the program

So I will try msvc. If it's indeed tcc I can retitle this issue.