Error Groups

Three fetches start at the same time, and one of them fails after 30 ms. What should happen to the other two, and what should the caller receive?

In most programs, the answer is the same. The caller needs all three pages, so one failure means the whole operation has failed. The two fetches still running are now wasted work and should stop. The caller should receive the error that caused the failure. It should receive it only after every goroutine has returned, so that nothing is left running.