double free or corruption error when using parallel foreach

[Minas Mina]

Hi. I want to make my raytracer run in parallel. My idea is to
use a parallel foreach.

That's what I do:
http://pastebin.com/V4zTKbVJ

Note that there is more code after bool hit = ...
but I didn't include it because the problem is in the trace
function (I commented it out and everything else worked -- apart
from the things are dependent on it of course)

Also, scene is of type Scene, which is a struct.

Sometimes I get this:

Rendering...
[xcb] Unknown request in queue while dequeuing
[xcb] Most likely this is a multi-threaded client and
XInitThreads has not been called
[xcb] Aborting, sorry about that.
raytracing: ../../src/xcb_io.c:178: dequeue_pending_request:
Assertion `!xcb_xlib_unknown_req_in_deq' failed.
bash: line 1: 18982 Aborted                 (core dumped)
/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing

Other times this:

Rendering...
*** glibc detected ***
/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing:
double free or corruption (fasttop): 0x0000000001ba4f30 ***
bash: line 1: 19007 Aborted                 (core dumped)
/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing

And other times:

Rendering...
*** glibc detected ***
/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing:
double free or corruption (fasttop): 0x0000000001c22e40 ***
*** glibc detected ***
/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing:
double free or corruption (fasttop): 0x0000000001c44d10 ***
*** glibc detected ***
/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing:
double free or corruption (fasttop): 0x0000000001c44d10 ***
======= Backtrace: =========
======= Backtrace: =========
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x7eb96)[0x7ff7f2d41b96]
/lib/x86_64-linux-gnu/libc.so.6(+0x7eb96)[0x7ff7f2d41b96]
/lib/x86_64-linux-gnu/libc.so.6(+0x7eb96)[0x7ff7f2d41b96]
/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing(_D3std8typecons130__T10RefCountedTS3std9container40__T5ArrayTC10raytracing7surface7SurfaceZ5Array7PayloadVE3std8typecons24RefCountedAutoInitialize0Z10RefCounted6__dtorMFZv+0x3b/usr/lib/x86_64-linux-gnu/libSDL.so(+0x35012)[0x7ff7f2a61012]
/usr/lib/x86_64-linux-gnu/libSDL.so(SDL_QuitSubSystem+0x95)[0x7ff7f2a364f5]
/usr/lib/x86_64-linux-gnu/libSDL.so(SDL_Quit+0xe)[0x7ff7f2a3655e]
/usr/lib/x86_64-linux-gnu/libSDL.so(+0xabaf)[0x7ff7f2a36baf]
/lib/x86_64-linux-gnu/libpthread.so.0(+0xfcb0)[0x7ff7f3595cb0]
00400000-004d1000 r-xp 00000000 08:06 5648092

/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing
006d1000-006d2000 r--p 000d1000 08:06 5648092

/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing
006d2000-006e3000 rw-p 000d2000 08:06 5648092

