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The C++ "Mapping for Sequence Types" says about the length() function, "Increasing the length of a sequence adds new elements at the tail. The newly-added elements behave as if they are default-constructed when the sequence length is increased." Also, it says, "For both bounded and unbounded sequences, the default constructor sets the sequence length equal to 0." TAO does not comply with that. If a sequence contains a sequence, and the outer sequence is shrunk and grown again, then its elements are not re-initialized, but continue their prior existence. This is a bug. A test case is attached. When built, the test program should print "passed."
Created attachment 364 [details] Test Case (ZIP file)
Attached below is a quick-and-somewhat-dirty patch for this bug. It implements the _shrink_buffer() operation for generic sequences, and uses it to re-initialize all elements (by assigning a default- constructed element) that are shrunk. This way, new elements between a sequence's length() and its maximum() remain freshly initialized when the sequence grows again. I say "somewhat" dirty, because this patch may mean throw-away work, e.g., if the sequence never re-grows, or if the sequence is reallocated during re-growth. (Also, calling the destructor and the constructor might be better than creating and assigning a temporary.) However, I think it is critical to apply this patch, because this bug causes subtle problems in code that manipulates sequences and assumes elements to be default-constructed.
Created attachment 365 [details] Patch to fix bug.
Accepting, Frank, we are considering what to do. Carlos made a new sequence implementation but that is not 100% finished yet, but will solve several issues.
Added blocks
Thu Oct 27 09:34:12 UTC 2005 Johnny Willemsen <jwillemsen@remedy.nl> * tao/Sequence_T.{h,cpp}: Applied the fix of bug 2201, when shrinking a sequence we re initialize the elements. Fixes bugzilla 2201. Thanks to Frank Pilhofer <fp at mc dot com> for reporting this and supplying the patch. Thu Oct 27 09:27:12 UTC 2005 Johnny Willemsen <jwillemsen@remedy.nl> * tests/Bug_2201_Regression/*: Added regression for bug 2201 to the cvs archive
For the new sequence implementation regresions are also added for this bug, for the simple value sequences this problem was there and fixed in the new implementation
For testing fixes for this bug I wrote some small application to show the details of shrinking and regrowing of sequences. The app will output it's PASSED or FAILED depending whether the objects that have been "out-sized" by the shrinking were initialized.
Created attachment 417 [details] testTAO_IDL application for checking resizing of CORBA-sequences