std::experimental::latch::count_down
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                    < cpp | experimental | latch
                    
                                                            
                    | void count_down( ptrdiff_t n = 1); | (1) | (concurrency TS) | 
Atomically decrements the internal counter by n without blocking the caller.
If n is greater than the value of the internal counter or is negative, the behavior is undefined.
This operation synchronizes with all calls that block on this latch and all is_ready calls on this latch that returns true.
Parameters
| n | - | the value by which the internal counter is decreased | 
Return value
(none)
Exceptions
Throws nothing.