32 Concurrency support library [thread]

32.4 Threads [thread.threads]

32.4.4 Class jthread [thread.jthread.class]

32.4.4.2 Constructors, move, and assignment [thread.jthread.cons]

jthread() noexcept;

Effects: Constructs a jthread object that does not represent a thread of execution.

Postconditions: get_id() == id() is true and ssource.stop_possible() is false.

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template<class... Args> explicit jthread(Args&&... args);

Constraints:

(3.1)
Args is not an empty pack, and
(3.2)
remove_cvref_t<Args...[0]> is not the same type as jthread.

Let i be the smallest value such that decay_t<Args...[i]> is not a thread attribute type, if such a value exists.

Then the following notation is used:

(4.1)
Let F be Args...[i].
(4.2)
Let f be args...[i].
(4.3)
Let Attrs be a pack of the types Args...[j] for each j such that $0 \leq j < i$ .
(4.4)
Let attrs be a pack of the expressions args...[j] for each j such that $0 \leq j < i$ .
(4.5)
Let FArgs be a pack of the types Args...[j] for each j such that $i < j < sizeof...(args)$ .
(4.6)
Let fargs be a pack of the expressions args...[j] for each j such that $i < j < sizeof...(args)$ .

Mandates: The value i exists, and the following are all true:

(5.1)
is_constructible_v<decay_t<F>, F>,
(5.2)
(is_constructible_v<decay_t<FArgs>, FArgs> && ...),
(5.3)
is_invocable_v<decay_t<F>, decay_t<FArgs>...> ||

is_invocable_v<decay_t<F>, stop_token, decay_t<FArgs>...>, and
(5.4)
no type is present more than once in the pack remove_cvref_t<Attrs>.

Effects: Initializes ssource.

The new thread of execution executes invoke(auto(std::forward<F>(f)), get_stop_token(), // for invoke, see [func.invoke] auto(std::forward<FArgs>(fargs))...) if that expression is well-formed, otherwise invoke(auto(std::forward<F>(f)), auto(std::forward<FArgs>(fargs))...) with the values produced by auto being materialized ([conv.rval]) in the constructing thread.

Any return value from this invocation is ignored.

[Note 1:

This implies that any exceptions not thrown from the invocation of the copy of f will be thrown in the constructing thread, not the new thread.

— end note]

If the invoke expression exits via an exception, terminate is called.

[Note 2:

The parameters attrs... can affect the behavior of the new thread ([thread.attributes]).

— end note]

Synchronization: The completion of the invocation of the constructor synchronizes with the beginning of the invocation of the copy of f.

Postconditions: get_id() != id() is true and ssource.stop_possible() is true and *this represents the newly started thread.

[Note 3:

The calling thread can make a stop request only once, because it cannot replace this stop token.

— end note]

Throws: system_error if unable to start the new thread.

Error conditions:

(10.1)
resource_unavailable_try_again — the system lacked the necessary resources to create another thread, or the system-imposed limit on the number of threads in a process would be exceeded.

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jthread(jthread&& x) noexcept;

Postconditions: x.get_id() == id() and get_id() returns the value of x.get_id() prior to the start of construction.

ssource has the value of x.ssource prior to the start of construction and x.ssource.stop_possible() is false.

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~jthread();

Effects: If joinable() is true, calls request_stop() and then join().

[Note 4:

Operations on *this are not synchronized.

— end note]

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jthread& operator=(jthread&& x) noexcept;

Effects: If &x == this is true, there are no effects.

Otherwise, if joinable() is true, calls request_stop() and then join(), then assigns the state of x to *this and sets x to a default constructed state.

Postconditions: get_id() returns the value of x.get_id() prior to the assignment.

ssource has the value of x.ssource prior to the assignment.

Returns: *this.