Re: Parallel fetch and commit graph writing results in locking failure (even on linux)

[Derrick Stolee <stolee@gmail.com>]

On 12/13/2019 2:52 PM, Jeff King wrote:
> On Fri, Dec 13, 2019 at 02:35:47PM -0500, Derrick Stolee wrote:
> 
>> I don't think so. I think you just found a bug where the
>> fetch.writeCommitGraph logic doesn't work with parallel fetch
>> jobs (only one can write at a time).
>>
>> I believe the fix would be to write the commit-graph after
>> all of the jobs have completed, which should mean we need to
>> move the call to write_commit_graph_reachable() somewhere else
>> inside builtin/fetch.c.
> 
> This should be fixed in master by bcb06e204c (Merge branch
> 'js/fetch-multi-lockfix', 2019-12-01), I think.

Thanks, Peff. That exactly looks like the right fix. The
actual commit is 7d8e72b9 ("fetch: avoid locking issues between
fetch.jobs/fetch.writeCommitGraph" 2019-11-03). I had forgotten
that this was already fixed.

Here is the diff, for reference:

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 8d27f8abb7..20bcda09c4 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1602,7 +1602,8 @@ static int fetch_multiple(struct string_list *list, int max_children)
                        return errcode;
        }
 
-       argv_array_pushl(&argv, "fetch", "--append", "--no-auto-gc", NULL);
+       argv_array_pushl(&argv, "fetch", "--append", "--no-auto-gc",
+                       "--no-write-commit-graph", NULL);
        add_options_to_argv(&argv);
 
        if (max_children != 1 && list->nr != 1) {

-Stolee