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 While it may happen that the stack is out-of-date at this point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that an out-of-date stack will be reloaded after having been locked.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@xxxxxx>
---
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 c500fb820a7..d4b383ca179 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -766,7 +766,8 @@ 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
