Add exception guard for constructor vector(n, x, a)

[winner245]

Added exception guard to the vector(n, x, a) constructor to enhance exception safety. This change ensures that the vector(n, x, a) constructor is consistent with other constructors, such as vector(n), vector(n, x), vector(n, a), in terms of exception safety.

[github-actions]

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[llvmbot]

@llvm/pr-subscribers-libcxx

Author: None (winner245)

Changes

Added exception guard to the vector(n, x, a) constructor to enhance exception safety. This change ensures that the vector(n, x, a) constructor is consistent with other constructors, such as vector(n), vector(n, x), vector(n, a), in terms of exception safety.

---

Full diff: https://github.com/llvm/llvm-project/pull/113086.diff

1 Files Affected:

• (modified) libcxx/include/vector (+2)

diff --git a/libcxx/include/vector b/libcxx/include/vector
index dc31f31838264c..700cb51f41eeb2 100644
--- a/libcxx/include/vector
+++ b/libcxx/include/vector
@@ -487,10 +487,12 @@ public:
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI
   vector(size_type __n, const value_type& __x, const allocator_type& __a)
       : __alloc_(__a) {
+    auto __guard = std::__make_exception_guard(__destroy_vector(*this));
     if (__n > 0) {
       __vallocate(__n);
       __construct_at_end(__n, __x);
     }
+    __guard.__complete();
   }
 
   template <class _InputIterator,

[frederick-vs-ja]

I think I've found the memory leaking case that can be fixed by this PR (Godbolt link).

Could you add a new .pass.cpp to libcxx/test/libcxx/containers/sequences/vector/vector.cons which asserts that memory leak doesn't raise from this constructor when an exception is thrown?

[frederick-vs-ja]

Looks like a missing piece of 8ff4d21 (https://reviews.llvm.org/D138601). CC @philnik777.

[winner245]

@frederick-vs-ja Thank you for your guidance and for providing the memory leak test case. I will include the test in a .pass.cpp file and make sure my change passes the test. Also, I really appreciate you pointing out that my PR is related to 8ff4d21 by @philnik777. I will definitely look into that as well.

Best regards,
Peng

[winner245]

Hi team,

Following @frederick-vs-ja's suggestion and reviewing the prior work by @philnik777, I have included an additional exception test in the existing file libcxx/test/std/containers/sequences/vector/vector.cons/exceptions.pass.cpp. This new test checks for memory leaks in scenarios where vector(size_type, value_type, const allocator_type&) might throw, ensuring no memory is leaked in such cases. I have compiled the entire project and run the new test to confirm that this change does not introduce new problems.

Thank you, @frederick-vs-ja, for your valuable suggestion!

[ldionne]

LGTM, thanks for the fix. Can you please rebase your patch onto main? That will fix the CI issues, which have been fixed on the latest main.

[ldionne]

LGTM once CI is green. Thanks!

[winner245]

Thank you @ldionne so much for your prompt fix. The failing checks are now passing. Once again, I would like to thank you both, @frederick-vs-ja and @ldionne, for your patience and guidance. I am so proud to have the opportunity to work with you.

[winner245]

Hi team, I have resolved the conflicts due to the split of libcxx/include/vector into 2 separate files vector.h and vector_bool.h. This PR is now ready to merge. Could someone with merge permissions please help me merge it into the main branch? Thanks in advance. Cheers,

[frederick-vs-ja]

I'm merging this, hoping everything is OK.

[github-actions]

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