/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing
006e3000-006e4000 rw-p 00000000 00:00 0
01bde000-01c57000 rw-p 00000000 00:00 0
          [heap]
7ff7dc000000-7ff7dc021000 rw-p 00000000 00:00 0
7ff7dc021000-7ff7e0000000 ---p 00000000 00:00 0
7ff7e0000000-7ff7e0021000 rw-p 00000000 00:00 0
7ff7e0021000-7ff7e4000000 ---p 00000000 00:00 0
7ff7e4000000-7ff7e4021000 rw-p 00000000 00:00 0
7ff7e4021000-7ff7e8000000 ---p 00000000 00:00 0
7ff7e904c000-7ff7e904d000 ---p 00000000 00:00 0
7ff7e904d000-7ff7e984d000 rw-p 00000000 00:00 0
          [stack:19036]
7ff7ebc20000-7ff7ebc35000 r-xp 00000000 08:06 5384474
          /lib/x86_64-linux-gnu/libgcc_s.so.1
7ff7ebc35000-7ff7ebe34000 ---p 00015000 08:06 5384474
          /lib/x86_64-linux-gnu/libgcc_s.so.1
7ff7ebe34000-7ff7ebe35000 r--p 00014000 08:06 5384474
          /lib/x86_64-linux-gnu/libgcc_s.so.1
7ff7ebe35000-7ff7ebe36000 rw-p 00015000 08:06 5384474
          /lib/x86_64-linux-gnu/libgcc_s.so.1
7ff7ebe36000-7ff7ebe37000 ---p 00000000 00:00 0
7ff7ebe37000-7ff7ec637000 rw-p 00000000 00:00 0
          [stack:19038]
7ff7ec637000-7ff7ec638000 ---p 00000000 00:00 0
7ff7ec638000-7ff7ed679000 rw-p 00000000 00:00 0
          [stack:19037]
7ff7ed679000-7ff7ed84e000 rw-s 00000000 00:04 6488069
          /SYSV00000000 (deleted)
7ff7ed84e000-7ff7ed853000 r-xp 00000000 08:06 7365724
          /usr/lib/x86_64-linux-gnu/libXfixes.so.3.1.0
7ff7ed853000-7ff7eda52000 ---p 00005000 08:06 7365724
          /usr/lib/x86_64-linux-gnu/libXfixes.so.3.1.0
7ff7eda52000-7ff7eda53000 r--p
00/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing(_D3std9container40__T5ArrayTC10raytracing7surface7SurfaceZ5Array7opIndexMFmZC10raytracing7surface7Surface+0x59)[0x481d0d]
======= Memory map: ========
004000 08:06 7365724
/usr/lib/x86_64-linux-gnu/libXfixes.so.3.1.0
7ff7eda53000-7ff7eda54000 rw-p 00005000 08:06 7365724
          /usr/lib/x86_64-linux-gnu/libXfixes.so.3.1.0
7ff7eda54000-7ff7eda5d000 r-xp 00000000 08:06 7356454
          /usr/lib/x86_64-linux-gnu/libXrender.so.1.3.0
7ff7eda5d000-7ff7edc5c000 ---p 00009000 08:06 7356454
          /usr/lib/x86_64-linux-gnu/libXrender.so.1.3.0
7ff7edc5c000-7ff7edc5d000 r--p 00008000 08:06 7356454
          /usr/lib/x86_64-linux-gnu/libXrender.so.1.3.0
7ff7edc5d000-7ff7edc5e000 rw-p 00009000 08:06 7356454
          /usr/lib/x86_64-linux-gnu/libXrender.so.1.3.0
7ff7edc5e000-7ff7edc67000 r-xp 00000000 08:06 7357883
          /usr/lib/x86_64-linux-gnu/libXcursor.so.1.0.2
7ff7edc67000-7ff7ede67000 ---p 00009000 08:06 7357883
          /usr/lib/x86_64-linux-gnu/libXcursor.so.1.0.2
7ff7ede67000-7ff7ede68000 r--p 00009000 08:06 7357883
          /usr/lib/x86_64-linux-gnu/libXcurs00400000-004d1000 r-xp
00000000 08:06 5648092
/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing
006d1000-006d2000 r--p 000d1000 08:06 5648092

/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing
006d2000-006e3000 rw-p 000d2000 08:06 5648092

/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing
006e3000-006e4000 rw-p 00000000 00:00 0
01bde000-01c57000 rw-p 00000000 00:00 0
          [heap]
7ff7dc000000-7ff7dc021000 rw-p 00000000 00:00 0
7ff7dc021000-7ff7e0000000 ---p 00000000 00:00 0
7ff7e0000000-7ff7e0021000 rw-p 00000000 00:00 0
7ff7e0021000-7ff7e4000000 ---p 00000000 00:00 0
7ff7e4000000-7ff7e4021000 rw-p 00000000 00:00 0
7ff7e4021000-7ff7e8000000 ---p 00000000 00:00 0
7ff7e904c000-7ff7e904d000 ---p 00000000 00:00 0
7ff7e904d000-7ff7e984d000 rw-p 00000000 00:00 0
          [stack:19036]
7ff7ebc20000-7ff7ebc35000 r-xp 00000000 08:06 5384474
          /lib/x86_64-linux-gnu/libgcc_s.so.1
7ff7ebc35000-7ff7ebe34000 ---p 00015000 08:06 5384474
          /lib/x86_64-linux-gnu/libgcc_s.so.1
7ff7ebe34000-7ff7ebe35000 r--p 00014000 08:06 5384474
          /lib/x86_64-linux-gnu/libgcc_s.so.1
7ff7ebe35000-7ff7ebe36000 rw-p 00015000 08:06 5384474
          /lib/x86_64-linux-gnu/libgcc_s.so.1
7ff7ebe36000-7ff7ebe37000 ---p 00000000 00:00 0
7ff7ebe37000-7ff7ec637000 rw-p 00000000 00:00 0
          [stack:19038]
7ff7ec637000-7ff7ec638000 ---p 00000000 00:00 0
7ff7ec638000-7ff7ed679000 rw-p 00000000 00:00 0
          [stack:19037]
7ff7ed679000-7ff7ed84e000 rw-s 00000000 00:04 6488069
          /SYSV00000000 (deleted)
7ff7ed84e000-7ff7ed853000 r-xp 00000000 08:06 7365724
          /usr/lib/x86_64-linux-gnu/libXfixes.so.3.1.0
7ff7ed853000-7ff7eda52000 ---p 00005000 08:06 7365724
          /usr/lib/x86_64-linux-gnu/libXfixes.so.3.1.0
7ff7eda52000-7ff7eda53000 r--p 00bash: line 1: 19033 Aborted
              (core dumped)
/home/minas/Projects/D/raytracing/raytracing/bin/Release/raytracing