Re: [PATCH 2/2] lock_packed_refs(): allow retries when acquiring the packed-refs lock

On Mon, May 11, 2015 at 10:49 AM, Stefan Beller [off-list ref] wrote:

On Mon, May 11, 2015 at 9:49 AM, Jeff King [off-list ref] wrote:

quoted

On Mon, May 11, 2015 at 12:26:23PM +0200, Michael Haggerty wrote:

quoted

quoted

So something like 100ms max backoff makes sense to me, in that it keeps
us in the same order of magnitude as the expected time that the lock is
held. [...]

I don't understand your argument. If another process blocks us for on
the order of 100 ms, the backoff time (reading from my table) is less
than half of that.

I think it is just that I was agreeing with you, but communicated it
badly. I think your series is fine as-is.

By now I also think your series is fine as is.
I am currently implementing something similar for Gerrit and I realize
testing time based things is a royal pain in the butt. The tests you propose
just take wall clock time and all should is good, though slowing down
the test suite
by another second or three in the worst case.

So for tests in Gerrit I use a dedicated java class which is
specialized to pretend different
times, such that you can write:

    doThings();
    pretendTimePassing(1 second);
    checkResultsFromThreads();

but running the tests takes less than 1 second as it's no real wall
clock time passing.

On my machine there is
/bin/usleep - sleep some number of microseconds

As we're using perl anyway we may even want to just do

    perl -e "select(undef,undef,undef,0.1);"

as found at
http://serverfault.com/questions/469247/how-do-i-sleep-for-a-millisecond-in-bash-or-ksh