attr.c: outline the future plans by heavily commenting

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/attr.c b/attr.c
index 8026d68bd1722c4900616592d464e3e248c22d75..50e5ee393489eb065326f5a25eb6e0cccb3b9c9f 100644 (file)
--- a/attr.c
+++ b/attr.c
@@ -30,6 +30,11 @@ static const char git_attr__unknown[] = "(builtin)unknown";
 #define DEBUG_ATTR 0
 #endif
 
 #define DEBUG_ATTR 0
 #endif
 

+/*
+ * NEEDSWORK: the global dictionary of the interned attributes
+ * must stay a singleton even after we become thread-ready.
+ * Access to these must be surrounded with mutex when it happens.
+ */

 struct git_attr {
        struct git_attr *next;
        unsigned h;
 struct git_attr {
        struct git_attr *next;
        unsigned h;


@@ -39,10 +44,19 @@ struct git_attr {
        char name[FLEX_ARRAY];
 };
 static int attr_nr;
        char name[FLEX_ARRAY];
 };
 static int attr_nr;

+static struct git_attr *(git_attr_hash[HASHSIZE]);
+
+/*
+ * NEEDSWORK: maybe-real, maybe-macro are not property of
+ * an attribute, as it depends on what .gitattributes are
+ * read.  Once we introduce per git_attr_check attr_stack
+ * and check_all_attr, the optimization based on them will
+ * become unnecessary and can go away.  So is this variable.
+ */

 static int cannot_trust_maybe_real;
 
 static int cannot_trust_maybe_real;
 

+/* NEEDSWORK: This will become per git_attr_check */

 static struct git_attr_check *check_all_attr;
 static struct git_attr_check *check_all_attr;

-static struct git_attr *(git_attr_hash[HASHSIZE]);

 
 const char *git_attr_name(const struct git_attr *attr)
 {
 
 const char *git_attr_name(const struct git_attr *attr)
 {


@@ -102,6 +116,11 @@ static struct git_attr *git_attr_internal(const char *name, int len)
        a->maybe_real = 0;
        git_attr_hash[pos] = a;
 
        a->maybe_real = 0;
        git_attr_hash[pos] = a;
 

+       /*
+        * NEEDSWORK: per git_attr_check check_all_attr
+        * will be initialized a lot more lazily, not
+        * like this, and not here.
+        */

        REALLOC_ARRAY(check_all_attr, attr_nr);
        check_all_attr[a->attr_nr].attr = a;
        check_all_attr[a->attr_nr].value = ATTR__UNKNOWN;
        REALLOC_ARRAY(check_all_attr, attr_nr);
        check_all_attr[a->attr_nr].attr = a;
        check_all_attr[a->attr_nr].value = ATTR__UNKNOWN;


@@ -318,6 +337,7 @@ static struct match_attr *parse_attr_line(const char *line, const char *src,
  * .gitignore file and info/excludes file as a fallback.
  */
 
  * .gitignore file and info/excludes file as a fallback.
  */
 

+/* NEEDSWORK: This will become per git_attr_check */

 static struct attr_stack {
        struct attr_stack *prev;
        char *origin;
 static struct attr_stack {
        struct attr_stack *prev;
        char *origin;


@@ -382,6 +402,24 @@ static struct attr_stack *read_attr_from_array(const char **list)
        return res;
 }
 
        return res;
 }
 

+/*
+ * NEEDSWORK: these two are tricky.  The callers assume there is a
+ * single, system-wide global state "where we read attributes from?"
+ * and when the state is flipped by calling git_attr_set_direction(),
+ * attr_stack is discarded so that subsequent attr_check will lazily
+ * read from the right place.  And they do not know or care who called
+ * by them uses the attribute subsystem, hence have no knowledge of
+ * existing git_attr_check instances or future ones that will be
+ * created).
+ *
+ * Probably we need a thread_local that holds these two variables,
+ * and a list of git_attr_check instances (which need to be maintained
+ * by hooking into git_attr_check_alloc(), git_attr_check_initl(), and
+ * git_attr_check_clear().  Then git_attr_set_direction() updates the
+ * fields in that thread_local for these two variables, iterate over
+ * all the active git_attr_check instances and discard the attr_stack
+ * they hold.  Yuck, but it sounds doable.
+ */

 static enum git_attr_direction direction;
 static struct index_state *use_index;
 
 static enum git_attr_direction direction;
 static struct index_state *use_index;