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Merged
StephanTLavavej merged 3 commits into from
Dec 3, 2020
Merged

Allow discarding unique_lock and shared_lock #1514

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e414a85
Allow discarding unique_lock
CaseyCarter Dec 3, 2020
08c12ef
Tag constructors instead; add smoke test
CaseyCarter Dec 3, 2020
709f6f4
Mark shared_lock's move ctor as _NODISCARD_CTOR.
StephanTLavavej Dec 3, 2020
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17 changes: 9 additions & 8 deletions stl/inc/mutex
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Original file line number Diff line number Diff line change
Expand Up @@ -125,41 +125,42 @@ _INLINE_VAR constexpr try_to_lock_t try_to_lock{};

// CLASS TEMPLATE unique_lock
template <class _Mutex>
class _NODISCARD unique_lock { // whizzy class with destructor that unlocks mutex
class unique_lock { // whizzy class with destructor that unlocks mutex
public:
using mutex_type = _Mutex;

// CONSTRUCT, ASSIGN, AND DESTROY
unique_lock() noexcept : _Pmtx(nullptr), _Owns(false) {}

explicit unique_lock(_Mutex& _Mtx) : _Pmtx(_STD addressof(_Mtx)), _Owns(false) { // construct and lock
_NODISCARD_CTOR explicit unique_lock(_Mutex& _Mtx)
: _Pmtx(_STD addressof(_Mtx)), _Owns(false) { // construct and lock
_Pmtx->lock();
_Owns = true;
}

unique_lock(_Mutex& _Mtx, adopt_lock_t)
_NODISCARD_CTOR unique_lock(_Mutex& _Mtx, adopt_lock_t)
: _Pmtx(_STD addressof(_Mtx)), _Owns(true) {} // construct and assume already locked

unique_lock(_Mutex& _Mtx, defer_lock_t) noexcept
: _Pmtx(_STD addressof(_Mtx)), _Owns(false) {} // construct but don't lock

unique_lock(_Mutex& _Mtx, try_to_lock_t)
_NODISCARD_CTOR unique_lock(_Mutex& _Mtx, try_to_lock_t)
: _Pmtx(_STD addressof(_Mtx)), _Owns(_Pmtx->try_lock()) {} // construct and try to lock

template <class _Rep, class _Period>
unique_lock(_Mutex& _Mtx, const chrono::duration<_Rep, _Period>& _Rel_time)
_NODISCARD_CTOR unique_lock(_Mutex& _Mtx, const chrono::duration<_Rep, _Period>& _Rel_time)
: _Pmtx(_STD addressof(_Mtx)), _Owns(_Pmtx->try_lock_for(_Rel_time)) {} // construct and lock with timeout

template <class _Clock, class _Duration>
unique_lock(_Mutex& _Mtx, const chrono::time_point<_Clock, _Duration>& _Abs_time)
_NODISCARD_CTOR unique_lock(_Mutex& _Mtx, const chrono::time_point<_Clock, _Duration>& _Abs_time)
: _Pmtx(_STD addressof(_Mtx)), _Owns(_Pmtx->try_lock_until(_Abs_time)) {} // construct and lock with timeout

unique_lock(_Mutex& _Mtx, const xtime* _Abs_time)
_NODISCARD_CTOR unique_lock(_Mutex& _Mtx, const xtime* _Abs_time)
: _Pmtx(_STD addressof(_Mtx)), _Owns(false) { // try to lock until _Abs_time
_Owns = _Pmtx->try_lock_until(_Abs_time);
}

unique_lock(unique_lock&& _Other) noexcept : _Pmtx(_Other._Pmtx), _Owns(_Other._Owns) {
_NODISCARD_CTOR unique_lock(unique_lock&& _Other) noexcept : _Pmtx(_Other._Pmtx), _Owns(_Other._Owns) {
_Other._Pmtx = nullptr;
_Other._Owns = false;
}
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14 changes: 7 additions & 7 deletions stl/inc/shared_mutex
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Expand Up @@ -227,34 +227,34 @@ private:

