• Johan (103/103) Nov 22 2020 Hi all, Ali,
• Walter Bright (2/5) Nov 22 2020 Excellent!
• =?UTF-8?Q?Ali_=c3=87ehreli?= (4/7) Nov 23 2020 I love it! I am happy that for once I knew that my code on the slides

Johan <j j.nl> writes:

Hi all, Ali,
   Thanks Ali for your talk on DConf Online 2020, it was nice to 
watch.

The std.parallelism.parallel example [1] immediately triggered 
me. I had to stop the video, and see whether ThreadSanitizer 
(TSan) shipped with LDC 1.24 can catch it. It does!

Testcase:
```
import std.parallelism;

void main() {
     // defaultPoolThreads(4); // [2]

     int[] elements = [0, 1, 2, 3];
     int[] results;
     foreach (e; elements.parallel) {  // test.d:8
         results ~= e;                 // test.d:9
     }
}
```

Let's compile it with ThreadSanitizer enabled and run it!
```
❯ bin/ldc2 -g -fsanitize=thread -run test.d
==================
WARNING: ThreadSanitizer: data race (pid=19606)
   Read of size 1 at 0x7f311b105010 by thread T7:



_D3std11parallelism__T15ParallelForeachTAiZQv7opApplyMFMDFKiZiZ4doItMFZv
phobos/std/parallelism.d-mixin-4048:4094 (test-b40741e-06cb93+0x2886e)

(test-b40741e-06cb93+0x293af)

   Previous write of size 4 at 0x7f311b105010 by thread T6:

(test-b40741e-06cb93+0x28284)

_D3std11parallelism__T15ParallelForeachTAiZQv7opApplyMFMDFKiZiZ4doItMFZv
phobos/std/parallelism.d-mixin-4048:4094 (test-b40741e-06cb93+0x2886e)

(test-b40741e-06cb93+0x293af)

   Thread T7 (tid=19614, running) created by main thread at:


<null> (test-b40741e-06cb93+0x5508b)


(test-b40741e-06cb93+0x5aeeb)


   Thread T6 (tid=19613, running) created by main thread at:


<null> (test-b40741e-06cb93+0x5508b)


(test-b40741e-06cb93+0x5aeeb)


SUMMARY: ThreadSanitizer: data race 
(/usr/lib/x86_64-linux-gnu/libtsan.so.0+0x32505) in memcpy
==================
==================
WARNING: ThreadSanitizer: data race (pid=19606)
   Read of size 1 at 0x7f311b105010 by thread T4:



_D3std11parallelism__T15ParallelForeachTAiZQv7opApplyMFMDFKiZiZ4doItMFZv
phobos/std/parallelism.d-mixin-4048:4094 (test-b40741e-06cb93+0x2886e)

(test-b40741e-06cb93+0x293af)

   Previous write of size 4 at 0x7f311b105010 by thread T6:

(test-b40741e-06cb93+0x28284)

_D3std11parallelism__T15ParallelForeachTAiZQv7opApplyMFMDFKiZiZ4doItMFZv
phobos/std/parallelism.d-mixin-4048:4094 (test-b40741e-06cb93+0x2886e)

(test-b40741e-06cb93+0x293af)

   Thread T4 (tid=19611, running) created by main thread at:


<null> (test-b40741e-06cb93+0x5508b)


(test-b40741e-06cb93+0x5aeeb)


   Thread T6 (tid=19613, running) created by main thread at:


<null> (test-b40741e-06cb93+0x5508b)


(test-b40741e-06cb93+0x5aeeb)


SUMMARY: ThreadSanitizer: data race 
(/usr/lib/x86_64-linux-gnu/libtsan.so.0+0x32505) in memcpy
==================
ThreadSanitizer: reported 2 warnings
Error: /tmp/johan/test-b40741e-06cb93 failed with status: 66
```

I tested this using WSL2, the Linux environment available on 
Windows 10. I think TSan should be supported on Windows and macOS 
too, but I did not test this example.

Cheers,
   Johan


[1] 
https://www.youtube.com/watch?v=dRORNQIB2wA&feature=youtu.be&list=PLIldXzSkPUXWsvFA4AuawPoMnq9Bh1lIZ&t=1471
[2] Use this line of code if by default only a single thread is 
available in the pool (e.g. in a container).

Walter Bright <newshound2 digitalmars.com> writes:

On 11/22/2020 4:49 AM, Johan wrote:
 The std.parallelism.parallel example [1] immediately triggered me. I had to
stop 
 the video, and see whether ThreadSanitizer (TSan) shipped with LDC 1.24 can 
 catch it. It does!

Excellent!

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 11/22/20 4:49 AM, Johan wrote:

 The std.parallelism.parallel example [1] immediately triggered me. I had
 to stop the video, and see whether ThreadSanitizer (TSan) shipped with
 LDC 1.24 can catch it. It does!

I love it! I am happy that for once I knew that my code on the slides 
had a bug. Phew... :)

Ali