tree a5548a0626b6a621fc0a0994c841a0ee3933b945
parent c2a85435cae28de5c63406fad154a310eda7409f
author Han-Wen Nienhuys <hanwen@google.com> 1516092088 +0100
committer Han-Wen Nienhuys <hanwen@google.com> 1516092386 +0100

shards: use x/sync/semaphore for throttling

A buffered channel is a simple and wrong solution for throttling: if
the lock() method

        n := cap(s.throttle)
        for n > 0 {
                s.throttle <- struct{}{}
                n--
        }

is called from multiple goroutines concurrently, none of them will
succeed inserting N items into the queue, deadlocking all of them.

Fixes #23.

Change-Id: I265655ba192755b096a062f9c164a8d872911964