class LockedPtrBase;
template <class LockedType, class LockPolicy>
class LockedPtr;
+template <class LockedType, class LockPolicy = LockPolicyExclusive>
+class LockedGuardPtr;
/**
* SynchronizedBase is a helper parent class for Synchronized<T>.
const std::chrono::duration<Rep, Period>& timeout) const {
return ConstLockedPtr(static_cast<const Subclass*>(this), timeout);
}
+
+ /*
+ * Note: C++ 17 adds guaranteed copy elision. (http://wg21.link/P0135)
+ * Once compilers support this, it would be nice to add wguard() and rguard()
+ * methods that return LockedGuardPtr objects.
+ */
+
+ /**
+ * Invoke a function while holding the lock exclusively.
+ *
+ * A reference to the datum will be passed into the function as its only
+ * argument.
+ *
+ * This can be used with a lambda argument for easily defining small critical
+ * sections in the code. For example:
+ *
+ * auto value = obj.withWLock([](auto& data) {
+ * data.doStuff();
+ * return data.getValue();
+ * });
+ */
+ template <class Function>
+ auto withWLock(Function&& function) {
+ LockedGuardPtr<Subclass, LockPolicyExclusive> guardPtr(
+ static_cast<Subclass*>(this));
+ return function(*guardPtr);
+ }
+ template <class Function>
+ auto withWLock(Function&& function) const {
+ LockedGuardPtr<const Subclass, LockPolicyExclusive> guardPtr(
+ static_cast<const Subclass*>(this));
+ return function(*guardPtr);
+ }
+
+ /**
+ * Invoke a function while holding the lock exclusively.
+ *
+ * This is similar to withWLock(), but the function will be passed a
+ * LockedPtr rather than a reference to the data itself.
+ *
+ * This allows scopedUnlock() to be called on the LockedPtr argument if
+ * desired.
+ */
+ template <class Function>
+ auto withWLockPtr(Function&& function) {
+ return function(wlock());
+ }
+ template <class Function>
+ auto withWLockPtr(Function&& function) const {
+ return function(wlock());
+ }
+
+ /**
+ * Invoke a function while holding an the lock in shared mode.
+ *
+ * A const reference to the datum will be passed into the function as its
+ * only argument.
+ */
+ template <class Function>
+ auto withRLock(Function&& function) const {
+ LockedGuardPtr<const Subclass, LockPolicyShared> guardPtr(
+ static_cast<const Subclass*>(this));
+ return function(*guardPtr);
+ }
+
+ template <class Function>
+ auto withRLockPtr(Function&& function) const {
+ return function(rlock());
+ }
};
/**
ConstLockedPtr lock(const std::chrono::duration<Rep, Period>& timeout) const {
return ConstLockedPtr(static_cast<const Subclass*>(this), timeout);
}
+
+ /*
+ * Note: C++ 17 adds guaranteed copy elision. (http://wg21.link/P0135)
+ * Once compilers support this, it would be nice to add guard() methods that
+ * return LockedGuardPtr objects.
+ */
+
+ /**
+ * Invoke a function while holding the lock.
+ *
+ * A reference to the datum will be passed into the function as its only
+ * argument.
+ *
+ * This can be used with a lambda argument for easily defining small critical
+ * sections in the code. For example:
+ *
+ * auto value = obj.withLock([](auto& data) {
+ * data.doStuff();
+ * return data.getValue();
+ * });
+ */
+ template <class Function>
+ auto withLock(Function&& function) {
+ LockedGuardPtr<Subclass, LockPolicyExclusive> guardPtr(
+ static_cast<Subclass*>(this));
+ return function(*guardPtr);
+ }
+ template <class Function>
+ auto withLock(Function&& function) const {
+ LockedGuardPtr<const Subclass, LockPolicyExclusive> guardPtr(
+ static_cast<const Subclass*>(this));
+ return function(*guardPtr);
+ }
+
+ /**
+ * Invoke a function while holding the lock exclusively.
+ *
+ * This is similar to withWLock(), but the function will be passed a
+ * LockedPtr rather than a reference to the data itself.
+ *
+ * This allows scopedUnlock() and getUniqueLock() to be called on the
+ * LockedPtr argument.
