Permalink
Browse files

refs: store references hierarchically

Store references hierarchically in a tree that matches the
pseudo-directory structure of the reference names.  Add a new kind of
ref_entry (with flag REF_DIR) to represent a whole subdirectory of
references.  Sort ref_dirs one subdirectory at a time.

NOTE: the dirs can now be sorted as a side-effect of other function
calls.  Therefore, it would be problematic to do something from a
each_ref_fn callback that could provoke the sorting of a directory
that is currently being iterated over (i.e., the directory containing
the entry that is being processed or any of its parents).

This is a bit far-fetched, because a directory is always sorted just
before being iterated over.  Therefore, read-only accesses cannot
trigger the sorting of a directory whose iteration has already
started.  But if a callback function would add a reference to a parent
directory of the reference in the iteration, then try to resolve a
reference under that directory, a re-sort could be triggered and cause
the iteration to work incorrectly.

Nevertheless...add a comment in refs.h warning against modifications
during iteration.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
  • Loading branch information...
1 parent 81a79d8 commit 432ad41e60cedb87ceec446ab034d46a53f5f9d8 @mhagger mhagger committed with Apr 10, 2012
Showing with 232 additions and 49 deletions.
  1. +227 −47 refs.c
  2. +5 −2 refs.h
View
274 refs.c
@@ -120,15 +120,54 @@ struct ref_dir {
struct ref_entry **entries;
};
-/* ISSYMREF=0x01, ISPACKED=0x02 and ISBROKEN=0x04 are public interfaces */
-#define REF_KNOWS_PEELED 0x10
+/* ISSYMREF=0x01, ISPACKED=0x02, and ISBROKEN=0x04 are public interfaces */
+#define REF_KNOWS_PEELED 0x08
+#define REF_DIR 0x10
+/*
+ * A ref_entry represents either a reference or a "subdirectory" of
+ * references. Each directory in the reference namespace is
+ * represented by a ref_entry with (flags & REF_DIR) set and
+ * containing a subdir member that holds the entries in that
+ * directory. References are represented by a ref_entry with (flags &
+ * REF_DIR) unset and a value member that describes the reference's
+ * value. The flag member is at the ref_entry level, but it is also
+ * needed to interpret the contents of the value field (in other
+ * words, a ref_value object is not very much use without the
+ * enclosing ref_entry).
+ *
+ * Reference names cannot end with slash and directories' names are
+ * always stored with a trailing slash (except for the top-level
+ * directory, which is always denoted by ""). This has two nice
+ * consequences: (1) when the entries in each subdir are sorted
+ * lexicographically by name (as they usually are), the references in
+ * a whole tree can be generated in lexicographic order by traversing
+ * the tree in left-to-right, depth-first order; (2) the names of
+ * references and subdirectories cannot conflict, and therefore the
+ * presence of an empty subdirectory does not block the creation of a
+ * similarly-named reference. (The fact that reference names with the
+ * same leading components can conflict *with each other* is a
+ * separate issue that is regulated by is_refname_available().)
+ *
+ * Please note that the name field contains the fully-qualified
+ * reference (or subdirectory) name. Space could be saved by only
+ * storing the relative names. But that would require the full names
+ * to be generated on the fly when iterating in do_for_each_ref(), and
+ * would break callback functions, who have always been able to assume
+ * that the name strings that they are passed will not be freed during
+ * the iteration.
+ */
struct ref_entry {
unsigned char flag; /* ISSYMREF? ISPACKED? */
union {
- struct ref_value value;
+ struct ref_value value; /* if not (flags&REF_DIR) */
