This revamps the API of the attr subsystem to be thread safe.
Before we had the question and its results in one struct type.
The typical usage of the API was

    static struct git_attr_check *check;

    if (!check)
        check = git_attr_check_initl("text", NULL);

    git_check_attr(path, check);
    act_on(check->value[0]);

This has a couple of issues when it comes to thread safety:

* the initialization is racy in this implementation. To make it
  thread safe, we need to acquire a mutex, such that only one
  thread is executing the code in git_attr_check_initl.
  As we do not want to introduce a mutex at each call site,
  this is best done in the attr code. However to do so, we need
  to have access to the `check` variable, i.e. the API has to
  look like
    git_attr_check_initl(struct git_attr_check*, ...);
  Then one of the threads calling git_attr_check_initl will
  acquire the mutex and init the `check`, while all other threads
  will wait on the mutex just to realize they're late to the
  party and they'll return with no work done.

* While the check for attributes to be questioned only need to
  be initalized once as that part will be read only after its
  initialisation, the answer may be different for each path.
  Because of that we need to decouple the check and the answer,
  such that each thread can obtain an answer for the path it
  is currently processing.

This commit changes the API and adds locking in
git_attr_check_initl that provides the thread safety.

The usage of the new API will be:

    /*
     * The initl call will thread-safely check whether the
     * struct git_attr_check has been initialized. We only
     * want to do the initialization work once, hence we do
     * that work inside a thread safe environment.
     */
    static struct git_attr_check *check;
    git_attr_check_initl(&check, "text", NULL);

    /*
     * Resize internal data structures in the result to match
     * the size of `check`:
     */
    struct git_attr_result *result = GIT_ATTR_RESULT_INIT;
    git_attr_result_init(&result, check);

    /* Perform the check and act on it: */
    git_check_attr(path, check, &result);
    act_on(check->value[0]);

    /*
     * Free the result.
     * The check is static, so doesn't require free'ing
     */
    git_attr_result_clear(&result);

Signed-off-by: Stefan Beller <sbel...@google.com>
---

 * Do not use the Double Check Locking Pattern
 * The callers are all thread safe now (i.e. no static result)
 * So this is roughly what we want for the first version of the conversion?
 
 Thanks,
 Stefan

 Documentation/technical/api-gitattributes.txt |  93 +++++++++++++------
 archive.c                                     |  18 ++--
 attr.c                                        | 125 +++++++++++++++++---------
 attr.h                                        |  80 +++++++++++------
 builtin/check-attr.c                          |  31 ++++---
 builtin/pack-objects.c                        |  20 +++--
 convert.c                                     |  43 +++++----
 ll-merge.c                                    |  28 +++---
 userdiff.c                                    |  24 +++--
 ws.c                                          |  17 ++--
 10 files changed, 314 insertions(+), 165 deletions(-)

diff --git a/Documentation/technical/api-gitattributes.txt 
b/Documentation/technical/api-gitattributes.txt
index 92fc32a..ac97244 100644
--- a/Documentation/technical/api-gitattributes.txt
+++ b/Documentation/technical/api-gitattributes.txt
@@ -8,6 +8,18 @@ attributes to set of paths.
 Data Structure
 --------------
 
+extern struct git_attr *git_attr(const char *);
+
+/*
+ * Return the name of the attribute represented by the argument.  The
+ * return value is a pointer to a null-delimited string that is part
+ * of the internal data structure; it should not be modified or freed.
+ */
+extern const char *git_attr_name(const struct git_attr *);
+
+extern int attr_name_valid(const char *name, size_t namelen);
+extern void invalid_attr_name_message(struct strbuf *, const char *, int);
+
 `struct git_attr`::
 
        An attribute is an opaque object that is identified by its name.
@@ -16,15 +28,17 @@ Data Structure
        of no interest to the calling programs.  The name of the
        attribute can be retrieved by calling `git_attr_name()`.
 
-`struct git_attr_check_elem`::
-
-       This structure represents one attribute and its value.
-
 `struct git_attr_check`::
 
-       This structure represents a collection of `git_attr_check_elem`.
+       This structure represents a collection of `struct git_attrs`.
        It is passed to `git_check_attr()` function, specifying the
-       attributes to check, and receives their values.
+       attributes to check, and receives their values into a corresponding
+       `struct git_attr_result`.
+
+`struct git_attr_result`::
+
+       This structure represents a collection of results to its
+       corresponding `struct git_attr_check`, that has the same order.
 
