[Issue 22843] New: Program hangs on full gc collect with --DRT-gcopt=fork:1 if run under valgrind/callgrind

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22843

          Issue ID: 22843
           Summary: Program hangs on full gc collect with
                    --DRT-gcopt=fork:1 if run under valgrind/callgrind
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: zorael at gmail.com

Manjaro/Arch x86_64, dmd 2.098.1, ldc 1.28.1.

When the new forking garbage collector is enabled, the program hangs on what I
imagine is the first collection, if run under the valgrind/callgrind profiler.

```d
import std.string : succ;

extern(C) __gshared string[] rt_options = [ "gcopt=profile:1 fork:1
initReserve:0 minPoolSize:0" ];

void main()
{
    string[string] aa;
    string key = "a";

    foreach (immutable i; 0..1_000)
    {
        aa[key] = key;
        key = key.succ;
    }
}
```

```
$ dmd fork.d && valgrind --tool=callgrind ./fork
==799709== Callgrind, a call-graph generating cache profiler
==799709== Copyright (C) 2002-2017, and GNU GPL'd, by Josef Weidendorfer et al.
==799709== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==799709== Command: ./fork
==799709== 
==799709== For interactive control, run 'callgrind_control -h'.

[hangs here, 100% cpu use until Ctrl+C]
```

```
$ callgrind_control -b | ddemangle
PID 799709: ./fork                                                              
sending command status internal to pid 799709                                   

  Frame: Backtrace for Thread 1                                                
                                                                               
                          [ 0]  clock_gettime@@GLIBC_2.17 (32260048 x)         
                                                                               
                                                 [ 1]  nothrow ulong
core.internal.gc.impl.conservative.gc.Gcx.fullcollect(bool, bool, bool) (1 x)
   [ 2]  nothrow void*
core.internal.gc.impl.conservative.gc.Gcx.smallAlloc(ulong, ref ulong, uint,
const(TypeInfo)) (2 x)
   [ 3]  nothrow void*
core.internal.gc.impl.conservative.gc.ConservativeGC.runLocked!(core.internal.gc.impl.conservative.gc.ConservativeGC.mallocNoSync(ulong,
uint, ref ulong, const(
TypeInfo)), core.internal.gc.impl.conservative.gc.mallocTime,
core.internal.gc.impl.conservative.gc.numMallocs, ulong, uint, ulong,
const(TypeInfo)).runLocked(ref ulong, ref uint, ref
 ulong, ref const(TypeInfo)) (1 x)                                              
   [ 4]  nothrow void*
core.internal.gc.impl.conservative.gc.ConservativeGC.calloc(ulong, uint,
const(TypeInfo)) (1 x)
   [ 5]  _THUNK16 (1 x)
   [ 6]  gc_calloc (1 x)                     
   [ 7]  ref rt.aaA.Impl rt.aaA.Impl.__ctor(scope
const(TypeInfo_AssociativeArray), ulong) (1 x)                    
   [ 8]  _aaGetX (1 x)                                                          
   [ 9]  _aaGetY (1 x)                                                          
   [10]  _Dmain (1 x)                                                           
   [11]  void rt.dmain2._d_run_main2(char[][], ulong, extern (C) int
function(char[][])*).runAll().__lambda2() (1 x)
   [12]  void rt.dmain2._d_run_main2(char[][], ulong, extern (C) int
function(char[][])*).tryExec(scope void delegate()) (1 x)
   [13]  void rt.dmain2._d_run_main2(char[][], ulong, extern (C) int
function(char[][])*).runAll() (1 x)
   [14]  void rt.dmain2._d_run_main2(char[][], ulong, extern (C) int
function(char[][])*).tryExec(scope void delegate()) (1 x)
   [15]  _d_run_main2 (1 x)
   [16]  __alloca (1 x)   
   [17]  _d_run_main2 (1 x)                  
   [18]  _d_run_main (1 x) 
   [19]  __alloca (1 x)                     
   [20]  _d_run_main (1 x) 
   [21]  main (1 x)                          
   [22]  (below main) (1 x)
   [23]  __libc_start_main@@GLIBC_2.34 (1 x)
   [24]  (below main) (1 x)                                                     
   [25]  0x000000000001d930
```

I could reproduce it with both dmd and ldc, though naturally the backtrace
differs slightly between them. It does not happen with `--DRT-gcopt="fork:0"`.

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