Compiler randomly crashes when parallel compilation is enabled

[XiaoPangxie732]

Describe the bug

The compiler randomly crashes for an unknown reason when parallel compilation is enabled

Reproduction Steps

1. Clone the repo
2. Run v . or v run .
3. The compiler either crashes(chances are ~1/10, and using v run . seems to have a higher chance) or compiles fine

Expected Behavior

Always compiles fine

Current Behavior

Randomly crashes. Error message(with v -g self):

Unhandled Exception 0xf5fd2a0
C:/Users/***/AppData/Local/Temp/v_0/E:\Programs\v\vlib\builtin\backtraces_windows.c.v:168: at print_backtrace_skipping_top_frames_tcc: Backtrace
C:/Users/***/AppData/Local/Temp/v_0/E:\Programs\v\vlib\builtin\backtraces_windows.c.v:70: by print_backtrace_skipping_top_frames
C:/Users/***/AppData/Local/Temp/v_0/E:\Programs\v\vlib\builtin\builtin_windows.c.v:132: by unhandled_exception_handler
7ffdcb053556 : by ???

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.9 87b1de8

Environment details (OS name and version, etc.)

V full version	V 0.4.9 725e259.87b1de8
OS	windows, Microsoft Windows 11 Pro 26100 64-bit
Processor	12 cpus, 64bit, little endian, Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz
Memory	2.4GB/15.86GB
V executable	E:\Programs\v\v.exe
V last modified time	2025-03-19 18:21:49
V home dir	OK, value: E:\Programs\v
VMODULES	OK, value: C:\Users***.vmodules
VTMP	OK, value: C:\Users***\AppData\Local\Temp\v_0
Current working dir	OK, value: F:\Projects\PistonMC\Shovel
Git version	git version 2.38.1.windows.1
V git status	weekly.2025.12-6-g87b1de82
.git/config present	true
cc version	N/A
gcc version	N/A
clang version	N/A
msvc version	N/A
tcc version	tcc version 0.9.27 (x86_64 Windows)
tcc git status	thirdparty-windows-amd64 b425ac82
emcc version	N/A
glibc version	N/A

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[huly-for-github]

Connected to Huly®: V_0.6-22375

[kbkpbot]

If you have msvc, you can try msvc first, this bug may cause by tcc.

v . -cc msvc

[felipensp]

Does it started to crash after this specific commit PistonMinecraft/Shovel@f3b6786 ?

Looks like MinecraftDecompilerCommandLine.class is missing on the repo as well.

[XiaoPangxie732]

Does it started to crash after this specific commit PistonMinecraft/Shovel@f3b6786 ?

Yes

Looks like MinecraftDecompilerCommandLine.class is missing on the repo as well.

The program didn't even start running. I don't think it's related to that file

[XiaoPangxie732]

If you have msvc, you can try msvc first, this bug may cause by tcc.

v . -cc msvc

No, it's not
The issue remains when using v . -cc msvc

[felipensp]

Got it

corrupted size vs. prev_size
0x7f6a00f0db2c: at ???: RUNTIME ERROR: abort() called
0x7f6a00eb427e: by ???
0x7f6a00e978ff: by ???
0x7f6a00e987b6: by ???
0x7f6a00f17ff5: by ???
0x7f6a00f18b96: by ???
0x7f6a00f1a0e3: by ???
0x7f6a00f1c098: by ???
0x7f6a00f1d1e6: by ???
/home/felipe/v/vlib/builtin/builtin.c.v:620: by realloc_data
/home/felipe/v/vlib/builtin/map.v:133: by DenseArray_expand
/home/felipe/v/vlib/builtin/map.v:434: by map_set
/home/felipe/v/vlib/v/ast/types.v:1421: by v__ast__Table_type_to_str_using_aliases
/home/felipe/v/vlib/v/ast/types.v:1358: by v__ast__Table_type_to_str
/home/felipe/v/vlib/v/ast/str.v:464: by v__ast__Expr_str
/home/felipe/v/vlib/v/gen/c/assign.v:168: by v__gen__c__Gen_expr_with_opt
/home/felipe/v/vlib/v/gen/c/assign.v:53: by v__gen__c__Gen_expr_with_opt_or_block
/home/felipe/v/vlib/v/gen/c/assign.v:936: by v__gen__c__Gen_assign_stmt
/home/felipe/v/vlib/v/gen/c/cgen.v:2414: by v__gen__c__Gen_stmt
/home/felipe/v/vlib/v/gen/c/cgen.v:2189: by v__gen__c__Gen_stmts_with_tmp_var
/home/felipe/v/vlib/v/gen/c/cgen.v:2040: by v__gen__c__Gen_stmts
/home/felipe/v/vlib/v/gen/c/fn.v:509: by v__gen__c__Gen_gen_fn_decl
/home/felipe/v/vlib/v/gen/c/fn.v:139: by v__gen__c__Gen_fn_decl
/home/felipe/v/vlib/v/gen/c/cgen.v:2400: by v__gen__c__Gen_stmt
/home/felipe/v/vlib/v/gen/c/cgen.v:2189: by v__gen__c__Gen_stmts_with_tmp_var