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[PATCH 10/15] refs.c: allow multiple reflog updates during a single transaction

From
Ronnie Sahlberg <sahlberg@google.com>
Date
Jul 23, 2014, 17:03 UTC
Message-ID
<1406135035-26441-11-git-send-email-sahlberg@google.com>
In-Reply-To
<1406135035-26441-1-git-send-email-sahlberg@google.com>

Allow to make multiple reflog updates to the same ref during a transaction. This means we only need to lock the reflog once, during the first update that touches the reflog, and that all further updates can just write the reflog entry since the reflog is already locked.

This allows us to write code such as:
t = transaction_begin()
transaction_reflog_update(t, "foo", REFLOG_TRUNCATE, NULL);
loop-over-somehting...
   transaction_reflog_update(t, "foo", 0, <message>);
transaction_commit(t)

where we first truncate the reflog and then build the new content one line at a time.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 refs.c | 46 +++++++++++++++++++++++++++++++++++++---------
 1 file changed, 37 insertions(+), 9 deletions(-)
diff --git a/refs.c b/refs.c
index c431088..12ff916 100644
--- a/refs.c
+++ b/refs.c
@@ -30,6 +30,12 @@ static unsigned char refname_disposition[256] = {
  */
 #define REF_ISPRUNING	0x0100
 /*
+ * Only the first reflog update needs to lock the reflog file. Further updates
+ * just use the lock taken by the first update.
+ */
+#define UPDATE_REFLOG_NOLOCK 0x0200
+
+/*
  * Try to read one refname component from the front of refname.
  * Return the length of the component found, or -1 if the component is
  * not legal.  It is legal if it is something reasonable to have under
@@ -3389,7 +3395,7 @@ enum transaction_update_type {
        UPDATE_LOG = 1
 };
 
-/**
+/*
  * Information needed for a single ref update.  Set new_sha1 to the
  * new value or to zero to delete the ref.  To check the old value
  * while locking the ref, set have_old to 1 and set old_sha1 to the
@@ -3399,7 +3405,7 @@ struct ref_update {
 	enum transaction_update_type update_type;
 	unsigned char new_sha1[20];
 	unsigned char old_sha1[20];
-	int flags; /* REF_NODEREF? */
+	int flags; /* REF_NODEREF? or private flags */
 	int have_old; /* 1 if old_sha1 is valid, 0 otherwise */
 	struct ref_lock *lock;
 	int type;
@@ -3407,8 +3413,9 @@ struct ref_update {
 
 	/* used by reflog updates */
 	int reflog_fd;
-	struct lock_file reflog_lock;
+	struct lock_file *reflog_lock;
 	char *committer;
+	struct ref_update *orig_update; /* For UPDATE_REFLOG_NOLOCK */
 
 	const char refname[FLEX_ARRAY];
 };
@@ -3489,12 +3496,27 @@ int transaction_update_reflog(struct ref_transaction *transaction,
 			      struct strbuf *err)
 {
 	struct ref_update *update;
+	int i;
 
 	if (transaction->state != REF_TRANSACTION_OPEN)
 		die("BUG: update_reflog called for transaction that is not "
 		    "open");
 
 	update = add_update(transaction, refname, UPDATE_LOG);
+	update->flags = flags;
+	for (i = 0; i < transaction->nr - 1; i++) {
+		if (transaction->updates[i]->update_type != UPDATE_LOG)
+			continue;
+		if (!strcmp(transaction->updates[i]->refname,
+			    update->refname)) {
+			update->flags |= UPDATE_REFLOG_NOLOCK;
+			update->orig_update = transaction->updates[i];
+			break;
+		}
+	}
+	if (!(update->flags & UPDATE_REFLOG_NOLOCK))
+		update->reflog_lock = xcalloc(1, sizeof(struct lock_file));
+
 	hashcpy(update->new_sha1, new_sha1);
 	hashcpy(update->old_sha1, old_sha1);
 	update->reflog_fd = -1;
@@ -3510,7 +3532,6 @@ int transaction_update_reflog(struct ref_transaction *transaction,
 	}
 	if (msg)
 		update->msg = xstrdup(msg);
-	update->flags = flags;
 
 	return 0;
 }
@@ -3696,10 +3717,15 @@ int transaction_commit(struct ref_transaction *transaction,
 
 		if (update->update_type != UPDATE_LOG)
 			continue;
+		if (update->flags & UPDATE_REFLOG_NOLOCK) {
+			update->reflog_fd = update->orig_update->reflog_fd;
+			update->reflog_lock = update->orig_update->reflog_lock;
+			continue;
+		}
 		update->reflog_fd = hold_lock_file_for_append(
-					&update->reflog_lock,
+					update->reflog_lock,
 					git_path("logs/%s", update->refname),
-					0);
+					LOCK_NODEREF);
 		if (update->reflog_fd < 0) {
 			const char *str = "Cannot lock reflog for '%s'. %s";
 
