Defined in header <thread> | ||
|---|---|---|
class jthread; | (since C++20) |
The class jthread represents a single thread of execution. It has the same general behavior as std::thread, except that jthread automatically rejoins on destruction, and can be cancelled/stopped in certain situations.
Threads begin execution immediately upon construction of the associated thread object (pending any OS scheduling delays), starting at the top-level function provided as a constructor argument. The return value of the top-level function is ignored and if it terminates by throwing an exception, std::terminate is called. The top-level function may communicate its return value or an exception to the caller via std::promise or by modifying shared variables (which may require synchronization, see std::mutex and std::atomic).
Unlike std::thread, the jthread logically holds an internal private member of type std::stop_source, which maintains a shared stop-state. The jthread constructor accepts a function that takes a std::stop_token as its first argument, which will be passed in by the jthread from its internal std::stop_source. This allows the function to check if stop has been requested during its execution, and return if it has.
std::jthread objects may also be in the state that does not represent any thread (after default construction, move from, detach, or join), and a thread of execution may be not associated with any jthread objects (after detach).
No two std::jthread objects may represent the same thread of execution; std::jthread is not CopyConstructible or CopyAssignable, although it is MoveConstructible and MoveAssignable.
| Member type | Definition |
|---|---|
id | std::thread::id |
native_handle_type(not always present) | std::thread::native_handle_type |
constructs new jthread object (public member function) |
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| if the thread is joinable, then a stop is requested and the thread joins (public member function) |
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| moves the jthread object (public member function) |
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Observers |
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| checks whether the thread is joinable, i.e. potentially running in parallel context (public member function) |
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| returns the id of the thread (public member function) |
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| returns the underlying implementation-defined thread handle (public member function) |
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|
[static] | returns the number of concurrent threads supported by the implementation (public static member function) |
Operations |
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| waits for the thread to finish its execution (public member function) |
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| permits the thread to execute independently from the thread handle (public member function) |
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| swaps two jthread objects (public member function) |
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Stop token handling |
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| returns a stop_source object associated with the shared stop state of the thread (public member function) |
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| returns a stop_token associated with the shared stop state of the thread (public member function) |
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| requests execution stop via the shared stop state of the thread (public member function) |
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(C++20) | specializes the std::swap algorithm (function) |
| Feature-test macro | Value | Std | Comment |
|---|---|---|---|
__cpp_lib_jthread | 201911L | (C++20) | Stop token and joining thread |
|
(C++11) | manages a separate thread (class) |
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