From bc39b6a796eb707c34ffb759d50a75f96313f26c Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Tue, 24 Sep 2024 07:33:02 +0200 Subject: refs/reftable: introduce "reftable.lockTimeout" When multiple concurrent processes try to update references in a repository they may try to lock the same lockfiles. This can happen even when the updates are non-conflicting and can both be applied, so it doesn't always make sense to abort the transaction immediately. Both the "loose" and "packed" backends thus have a grace period that they wait for the lock to be released that can be controlled via the config values "core.filesRefLockTimeout" and "core.packedRefsTimeout", respectively. The reftable backend doesn't have such a setting yet and instead fails immediately when it sees such a lock. But the exact same concepts apply here as they do apply to the other backends. Introduce a new "reftable.lockTimeout" config that controls how long we may wait for a "tables.list" lock to be released. The default value of this config is 100ms, which is the same default as we have it for the "loose" backend. Note that even though we also lock individual tables, this config really only applies to the "tables.list" file. This is because individual tables are only ever locked when we already hold the "tables.list" lock during compaction. When we observe such a lock we in fact do not want to compact the table at all because it is already in the process of being compacted by a concurrent process. So applying the same timeout here would not make any sense and only delay progress. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- reftable/reftable-writer.h | 11 +++++++++++ reftable/stack.c | 18 ++++++++++++------ 2 files changed, 23 insertions(+), 6 deletions(-) (limited to 'reftable') diff --git a/reftable/reftable-writer.h b/reftable/reftable-writer.h index 189b1f4144..f5e25cfda1 100644 --- a/reftable/reftable-writer.h +++ b/reftable/reftable-writer.h @@ -51,6 +51,17 @@ struct reftable_write_options { * tables to compact. Defaults to 2 if unset. */ uint8_t auto_compaction_factor; + + /* + * The number of milliseconds to wait when trying to lock "tables.list". + * Note that this does not apply to locking individual tables, as these + * should only ever be locked when already holding the "tables.list" + * lock. + * + * Passing 0 will fail immediately when the file is locked, passing a + * negative value will cause us to block indefinitely. + */ + long lock_timeout_ms; }; /* reftable_block_stats holds statistics for a single block type */ diff --git a/reftable/stack.c b/reftable/stack.c index ce0a35216b..5ccad2cff3 100644 --- a/reftable/stack.c +++ b/reftable/stack.c @@ -603,8 +603,10 @@ static int reftable_stack_init_addition(struct reftable_addition *add, add->stack = st; - err = hold_lock_file_for_update(&add->tables_list_lock, st->list_file, - LOCK_NO_DEREF); + err = hold_lock_file_for_update_timeout(&add->tables_list_lock, + st->list_file, + LOCK_NO_DEREF, + st->opts.lock_timeout_ms); if (err < 0) { if (errno == EEXIST) { err = REFTABLE_LOCK_ERROR; @@ -1056,8 +1058,10 @@ static int stack_compact_range(struct reftable_stack *st, * Hold the lock so that we can read "tables.list" and lock all tables * which are part of the user-specified range. */ - err = hold_lock_file_for_update(&tables_list_lock, st->list_file, - LOCK_NO_DEREF); + err = hold_lock_file_for_update_timeout(&tables_list_lock, + st->list_file, + LOCK_NO_DEREF, + st->opts.lock_timeout_ms); if (err < 0) { if (errno == EEXIST) err = REFTABLE_LOCK_ERROR; @@ -1156,8 +1160,10 @@ static int stack_compact_range(struct reftable_stack *st, * "tables.list". We'll then replace the compacted range of tables with * the new table. */ - err = hold_lock_file_for_update(&tables_list_lock, st->list_file, - LOCK_NO_DEREF); + err = hold_lock_file_for_update_timeout(&tables_list_lock, + st->list_file, + LOCK_NO_DEREF, + st->opts.lock_timeout_ms); if (err < 0) { if (errno == EEXIST) err = REFTABLE_LOCK_ERROR; -- cgit 1.2.3-korg From 80e7342ea8ecda48bdf034e77c32ac1c5d2bda85 Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Tue, 24 Sep 2024 07:33:05 +0200 Subject: reftable/stack: allow locking of outdated stacks In `reftable_stack_new_addition()` we first lock the stack and then check whether it is still up-to-date. If it is not we return an error to the caller indicating that the stack is outdated. This is overly restrictive in our ref transaction interface though: we lock the stack right before we start to verify the transaction, so we do not really care whether it is outdated or not. What we really want is that the stack is up-to-date after it has been locked so that we can verify queued updates against its current state while we know that it is locked for concurrent modification. Introduce a new flag `REFTABLE_STACK_NEW_ADDITION_RELOAD` that alters the behaviour of `reftable_stack_init_addition()` in this case: when we notice that it is out-of-date we reload it instead of returning an error to the caller. This logic will be wired up in the reftable backend in the next commit. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- refs/reftable-backend.c | 4 +-- reftable/reftable-stack.h | 13 ++++++-- reftable/stack.c | 20 +++++++----- t/unit-tests/t-reftable-stack.c | 67 +++++++++++++++++++++++++++++++++++++++-- 4 files changed, 91 insertions(+), 13 deletions(-) (limited to 'reftable') diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c index ca281e39a2..6ca00627dd 100644 --- a/refs/reftable-backend.c +++ b/refs/reftable-backend.c @@ -770,7 +770,7 @@ static int prepare_transaction_update(struct write_transaction_table_arg **out, if (ret) return ret; - ret = reftable_stack_new_addition(&addition, stack); + ret = reftable_stack_new_addition(&addition, stack, 0); if (ret) { if (ret == REFTABLE_LOCK_ERROR) strbuf_addstr(err, "cannot lock references"); @@ -2207,7 +2207,7 @@ static int reftable_be_reflog_expire(struct ref_store *ref_store, if (ret < 0) goto done; - ret = reftable_stack_new_addition(&add, stack); + ret = reftable_stack_new_addition(&add, stack, 0); if (ret < 0) goto done; diff --git a/reftable/reftable-stack.h b/reftable/reftable-stack.h index f4f8cabc7f..6370fe45dd 100644 --- a/reftable/reftable-stack.h +++ b/reftable/reftable-stack.h @@ -37,12 +37,21 @@ uint64_t reftable_stack_next_update_index(struct reftable_stack *st); /* holds a transaction to add tables at the top of a stack. */ struct reftable_addition; +enum { + /* + * Reload the stack when the stack is out-of-date after locking it. + */ + REFTABLE_STACK_NEW_ADDITION_RELOAD = (1 << 0), +}; + /* * returns a new transaction to add reftables to the given stack. As a side - * effect, the ref database is locked. + * effect, the ref database is locked. Accepts REFTABLE_STACK_NEW_ADDITION_* + * flags. */ int reftable_stack_new_addition(struct reftable_addition **dest, - struct reftable_stack *st); + struct reftable_stack *st, + unsigned int flags); /* Adds a reftable to transaction. */ int reftable_addition_add(struct reftable_addition *add, diff --git a/reftable/stack.c b/reftable/stack.c index 5ccad2cff3..84cf37a2ad 100644 --- a/reftable/stack.c +++ b/reftable/stack.c @@ -596,7 +596,8 @@ struct reftable_addition { #define REFTABLE_ADDITION_INIT {0} static int reftable_stack_init_addition(struct reftable_addition *add, - struct reftable_stack *st) + struct reftable_stack *st, + unsigned int flags) { struct strbuf lock_file_name = STRBUF_INIT; int err; @@ -626,6 +627,11 @@ static int reftable_stack_init_addition(struct reftable_addition *add, err = stack_uptodate(st); if (err < 0) goto done; + if (err > 0 && flags & REFTABLE_STACK_NEW_ADDITION_RELOAD) { + err = reftable_stack_reload_maybe_reuse(add->stack, 1); + if (err) + goto done; + } if (err > 0) { err = REFTABLE_OUTDATED_ERROR; goto done; @@ -633,9 +639,8 @@ static int reftable_stack_init_addition(struct reftable_addition *add, add->next_update_index = reftable_stack_next_update_index(st); done: - if (err) { + if (err) reftable_addition_close(add); - } strbuf_release(&lock_file_name); return err; } @@ -739,13 +744,14 @@ int reftable_addition_commit(struct reftable_addition *add) } int reftable_stack_new_addition(struct reftable_addition **dest, - struct reftable_stack *st) + struct reftable_stack *st, + unsigned int flags) { int err = 0; struct reftable_addition empty = REFTABLE_ADDITION_INIT; REFTABLE_CALLOC_ARRAY(*dest, 1); **dest = empty; - err = reftable_stack_init_addition(*dest, st); + err = reftable_stack_init_addition(*dest, st, flags); if (err) { reftable_free(*dest); *dest = NULL; @@ -759,7 +765,7 @@ static int stack_try_add(struct reftable_stack *st, void *arg) { struct reftable_addition add = REFTABLE_ADDITION_INIT; - int err = reftable_stack_init_addition(&add, st); + int err = reftable_stack_init_addition(&add, st, 0); if (err < 0) goto done; @@ -1608,7 +1614,7 @@ static int reftable_stack_clean_locked(struct reftable_stack *st) int reftable_stack_clean(struct reftable_stack *st) { struct reftable_addition *add = NULL; - int err = reftable_stack_new_addition(&add, st); + int err = reftable_stack_new_addition(&add, st, 0); if (err < 0) { goto done; } diff --git a/t/unit-tests/t-reftable-stack.c b/t/unit-tests/t-reftable-stack.c index d62a9c1bed..a37cc698d8 100644 --- a/t/unit-tests/t-reftable-stack.c +++ b/t/unit-tests/t-reftable-stack.c @@ -271,7 +271,7 @@ static void t_reftable_stack_transaction_api(void) reftable_addition_destroy(add); - err = reftable_stack_new_addition(&add, st); + err = reftable_stack_new_addition(&add, st, 0); check(!err); err = reftable_addition_add(add, write_test_ref, &ref); @@ -292,6 +292,68 @@ static void t_reftable_stack_transaction_api(void) clear_dir(dir); } +static void t_reftable_stack_transaction_with_reload(void) +{ + char *dir = get_tmp_dir(__LINE__); + struct reftable_stack *st1 = NULL, *st2 = NULL; + int err; + struct reftable_addition *add = NULL; + struct reftable_ref_record refs[2] = { + { + .refname = (char *) "refs/heads/a", + .update_index = 1, + .value_type = REFTABLE_REF_VAL1, + .value.val1 = { '1' }, + }, + { + .refname = (char *) "refs/heads/b", + .update_index = 2, + .value_type = REFTABLE_REF_VAL1, + .value.val1 = { '1' }, + }, + }; + struct reftable_ref_record ref = { 0 }; + + err = reftable_new_stack(&st1, dir, NULL); + check(!err); + err = reftable_new_stack(&st2, dir, NULL); + check(!err); + + err = reftable_stack_new_addition(&add, st1, 0); + check(!err); + err = reftable_addition_add(add, write_test_ref, &refs[0]); + check(!err); + err = reftable_addition_commit(add); + check(!err); + reftable_addition_destroy(add); + + /* + * The second stack is now outdated, which we should notice. We do not + * create the addition and lock the stack by default, but allow the + * reload to happen when REFTABLE_STACK_NEW_ADDITION_RELOAD is set. + */ + err = reftable_stack_new_addition(&add, st2, 0); + check_int(err, ==, REFTABLE_OUTDATED_ERROR); + err = reftable_stack_new_addition(&add, st2, REFTABLE_STACK_NEW_ADDITION_RELOAD); + check(!err); + err = reftable_addition_add(add, write_test_ref, &refs[1]); + check(!err); + err = reftable_addition_commit(add); + check(!err); + reftable_addition_destroy(add); + + for (size_t i = 0; i < ARRAY_SIZE(refs); i++) { + err = reftable_stack_read_ref(st2, refs[i].refname, &ref); + check(!err); + check(reftable_ref_record_equal(&refs[i], &ref, GIT_SHA1_RAWSZ)); + } + + reftable_ref_record_release(&ref); + reftable_stack_destroy(st1); + reftable_stack_destroy(st2); + clear_dir(dir); +} + static void t_reftable_stack_transaction_api_performs_auto_compaction(void) { char *dir = get_tmp_dir(__LINE__); @@ -322,7 +384,7 @@ static void t_reftable_stack_transaction_api_performs_auto_compaction(void) */ st->opts.disable_auto_compact = i != n; - err = reftable_stack_new_addition(&add, st); + err = reftable_stack_new_addition(&add, st, 0); check(!err); err = reftable_addition_add(add, write_test_ref, &ref); @@ -1314,6 +1376,7 @@ int cmd_main(int argc UNUSED, const char *argv[] UNUSED) TEST(t_reftable_stack_reload_with_missing_table(), "stack iteration with garbage tables"); TEST(t_reftable_stack_tombstone(), "'tombstone' refs in stack"); TEST(t_reftable_stack_transaction_api(), "update transaction to stack"); + TEST(t_reftable_stack_transaction_with_reload(), "transaction with reload"); TEST(t_reftable_stack_transaction_api_performs_auto_compaction(), "update transaction triggers auto-compaction"); TEST(t_reftable_stack_update_index_check(), "update transactions with equal update indices"); TEST(t_reftable_stack_uptodate(), "stack must be reloaded before ref update"); -- cgit 1.2.3-korg