 
 Attribute Values
@@ -53,19 +67,30 @@ value of the attribute for the path.
 Querying Specific Attributes
 ----------------------------
 
-* Prepare `struct git_attr_check` using git_attr_check_initl()
+* Prepare a `struct git_attr_check` using `git_attr_check_initl()`
   function, enumerating the names of attributes whose values you are
   interested in, terminated with a NULL pointer.  Alternatively, an
-  empty `struct git_attr_check` can be prepared by calling
-  `git_attr_check_alloc()` function and then attributes you want to
-  ask about can be added to it with `git_attr_check_append()`
-  function.
-
-* Call `git_check_attr()` to check the attributes for the path.
-
-* Inspect `git_attr_check` structure to see how each of the
-  attribute in the array is defined for the path.
-
+  empty `struct git_attr_check` as allocated by git_attr_check_alloc()
+  can be prepared by calling `git_attr_check_alloc()` function and
+  then attributes you want to ask about can be added to it with
+  `git_attr_check_append()` function.
+  `git_attr_check_initl()` is thread safe, i.e. you can call it
+  from different threads at the same time; when check determines
+  the initialzisation is still needed, the threads will use a
+  single global mutex to perform the initialization just once, the
+  others will wait on the the thread to actually perform the
+  initialization.
+
+* Prepare a `struct git_attr_result` using `git_attr_result_init()`
+  for the check struct. The call to initialize the result is not thread
+  safe, because different threads need their own thread local result
+  anyway.
+
+* Call `git_check_attr()` to check the attributes for the path,
+  the returned `git_attr_result` contains the result.
+
+* Inspect the returned `git_attr_result` structure to see how
+  each of the attribute in the array is defined for the path.
 
 Example
 -------
@@ -89,15 +114,20 @@ static void setup_check(void)
 
 ------------
        const char *path;
+       struct git_attr_result *result;
 
        setup_check();
-       git_check_attr(path, check);
+       result = git_check_attr(path, check);
 ------------
 
-. Act on `.value` member of the result, left in `check->check[]`:
+The `result` must not be free'd as it is owned by the attr subsystem.
+It is reused by the same thread, so a subsequent call to git_check_attr
+in the same thread will overwrite the result.
+
+. Act on `result->value[]`:
 
 ------------
-       const char *value = check->check[0].value;
+       const char *value = result->value[0];
 
        if (ATTR_TRUE(value)) {
                The attribute is Set, by listing only the name of the
@@ -123,6 +153,8 @@ the first step in the above would be different.
 static struct git_attr_check *check;
 static void setup_check(const char **argv)
 {
+       if (check)
+               return; /* already done */
        check = git_attr_check_alloc();
        while (*argv) {
                struct git_attr *attr = git_attr(*argv);
@@ -138,17 +170,20 @@ Querying All Attributes
 
 To get the values of all attributes associated with a file:
 
-* Prepare an empty `git_attr_check` structure by calling
-  `git_attr_check_alloc()`.
+* Setup a local variables on the stack for both the question
+  `struct git_attr_check` as well as the result `struct git_attr_result`.
+  Zero them out via their respective _INIT macro.
 
-* Call `git_all_attrs()`, which populates the `git_attr_check`
-  with the attributes attached to the path.
+* Call `git_all_attrs()`
 
-* Iterate over the `git_attr_check.check[]` array to examine
-  the attribute names and values.  The name of the attribute
-  described by a  `git_attr_check.check[]` object can be retrieved via
-  `git_attr_name(check->check[i].attr)`.  (Please note that no items
+* Iterate over the `git_attr_check.attr[]` array to examine the
+  attribute names.  The name of the attribute described by a
+  `git_attr_check.attr[]` object can be retrieved via
+  `git_attr_name(check->attr[i])`.  (Please note that no items
   will be returned for unset attributes, so `ATTR_UNSET()` will return
   false for all returned `git_array_check` objects.)
+  The respective value for an attribute can be found in the same
+  index position in of `git_attr_result`.
 
