[LLVMbugs] [Bug 20003] Crashing on pthread_join

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20003

Richard Smith <richard-llvm at metafoo.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |richard-llvm at metafoo.co.uk
         Resolution|---                         |INVALID

--- Comment #1 from Richard Smith <richard-llvm at metafoo.co.uk> ---
Your code has a data race. Building with -fsanitize=thread gives this:


WARNING: ThreadSanitizer: data race (pid=24036)
  Read of size 8 at 0x7d080000efc0 by main thread:
    #0 printMatrix <null>:0 (a.out+0x00000009f486)
    #1 main <null>:0 (a.out+0x0000000a056d)

  Previous write of size 8 at 0x7d080000efc0 by thread T1:
    #0 multMatrix <null>:0 (a.out+0x00000009e499)
    #1 multMatrixThread <null>:0 (a.out+0x00000009e881)

  As if synchronized via sleep:
    #0 sleep
/usr/local/google/home/richardsmith/build/llvm-3/src/projects/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc:243
(a.out+0x000000035d20)
    #1 main <null>:0 (a.out+0x0000000a0366)

  Location is heap block of size 32 at 0x7d080000efc0 allocated by main thread:
    #0 malloc
/usr/local/google/home/richardsmith/build/llvm-3/src/projects/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc:460
(a.out+0x0000000370ad)
    #1 allocMatrix <null>:0 (a.out+0x00000009dcf1)
    #2 main <null>:0 (a.out+0x00000009fac7)

  Thread T1 (tid=24039, finished) created by main thread at:
    #0 pthread_create
/usr/local/google/home/richardsmith/build/llvm-3/src/projects/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc:842
(a.out+0x00000003ac6f)
    #1 main <null>:0 (a.out+0x0000000a02fa)

SUMMARY: ThreadSanitizer: data race ??:0 printMatrix


Note that you increment 'i' at the wrong place in your loop, so you never
actually join the thread you created. Fixing that bug removes the data race and
makes your code work.

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