33 Concurrency support library [thread]

33.4 Threads [thread.threads]

33.4.3 Class thread [thread.thread.class]

33.4.3.2 Class thread​::​id [thread.thread.id]

namespace std { class thread::id { public: id() noexcept; }; bool operator==(thread::id x, thread::id y) noexcept; strong_ordering operator<=>(thread::id x, thread::id y) noexcept; template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out, thread::id id); // hash support template<class T> struct hash; template<> struct hash<thread::id>; }
An object of type thread​::​id provides a unique identifier for each thread of execution and a single distinct value for all thread objects that do not represent a thread of execution ([thread.thread.class]).
Each thread of execution has an associated thread​::​id object that is not equal to the thread​::​id object of any other thread of execution and that is not equal to the thread​::​id object of any thread object that does not represent threads of execution.
thread​::​id is a trivially copyable class ([class.prop]).
The library may reuse the value of a thread​::​id of a terminated thread that can no longer be joined.
[Note 1:
Relational operators allow thread​::​id objects to be used as keys in associative containers.
— end note]
id() noexcept;
Postconditions: The constructed object does not represent a thread of execution.
bool operator==(thread::id x, thread::id y) noexcept;
Returns: true only if x and y represent the same thread of execution or neither x nor y represents a thread of execution.
strong_ordering operator<=>(thread::id x, thread::id y) noexcept;
Let be an unspecified total ordering over thread​::​id as described in [alg.sorting].
Returns: strong_­ordering​::​less if is true.
Otherwise, strong_­ordering​::​greater if is true.
Otherwise, strong_­ordering​::​equal.
template<class charT, class traits> basic_ostream<charT, traits>& operator<< (basic_ostream<charT, traits>& out, thread::id id);
Effects: Inserts an unspecified text representation of id into out.
For two objects of type thread​::​id x and y, if x == y the thread​::​id objects have the same text representation and if x != y the thread​::​id objects have distinct text representations.
Returns: out.
template<> struct hash<thread::id>;
The specialization is enabled ([unord.hash]).