B is a type passed to Benchmark functions to manage benchmark timing and to specify the number of iterations to run.

A benchmark ends when its Benchmark function returns or calls any of the methods FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. Those methods must be called only from the goroutine running the Benchmark function. The other reporting methods, such as the variations of Log and Error, may be called simultaneously from multiple goroutines.

Like in tests, benchmark logs are accumulated during execution and dumped to standard error when done. Unlike in tests, benchmark logs are always printed, so as not to hide output whose existence may be affecting benchmark results.