Case 110: concurrent_unordered_map API Drift¶

Field	Value
Verdict	🔴 BREAKING
Category	Breaking
Platforms	Linux, macOS, Windows
Flags	ABI break, API break
Detected `ChangeKind`s	`func_removed`
Source files	browse on GitHub

Category: ABI + source break / oneTBB regression suite | Verdict: 🔴 BREAKING

What breaks¶

A public member function (insert) loses one of its parameters between versions. The mangled symbol of the old overload disappears from the .so; the new overload has a different mangled name. Both the .so symbol table and any consumer source that called the old form change.

Why this is in the oneTBB regression suite¶

Mirrors several documented historical signature tightenings on tbb::concurrent_unordered_map (and friends) where helper / hint parameters were dropped or reordered between releases. These changes are doubly bad: they break source AND they break linking of consumers that were built against the old headers.

How abicheck catches it¶

The diff exposes:

FUNC_REMOVED: old mangled insert(int, size_t)
FUNC_ADDED: new mangled insert(int) (informational; helps the reporter identify a candidate replacement)

FUNC_REMOVED on a public symbol is unconditionally BREAKING — there is no new detector required to flag this case.

Code diff¶

v1	v2
`void insert(int key, std::size_t rehash_hint);`	`void insert(int key);`

How to fix (as a library maintainer)¶

Keep both overloads through a deprecation window: in release N–1, mark the hint-form overload [[deprecated]] and have it call into the hint-free implementation. In release N, remove it.
If the hint argument is genuinely dead, prefer making it a default argument first (std::size_t rehash_hint = 0) — that preserves the symbol name on platforms where the mangled signature includes the parameter, and only later remove it.

Real failure demo¶

# v1 header, v1 .so:
g++ -std=c++17 -I. app.cpp -L. -lmylib -o app   # compiles, links, runs

# v2 header, v2 .so: app.cpp's 2-arg insert is gone.
g++ -std=c++17 -I. app.cpp -L. -lmylib -o app
# → error: no matching function for call to 'insert(int, int)'

References¶

oneTBB 2021 migration guide: concurrent_unordered_map API changes.