| [[nodiscard]] arrival_token arrive( std::ptrdiff_t n = 1 ); | (since C++20) | 
Constructs an arrival_token object associated with the phase synchronization point for the current phase. Then, decrements the expected count by n.
This function executes atomically. The call to this function strongly happens-before the start of the phase completion step for the current phase.
The behavior is undefined if n is less than or equal to 0 or greater than the expected count for the current barrier phase.
| n | - | the value by which the expected count is decreased | 
The constructed arrival_token object.
Throws std::system_error with an error code allowed for mutex types on error.
This function can cause the completion step for the current phase to start.
| blocks at the phase synchronization point until its phase completion step is run (public member function) | 
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