-* Free the `git_array_check` by calling `git_attr_check_free()`.
+* Clear the local variables by calling `git_attr_check_clear()` and
+  `git_attr_result_clear()`.
diff --git a/archive.c b/archive.c
index 11e3951..15849a8 100644
--- a/archive.c
+++ b/archive.c
@@ -107,10 +107,12 @@ static int write_archive_entry(const unsigned char *sha1, 
const char *base,
                void *context)
 {
        static struct strbuf path = STRBUF_INIT;
+       static struct git_attr_check *check;
+
        struct archiver_context *c = context;
        struct archiver_args *args = c->args;
        write_archive_entry_fn_t write_entry = c->write_entry;
-       static struct git_attr_check *check;
+       struct git_attr_result result = GIT_ATTR_RESULT_INIT;
        const char *path_without_prefix;
        int err;
 
@@ -124,12 +126,16 @@ static int write_archive_entry(const unsigned char *sha1, 
const char *base,
                strbuf_addch(&path, '/');
        path_without_prefix = path.buf + args->baselen;
 
-       if (!check)
-               check = git_attr_check_initl("export-ignore", "export-subst", 
NULL);
-       if (!git_check_attr(path_without_prefix, check)) {
-               if (ATTR_TRUE(check->check[0].value))
+       git_attr_check_initl(&check, "export-ignore", "export-subst", NULL);
+       git_attr_result_init(&result, check);
+
+       if (!git_check_attr(path_without_prefix, check, &result)) {
+               if (ATTR_TRUE(result.value[0])) {
+                       git_attr_result_clear(&result);
                        return 0;
-               args->convert = ATTR_TRUE(check->check[1].value);
+               }
+               args->convert = ATTR_TRUE(result.value[1]);
+               git_attr_result_clear(&result);
        }
 
        if (S_ISDIR(mode) || S_ISGITLINK(mode)) {
diff --git a/attr.c b/attr.c
index 0faa69f..648c4f9 100644
--- a/attr.c
+++ b/attr.c
@@ -14,6 +14,7 @@
 #include "dir.h"
 #include "utf8.h"
 #include "quote.h"
+#include "thread-utils.h"
 
 const char git_attr__true[] = "(builtin)true";
 const char git_attr__false[] = "\0(builtin)false";
@@ -46,6 +47,19 @@ struct git_attr {
 static int attr_nr;
 static struct git_attr *(git_attr_hash[HASHSIZE]);
 
+#ifndef NO_PTHREADS
+
+static pthread_mutex_t attr_mutex;
+#define attr_lock()            pthread_mutex_lock(&attr_mutex)
+#define attr_unlock()          pthread_mutex_unlock(&attr_mutex)
+
+#else
+
+#define attr_lock()            (void)0
+#define attr_unlock()          (void)0
+
+#endif /* NO_PTHREADS */
+
 /*
  * NEEDSWORK: maybe-real, maybe-macro are not property of
  * an attribute, as it depends on what .gitattributes are
@@ -55,6 +69,16 @@ static struct git_attr *(git_attr_hash[HASHSIZE]);
  */
 static int cannot_trust_maybe_real;
 
+/*
+ * Send one or more git_attr_check to git_check_attrs(), and
+ * each 'value' member tells what its value is.
+ * Unset one is returned as NULL.
+ */
+struct git_attr_check_elem {
+       const struct git_attr *attr;
+       const char *value;
+};
+
 /* NEEDSWORK: This will become per git_attr_check */
 static struct git_attr_check_elem *check_all_attr;
 
@@ -781,7 +805,7 @@ static int macroexpand_one(int nr, int rem)
 
 static int attr_check_is_dynamic(const struct git_attr_check *check)
 {
-       return (void *)(check->check) != (void *)(check + 1);
+       return (void *)(check->attr) != (void *)(check + 1);
 }
 
 static void empty_attr_check_elems(struct git_attr_check *check)
@@ -799,7 +823,8 @@ static void empty_attr_check_elems(struct git_attr_check 
*check)
  * any and all attributes that are visible are collected in it.
  */
 static void collect_some_attrs(const char *path, int pathlen,
-                              struct git_attr_check *check, int collect_all)
+                              struct git_attr_check *check,
+                              struct git_attr_result *result, int collect_all)
 
