[thread.jthread.cons]

# 32 Concurrency support library [[thread]](./#thread)

## 32.4 Threads [[thread.threads]](thread.threads#thread.jthread.cons)

### 32.4.4 Class jthread [[thread.jthread.class]](thread.jthread.class#thread.jthread.cons)

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

[🔗](#lib:jthread,constructor)

`jthread() noexcept;
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L1984)

*Effects*: Constructs a jthread object that does not represent
a thread of execution[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L1989)

*Postconditions*: get_id() == id() is true and ssource.stop_possible() is false[.](#2.sentence-1)

[🔗](#lib:jthread,constructor_)

`template<class F, class... Args> explicit jthread(F&& f, Args&&... args);
`

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2001)

*Constraints*: remove_cvref_t<F> is not the same type as jthread[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2005)

*Mandates*: The following are all true:

- [(4.1)](#4.1)

is_constructible_v<decay_t<F>, F>,

- [(4.2)](#4.2)

(is_constructible_v<decay_t<Args>, Args> && ...), and

- [(4.3)](#4.3)

is_invocable_v<decay_t<F>, decay_t<Args>...> ||   
   is_invocable_v<decay_t<F>, stop_token, decay_t<Args>...>[.](#4.3.sentence-2)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2014)

*Effects*: Initializes ssource[.](#5.sentence-1)

The new thread of execution executesinvoke(auto(std::forward<F>(f)), get_stop_token(), // for invoke, see [[func.invoke]](func.invoke "22.10.5 invoke functions")auto(std::forward<Args>(args))...) if that expression is well-formed,
otherwiseinvoke(auto(std::forward<F>(f)), auto(std::forward<Args>(args))...) with the values produced by auto being materialized ([[conv.rval]](conv.rval "7.3.5 Temporary materialization conversion")) in the constructing thread[.](#5.sentence-2)

Any return value from this invocation is ignored[.](#5.sentence-3)

[*Note [1](#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[.](#5.sentence-4)

— *end note*]

If the invoke expression exits via an exception,terminate is called[.](#5.sentence-5)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2037)

*Synchronization*: The completion of the invocation of the constructor
synchronizes with the beginning of the invocation of the copy of f[.](#6.sentence-1)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2042)

*Postconditions*: get_id() != id() is true and ssource.stop_possible() is true and *this represents the newly started thread[.](#7.sentence-1)

[*Note [2](#note-2)*:

The calling thread can make a stop request only once,
because it cannot replace this stop token[.](#7.sentence-2)

— *end note*]

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2052)

*Throws*: system_error if unable to start the new thread[.](#8.sentence-1)

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2056)

*Error conditions*: 

- [(9.1)](#9.1)

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[.](#9.sentence-1)

[🔗](#lib:jthread,constructor__)

`jthread(jthread&& x) noexcept;
`

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2072)

*Postconditions*: x.get_id() == id() and get_id() returns the value of x.get_id() prior to the start of construction[.](#10.sentence-1)

ssource has the value of x.ssource prior to the start of construction
and x.ssource.stop_possible() is false[.](#10.sentence-2)

[🔗](#lib:jthread,destructor)

`~jthread();
`

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2088)

*Effects*: If joinable() is true,
calls request_stop() and then join()[.](#11.sentence-1)

[*Note [3](#note-3)*:

Operations on *this are not synchronized[.](#11.sentence-2)

— *end note*]

[🔗](#lib:operator=,jthread)

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

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2103)

*Effects*: If &x == this is true, there are no effects[.](#12.sentence-1)

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[.](#12.sentence-2)

[13](#13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2111)

*Postconditions*: get_id() returns the value of x.get_id() prior to the assignment[.](#13.sentence-1)

ssource has the value of x.ssource prior to the assignment[.](#13.sentence-2)

[14](#14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L2118)

*Returns*: *this[.](#14.sentence-1)