my \a = lazy loop { 1 }; my \b = lazy loop { 1 }; for ^100000 -> $i { await start { a.AT-POS($i) }, start { b.AT-POS($i) } }

gistfile1.txt

dogbert@dogbert-VirtualBox ~/repos/rakudo $ gdb --args /home/dogbert/repos/rakudo/install/bin/moar --libpath="/home/dogbert/repos/rakudo/install/share/nqp/lib" --libpath="." /home/dogbert/repos/rakudo/perl6.moarvm -I /home/dogbert/repos/rakudo/install/share/perl6/site/lib ~/test.pl6
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
Copyright (C) 2014 Free Software Foundation, Inc.
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Reading symbols from /home/dogbert/repos/rakudo/install/bin/moar...done.
(gdb) b VMArray.c:9
No source file named VMArray.c.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (VMArray.c:9) pending.
(gdb) r
Starting program: /home/dogbert/repos/rakudo/install/bin/moar --libpath=/home/dogbert/repos/rakudo/install/share/nqp/lib --libpath=. /home/dogbert/repos/rakudo/perl6.moarvm -I /home/dogbert/repos/rakudo/install/share/perl6/site/lib /home/dogbert/test.pl6
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/i386-linux-gnu/libthread_db.so.1".
[New Thread 0xb5db4b40 (LWP 7666)]
[New Thread 0xb4ffeb40 (LWP 7667)]
[New Thread 0xb41feb40 (LWP 7668)]
[New Thread 0xb35fcb40 (LWP 7669)]
[New Thread 0xb27feb40 (LWP 7670)]
[New Thread 0xb17feb40 (LWP 7671)]
[New Thread 0xb0bfcb40 (LWP 7672)]
[New Thread 0xafffab40 (LWP 7673)]
[New Thread 0xaf3f8b40 (LWP 7674)]
[New Thread 0xae7f6b40 (LWP 7675)]
[New Thread 0xadbf4b40 (LWP 7676)]
[New Thread 0xacff2b40 (LWP 7677)]
[New Thread 0xac3f0b40 (LWP 7678)]
[New Thread 0xab7eeb40 (LWP 7679)]
[New Thread 0xaabecb40 (LWP 7680)]
[New Thread 0xa9feab40 (LWP 7681)]
[Switching to Thread 0xac3f0b40 (LWP 7678)]

Breakpoint 1, enter_single_user (tc=0x9fba7d8, arr=0xb5405918) at src/6model/reprs/VMArray.c:9
9	        MVM_dump_backtrace(tc);
(gdb) info threads
  Id   Target Id         Frame 
  17   Thread 0xa9feab40 (LWP 7681) "moar" 0xb7fdccb0 in ?? ()
  16   Thread 0xaabecb40 (LWP 7680) "moar" 0xb7fdccb0 in ?? ()
  15   Thread 0xab7eeb40 (LWP 7679) "moar" 0xb7fdccb0 in ?? ()
* 14   Thread 0xac3f0b40 (LWP 7678) "moar" enter_single_user (tc=0x9fba7d8, arr=0xb5405918) at src/6model/reprs/VMArray.c:9
  13   Thread 0xacff2b40 (LWP 7677) "moar" 0xb7fdccb0 in ?? ()
  12   Thread 0xadbf4b40 (LWP 7676) "moar" 0xb7fdccb0 in ?? ()
  11   Thread 0xae7f6b40 (LWP 7675) "moar" 0xb7fdccb0 in ?? ()
  10   Thread 0xaf3f8b40 (LWP 7674) "moar" 0xb7fdccb0 in ?? ()
  9    Thread 0xafffab40 (LWP 7673) "moar" 0xb7fdccb0 in ?? ()
  8    Thread 0xb0bfcb40 (LWP 7672) "moar" 0xb7fdccb0 in ?? ()
  7    Thread 0xb17feb40 (LWP 7671) "moar" 0xb7fdccb0 in ?? ()
  6    Thread 0xb27feb40 (LWP 7670) "moar" 0xb7fdccb0 in ?? ()
  5    Thread 0xb35fcb40 (LWP 7669) "moar" 0xb7fdccb0 in ?? ()
  4    Thread 0xb41feb40 (LWP 7668) "moar" 0xb7fdccb0 in ?? ()
  3    Thread 0xb4ffeb40 (LWP 7667) "moar" 0xb7c12499 in MVM_interp_run (tc=0x9e28020, initial_invoke=0xb7c31e51 <thread_initial_invoke>, invoke_data=0x9e23e78) at src/core/interp.c:3061
  2    Thread 0xb5db4b40 (LWP 7666) "moar" 0xb7fdccb0 in ?? ()
  1    Thread 0xb7932700 (LWP 7662) "moar" 0xb7c09acf in MVM_interp_run (tc=0x804c450, initial_invoke=0xb7cf9bc7 <toplevel_initial_invoke>, invoke_data=0x80b8b18) at src/core/interp.c:1766
(gdb) thread apply 14 3 1 bt