+ */
+ template <class Function>
+ auto withLockPtr(Function&& function) {
+ return function(lock());
+ }
+ template <class Function>
+ auto withLockPtr(Function&& function) const {
+ return function(lock());
+ }
};
/**
friend class folly::LockedPtrBase;
template <class LockedType, class LockPolicy>
friend class folly::LockedPtr;
+ template <class LockedType, class LockPolicy>
+ friend class folly::LockedGuardPtr;
/**
* Helper constructors to enable Synchronized for
template <class SynchronizedType, class LockPolicy>
class ScopedUnlocker;
+namespace detail {
+/*
+ * A helper alias that resolves to "const T" if the template parameter
+ * is a const Synchronized<T>, or "T" if the parameter is not const.
+ */
+template <class SynchronizedType>
+using SynchronizedDataType = typename std::conditional<
+ std::is_const<SynchronizedType>::value,
+ typename SynchronizedType::DataType const,
+ typename SynchronizedType::DataType>::type;
+/*
+ * A helper alias that resolves to a ConstLockedPtr if the template parameter
+ * is a const Synchronized<T>, or a LockedPtr if the parameter is not const.
+ */
+template <class SynchronizedType>
+using LockedPtrType = typename std::conditional<
+ std::is_const<SynchronizedType>::value,
+ typename SynchronizedType::ConstLockedPtr,
+ typename SynchronizedType::LockedPtr>::type;
+} // detail
+
/**
* A helper base class for implementing LockedPtr.
*
LockPolicy>;
using UnlockerData = typename Base::UnlockerData;
// CDataType is the DataType with the appropriate const-qualification
- using CDataType = typename std::conditional<
- std::is_const<SynchronizedType>::value,
- typename SynchronizedType::DataType const,
- typename SynchronizedType::DataType>::type;
+ using CDataType = detail::SynchronizedDataType<SynchronizedType>;
public:
using DataType = typename SynchronizedType::DataType;
}
};
-namespace detail {
-/*
- * A helper alias to select a ConstLockedPtr if the template parameter is a
- * const Synchronized<T>, or a LockedPtr if the parameter is not const.
+/**
+ * LockedGuardPtr is a simplified version of LockedPtr.
+ *
+ * It is non-movable, and supports fewer features than LockedPtr. However, it
+ * is ever-so-slightly more performant than LockedPtr. (The destructor can
+ * unconditionally release the lock, without requiring a conditional branch.)
+ *
+ * The relationship between LockedGuardPtr and LockedPtr is similar to that
+ * between std::lock_guard and std::unique_lock.
*/
-template <class SynchronizedType>
-using LockedPtrType = typename std::conditional<
- std::is_const<SynchronizedType>::value,
- typename SynchronizedType::ConstLockedPtr,
- typename SynchronizedType::LockedPtr>::type;
-} // detail
+template <class SynchronizedType, class LockPolicy>
+class LockedGuardPtr {
+ private:
+ // CDataType is the DataType with the appropriate const-qualification
+ using CDataType = detail::SynchronizedDataType<SynchronizedType>;
+
+ public:
+ using DataType = typename SynchronizedType::DataType;
+ using MutexType = typename SynchronizedType::MutexType;
+ using Synchronized = typename std::remove_const<SynchronizedType>::type;
+
+ LockedGuardPtr() = delete;
+
+ /**
+ * Takes a Synchronized<T> and locks it.
+ */
+ explicit LockedGuardPtr(SynchronizedType* parent) : parent_(parent) {
+ LockPolicy::lock(parent_->mutex_);
+ }
+
+ /**
+ * Destructor releases.
+ */
+ ~LockedGuardPtr() {
+ LockPolicy::unlock(parent_->mutex_);
+ }
+
+ /**
+ * Access the locked data.
+ */
+ CDataType* operator->() const {
+ return &parent_->datum_;
+ }
+
+ /**
+ * Access the locked data.
+ */
+ CDataType& operator*() const {
+ return parent_->datum_;
+ }
+
+ private:
+ // This is the entire state of LockedGuardPtr.
+ SynchronizedType* const parent_{nullptr};
+};
/**
* Acquire locks for multiple Synchronized<T> objects, in a deadlock-safe
projects / folly.git / blobdiff