__gnu_parallel::accumulate gives a segfault when accumulating over 1000 elements (but not 999).

This was originally asked as a question on  StackOverflow - http://stackoverflow.com/questions/5769908/unexpected-segfault-with-gnu-parallelaccumulate:

Sehe diagnosed the problem as a bug in c++/4.4/parallel/par_loop.h:87

"
#   pragma omp single
      {
        num_threads = omp_get_num_threads();
        thread_results = static_cast<Result*>(
                            ::operator new(num_threads * sizeof(Result)));
        constructed = new bool[num_threads];
      }
But line 127 deletes it with

delete[] thread_results;

_Apparently, the construction of thread_results was optimized at one stage, but the deletion statement was never updated to reflect this. The optimization makes sense over just newing up the array (new Result[num_threads]) because it avoids constructing the elements._

Fixing that to

delete thread_results;

removes the bug. You will want to report this to the gnu devs.
"

SYSTEM
Ubuntu 10-10 on AMD64 dual core.

TO RECREATE:



#include <vector> 
#include <parallel/algorithm> 
#include <parallel/numeric> 


class NaturalParameters
{
public:
  
  NaturalParameters()
    : m_data(2) //defualt constructor
  {  }
      
  std::vector<double>::const_iterator
  begin() const
  {
    return m_data.begin();
  }

  std::vector<double>::const_iterator
  end() const
  {
    return m_data.begin();
  }

  NaturalParameters& 
  operator+=(const NaturalParameters& other)
  {
    //do something - well actually ... nothing for the purposes of this bug report.
    return *this;
  }
  
private:
  std::vector<double> m_data;
};

inline
NaturalParameters
operator+(const NaturalParameters& a, const NaturalParameters& b)
{
  NaturalParameters tmp = a;
  return tmp+=b;
}  

int
main  (int ac, char **av)
{
  //This one succeeds
  for(size_t i=0;i<1000;++i){
    std::vector<NaturalParameters> ChildrenNP(999);
    NaturalParameters init;
    NaturalParameters NP = __gnu_parallel::accumulate(ChildrenNP.begin(), ChildrenNP.end(), init ); 
  }
  //This one fails with a segfault
  for(size_t i=0;i<1000;++i){
    std::vector<NaturalParameters> ChildrenNP(1000);
    NaturalParameters init;
    NaturalParameters NP = __gnu_parallel::accumulate(ChildrenNP.begin(), ChildrenNP.end(), init ); 
  }
}


Preprocessed file attached

COMMAND:

 g++ -v  gnu_parallel_bug.cpp -g -fopenmp -Wall -D_GLIBCXX_PARALLEL -save-temps
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.4.4-14ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.4 --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5) 
COLLECT_GCC_OPTIONS='-v' '-g' '-fopenmp' '-Wall' '-D_GLIBCXX_PARALLEL' '-save-temps' '-shared-libgcc' '-mtune=generic' '-pthread'
 /usr/lib/gcc/x86_64-linux-gnu/4.4.5/cc1plus -E -quiet -v -D_GNU_SOURCE -D_REENTRANT -D_GLIBCXX_PARALLEL gnu_parallel_bug.cpp -D_FORTIFY_SOURCE=2 -mtune=generic -Wall -fopenmp -g -fworking-directory -fpch-preprocess -fstack-protector -o gnu_parallel_bug.ii
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../x86_64-linux-gnu/include"
ignoring nonexistent directory "/usr/include/x86_64-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/4.4
 /usr/include/c++/4.4/x86_64-linux-gnu
 /usr/include/c++/4.4/backward
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/4.4.5/include
 /usr/lib/gcc/x86_64-linux-gnu/4.4.5/include-fixed
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-g' '-fopenmp' '-Wall' '-D_GLIBCXX_PARALLEL' '-save-temps' '-shared-libgcc' '-mtune=generic' '-pthread'
 /usr/lib/gcc/x86_64-linux-gnu/4.4.5/cc1plus -fpreprocessed gnu_parallel_bug.ii -quiet -dumpbase gnu_parallel_bug.cpp -mtune=generic -auxbase gnu_parallel_bug -g -Wall -version -fopenmp -fstack-protector -o gnu_parallel_bug.s
GNU C++ (Ubuntu/Linaro 4.4.4-14ubuntu5) version 4.4.5 (x86_64-linux-gnu)
	compiled by GNU C version 4.4.5, GMP version 4.3.2, MPFR version 3.0.0-p3.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: b408a5c1addf39d3fcc1ff19852f1cfe
COLLECT_GCC_OPTIONS='-v' '-g' '-fopenmp' '-Wall' '-D_GLIBCXX_PARALLEL' '-save-temps' '-shared-libgcc' '-mtune=generic' '-pthread'
 as -V -Qy -o gnu_parallel_bug.o gnu_parallel_bug.s
GNU assembler version 2.20.51 (x86_64-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.20.51-system.20100908
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../:/lib/:/usr/lib/
Reading specs from /usr/lib/gcc/x86_64-linux-gnu/4.4.5/libgomp.spec
COLLECT_GCC_OPTIONS='-v' '-g' '-fopenmp' '-Wall' '-D_GLIBCXX_PARALLEL' '-save-temps' '-shared-libgcc' '-mtune=generic' '-pthread'
 /usr/lib/gcc/x86_64-linux-gnu/4.4.5/collect2 --build-id --eh-frame-hdr -m elf_x86_64 --hash-style=gnu -dynamic-linker /lib64/ld-linux-x86-64.so.2 -z relro /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crt1.o /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crti.o /usr/lib/gcc/x86_64-linux-gnu/4.4.5/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5 -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5 -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib -L/lib/../lib -L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../.. gnu_parallel_bug.o -lstdc++ -lm -lgomp -lgcc_s -lgcc -lpthread -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-linux-gnu/4.4.5/crtend.o /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crtn.o

Output:
./a.out 
Segmentation fault

SEE ALSO:

Additional comment on:

http://stackoverflow.com/questions/5769908/unexpected-segfault-with-gnu-parallelaccumulate

"
You might still have some residu problems with the threadsafety of std::__cxx1998::vector::operator=. You can see what I mean by using valgrind. However, it is entirely possible that valgrind reports a fasle positive there.

I just tested the other way around: when using new Result[num_threads] with delete[] (instead of the optimized version in the GNU source) you'll get a clean valgrind run all the way. I'm pretty sure this will be a false positive, but I'd sure mention it to the GNU devs while you report the bug.
"