 {
        struct attr_stack *stk;
@@ -825,13 +850,11 @@ static void collect_some_attrs(const char *path, int 
pathlen,
                check_all_attr[i].value = ATTR__UNKNOWN;
 
        if (!collect_all && !cannot_trust_maybe_real) {
-               struct git_attr_check_elem *celem = check->check;
-
                rem = 0;
                for (i = 0; i < check->check_nr; i++) {
-                       if (!celem[i].attr->maybe_real) {
+                       if (!check->attr[i]->maybe_real) {
                                struct git_attr_check_elem *c;
-                               c = check_all_attr + celem[i].attr->attr_nr;
+                               c = check_all_attr + check->attr[i]->attr_nr;
                                c->value = ATTR__UNSET;
                                rem++;
                        }
@@ -845,38 +868,45 @@ static void collect_some_attrs(const char *path, int 
pathlen,
                rem = fill(path, pathlen, basename_offset, stk, rem);
 
        if (collect_all) {
-               empty_attr_check_elems(check);
                for (i = 0; i < attr_nr; i++) {
                        const struct git_attr *attr = check_all_attr[i].attr;
                        const char *value = check_all_attr[i].value;
                        if (value == ATTR__UNSET || value == ATTR__UNKNOWN)
                                continue;
-                       git_attr_check_append(check, attr)->value = value;
+
+                       git_attr_check_append(check, attr);
+
+                       ALLOC_GROW(result->value,
+                                  result->check_nr + 1,
+                                  result->check_alloc);
+                       result->value[result->check_nr++] = value;
                }
        }
 }
 
 static int git_check_attrs(const char *path, int pathlen,
-                          struct git_attr_check *check)
+                          struct git_attr_check *check,
+                          struct git_attr_result *result)
 {
        int i;
-       struct git_attr_check_elem *celem = check->check;
 
-       collect_some_attrs(path, pathlen, check, 0);
+       collect_some_attrs(path, pathlen, check, result, 0);
 
        for (i = 0; i < check->check_nr; i++) {
-               const char *value = 
check_all_attr[celem[i].attr->attr_nr].value;
+               const char *value = 
check_all_attr[check->attr[i]->attr_nr].value;
                if (value == ATTR__UNKNOWN)
                        value = ATTR__UNSET;
-               celem[i].value = value;
+               result->value[i] = value;
        }
 
        return 0;
 }
 
-void git_all_attrs(const char *path, struct git_attr_check *check)
+void git_all_attrs(const char *path,
+                  struct git_attr_check *check,
+                  struct git_attr_result *result)
 {
-       collect_some_attrs(path, strlen(path), check, 1);
+       collect_some_attrs(path, strlen(path), check, result, 1);
 }
 
 void git_attr_set_direction(enum git_attr_direction new, struct index_state 
*istate)
@@ -892,36 +922,42 @@ void git_attr_set_direction(enum git_attr_direction new, 
struct index_state *ist
        use_index = istate;
 }
 
-static int git_check_attr_counted(const char *path, int pathlen,
-                                 struct git_attr_check *check)
+int git_check_attr(const char *path,
+                   struct git_attr_check *check,
+                   struct git_attr_result *result)
 {
+       if (result->check_nr != check->check_nr)
+               die("BUG: git_attr_result is not prepared correctly");
        check->finalized = 1;
-       return git_check_attrs(path, pathlen, check);
+       return git_check_attrs(path, strlen(path), check, result);
 }
 
-int git_check_attr(const char *path, struct git_attr_check *check)
+void git_attr_check_initl(struct git_attr_check **check_,
+                         const char *one, ...)
 {
-       return git_check_attr_counted(path, strlen(path), check);
-}
-
-struct git_attr_check *git_attr_check_initl(const char *one, ...)
-{
-       struct git_attr_check *check;
        int cnt;
        va_list params;
        const char *param;
+       struct git_attr_check *check;
+
+       attr_lock();
+       if (*check_) {
+               attr_unlock();
+               return;
+       }
 
        va_start(params, one);
        for (cnt = 1; (param = va_arg(params, const char *)) != NULL; cnt++)
                ;
        va_end(params);
+
        check = xcalloc(1,
-                       sizeof(*check) + cnt * sizeof(*(check->check)));
+                       sizeof(*check) + cnt * sizeof(*(check->attr)));
        check->check_nr = cnt;
        check->finalized = 1;
-       check->check = (struct git_attr_check_elem *)(check + 1);
+       check->attr = (const struct git_attr **)(check + 1);
 