// CLASS TEMPLATE shared_lock
template <class _Mutex>
class _NODISCARD shared_lock { // shareable lock
class shared_lock { // shareable lock
public:
using mutex_type = _Mutex;

shared_lock() noexcept : _Pmtx(nullptr), _Owns(false) {}

explicit shared_lock(mutex_type& _Mtx)
_NODISCARD_CTOR explicit shared_lock(mutex_type& _Mtx)
: _Pmtx(_STD addressof(_Mtx)), _Owns(true) { // construct with mutex and lock shared
_Mtx.lock_shared();
}

shared_lock(mutex_type& _Mtx, defer_lock_t) noexcept
: _Pmtx(_STD addressof(_Mtx)), _Owns(false) {} // construct with unlocked mutex

shared_lock(mutex_type& _Mtx, try_to_lock_t)
_NODISCARD_CTOR shared_lock(mutex_type& _Mtx, try_to_lock_t)
: _Pmtx(_STD addressof(_Mtx)), _Owns(_Mtx.try_lock_shared()) {} // construct with mutex and try to lock shared

shared_lock(mutex_type& _Mtx, adopt_lock_t)
_NODISCARD_CTOR shared_lock(mutex_type& _Mtx, adopt_lock_t)
: _Pmtx(_STD addressof(_Mtx)), _Owns(true) {} // construct with mutex and adopt ownership

template <class _Rep, class _Period>
shared_lock(mutex_type& _Mtx, const chrono::duration<_Rep, _Period>& _Rel_time)
_NODISCARD_CTOR shared_lock(mutex_type& _Mtx, const chrono::duration<_Rep, _Period>& _Rel_time)
: _Pmtx(_STD addressof(_Mtx)), _Owns(_Mtx.try_lock_shared_for(_Rel_time)) {
// construct with mutex and try to lock for relative time
}

template <class _Clock, class _Duration>
shared_lock(mutex_type& _Mtx, const chrono::time_point<_Clock, _Duration>& _Abs_time)
_NODISCARD_CTOR shared_lock(mutex_type& _Mtx, const chrono::time_point<_Clock, _Duration>& _Abs_time)
: _Pmtx(_STD addressof(_Mtx)), _Owns(_Mtx.try_lock_shared_until(_Abs_time)) {
// construct with mutex and try to lock until absolute time
}
Expand All @@ -265,7 +265,7 @@ public:
}
}

shared_lock(shared_lock&& _Other) noexcept : _Pmtx(_Other._Pmtx), _Owns(_Other._Owns) {
_NODISCARD_CTOR shared_lock(shared_lock&& _Other) noexcept : _Pmtx(_Other._Pmtx), _Owns(_Other._Owns) {
_Other._Pmtx = nullptr;
_Other._Owns = false;
}
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17 changes: 17 additions & 0 deletions tests/std/tests/VSO_0226079_mutex/test.cpp
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Expand Up @@ -496,6 +496,21 @@ void test_nonmember_try_lock() {
rtOt.join();
}

// Also test VSO-1253916, in which RWC like the following broke when we annotated unique_lock with [[nodiscard]].
unique_lock<shared_mutex> do_locked_things(unique_lock<shared_mutex> lck) {
return lck;
}

shared_lock<shared_mutex> do_shared_locked_things(shared_lock<shared_mutex> lck) {
return lck;
}

void test_vso_1253916() {
shared_mutex mtx;
do_locked_things(unique_lock<shared_mutex>{mtx});
do_shared_locked_things(shared_lock<shared_mutex>{mtx});
}

int main() {
{
mutex_test_fixture<mutex> fixture;
Expand Down Expand Up @@ -537,4 +552,6 @@ int main() {

test_nonmember_lock();
test_nonmember_try_lock();

test_vso_1253916();
}