@matheusbsbs / matheus-bagliano / commits / 6241ce2170

refs/reftable: reload locked stack when preparing transaction

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 While it may happen that the stack is out-of-date at this point in time we don't really care: transactional updates encode the expected state of a certain reference, so all that we really want to verify is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 Pass `REFTABLE_STACK_NEW_ADDITION_RELOAD` when locking the stack such that an out-of-date stack will be reloaded after having been locked.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> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Patrick Steinhardt committed Sep 24, 2024 at 07:33 UTC 6241ce217046cc77d306bda06ad80ac1973b4932

2 files changed +33 -1

refs/reftable-backend.c

+2 -1

@@ -770,7 +770,8 @@ static int prepare_transaction_update(struct write_transaction_table_arg **out,

770 if (ret)

771 return ret;

772

773 - ret = reftable_stack_new_addition(&addition, stack, 0);

773 + ret = reftable_stack_new_addition(&addition, stack,

774 + REFTABLE_STACK_NEW_ADDITION_RELOAD);

775 if (ret) {

776 if (ret == REFTABLE_LOCK_ERROR)

777 strbuf_addstr(err, "cannot lock references");

t/t0610-reftable-basics.sh

+31

@@ -450,6 +450,37 @@ test_expect_success 'ref transaction: retry acquiring tables.list lock' '

450 )

451 '

452

453 +test_expect_success 'ref transaction: many concurrent writers' '

454 + test_when_finished "rm -rf repo" &&

455 + git init repo &&

456 + (

457 + cd repo &&

458 + # Set a high timeout such that a busy CI machine will not abort

459 + # early. 10 seconds should hopefully be ample of time to make

460 + # this non-flaky.

461 + git config set reftable.lockTimeout 10000 &&

462 + test_commit --no-tag initial &&

463 +

464 + head=$(git rev-parse HEAD) &&

465 + for i in $(test_seq 100)

466 + do

467 + printf "%s commit\trefs/heads/branch-%s\n" "$head" "$i" ||

468 + return 1

469 + done >expect &&

470 + printf "%s commit\trefs/heads/main\n" "$head" >>expect &&

471 +

472 + for i in $(test_seq 100)

473 + do

474 + { git update-ref refs/heads/branch-$i HEAD& } ||

475 + return 1

476 + done &&

477 +

478 + wait &&

479 + git for-each-ref --sort=v:refname >actual &&

480 + test_cmp expect actual

481 + )

482 +'

483 +

484 test_expect_success 'pack-refs: compacts tables' '

485 test_when_finished "rm -rf repo" &&

486 git init repo &&