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[PATCH v3 17/19] update_ref(): don't read old reference value before delete

From
Michael Haggerty <mhagger@alum.mit.edu>
Date
Jun 22, 2015, 14:03 UTC
Message-ID
<2104214a318e7bb636507888e4a31c5b739a7f40.1434980615.git.mhagger@alum.mit.edu>
In-Reply-To
<cover.1434980615.git.mhagger@alum.mit.edu>

If we are deleting the reference, then we don't need to read the reference's old value. It doesn't provide any race safety, because the value read just before the delete is no "better" than the value that would be read under lock during the delete. And even if the reference previously didn't exist, we can call delete_ref() on it if we don't provide an old_sha1 value.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 fast-import.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/fast-import.c b/fast-import.c
index 6378726..d7ed065 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -1692,13 +1692,13 @@ static int update_branch(struct branch *b)
 	unsigned char old_sha1[20];
 	struct strbuf err = STRBUF_INIT;
 
-	if (read_ref(b->name, old_sha1))
-		hashclr(old_sha1);
 	if (is_null_sha1(b->sha1)) {
 		if (b->delete)
-			delete_ref(b->name, old_sha1, 0);
+			delete_ref(b->name, NULL, 0);
 		return 0;
 	}
+	if (read_ref(b->name, old_sha1))
+		hashclr(old_sha1);
 	if (!force_update && !is_null_sha1(old_sha1)) {
 		struct commit *old_cmit, *new_cmit;
 

-- 
2.1.4
Previous: Michael HaggertyNext: Michael Haggerty
Message 21 of 24 in “Improve "refs" encapsulation and speed up deletes”
  1. 00/19 Improve "refs" encapsulation and speed up deletesMichael Haggerty, Jun 22, 2015
  2. 01/19 delete_ref(): move declaration to refs.hMichael Haggerty, Jun 22, 2015
  3. 02/19 remove_branches(): remove temporaryMichael Haggerty, Jun 22, 2015
  4. 03/19 delete_ref(): handle special case more explicitlyMichael Haggerty, Jun 22, 2015
  5. 04/19 delete_refs(): new function for the refs APIMichael Haggerty, Jun 22, 2015
  6. 05/19 delete_refs(): make error message more genericMichael Haggerty, Jun 22, 2015
  7. 06/19 delete_refs(): bail early if the packed-refs file cannot be rewrittenMichael Haggerty, Jun 22, 2015
  8. 07/19 prune_remote(): use delete_refs()Michael Haggerty, Jun 22, 2015
  9. 08/19 prune_refs(): use delete_refs()Michael Haggerty, Jun 22, 2015
  10. 09/19 repack_without_refs(): make function privateMichael Haggerty, Jun 22, 2015
  11. 10/19 initial_ref_transaction_commit(): function for initial ref creationMichael Haggerty, Jun 22, 2015
  12. 11/19 refs: remove some functions from the module's public interfaceMichael Haggerty, Jun 22, 2015
  13. 12/19 initial_ref_transaction_commit(): check for duplicate refsMichael Haggerty, Jun 22, 2015
  14. Junio C HamanoJun 22, 2015
  15. Michael HaggertyJun 23, 2015
  16. Junio C HamanoJun 23, 2015
  17. 13/19 initial_ref_transaction_commit(): check for ref D/F conflictsMichael Haggerty, Jun 22, 2015
  18. 14/19 refs: move the remaining ref module declarations to refs.hMichael Haggerty, Jun 22, 2015
  19. 15/19 refs.h: add some parameter names to function declarationsMichael Haggerty, Jun 22, 2015
  20. 16/19 check_branch_commit(): make first parameter constMichael Haggerty, Jun 22, 2015
  21. 17/19 update_ref(): don't read old reference value before deleteMichael Haggerty, Jun 22, 2015
  22. 18/19 cmd_update_ref(): make logic more straightforwardMichael Haggerty, Jun 22, 2015
  23. 19/19 delete_ref(): use the usual convention for old_sha1Michael Haggerty, Jun 22, 2015
  24. Junio C HamanoJun 22, 2015

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