Avoid integer overflow with infinite time limit in CPU Feasibility Jump - #1844
Avoid integer overflow with infinite time limit in CPU Feasibility Jump#1844vitor1001 wants to merge 3 commits into
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When in_time_limit is infinity, multiplying by 1000 and casting to an integer causes undefined behavior / integer overflow (trapping under UBSan). Guard against infinity and use std::chrono::milliseconds::max().
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Included review availability: Your plan provides up to 12 included reviews per hour; 11 remain after this review. 📝 WalkthroughWalkthroughThe CPU feasibility-jump solver validates time limits, safely converts finite values, handles infinite and oversized values, and checks elapsed milliseconds for finite limits. Unit tests cover valid and invalid boundary cases. ChangesFeasibility jump time-limit handling
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to CPU feasibility-jump time limits now safely reject invalid negative and NaN values while handling infinite and oversized limits without unsafe duration conversion. No current merge-blocking risk is identified. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches 💡 1🛠️ Fix failing CI checks 💡
🧪 Generate unit tests (beta)
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Inline comments:
In `@cpp/src/mip_heuristics/feasibility_jump/fj_cpu.cu`:
- Line 1899: Update the finite time-limit conversion near the
std::chrono::milliseconds construction to validate in_time_limit against the
representable i_t millisecond range before multiplying or casting. For values
above std::numeric_limits<i_t>::max() / 1000.0, clamp or reject them explicitly;
preserve the existing behavior for representable finite limits and use the
surrounding feasibility-jump time-limit logic to apply the chosen outcome.
- Around line 1898-1900: Add gtest regression coverage for the duration
conversion around time_limit, testing positive infinity, a normal finite value,
and an oversized finite value. Set an explicit iteration limit in each test so
results are independent of wall-clock timing, following the existing patterns
under cpp/src/tests.
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cpp/src/mip_heuristics/feasibility_jump/fj_cpu.cu
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| auto time_limit = (in_time_limit < std::numeric_limits<f_t>::infinity()) | ||
| ? std::chrono::milliseconds(static_cast<i_t>(std::floor(in_time_limit * 1000.0))) | ||
| : std::chrono::milliseconds::max(); |
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📐 Maintainability & Code Quality | 🟠 Major | ⚡ Quick win
Add regression tests for the duration boundary cases.
Add gtest coverage for the default positive-infinite limit, a normal finite limit, and an oversized finite limit. Set the iteration limit so the tests do not depend on wall-clock timing.
As per coding guidelines: “**/*.{cpp,cc,cxx,h,hpp,cu,cuh}: Add unit tests. Please refer to cpp/src/tests for examples of unit tests on C and C++ using gtest.”
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In `@cpp/src/mip_heuristics/feasibility_jump/fj_cpu.cu` around lines 1898 - 1900,
Add gtest regression coverage for the duration conversion around time_limit,
testing positive infinity, a normal finite value, and an oversized finite value.
Set an explicit iteration limit in each test so results are independent of
wall-clock timing, following the existing patterns under cpp/src/tests.
After applying the fix, consider running `coderabbit review --agent` for local
review. Visit https://docs.coderabbit.ai/cli.
Source: Coding guidelines
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The new guard only special-cases positive infinity via in_time_limit < +infinity. -infinity still takes the floor(... * 1000) / integer-cast path and hits the same out-of-range conversion this PR is trying to remove, while NaN falls into the milliseconds::max() branch and is silently treated as unlimited. Could this use an explicit finiteness/non-finite policy (and validate NaN/negative infinity) with regressions for those inputs?
…ersized limits - Validate in_time_limit against NaN and negative values (including -infinity), throwing ValidationError. - Clamp oversized finite limits (and infinite limits) to std::chrono::milliseconds::max(), avoiding integer overflow when multiplying by 1000. - Use std::chrono::milliseconds::rep (int64_t) instead of i_t (int32_t) for millisecond duration representation. - Compute elapsed time as std::chrono::milliseconds before comparing against time_limit, avoiding signed integer overflow when comparing against nanosecond clock duration. - Add regression tests in cpp/tests/mip/unit_test.cu covering default infinity, explicit infinity, normal finite, oversized finite, negative finite, negative infinity, and NaN limits.
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Thanks for the quick review, did the suggested changes. |
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Inline comments:
In `@cpp/src/mip_heuristics/feasibility_jump/fj_cpu.cu`:
- Line 1926: Update the elapsed-time guard in the feasibility-jump loop to use a
greater-than-or-equal comparison so zero and exact millisecond limits stop
before another iteration. Add regression coverage for zero and exact millisecond
limits, asserting both accepted boundary values and rejection of invalid limits.
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Thanks for the quick fix. The NaN/negative-infinity policy I raised is addressed now with explicit validation and regression coverage. There is still the separate exact-boundary timing issue already flagged in review ( |
Agreed, done! |
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Re-reviewed current 16aca33. The non-finite policy is explicit now, oversized finite limits avoid the integer-conversion overflow, and the loop uses elapsed >= time_limit, which closes the exact-boundary/zero-limit case I had left open. The added corner-case coverage also pins NaN, negative infinity, positive infinity and oversized finite inputs. No remaining blocker from my earlier timing findings.
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When in_time_limit is infinity, multiplying by 1000 and casting to an integer causes undefined behavior / integer overflow (trapping under UBSan). Guard against infinity and use std::chrono::milliseconds::max().
Full disclosure: done with the help of Gemini AI.
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