[DRAFT] [starvation] report deadlocks on global and C struct locks in per-file mode - #2189
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Starvation only knows a fixed list of scoped guards. With any other, eg android::Mutex::Autolock,
the lock taken in the guard's constructor was read as a lock of the caller, so all guards
collapsed into one lock: inversions were missed and self deadlocks reported.
```cpp
#include <mutex>
struct Guard {
explicit Guard(std::mutex& m) : m_(m) { m_.lock(); }
~Guard() { m_.unlock(); }
std::mutex& m_;
};
class C {
std::mutex mu1_, mu2_;
public:
void thread1() { Guard a(mu1_); Guard b(mu2_); } // false positive: self deadlock
void thread2() { Guard b(mu2_); Guard a(mu1_); } // same; Infer missed: deadlock with thread1
};
```
Callee locks are now substituted for every argument and at every call depth, and dropped when the
caller cannot express them. A local object whose constructor (or by-value return, if its
destructor releases a lock) leaves one lock held becomes a guard of that lock. android::Mutex and
Autolock are modelled, tryLock and timedLock as trylocks returning zero on success; RacerD now
also reports races in classes using them.
Trade-off: callee locks and unlocks the caller cannot express are dropped, missing deadlocks
through objects returned by calls (eg Java singletons) and keeping locks released through a local
guard struct.
## Test plan
New tests in c/starvation/lock_wrappers.c, cpp/starvation (android_mutex.cpp, custom_guards.cpp,
substitution.cpp), cpp/racerd/android_mutex.cpp and java/starvation/Parameters.java, with FP_/FN_
tests for the limitations. The codetoanalyze tests pass.
…e mode
Per-file mode searches for the other side of a lock-order inversion only among the methods of the
lock's root class, missing inversions on global, static and C struct locks. Deduplication also
dropped both sides of a deadlock locked at the same line of a helper, and global `std::mutex` locks
counted as recursive.
```cpp
std::mutex m1, m2;
void take(std::mutex& m) { std::lock_guard<std::mutex> l(m); }
void f() {
std::lock_guard<std::mutex> l(m1);
take(m2);
}
void g() {
std::lock_guard<std::mutex> l(m2);
take(m1); // Infer missed: deadlock with f()
}
```
Starvation now also searches the current file's C/C++/ObjC procedures, indexed by held lock. Under
deduplication, a side reports a deadlock the other side cannot find, and location ties are broken
by the locks, also fixing Java and whole-program mode.
Limitations: cross-file inversions on global and C struct locks still need
`--starvation-whole-program`; global initializers are assumed to run before threads start, so only
their self deadlocks are reported.
## Test plan
New `c/starvation-per-file` and `cpp/starvation-dedup` test directories, and new tests in
`cpp/starvation/globals.cpp` (including initializers) and `java/starvation-dedup/Interproc.java`.
The codetoanalyze tests pass.
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Stack: #2182 → #2189 (review only the top commit; lands after #2182)
Per-file mode searches for the other side of a lock-order inversion only among the methods of the
lock's root class, missing inversions on global, static and C struct locks. Deduplication also
dropped both sides of a deadlock locked at the same line of a helper, and global
std::mutexlockscounted as recursive.
Starvation now also searches the current file's C/C++/ObjC procedures, indexed by held lock. Under
deduplication, a side reports a deadlock the other side cannot find, and location ties are broken
by the locks, also fixing Java and whole-program mode.
Limitations: cross-file inversions on global and C struct locks still need
--starvation-whole-program; global initializers are assumed to run before threads start, so onlytheir self deadlocks are reported.
Test plan
New
c/starvation-per-fileandcpp/starvation-deduptest directories, and new tests incpp/starvation/globals.cpp(including initializers) andjava/starvation-dedup/Interproc.java.The codetoanalyze tests pass.