@@ -3765,7 +3791,7 @@ int transaction_commit(struct ref_transaction *transaction,
 				ftruncate(update->reflog_fd, 0)) {
 				error("Could not truncate reflog: %s. %s",
 				      update->refname, strerror(errno));
-				rollback_lock_file(&update->reflog_lock);
+				rollback_lock_file(update->reflog_lock);
 				update->reflog_fd = -1;
 				continue;
 			}
@@ -3775,7 +3801,7 @@ int transaction_commit(struct ref_transaction *transaction,
 				     update->committer, update->msg)) {
 			error("Could write to reflog: %s. %s",
 			      update->refname, strerror(errno));
-			rollback_lock_file(&update->reflog_lock);
+			rollback_lock_file(update->reflog_lock);
 			update->reflog_fd = -1;
 		}
 	}
@@ -3786,9 +3812,11 @@ int transaction_commit(struct ref_transaction *transaction,
 
 		if (update->update_type != UPDATE_LOG)
 			continue;
+		if (update->flags & UPDATE_REFLOG_NOLOCK)
+			continue;
 		if (update->reflog_fd == -1)
 			continue;
-		if (commit_lock_file(&update->reflog_lock)) {
+		if (commit_lock_file(update->reflog_lock)) {
 			error("Could not commit reflog: %s. %s",
 			      update->refname, strerror(errno));
 			update->reflog_fd = -1;

-- 
2.0.1.508.g763ab16
Previous: Ronnie SahlbergNext: Ronnie Sahlberg
Message 12 of 19 in “ref-transactions for reflogs”
  1. 00/15 ref-transactions for reflogsRonnie Sahlberg, Jul 23, 2014
  2. 01/15 refs.c make ref_transaction_create a wrapper to ref_transaction_updateRonnie Sahlberg, Jul 23, 2014
  3. Junio C HamanoJul 23, 2014
  4. 02/15 refs.c: make ref_transaction_delete a wrapper for ref_transaction_updateRonnie Sahlberg, Jul 23, 2014
  5. 03/15 refs.c: rename the transaction functionsRonnie Sahlberg, Jul 23, 2014
  6. 04/15 refs.c: add a new update_type field to ref_updateRonnie Sahlberg, Jul 23, 2014
  7. 05/15 refs.c: add a function to append a reflog entry to a fdRonnie Sahlberg, Jul 23, 2014
  8. 06/15 lockfile.c: make hold_lock_file_for_append preserve meaningful errnoRonnie Sahlberg, Jul 23, 2014
  9. 07/15 refs.c: add a transaction function to append a reflog entryRonnie Sahlberg, Jul 23, 2014
  10. 08/15 refs.c: add a flag to allow reflog updates to truncate the logRonnie Sahlberg, Jul 23, 2014
  11. 09/15 refs.c: only write reflog update if msg is non-NULLRonnie Sahlberg, Jul 23, 2014
  12. 10/15 refs.c: allow multiple reflog updates during a single transactionRonnie Sahlberg, Jul 23, 2014
  13. 11/15 reflog.c: use a reflog transaction when writing during expireRonnie Sahlberg, Jul 23, 2014
  14. 12/15 refs.c: rename log_ref_setup to create_reflogRonnie Sahlberg, Jul 23, 2014
  15. 13/15 refs.c: make unlock_ref/close_ref/commit_ref staticRonnie Sahlberg, Jul 23, 2014
  16. 14/15 refs.c: remove lock_any_ref_for_updateRonnie Sahlberg, Jul 23, 2014
  17. 15/15 refs.c: allow deleting refs with a broken sha1Ronnie Sahlberg, Jul 23, 2014
  18. Eric SunshineJul 23, 2014
  19. Junio C HamanoJul 23, 2014

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