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Seastar
High performance C++ framework for concurrent servers
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Smart pointer wrapper which makes it safe to move across CPUs.
foreign_ptr<> is a smart pointer wrapper which, unlike shared_ptr and lw_shared_ptr, is safe to move to a different core.
As seastar avoids locking, any but the most trivial objects must be destroyed on the same core they were created on, so that, for example, their destructors can unlink references to the object from various containers. In addition, for performance reasons, the shared pointer types do not use atomic operations to manage their reference counts. As a result they cannot be used on multiple cores in parallel.
foreign_ptr<> provides a solution to that problem. foreign_ptr<> wraps any pointer type – raw pointer, shared_ptr<>, or similar, and remembers on what core this happened. When the foreign_ptr<> object is destroyed, it sends a message to the original core so that the wrapped object can be safely destroyed.
foreign_ptr<> is a move-only object; it cannot be copied.
#include <seastar/core/sharded.hh>
Public Types | |
| using | element_type = typename std::pointer_traits< PtrType >::element_type |
| using | pointer = element_type * |
Public Member Functions | |
| foreign_ptr () | |
Constructs a null foreign_ptr<>. | |
| foreign_ptr (std::nullptr_t) | |
Constructs a null foreign_ptr<>. | |
| foreign_ptr (PtrType value) | |
| Wraps a pointer object and remembers the current core. | |
| foreign_ptr (const foreign_ptr &)=delete | |
| foreign_ptr (foreign_ptr &&other)=default | |
Moves a foreign_ptr<> to another object. | |
| ~foreign_ptr () | |
| Destroys the wrapped object on its original cpu. | |
| future< foreign_ptr > | copy () const |
| Creates a copy of this foreign ptr. Only works if the stored ptr is copyable. | |
| element_type & | operator* () const |
| Accesses the wrapped object. | |
| element_type * | operator-> () const |
| Accesses the wrapped object. | |
| pointer | get () const |
| Access the raw pointer to the wrapped object. | |
| unsigned | get_owner_shard () const |
| operator bool () const | |
| Checks whether the wrapped pointer is non-null. | |
| foreign_ptr & | operator= (foreign_ptr &&other)=default |
Move-assigns a foreign_ptr<>. | |
| PtrType | release () |
| void | reset (PtrType new_ptr) |
| void | reset (std::nullptr_t=nullptr) |
Related Functions | |
(Note that these are not member functions.) | |
| template<typename T > | |
| foreign_ptr< T > | make_foreign (T ptr) |
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inline |
Return the owner-shard of this pointer.
The owner shard of the pointer can change as a result of move-assigment or a call to reset().
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inline |
Releases the owned pointer
Warning: the caller is now responsible for destroying the pointer on its owner shard. This method is best called on the owner shard to avoid accidents.
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inline |
Replace the managed pointer with new_ptr.
The previous managed pointer is destroyed on its owner shard.
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inline |
Replace the managed pointer with a null value.
The previous managed pointer is destroyed on its owner shard.
1.8.14