| Defined in header <shared_mutex> | ||
|---|---|---|
class shared_mutex; | (since C++17) |
The shared_mutex class is a synchronization primitive that can be used to protect shared data from being simultaneously accessed by multiple threads. In contrast to other mutex types which facilitate exclusive access, a shared_mutex has two levels of access:
- shared - several threads can share ownership of the same mutex.
- exclusive - only one thread can own the mutex.
Shared mutexes are usually used in situations when multiple readers can access the same resource at the same time without causing data races, but only one writer can do so.
The shared_mutex class satisfies all requirements of SharedMutex and StandardLayoutType.
Member types
| Member type | Definition |
|---|---|
native_handle_type | implementation-defined |
Member functions
| constructs the mutex (public member function) | |
| (destructor)
| destroys the mutex (public member function) |
| operator= [deleted] | not copy-assignable (public member function) |
Exclusive locking | |
| locks the mutex, blocks if the mutex is not available (public member function) | |
| tries to lock the mutex, returns if the mutex is not available (public member function) | |
| unlocks the mutex (public member function) | |
Shared locking | |
| locks the mutex for shared ownership, blocks if the mutex is not available (public member function) | |
| tries to lock the mutex for shared ownership, returns if the mutex is not available (public member function) | |
| unlocks the mutex (shared ownership) (public member function) | |
Native handle | |
| returns the underlying implementation-defined thread handle (public member function) | |
A copy assignment operator for a class that holds resources that can handle multiple readers, but only one writer.
class R
{
mutable std::shared_mutex mut;
/* data */
public:
R& operator=(const R& other)
{
// requires exclusive ownership to write to *this
std::unique_lock<std::shared_mutex> lhs(mut, std::defer_lock);
// requires shared ownership to read from other
std::shared_lock<std::shared_mutex> rhs(other.mut, std::defer_lock);
std::lock(lhs, rhs);
/* assign data */
return *this;
}
}See also
| (C++14) | provides shared mutual exclusion facility (class) |
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