[PATCH v3 3/3] refs/reftable: reload locked stack when preparing transaction
- From
Patrick Steinhardt <ps@pks.im>
- Date
- Sep 18, 2024, 09:59 UTC
- Message-ID
- <25d4e513a368a0787b6f78466f85a3155ca3a740.1726653185.git.ps@pks.im>
- In-Reply-To
- <cover.1726653185.git.ps@pks.im>
When starting a reftable transaction we lock all stacks we are about to modify. While it may happen that the stack is out-of-date at this point in time we don't really care: transactional updates encode the expected state of a certain reference, so all that we really want to verify is that the _current_ value matches that expected state.
Pass `REFTABLE_STACK_NEW_ADDITION_RELOAD` when locking the stack such that an out-of-date stack will be reloaded after having been locked. This change is safe because all verifications of the expected state happen after this step anyway.
Add a testcase that verifies that many writers are now able to write to the stack concurrently without failures and with a deterministic end result.
Signed-off-by: Patrick Steinhardt <ps@pks.im> --- refs/reftable-backend.c | 3 ++- t/t0610-reftable-basics.sh | 31 +++++++++++++++++++++++++++++++ 2 files changed, 33 insertions(+), 1 deletion(-)
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c index 6ca00627dd7..efe2b0258ca 100644 --- a/refs/reftable-backend.c +++ b/refs/reftable-backend.c @@ -770,7 +770,8 @@ static int prepare_transaction_update(struct write_transaction_table_arg **out, if (ret) return ret; - ret = reftable_stack_new_addition(&addition, stack, 0); + ret = reftable_stack_new_addition(&addition, stack, + REFTABLE_STACK_NEW_ADDITION_RELOAD); if (ret) { if (ret == REFTABLE_LOCK_ERROR) strbuf_addstr(err, "cannot lock references"); diff --git a/t/t0610-reftable-basics.sh b/t/t0610-reftable-basics.sh index 62da3e37823..2d951c8ceb6 100755 --- a/t/t0610-reftable-basics.sh +++ b/t/t0610-reftable-basics.sh @@ -450,6 +450,37 @@ test_expect_success 'ref transaction: retry acquiring tables.list lock' ' ) ' +test_expect_success 'ref transaction: many concurrent writers' ' + test_when_finished "rm -rf repo" && + git init repo && + ( + cd repo && + # Set a high timeout such that a busy CI machine will not abort + # early. 10 seconds should hopefully be ample of time to make + # this non-flaky. + git config set reftable.lockTimeout 10000 && + test_commit --no-tag initial && + + head=$(git rev-parse HEAD) && + for i in $(test_seq 100) + do + printf "%s commit\trefs/heads/branch-%s\n" "$head" "$i" || + return 1 + done >expect && + printf "%s commit\trefs/heads/main\n" "$head" >>expect && + + for i in $(test_seq 100) + do + { git update-ref refs/heads/branch-$i HEAD& } || + return 1 + done && + + wait && + git for-each-ref --sort=v:refname >actual && + test_cmp expect actual + ) +' + test_expect_success 'pack-refs: compacts tables' ' test_when_finished "rm -rf repo" && git init repo &&
-- 2.46.0.551.gc5ee8f2d1c.dirty