| 1 | /* |
| 2 | * Copyright (C) 2022 Jérémie Galarneau <jeremie.galarneau@efficios.com> |
| 3 | * |
| 4 | * SPDX-License-Identifier: LGPL-2.1-only |
| 5 | * |
| 6 | */ |
| 7 | |
| 8 | #ifndef LTTNG_LOCKED_REFERENCE_H |
| 9 | #define LTTNG_LOCKED_REFERENCE_H |
| 10 | |
| 11 | #define _LGPL_SOURCE |
| 12 | #include <mutex> |
| 13 | |
| 14 | namespace lttng { |
| 15 | |
| 16 | /* |
| 17 | * A locked reference is useful to return a reference to an object |
| 18 | * while ensuring that the caller uses it within a given locking context. |
| 19 | * |
| 20 | * For instance, a number of look-up APIs return an object and require the |
| 21 | * caller to hold the RCU reader lock for the duration of their use of the |
| 22 | * return value. |
| 23 | * |
| 24 | * Using a locked_reference, a function returning such an object can: |
| 25 | * - acquire the rcu read lock using a unique_read_lock, |
| 26 | * - perform its look-up |
| 27 | * - return a reference to which the unique_read_lock is transferred. |
| 28 | * |
| 29 | * Note that this locked reference can be used like a pointer |
| 30 | * (see operators `*` and `->`). However, note that it is a _reference_. |
| 31 | * Hence, _it can't be null_. |
| 32 | * |
| 33 | * Functions returning this type will most likely throw an exception |
| 34 | * when the look-up fails. |
| 35 | */ |
| 36 | template <class WrappedType, class UniqueLockType> |
| 37 | class locked_reference { |
| 38 | public: |
| 39 | locked_reference(WrappedType& value, UniqueLockType&& lock) : |
| 40 | _value(value), _lock(std::move(lock)) |
| 41 | { |
| 42 | } |
| 43 | |
| 44 | WrappedType& operator*() const |
| 45 | { |
| 46 | return _value; |
| 47 | } |
| 48 | |
| 49 | WrappedType *operator->() const |
| 50 | { |
| 51 | return &_value; |
| 52 | } |
| 53 | |
| 54 | private: |
| 55 | WrappedType& _value; |
| 56 | UniqueLockType _lock; |
| 57 | }; |
| 58 | |
| 59 | } /* namespace lttng */ |
| 60 | |
| 61 | #endif /* LTTNG_LOCKED_REFERENCE_H */ |