Thread 14 (Thread 0xac3f0b40 (LWP 7678)):
#0  enter_single_user (tc=0x9fba7d8, arr=0xb5405918) at src/6model/reprs/VMArray.c:9
#1  0xb7c6c5e1 in push (tc=0x9fba7d8, st=0x8d86748, root=0xb5405908, data=0xb5405918, value=..., kind=8) at src/6model/reprs/VMArray.c:459
#2  0xb7c0d038 in MVM_interp_run (tc=0x9fba7d8, initial_invoke=0xb7c31e51 <thread_initial_invoke>, invoke_data=0x9f761c0) at src/core/interp.c:2202
#3  0xb7c31f93 in start_thread (data=data@entry=0x9f761c0) at src/core/threads.c:80
#4  0xb7d15a37 in uv__thread_start (arg=0x9fba178) at 3rdparty/libuv/src/unix/thread.c:49
#5  0xb7948f72 in start_thread (arg=0xac3f0b40) at pthread_create.c:312
#6  0xb7a90f8e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:129

Thread 3 (Thread 0xb4ffeb40 (LWP 7667)):
#0  0xb7c12499 in MVM_interp_run (tc=0x9e28020, initial_invoke=0xb7c31e51 <thread_initial_invoke>, invoke_data=0x9e23e78) at src/core/interp.c:3061
#1  0xb7c31f93 in start_thread (data=data@entry=0x9e23e78) at src/core/threads.c:80
#2  0xb7d15a37 in uv__thread_start (arg=0x9e27fd8) at 3rdparty/libuv/src/unix/thread.c:49
#3  0xb7948f72 in start_thread (arg=0xb4ffeb40) at pthread_create.c:312
#4  0xb7a90f8e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:129

Thread 1 (Thread 0xb7932700 (LWP 7662)):
#0  0xb7c09acf in MVM_interp_run (tc=0x804c450, initial_invoke=0xb7cf9bc7 <toplevel_initial_invoke>, invoke_data=0x80b8b18) at src/core/interp.c:1766
#1  0xb7cf9cf6 in MVM_vm_run_file (instance=0x804c008, filename=0xbffff2db "/home/dogbert/repos/rakudo/perl6.moarvm") at src/moar.c:310
#2  0x08048e76 in main (argc=7, argv=0xbffff084) at src/main.c:201
(gdb) p MVM_dump_backtrace(tc)
   at <unknown>:1  (./CORE.setting.moarvm:push)
 from SETTING::src/core/Iterator.pm:31  (./CORE.setting.moarvm:push-exactly)
 from SETTING::src/core/Iterable.pm:98  (./CORE.setting.moarvm:push-exactly)
 from SETTING::src/core/Iterator.pm:49  (./CORE.setting.moarvm:push-at-least)
 from SETTING::src/core/List.pm:41  (./CORE.setting.moarvm:reify-at-least)
 from SETTING::src/core/List.pm:477  (./CORE.setting.moarvm:AT-POS)
 from SETTING::src/core/Seq.pm:193  (./CORE.setting.moarvm:AT-POS)
 from /home/dogbert/test.pl6:1  (<ephemeral file>:)
 from SETTING::src/core/Promise.pm:216  (./CORE.setting.moarvm:)
 from SETTING::src/core/ThreadPoolScheduler.pm:284  (./CORE.setting.moarvm:)
 from SETTING::src/core/ThreadPoolScheduler.pm:173  (./CORE.setting.moarvm:)
 from SETTING::src/core/ThreadPoolScheduler.pm:166  (./CORE.setting.moarvm:)
 from SETTING::src/core/ThreadPoolScheduler.pm:163  (./CORE.setting.moarvm:)
 from SETTING::src/core/Thread.pm:30  (./CORE.setting.moarvm:THREAD-ENTRY)
$1 = void
(gdb) info threads
  Id   Target Id         Frame 
  17   Thread 0xa9feab40 (LWP 7681) "moar" 0xb7fdccb0 in ?? ()
  16   Thread 0xaabecb40 (LWP 7680) "moar" 0xb7fdccb0 in ?? ()
  15   Thread 0xab7eeb40 (LWP 7679) "moar" 0xb7fdccb0 in ?? ()
* 14   Thread 0xac3f0b40 (LWP 7678) "moar" enter_single_user (tc=0x9fba7d8, arr=0xb5405918) at src/6model/reprs/VMArray.c:9
  13   Thread 0xacff2b40 (LWP 7677) "moar" 0xb7fdccb0 in ?? ()
  12   Thread 0xadbf4b40 (LWP 7676) "moar" 0xb7fdccb0 in ?? ()
  11   Thread 0xae7f6b40 (LWP 7675) "moar" 0xb7fdccb0 in ?? ()
  10   Thread 0xaf3f8b40 (LWP 7674) "moar" 0xb7fdccb0 in ?? ()
  9    Thread 0xafffab40 (LWP 7673) "moar" 0xb7fdccb0 in ?? ()
  8    Thread 0xb0bfcb40 (LWP 7672) "moar" 0xb7fdccb0 in ?? ()
  7    Thread 0xb17feb40 (LWP 7671) "moar" 0xb7fdccb0 in ?? ()
  6    Thread 0xb27feb40 (LWP 7670) "moar" 0xb7fdccb0 in ?? ()
  5    Thread 0xb35fcb40 (LWP 7669) "moar" 0xb7fdccb0 in ?? ()
  4    Thread 0xb41feb40 (LWP 7668) "moar" 0xb7fdccb0 in ?? ()
  3    Thread 0xb4ffeb40 (LWP 7667) "moar" 0xb7fdccb0 in ?? ()
  2    Thread 0xb5db4b40 (LWP 7666) "moar" 0xb7fdccb0 in ?? ()
  1    Thread 0xb7932700 (LWP 7662) "moar" 0xb7c4a809 in MVM_gc_allocate_object (tc=0x804c450, st=0x8b03e58) at src/gc/allocation.c:86
(gdb)