+ struct ref_dir subdir; /* if (flags&REF_DIR) */
} u;
- /* The full name of the reference (e.g., "refs/heads/master"): */
+ /*
+ * The full name of the reference (e.g., "refs/heads/master")
+ * or the full name of the directory with a trailing slash
+ * (e.g., "refs/heads/"):
+ */
char name[FLEX_ARRAY];
};
@@ -151,18 +190,29 @@ static struct ref_entry *create_ref_entry(const char *refname,
return ref;
}
+static void clear_ref_dir(struct ref_dir *dir);
+
static void free_ref_entry(struct ref_entry *entry)
{
+ if (entry->flag & REF_DIR)
+ clear_ref_dir(&entry->u.subdir);
free(entry);
}
-/* Add a ref_entry to the end of the ref_dir (unsorted). */
-static void add_ref(struct ref_dir *refs, struct ref_entry *ref)
+/*
+ * Add a ref_entry to the end of dir (unsorted). Entry is always
+ * stored directly in dir; no recursion into subdirectories is
+ * done.
+ */
+static void add_entry_to_dir(struct ref_dir *dir, struct ref_entry *entry)
{
- ALLOC_GROW(refs->entries, refs->nr + 1, refs->alloc);
- refs->entries[refs->nr++] = ref;
+ ALLOC_GROW(dir->entries, dir->nr + 1, dir->alloc);
+ dir->entries[dir->nr++] = entry;
}
+/*
+ * Clear and free all entries in dir, recursively.
+ */
static void clear_ref_dir(struct ref_dir *dir)
{
int i;
@@ -173,6 +223,21 @@ static void clear_ref_dir(struct ref_dir *dir)
dir->entries = NULL;
}
+/*
+ * Create a struct ref_entry object for the specified dirname.
+ * dirname is the name of the directory with a trailing slash (e.g.,
+ * "refs/heads/") or "" for the top-level directory.
+ */
+static struct ref_entry *create_dir_entry(const char *dirname)
+{
+ struct ref_entry *direntry;
+ int len = strlen(dirname);
+ direntry = xcalloc(1, sizeof(struct ref_entry) + len + 1);
+ memcpy(direntry->name, dirname, len + 1);
+ direntry->flag = REF_DIR;
+ return direntry;
+}
+
static int ref_entry_cmp(const void *a, const void *b)
{
struct ref_entry *one = *(struct ref_entry **)a;
@@ -182,17 +247,21 @@ static int ref_entry_cmp(const void *a, const void *b)
static void sort_ref_dir(struct ref_dir *dir);
+/*
+ * Return the entry with the given refname from the ref_dir
+ * (non-recursively), sorting dir if necessary. Return NULL if no
+ * such entry is found.
+ */
static struct ref_entry *search_ref_dir(struct ref_dir *dir, const char *refname)
{
struct ref_entry *e, **r;
int len;
- if (refname == NULL)
+ if (refname == NULL || !dir->nr)
return NULL;
- if (!dir->nr)
- return NULL;
sort_ref_dir(dir);
+
len = strlen(refname) + 1;
e = xmalloc(sizeof(struct ref_entry) + len);
memcpy(e->name, refname, len);
@@ -208,27 +277,96 @@ static struct ref_entry *search_ref_dir(struct ref_dir *dir, const char *refname
}
/*
+ * If refname is a reference name, find the ref_dir within the dir
+ * tree that should hold refname. If refname is a directory name
+ * (i.e., ends in '/'), then return that ref_dir itself. dir must
+ * represent the top-level directory. Sort ref_dirs and recurse into
+ * subdirectories as necessary. If mkdir is set, then create any
+ * missing directories; otherwise, return NULL if the desired
+ * directory cannot be found.
+ */
+static struct ref_dir *find_containing_dir(struct ref_dir *dir,
+ const char *refname, int mkdir)
+{
+ char *refname_copy = xstrdup(refname);
+ char *slash;
+ struct ref_entry *entry;
+ for (slash = strchr(refname_copy, '/'); slash; slash = strchr(slash + 1, '/')) {
+ char tmp = slash[1];
+ slash[1] = '\0';
+ entry = search_ref_dir(dir, refname_copy);
+ if (!entry) {
+ if (!mkdir) {
+ dir = NULL;
+ break;
+ }
+ entry = create_dir_entry(refname_copy);
+ add_entry_to_dir(dir, entry);
+ }
+ slash[1] = tmp;
+ assert(entry->flag & REF_DIR);
+ dir = &entry->u.subdir;
+ }
+
+ free(refname_copy);
+ return dir;
+}
+
+/*
+ * Find the value entry with the given name in dir, sorting ref_dirs
+ * and recursing into subdirectories as necessary. If the name is not
