IZ22824: UNORDERED_MAP NOT BEHAVING AS EXPECTED

April 2009 XL C/C++ Enterprise Edition V8.0 for AIX PTF
May 2008 XL C/C++ Enterprise Edition V8.0 for AIX PTF
August 2008 XL C/C++ Enterprise Edition V8.0 for AIX PTF
April 2010 XL C/C++ Enterprise Edition V8.0 for AIX PTF
June 2011 XL C/C++ Enterprise Edition V8.0 for AIX PTF
July 2009 XL C/C++ Enterprise Edition V8.0 for AIX PTF
October 2009 XL C/C++ Enterprise Edition V8.0 for AIX PTF
November 2008 XL C/C++ Enterprise Edition V8.0 for AIX PTF

APAR status

• Closed as program error.

Error description

• The test case is showing unexpected behaviour from the
  unordered_map class. After using the operator= or copy
  constructor, erase of target object does not preform as expected
  - it affects both the source and target objects.
  
  Basically, when an element in umap2 is erased, _Dump shows it
  erased from both umap2 and umap1. Iteration then shows that the
  element still exists in umap2.
  
  Using iterators yields the same result.
  
  A variation of this test case with std::map yields expected
  results.
  
  
  TESTCASE:
  
  #include <iostream>
  #include <unordered_map>
  #include <string>
  
  using namespace std;
  using namespace std::tr1;
  
  int main()
  {
      unordered_map<string, size_t> umap1, umap2;
      umap1["Key"] = 1;
      umap2 = umap1;
  
      cout << "Dump before erase:" << endl;
      cout << "umap1: " << endl; umap1._Dump();
      cout << "umap2: " << endl; umap2._Dump();
  
      umap2.erase("Key");
  
      cout << "Dump after erase:" << endl;
      cout << "umap1: " << endl; umap1._Dump();
      cout << "umap2: " << endl; umap2._Dump();
  
      cout << "Iteration after erase:" << endl;
      cout << "umap1: " << endl;
  
      for(unordered_map<string, size_t>::iterator iter =
  umap1.begin();
          iter != umap1.end();
          ++iter) {
          const unordered_map<string, size_t>::value_type vt =
  *iter;
          cout << "key="     << vt.first.c_str()
               << ", value=" << vt.second
               << endl;
      }
  
      cout << "umap2: " << endl;
  
      for(unordered_map<string, size_t>::iterator iter =
  umap2.begin();
          iter != umap2.end();
          ++iter) {
          const unordered_map<string, size_t>::value_type vt =
  *iter;
          cout << "key="     << vt.first.c_str()
               << ", value=" << vt.second
               << endl;
      }
  }
  
  Compile with xlC -D__IBMCPP_TR1__ t.cpp
  
  
  ACTUAL OUTPUT:
  
  Dump before erase:
  umap1:
  Bucket count is 3
  Bucket 0:
  Bucket 1:  Key
  Bucket 2:
  
  umap2:
  Bucket count is 3
  Bucket 0:
  Bucket 1:  Key
  Bucket 2:
  
  Dump after erase:
  umap1:
  Bucket count is 3
  Bucket 0:
  Bucket 1:
  Bucket 2:
  
  umap2:
  Bucket count is 3
  Bucket 0:
  Bucket 1:
  Bucket 2:
  
  Iteration after erase:
  umap1:
  umap2:
  key=Key, value=1
  
  
  EXPECTED OUTPUT:
  
  The element should be completely removed from the target object
  without affecting the source object.
  

Local fix

• n/a
  

Problem summary

• The copy construction and copy-assignment of the unordered
  containers was incorrect.
  

Problem conclusion

• An unordered container consists of a std::list that is used to
  store the contained elements, and an array of objects of type
  _Bucket.  Each _Bucket is essentially a pair of pointers that
  reference elements in the list.  After a copy was performed, all
  the elements of the source container were copied into the target
  container, but each _Bucket in the target container referenced
  the elements of the source container's list, rather than
  elements of the target container's list.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  IZ18515

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  XLC C++ AIX

• Fixed component ID

  5724M1200

Applicable component levels