33 Thread support library [thread]

33.3 Threads [thread.threads]

33.3.2 Class thread [thread.thread.class]

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

namespace std {
  class thread::id {
  public:
    id() noexcept;
  };

  bool operator==(thread::id x, thread::id y) noexcept;
  bool operator!=(thread::id x, thread::id y) noexcept;
  bool operator<(thread::id x, thread::id y) noexcept;
  bool operator<=(thread::id x, thread::id y) noexcept;
  bool operator>(thread::id x, thread::id y) noexcept;
  bool 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 shall be a trivially copyable class.
The library may reuse the value of a thread​::​id of a terminated thread that can no longer be joined.
[Note
:
Relational operators allow thread​::​id objects to be used as keys in associative containers.
end note
]
id() noexcept;
Effects: Constructs an object of type id.
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.
bool operator!=(thread::id x, thread::id y) noexcept;
Returns: !(x == y)
bool operator<(thread::id x, thread::id y) noexcept;
Returns: A value such that operator< is a total ordering as described in [alg.sorting].
bool operator<=(thread::id x, thread::id y) noexcept;
Returns: !(y < x).
bool operator>(thread::id x, thread::id y) noexcept;
Returns: y < x.
bool operator>=(thread::id x, thread::id y) noexcept;
Returns: !(x < y).
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 shall have the same text representation and if x != y the thread​::​id objects shall have distinct text representations.
Returns: out.
template <> struct hash<thread::id>;
The specialization is enabled ([unord.hash]).