32 Thread support library [thread]

32.4 Threads [thread.threads]

32.4.2 Class thread [thread.thread.class]

32.4.2.1 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>;
}
1
#
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.
2
#
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.
3
#
[Note
:
Relational operators allow thread​::​id objects to be used as keys in associative containers.
— end note
]
🔗
id() noexcept;
4
#
Postconditions: The constructed object does not represent a thread of execution.
🔗
bool operator==(thread::id x, thread::id y) noexcept;
5
#
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;
6
#
Let be an unspecified total ordering over thread​::​id as described in [alg.sorting].
7
#
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);
8
#
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.
9
#
Returns: out.
🔗
template<> struct hash<thread::id>;
10
#
The specialization is enabled ([unord.hash]).