commands: exit from the log loop at the right time Previously, we'd run the iterator one more time than necessary, potentially doing a lot of extra work in the process.

cmdutil: use a small initial window with --limit In a large repo, running a command like "log -l1 -p" was expensive because it would always traverse 8 commits, as 8 was the initial window size. We now choose the lesser of 8 or the limit, speeding up the "log -l1 -p" case by a factor of 5.

worker: handle worker failures more aggressively We now wait for worker processes in a separate thread, so that we can spot failures in a timely way, wihout waiting for the progress pipe to drain. If a worker fails, we recover the pre-parallel-update behaviour of failing early by killing its peers before propagating the failure.

worker: fix a race in SIGINT handling This is almost impossible to trigger due to the tiny time window involved.