+ * found or it corresponds to a directory entry, return NULL.
+ */
+static struct ref_entry *find_ref(struct ref_dir *dir, const char *refname)
+{
+ struct ref_entry *entry;
+ dir = find_containing_dir(dir, refname, 0);
+ if (!dir)
+ return NULL;
+ entry = search_ref_dir(dir, refname);
+ return (entry && !(entry->flag & REF_DIR)) ? entry : NULL;
+}
+
+/*
+ * Add a ref_entry to the ref_dir (unsorted), recursing into
+ * subdirectories as necessary. dir must represent the top-level
+ * directory. Return 0 on success.
+ */
+static int add_ref(struct ref_dir *dir, struct ref_entry *ref)
+{
+ dir = find_containing_dir(dir, ref->name, 1);
+ if (!dir)
+ return -1;
+ add_entry_to_dir(dir, ref);
+ return 0;
+}
+
+/*
* Emit a warning and return true iff ref1 and ref2 have the same name
* and the same sha1. Die if they have the same name but different
* sha1s.
*/
static int is_dup_ref(const struct ref_entry *ref1, const struct ref_entry *ref2)
{
- if (!strcmp(ref1->name, ref2->name)) {
- /* Duplicate name; make sure that the SHA1s match: */
- if (hashcmp(ref1->u.value.sha1, ref2->u.value.sha1))
- die("Duplicated ref, and SHA1s don't match: %s",
- ref1->name);
- warning("Duplicated ref: %s", ref1->name);
- return 1;
- } else {
+ if (strcmp(ref1->name, ref2->name))
return 0;
- }
+
+ /* Duplicate name; make sure that they don't conflict: */
+
+ if ((ref1->flag & REF_DIR) || (ref2->flag & REF_DIR))
+ /* This is impossible by construction */
+ die("Reference directory conflict: %s", ref1->name);
+
+ if (hashcmp(ref1->u.value.sha1, ref2->u.value.sha1))
+ die("Duplicated ref, and SHA1s don't match: %s", ref1->name);
+
+ warning("Duplicated ref: %s", ref1->name);
+ return 1;
}
/*
- * Sort the entries in dir (if they are not already sorted)
- * and remove any duplicate entries.
+ * Sort the entries in dir non-recursively (if they are not already
+ * sorted) and remove any duplicate entries.
*/
static void sort_ref_dir(struct ref_dir *dir)
{
@@ -282,8 +420,9 @@ static int do_one_ref(const char *base, each_ref_fn fn, int trim,
/*
* Call fn for each reference in dir that has index in the range
- * offset <= index < dir->nr. This function does not sort the dir;
- * sorting should be done by the caller.
+ * offset <= index < dir->nr. Recurse into subdirectories that are in
+ * that index range, sorting them before iterating. This function
+ * does not sort dir itself; it should be sorted beforehand.
*/
static int do_for_each_ref_in_dir(struct ref_dir *dir, int offset,
const char *base,
@@ -292,7 +431,15 @@ static int do_for_each_ref_in_dir(struct ref_dir *dir, int offset,
int i;
assert(dir->sorted == dir->nr);
for (i = offset; i < dir->nr; i++) {
- int retval = do_one_ref(base, fn, trim, flags, cb_data, dir->entries[i]);
+ struct ref_entry *entry = dir->entries[i];
+ int retval;
+ if (entry->flag & REF_DIR) {
+ sort_ref_dir(&entry->u.subdir);
+ retval = do_for_each_ref_in_dir(&entry->u.subdir, 0,
+ base, fn, trim, flags, cb_data);
+ } else {
+ retval = do_one_ref(base, fn, trim, flags, cb_data, entry);
+ }
if (retval)
return retval;
}
@@ -301,9 +448,10 @@ static int do_for_each_ref_in_dir(struct ref_dir *dir, int offset,
/*
* Call fn for each reference in the union of dir1 and dir2, in order
- * by refname. If an entry appears in both dir1 and dir2, then only
- * process the version that is in dir2. The input dirs must already
- * be sorted.
+ * by refname. Recurse into subdirectories. If a value entry appears
+ * in both dir1 and dir2, then only process the version that is in
+ * dir2. The input dirs must already be sorted, but subdirs will be
+ * sorted as needed.
*/
static int do_for_each_ref_in_dirs(struct ref_dir *dir1,
struct ref_dir *dir2,
@@ -315,22 +463,55 @@ static int do_for_each_ref_in_dirs(struct ref_dir *dir1,
assert(dir1->sorted == dir1->nr);
