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This code sometimes segfaults, sometimes tells me it's a malloc error:
    my @primes = grep { .is-prime }, 1 .. *; my @p = gather for 4000, 5, 100, 2000 -> $n { take start { @primes[$n] }; }; .say for await @p; Yes, I know the code is stupid (since one promise might be trying to access data that's not yet been calculated), but I would hope for something other than random error messages :)
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  • Nicholas Clark at Jan 8, 2016 at 8:24 pm
    Something between your mail client and my mail client hates us:
    On Thu, Jan 07, 2016 at 03:29:49PM -0800, curtis_ovid_poe@yahoo.com wrote:
    This code sometimes segfaults, sometimes tells me it's a malloc error:
    my @primes = grep { .is-prime }, 1 .. *; my @p = gather for 4000, 5, 100, 2000 -> $n { take start { @primes[$n] }; }; .say for await @p; Yes, I know the code is stupid (since one promise might be trying to access data that's not yet been calculated), but I would hope for something other than random error messages :)
    Nice find. ASAN says this, and memory corruption combined with concurrency
    would explain the non-deterministic results you're reporting:

    $ ./perl6-m -Ilib -e 'my @primes = grep { .is-prime }, 1 .. *; my @p = gather for 4000, 5, 100, 2000 -> $n { take start { @primes[$n] }; }; .say for await @p;'
    =================================================================
    ==16988==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x619000168e80 at pc 0x7feef89ff829 bp 0x7feef24dbff0 sp 0x7feef24dbfe8
    READ of size 8 at 0x619000168e80 thread T1
         #0 0x7feef89ff828 in at_pos src/6model/reprs/MVMArray.c:133
         #1 0x7feeedba94fd (+0x74fd)

    0x619000168e80 is located 0 bytes to the right of 1024-byte region [0x619000168a80,0x619000168e80)
    freed by thread T3 here:
         #0 0x7feef94ae8e6 in __interceptor_realloc ../../.././libsanitizer/asan/asan_malloc_linux.cc:93
         #1 0x7feef89fe3c6 in MVM_realloc src/core/alloc.h:20
         #2 0x7feef8a011a9 in set_size_internal src/6model/reprs/MVMArray.c:334
         #3 0x7feef8a020b9 in push src/6model/reprs/MVMArray.c:437
         #4 0x7feef89ef36b in MVM_repr_push_o src/6model/reprconv.c:339
         #5 0x7feeedb8e0cc (+0x40cc)
         #6 0x7feef8b2f290 in MVM_jit_enter_code src/jit/compile.c:125
         #7 0x7feef89211a2 in MVM_interp_run src/core/interp.c:5402
         #8 0x7feef8951ce7 in start_thread src/core/threads.c:77
         #9 0x7feef8bfa94d in uv__thread_start 3rdparty/libuv/src/unix/thread.c:49
         #10 0x7feef7cbc9d0 in start_thread (/lib64/libpthread.so.0+0x79d0)

    previously allocated by thread T1 here:
         #0 0x7feef94ae8e6 in __interceptor_realloc ../../.././libsanitizer/asan/asan_malloc_linux.cc:93
         #1 0x7feef89fe3c6 in MVM_realloc src/core/alloc.h:20
         #2 0x7feef8a011a9 in set_size_internal src/6model/reprs/MVMArray.c:334
         #3 0x7feef8a020b9 in push src/6model/reprs/MVMArray.c:437
         #4 0x7feef88d36ba in MVM_interp_run src/core/interp.c:2207
         #5 0x7feef8951ce7 in start_thread src/core/threads.c:77
         #6 0x7feef8bfa94d in uv__thread_start 3rdparty/libuv/src/unix/thread.c:49
         #7 0x7feef7cbc9d0 in start_thread (/lib64/libpthread.so.0+0x79d0)

    Thread T1 created by T0 here:
         #0 0x7feef947d6ea in __interceptor_pthread_create ../../.././libsanitizer/asan/asan_interceptors.cc:183
         #1 0x7feef8bfaa52 in uv_thread_create 3rdparty/libuv/src/unix/thread.c:66
         #2 0x7feef895203f in MVM_thread_run src/core/threads.c:126
         #3 0x7feef88fbd2b in MVM_interp_run src/core/interp.c:3933
         #4 0x7feef8b942dd in MVM_vm_run_file src/moar.c:304
         #5 0x401a4f in main src/main.c:191
         #6 0x7feef80f8d5c in __libc_start_main (/lib64/libc.so.6+0x1ed5c)

    Thread T3 created by T0 here:
         #0 0x7feef947d6ea in __interceptor_pthread_create ../../.././libsanitizer/asan/asan_interceptors.cc:183
         #1 0x7feef8bfaa52 in uv_thread_create 3rdparty/libuv/src/unix/thread.c:66
         #2 0x7feef895203f in MVM_thread_run src/core/threads.c:126
         #3 0x7feef88fbd2b in MVM_interp_run src/core/interp.c:3933
         #4 0x7feef8b942dd in MVM_vm_run_file src/moar.c:304
         #5 0x401a4f in main src/main.c:191
         #6 0x7feef80f8d5c in __libc_start_main (/lib64/libc.so.6+0x1ed5c)

    SUMMARY: AddressSanitizer: heap-buffer-overflow src/6model/reprs/MVMArray.c:133 at_pos
    Shadow bytes around the buggy address:
       0x0c3280025180: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
       0x0c3280025190: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
       0x0c32800251a0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
       0x0c32800251b0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
       0x0c32800251c0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
    =>0x0c32800251d0:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
       0x0c32800251e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
       0x0c32800251f0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
       0x0c3280025200: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
       0x0c3280025210: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
       0x0c3280025220: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
    Shadow byte legend (one shadow byte represents 8 application bytes):
       Addressable: 00
       Partially addressable: 01 02 03 04 05 06 07
       Heap left redzone: fa
       Heap right redzone: fb
       Freed heap region: fd
       Stack left redzone: f1
       Stack mid redzone: f2
       Stack right redzone: f3
       Stack partial redzone: f4
       Stack after return: f5
       Stack use after scope: f8
       Global redzone: f9
       Global init order: f6
       Poisoned by user: f7
       Contiguous container OOB:fc
       ASan internal: fe
    ==16988==ABORTING


    Nicholas Clark

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