Clang thread safety annotation and shared capabilities - multithreading

Question

The following code is generating one warning when I use clang thread annotations. I am trying to wrap boost::shared_mutex and boost::shared_lock. How can I express that this lock is a shared lock using the thread annotations?
source code:
#include <mutex>
#include "boost/thread/shared_mutex.hpp"
class __attribute__((shared_capability("mutex"))) BoostSharedMutex {
public:
boost::shared_mutex &getNativeHandle() { return m_mutex; }
private:
mutable boost::shared_mutex m_mutex;
};
class __attribute__((scoped_lockable)) MutexSharedLock {
public:
explicit MutexSharedLock(BoostSharedMutex &mutex) __attribute__((acquire_shared_capability(mutex)))
: m_lock(mutex.getNativeHandle()) {}
~MutexSharedLock() __attribute__((release_shared_capability())) = default;
private:
boost::shared_lock<boost::shared_mutex> m_lock;
};
int main() {
BoostSharedMutex mutex;
MutexSharedLock lock(mutex);
}
clang output:
clang++-3.6 --std=c++11 -Wall -Wthread-safety /tmp/foo.cpp -lboost_system
/tmp/foo.cpp:25:5: warning: releasing mutex 'lock' using shared access, expected exclusive access [-Wthread-safety-analysis]
}
^
1 warning generated.
EDIT: this compiles but seems wrong. Is it a problem on my side?
#include <mutex>
#include "boost/thread/shared_mutex.hpp"
class __attribute__((shared_capability("mutex"))) BoostSharedMutex {
public:
boost::shared_mutex &getNativeHandle() { return m_mutex; }
private:
mutable boost::shared_mutex m_mutex;
};
class __attribute__((scoped_lockable)) MutexSharedLock {
public:
explicit MutexSharedLock(BoostSharedMutex &mutex) __attribute__((acquire_capability(mutex))) // changed from acquired_shared_capability
: m_lock(mutex.getNativeHandle()) {}
~MutexSharedLock() __attribute__((release_capability())) = default; // changed from release_shared_capability
private:
boost::shared_lock<boost::shared_mutex> m_lock;
};
BoostSharedMutex mutex;
int locked_variable __attribute__((guarded_by(mutex)));
int main() {
MutexSharedLock lock(mutex);
std::cout << locked_variable << std::endl; // ok, guarded variable is only read
locked_variable = 42; // no warning while writing in the guarded variable while only holding a non-exclusive lock?
}

Answer 1

After trying several combinations, this seems to work:
#include <mutex>
#include "boost/thread/shared_mutex.hpp"
class __attribute__((capability("mutex"))) BoostSharedMutex {
public:
boost::shared_mutex &getNativeHandle() { return m_mutex; }
private:
mutable boost::shared_mutex m_mutex;
};
class __attribute__((scoped_lockable)) MutexSharedLock {
public:
explicit MutexSharedLock(BoostSharedMutex &mutex) __attribute__((acquire_shared_capability(mutex)))
: m_lock(mutex.getNativeHandle()) {}
~MutexSharedLock() __attribute__((release_capability())) = default;
private:
boost::shared_lock<boost::shared_mutex> m_lock;
};
class __attribute__((scoped_lockable)) MutexLock {
public:
explicit MutexLock(BoostSharedMutex &mutex) __attribute__((acquire_capability(mutex)))
: m_lock(mutex.getNativeHandle()) {}
~MutexLock() __attribute__((release_capability())) = default;
private:
std::unique_lock<boost::shared_mutex> m_lock;
};
BoostSharedMutex mutex;
int locked_variable __attribute__((guarded_by(mutex)));
int main() {
{
MutexSharedLock lock(mutex);
std::cout << locked_variable << std::endl;
// locked_variable = 42; -- triger a error as expected
}
{
MutexLock lock(mutex);
std::cout << locked_variable << std::endl;
locked_variable = 42;
}
}
I would be curious to hear why the MutexSharedLock should use acquire_shared_capability but release with release_capability ...
(I will let the question open in case anyone can confirm the code is correct now)

Answer 2

Just use unlock_function instead of release_shared_capability.
Same true also for try_acquire_capability/try_acquire_shared_capability - they just don't work, but previous exclusive_trylock_function/shared_trylock_function works well.
M.b. it is bug in clang.