assert(dir2->sorted == dir2->nr);
- while (i1 < dir1->nr && i2 < dir2->nr) {
- struct ref_entry *e1 = dir1->entries[i1];
- struct ref_entry *e2 = dir2->entries[i2];
- int cmp = strcmp(e1->name, e2->name);
- if (cmp < 0) {
- retval = do_one_ref(base, fn, trim, flags, cb_data, e1);
- i1++;
+ while (1) {
+ struct ref_entry *e1, *e2;
+ int cmp;
+ if (i1 == dir1->nr) {
+ return do_for_each_ref_in_dir(dir2, i2,
+ base, fn, trim, flags, cb_data);
+ }
+ if (i2 == dir2->nr) {
+ return do_for_each_ref_in_dir(dir1, i1,
+ base, fn, trim, flags, cb_data);
+ }
+ e1 = dir1->entries[i1];
+ e2 = dir2->entries[i2];
+ cmp = strcmp(e1->name, e2->name);
+ if (cmp == 0) {
+ if ((e1->flag & REF_DIR) && (e2->flag & REF_DIR)) {
+ /* Both are directories; descend them in parallel. */
+ sort_ref_dir(&e1->u.subdir);
+ sort_ref_dir(&e2->u.subdir);
+ retval = do_for_each_ref_in_dirs(
+ &e1->u.subdir, &e2->u.subdir,
+ base, fn, trim, flags, cb_data);
+ i1++;
+ i2++;
+ } else if (!(e1->flag & REF_DIR) && !(e2->flag & REF_DIR)) {
+ /* Both are references; ignore the one from dir1. */
+ retval = do_one_ref(base, fn, trim, flags, cb_data, e2);
+ i1++;
+ i2++;
+ } else {
+ die("conflict between reference and directory: %s",
+ e1->name);
+ }
} else {
- retval = do_one_ref(base, fn, trim, flags, cb_data, e2);
- i2++;
- if (cmp == 0) {
- /*
- * There was a ref in array1 with the
- * same name; ignore it.
- */
+ struct ref_entry *e;
+ if (cmp < 0) {
+ e = e1;
i1++;
+ } else {
+ e = e2;
+ i2++;
+ }
+ if (e->flag & REF_DIR) {
+ sort_ref_dir(&e->u.subdir);
+ retval = do_for_each_ref_in_dir(
+ &e->u.subdir, 0,
+ base, fn, trim, flags, cb_data);
+ } else {
+ retval = do_one_ref(base, fn, trim, flags, cb_data, e);
}
}
if (retval)
@@ -655,7 +836,7 @@ static int resolve_gitlink_packed_ref(struct ref_cache *refs,
struct ref_entry *ref;
struct ref_dir *dir = get_packed_refs(refs);
- ref = search_ref_dir(dir, refname);
+ ref = find_ref(dir, refname);
if (ref == NULL)
return -1;
@@ -727,7 +908,7 @@ int resolve_gitlink_ref(const char *path, const char *refname, unsigned char *sh
static int get_packed_ref(const char *refname, unsigned char *sha1)
{
struct ref_dir *packed = get_packed_refs(get_ref_cache(NULL));
- struct ref_entry *entry = search_ref_dir(packed, refname);
+ struct ref_entry *entry = find_ref(packed, refname);
if (entry) {
hashcpy(sha1, entry->u.value.sha1);
return 0;
@@ -904,7 +1085,7 @@ int peel_ref(const char *refname, unsigned char *sha1)
if ((flag & REF_ISPACKED)) {
struct ref_dir *dir = get_packed_refs(get_ref_cache(NULL));
- struct ref_entry *r = search_ref_dir(dir, refname);
+ struct ref_entry *r = find_ref(dir, refname);
if (r != NULL && r->flag & REF_KNOWS_PEELED) {
hashcpy(sha1, r->u.value.peeled);
@@ -1404,8 +1585,7 @@ static int repack_without_ref(const char *refname)
{
struct repack_without_ref_sb data;
struct ref_dir *packed = get_packed_refs(get_ref_cache(NULL));
- sort_ref_dir(packed);
- if (search_ref_dir(packed, refname) == NULL)
+ if (find_ref(packed, refname) == NULL)
return 0;
data.refname = refname;
data.fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
View
7 refs.h
@@ -15,8 +15,11 @@ struct ref_lock {
#define REF_ISBROKEN 0x04
/*
- * Calls the specified function for each ref file until it returns nonzero,
- * and returns the value
+ * Calls the specified function for each ref file until it returns
+ * nonzero, and returns the value. Please note that it is not safe to
+ * modify references while an iteration is in progress, unless the
+ * same callback function invocation that modifies the reference also
+ * returns a nonzero value to immediately stop the iteration.
*/
typedef int each_ref_fn(const char *refname, const unsigned char *sha1, int flags, void *cb_data);
extern int head_ref(each_ref_fn, void *);

0 comments on commit 432ad41

Please sign in to comment.