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digitalmars.D.ldc - TLS/GC issues on macOS

reply =?UTF-8?Q?S=c3=b6nke_Ludwig?= <sludwig+d outerproduct.org> writes:
There appears to be a GC visibility issue of TLS sections on macOS when 
multiple threads are involved. I added a test case to what looks like 
the same issue: https://github.com/ldc-developers/ldc/issues/2187

The question is, does anyone have enough insight on the TLS 
implementation to make a quick diagnosis or fix?

This is biting us pretty hard in our upcoming commercial project (DMD 
has codegen issues on macOS), so any help would be highly appreciated.
Jan 03 2019
next sibling parent reply Jacob Carlborg <doob me.com> writes:
On 2019-01-03 13:58, Sönke Ludwig wrote:

 There appears to be a GC visibility issue of TLS sections on macOS when 
 multiple threads are involved. I added a test case to what looks like 
 the same issue: https://github.com/ldc-developers/ldc/issues/2187
 
 The question is, does anyone have enough insight on the TLS 
 implementation to make a quick diagnosis or fix?
 
 This is biting us pretty hard in our upcoming commercial project (DMD 
 has codegen issues on macOS), so any help would be highly appreciated.


I haven't tested anything, but I noticed this [1] difference between LDC 
and DMD.

[1] 
https://github.com/ldc-developers/druntime/blob/4e745768c79f6b72f03af108a845145e382e71e4/src/rt/sections_elf_shared.d#L1005-L1011

-- 
/Jacob Carlborg
Jan 03 2019
parent reply "David Nadlinger" <code klickverbot.at> writes:
On 3 Jan 2019, at 19:35, Jacob Carlborg via digitalmars-d-ldc wrote:

 I haven't tested anything, but I noticed this [1] difference between 
 LDC and DMD.

 [1] 
 https://github.com/ldc-developers/druntime/blob/4e745768c79f6b72f03af108a845145e382e71e4/src/rt/sections_elf_shared.d#L1005-L1011


Doesn't DMD still use the old, non-shared-library rt.sections 
implementation on OS X?

  — David
Jan 03 2019
parent Jacob Carlborg <doob me.com> writes:
On 2019-01-03 20:55, David Nadlinger wrote:


 Doesn't DMD still use the old, non-shared-library rt.sections 
 implementation on OS X?


Yes.

-- 
/Jacob Carlborg
Jan 06 2019
prev sibling parent reply "David Nadlinger" <code klickverbot.at> writes:
On 3 Jan 2019, at 12:58, Sönke Ludwig via digitalmars-d-ldc wrote:

 There appears to be a GC visibility issue of TLS sections on macOS 
 when multiple threads are involved. I added a test case to what looks 
 like the same issue: https://github.com/ldc-developers/ldc/issues/2187


Try this patch:

```
diff --git a/src/rt/sections_elf_shared.d b/src/rt/sections_elf_shared.d
index a7b3336a..bc84a116 100644
--- a/src/rt/sections_elf_shared.d
+++ b/src/rt/sections_elf_shared.d
   -296,6 +296,20    else
          {
              _tlsRanges = cast(Array!(void[])*)calloc(1, 
Array!(void[]).sizeof);
              _tlsRanges || assert(0, "Could not allocate TLS range 
storage");
+
+            version (Shared) {} else
+            {
+                version (Linux)
+                {
+                    // Nothing to do; glibc allocates the TLS area for 
additional
+                    // threads at the beginning of the stack space, so 
they will already
+                    // be scanned.
+                }
+                else version (OSX)
+                {
+                    
_tlsRanges.insertBack(getTLSRange(&dummyTlsSymbol));
+                }
+            }
          }
          return _tlsRanges;
      }
```

Still trying to figure out how much of that code can be stripped away 
for non-Shared builds (it's a mess, as DMD partially supports shared 
libraries on Linux with a static runtime), or how on earth nobody has 
found this before.

Best,
David
Jan 03 2019
parent reply =?UTF-8?Q?S=c3=b6nke_Ludwig?= <sludwig+d outerproduct.org> writes:
Am 03.01.2019 um 21:18 schrieb David Nadlinger:

 On 3 Jan 2019, at 12:58, Sönke Ludwig via digitalmars-d-ldc wrote:

 There appears to be a GC visibility issue of TLS sections on macOS 
 when multiple threads are involved. I added a test case to what looks 
 like the same issue: https://github.com/ldc-developers/ldc/issues/2187


 
 Try this patch:
 
 (...)
 
 Still trying to figure out how much of that code can be stripped away 
 for non-Shared builds (it's a mess, as DMD partially supports shared 
 libraries on Linux with a static runtime), or how on earth nobody has 
 found this before.
 
 Best,
 David


That appears to fix it indeed. I still have to run the actual test case, 
but the application runs fine now.

Many thanks for the quick solution!
Jan 07 2019
parent "David Nadlinger" <code klickverbot.at> writes:
On 7 Jan 2019, at 8:02, Sönke Ludwig via digitalmars-d-ldc wrote:

 That appears to fix it indeed. I still have to run the actual test 
 case, but the application runs fine now.

 Many thanks for the quick solution!


Okay, good – I'll see about upstreaming a proper fix asap.

  — David
Jan 07 2019