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refs: read loose references lazily

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Instead of reading the whole directory of loose references the first
time any are needed, only read them on demand, one directory at a
time.

Use a new ref_entry flag bit REF_INCOMPLETE to indicate that the entry
represents a REF_DIR that hasn't been read yet.  Whenever any entries
from such a directory are needed, read all of the loose references
from that directory.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Michael Haggerty 2012-04-27 00:27:07 +02:00 committed by Junio C Hamano
parent 423a1afc0b
commit 28e6a34e25
1 changed files with 96 additions and 29 deletions
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125
refs.c
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@ -101,6 +101,12 @@ int check_refname_format(const char *refname, int flags)
struct ref_entry;
/*
* Information used (along with the information in ref_entry) to
* describe a single cached reference. This data structure only
* occurs embedded in a union in struct ref_entry, and only when
* (ref_entry->flag & REF_DIR) is zero.
*/
struct ref_value {
unsigned char sha1[20];
unsigned char peeled[20];
@ -108,6 +114,32 @@ struct ref_value {
struct ref_cache;
/*
* Information used (along with the information in ref_entry) to
* describe a level in the hierarchy of references. This data
* structure only occurs embedded in a union in struct ref_entry, and
* only when (ref_entry.flag & REF_DIR) is set. In that case,
* (ref_entry.flag & REF_INCOMPLETE) determines whether the references
* in the directory have already been read:
*
* (ref_entry.flag & REF_INCOMPLETE) unset -- a directory of loose
* or packed references, already read.
*
* (ref_entry.flag & REF_INCOMPLETE) set -- a directory of loose
* references that hasn't been read yet (nor has any of its
* subdirectories).
*
* Entries within a directory are stored within a growable array of
* pointers to ref_entries (entries, nr, alloc). Entries 0 <= i <
* sorted are sorted by their component name in strcmp() order and the
* remaining entries are unsorted.
*
* Loose references are read lazily, one directory at a time. When a
* directory of loose references is read, then all of the references
* in that directory are stored, and REF_INCOMPLETE stubs are created
* for any subdirectories, but the subdirectories themselves are not
* read. The reading is triggered by get_ref_dir().
*/
struct ref_dir {
int nr, alloc;
@ -127,19 +159,33 @@ struct ref_dir {
/* ISSYMREF=0x01, ISPACKED=0x02, and ISBROKEN=0x04 are public interfaces */
#define REF_KNOWS_PEELED 0x08
/* ref_entry represents a directory of references */
#define REF_DIR 0x10
/*
* Entry has not yet been read from disk (used only for REF_DIR
* entries representing loose references)
*/
#define REF_INCOMPLETE 0x20
/*
* 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).
* 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 that have been read so
* far. If (flags & REF_INCOMPLETE) is set, then the directory and
* its subdirectories haven't been read yet. REF_INCOMPLETE is only
* used for loose reference directories.
*
* 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
@ -176,10 +222,18 @@ struct ref_entry {
char name[FLEX_ARRAY];
};
static void read_loose_refs(const char *dirname, struct ref_dir *dir);
static struct ref_dir *get_ref_dir(struct ref_entry *entry)
{
struct ref_dir *dir;
assert(entry->flag & REF_DIR);
return &entry->u.subdir;
dir = &entry->u.subdir;
if (entry->flag & REF_INCOMPLETE) {
read_loose_refs(entry->name, dir);
entry->flag &= ~REF_INCOMPLETE;
}
return dir;
}
static struct ref_entry *create_ref_entry(const char *refname,
@ -240,14 +294,14 @@ static void clear_ref_dir(struct ref_dir *dir)
* "refs/heads/") or "" for the top-level directory.
*/
static struct ref_entry *create_dir_entry(struct ref_cache *ref_cache,
const char *dirname)
const char *dirname, int incomplete)
{
struct ref_entry *direntry;
int len = strlen(dirname);
direntry = xcalloc(1, sizeof(struct ref_entry) + len + 1);
memcpy(direntry->name, dirname, len + 1);
direntry->u.subdir.ref_cache = ref_cache;
direntry->flag = REF_DIR;
direntry->flag = REF_DIR | (incomplete ? REF_INCOMPLETE : 0);
return direntry;
}
@ -263,7 +317,7 @@ 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.
* such entry is found. dir must already be complete.
*/
static struct ref_entry *search_ref_dir(struct ref_dir *dir, const char *refname)
{
@ -294,7 +348,7 @@ static struct ref_entry *search_ref_dir(struct ref_dir *dir, const char *refname
* recursing). Sort dir if necessary. subdirname must be a directory
* name (i.e., end in '/'). If mkdir is set, then create the
* directory if it is missing; otherwise, return NULL if the desired
* directory cannot be found.
* directory cannot be found. dir must already be complete.
*/
static struct ref_dir *search_for_subdir(struct ref_dir *dir,
const char *subdirname, int mkdir)
@ -303,7 +357,13 @@ static struct ref_dir *search_for_subdir(struct ref_dir *dir,
if (!entry) {
if (!mkdir)
return NULL;
entry = create_dir_entry(dir->ref_cache, subdirname);
/*
* Since dir is complete, the absence of a subdir
* means that the subdir really doesn't exist;
* therefore, create an empty record for it but mark
* the record complete.
*/
entry = create_dir_entry(dir->ref_cache, subdirname, 0);
add_entry_to_dir(dir, entry);
}
return get_ref_dir(entry);
@ -313,10 +373,10 @@ static struct ref_dir *search_for_subdir(struct ref_dir *dir,
* 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.
* represent the top-level directory and must already be complete.
* 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)
@ -760,7 +820,7 @@ static struct ref_dir *get_packed_refs(struct ref_cache *refs)
const char *packed_refs_file;
FILE *f;
refs->packed = create_dir_entry(refs, "");
refs->packed = create_dir_entry(refs, "", 0);
if (*refs->name)
packed_refs_file = git_path_submodule(refs->name, "packed-refs");
else
@ -781,9 +841,9 @@ void add_packed_ref(const char *refname, const unsigned char *sha1)
}
/*
* Read the loose references for refs from the namespace dirname.
* dirname must end with '/'. dir must be the directory entry
* corresponding to dirname.
* Read the loose references from the namespace dirname into dir
* (without recursing). dirname must end with '/'. dir must be the
* directory entry corresponding to dirname.
*/
static void read_loose_refs(const char *dirname, struct ref_dir *dir)
{
@ -824,8 +884,8 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
; /* silently ignore */
} else if (S_ISDIR(st.st_mode)) {
strbuf_addch(&refname, '/');
read_loose_refs(refname.buf,
search_for_subdir(dir, refname.buf, 1));
add_entry_to_dir(dir,
create_dir_entry(refs, refname.buf, 1));
} else {
if (*refs->name) {
hashclr(sha1);
@ -850,10 +910,17 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
static struct ref_dir *get_loose_refs(struct ref_cache *refs)
{
if (!refs->loose) {
refs->loose = create_dir_entry(refs, "");
read_loose_refs("refs/",
search_for_subdir(get_ref_dir(refs->loose),
"refs/", 1));
/*
* Mark the top-level directory complete because we
* are about to read the only subdirectory that can
* hold references:
*/
refs->loose = create_dir_entry(refs, "", 0);
/*
* Create an incomplete entry for "refs/":
*/
add_entry_to_dir(get_ref_dir(refs->loose),
create_dir_entry(refs, "refs/", 1));
}
return get_ref_dir(refs->loose);
}