From: Junio C Hamano <gitster@pobox.com>
Date: Thu, 25 Jul 2013 02:21:02 +0000 (-0700)
Subject: Merge branch 'mh/ref-races-optim-invalidate-cached'
X-Git-Tag: v1.8.4-rc0~11
X-Git-Url: https://git.lorimer.id.au/gitweb.git/diff_plain/29143fc4e3e5236aa57a1f1ef63f775491159782?ds=inline;hp=-c

Merge branch 'mh/ref-races-optim-invalidate-cached'

* mh/ref-races-optim-invalidate-cached:
refs: do not invalidate the packed-refs cache unnecessarily
---

29143fc4e3e5236aa57a1f1ef63f775491159782
diff --combined refs.c
index 4302206649,038e5c72d7..a3f2302292
--- a/refs.c
+++ b/refs.c
@@@ -1295,37 -1295,6 +1295,37 @@@ static struct ref_entry *get_packed_ref
  	return find_ref(get_packed_refs(&ref_cache), refname);
  }
  
 +/*
 + * A loose ref file doesn't exist; check for a packed ref.  The
 + * options are forwarded from resolve_safe_unsafe().
 + */
 +static const char *handle_missing_loose_ref(const char *refname,
 +					    unsigned char *sha1,
 +					    int reading,
 +					    int *flag)
 +{
 +	struct ref_entry *entry;
 +
 +	/*
 +	 * The loose reference file does not exist; check for a packed
 +	 * reference.
 +	 */
 +	entry = get_packed_ref(refname);
 +	if (entry) {
 +		hashcpy(sha1, entry->u.value.sha1);
 +		if (flag)
 +			*flag |= REF_ISPACKED;
 +		return refname;
 +	}
 +	/* The reference is not a packed reference, either. */
 +	if (reading) {
 +		return NULL;
 +	} else {
 +		hashclr(sha1);
 +		return refname;
 +	}
 +}
 +
  const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int reading, int *flag)
  {
  	int depth = MAXDEPTH;
@@@ -1350,34 -1319,36 +1350,34 @@@
  
  		git_snpath(path, sizeof(path), "%s", refname);
  
 +		/*
 +		 * We might have to loop back here to avoid a race
 +		 * condition: first we lstat() the file, then we try
 +		 * to read it as a link or as a file.  But if somebody
 +		 * changes the type of the file (file <-> directory
 +		 * <-> symlink) between the lstat() and reading, then
 +		 * we don't want to report that as an error but rather
 +		 * try again starting with the lstat().
 +		 */
 +	stat_ref:
  		if (lstat(path, &st) < 0) {
 -			struct ref_entry *entry;
 -
 -			if (errno != ENOENT)
 -				return NULL;
 -			/*
 -			 * The loose reference file does not exist;
 -			 * check for a packed reference.
 -			 */
 -			entry = get_packed_ref(refname);
 -			if (entry) {
 -				hashcpy(sha1, entry->u.value.sha1);
 -				if (flag)
 -					*flag |= REF_ISPACKED;
 -				return refname;
 -			}
 -			/* The reference is not a packed reference, either. */
 -			if (reading) {
 +			if (errno == ENOENT)
 +				return handle_missing_loose_ref(refname, sha1,
 +								reading, flag);
 +			else
  				return NULL;
 -			} else {
 -				hashclr(sha1);
 -				return refname;
 -			}
  		}
  
  		/* Follow "normalized" - ie "refs/.." symlinks by hand */
  		if (S_ISLNK(st.st_mode)) {
  			len = readlink(path, buffer, sizeof(buffer)-1);
 -			if (len < 0)
 -				return NULL;
 +			if (len < 0) {
 +				if (errno == ENOENT || errno == EINVAL)
 +					/* inconsistent with lstat; retry */
 +					goto stat_ref;
 +				else
 +					return NULL;
 +			}
  			buffer[len] = 0;
  			if (!prefixcmp(buffer, "refs/") &&
  					!check_refname_format(buffer, 0)) {
@@@ -1400,13 -1371,8 +1400,13 @@@
  		 * a ref
  		 */
  		fd = open(path, O_RDONLY);
 -		if (fd < 0)
 -			return NULL;
 +		if (fd < 0) {
 +			if (errno == ENOENT)
 +				/* inconsistent with lstat; retry */
 +				goto stat_ref;
 +			else
 +				return NULL;
 +		}
  		len = read_in_full(fd, buffer, sizeof(buffer)-1);
  		close(fd);
  		if (len < 0)
@@@ -1418,19 -1384,8 +1418,19 @@@
  		/*
  		 * Is it a symbolic ref?
  		 */
 -		if (prefixcmp(buffer, "ref:"))
 -			break;
 +		if (prefixcmp(buffer, "ref:")) {
 +			/*
 +			 * Please note that FETCH_HEAD has a second
 +			 * line containing other data.
 +			 */
 +			if (get_sha1_hex(buffer, sha1) ||
 +			    (buffer[40] != '\0' && !isspace(buffer[40]))) {
 +				if (flag)
 +					*flag |= REF_ISBROKEN;
 +				return NULL;
 +			}
 +			return refname;
 +		}
  		if (flag)
  			*flag |= REF_ISSYMREF;
  		buf = buffer + 4;
@@@ -1443,6 -1398,13 +1443,6 @@@
  		}
  		refname = strcpy(refname_buffer, buf);
  	}
 -	/* Please note that FETCH_HEAD has a second line containing other data. */
 -	if (get_sha1_hex(buffer, sha1) || (buffer[40] != '\0' && !isspace(buffer[40]))) {
 -		if (flag)
 -			*flag |= REF_ISBROKEN;
 -		return NULL;
 -	}
 -	return refname;
  }
  
  char *resolve_refdup(const char *ref, unsigned char *sha1, int reading, int *flag)
@@@ -2174,11 -2136,14 +2174,14 @@@ int lock_packed_refs(int flags
  {
  	struct packed_ref_cache *packed_ref_cache;
  
- 	/* Discard the old cache because it might be invalid: */
- 	clear_packed_ref_cache(&ref_cache);
  	if (hold_lock_file_for_update(&packlock, git_path("packed-refs"), flags) < 0)
  		return -1;
- 	/* Read the current packed-refs while holding the lock: */
+ 	/*
+ 	 * Get the current packed-refs while holding the lock.  If the
+ 	 * packed-refs file has been modified since we last read it,
+ 	 * this will automatically invalidate the cache and re-read
+ 	 * the packed-refs file.
+ 	 */
  	packed_ref_cache = get_packed_ref_cache(&ref_cache);
  	packed_ref_cache->lock = &packlock;
  	/* Increment the reference count to prevent it from being freed: */