-       check->check[0].attr = git_attr(one);
+       check->attr[0] = git_attr(one);
        va_start(params, one);
        for (cnt = 1; cnt < check->check_nr; cnt++) {
                struct git_attr *attr;
@@ -932,10 +968,11 @@ struct git_attr_check *git_attr_check_initl(const char 
*one, ...)
                attr = git_attr(param);
                if (!attr)
                        die("BUG: %s: not a valid attribute name", param);
-               check->check[cnt].attr = attr;
+               check->attr[cnt] = attr;
        }
        va_end(params);
-       return check;
+       *check_ = check;
+       attr_unlock();
 }
 
 struct git_attr_check *git_attr_check_alloc(void)
@@ -943,18 +980,23 @@ struct git_attr_check *git_attr_check_alloc(void)
        return xcalloc(1, sizeof(struct git_attr_check));
 }
 
-struct git_attr_check_elem *git_attr_check_append(struct git_attr_check *check,
-                                                 const struct git_attr *attr)
+void git_attr_result_init(struct git_attr_result *result,
+                         struct git_attr_check *check)
+{
+       ALLOC_GROW(result->value, check->check_nr, result->check_alloc);
+       result->check_nr = check->check_nr;
+}
+
+
+void git_attr_check_append(struct git_attr_check *check,
+                          const struct git_attr *attr)
 {
-       struct git_attr_check_elem *elem;
        if (check->finalized)
                die("BUG: append after git_attr_check structure is finalized");
        if (!attr_check_is_dynamic(check))
                die("BUG: appending to a statically initialized 
git_attr_check");
-       ALLOC_GROW(check->check, check->check_nr + 1, check->check_alloc);
-       elem = &check->check[check->check_nr++];
-       elem->attr = attr;
-       return elem;
+       ALLOC_GROW(check->attr, check->check_nr + 1, check->check_alloc);
+       check->attr[check->check_nr++] = attr;
 }
 
 void git_attr_check_clear(struct git_attr_check *check)
@@ -962,12 +1004,13 @@ void git_attr_check_clear(struct git_attr_check *check)
        empty_attr_check_elems(check);
        if (!attr_check_is_dynamic(check))
                die("BUG: clearing a statically initialized git_attr_check");
-       free(check->check);
+       free(check->attr);
        check->check_alloc = 0;
 }
 
-void git_attr_check_free(struct git_attr_check *check)
+void git_attr_result_clear(struct git_attr_result *result)
 {
-       git_attr_check_clear(check);
-       free(check);
+       free(result->value);
+       result->check_nr = 0;
+       result->check_alloc = 0;
 }
diff --git a/attr.h b/attr.h
index 163fcd6..620f6f8 100644
--- a/attr.h
+++ b/attr.h
@@ -10,6 +10,13 @@ struct git_attr;
  */
 extern struct git_attr *git_attr(const char *);
 
+/*
+ * Return the name of the attribute represented by the argument.  The
+ * return value is a pointer to a null-delimited string that is part
+ * of the internal data structure; it should not be modified or freed.
+ */
+extern const char *git_attr_name(const struct git_attr *);
+
 extern int attr_name_valid(const char *name, size_t namelen);
 extern void invalid_attr_name_message(struct strbuf *, const char *, int);
 
@@ -22,44 +29,65 @@ extern const char git_attr__false[];
 #define ATTR_FALSE(v) ((v) == git_attr__false)
 #define ATTR_UNSET(v) ((v) == NULL)
 
-/*
- * Send one or more git_attr_check to git_check_attrs(), and
- * each 'value' member tells what its value is.
- * Unset one is returned as NULL.
- */
-struct git_attr_check_elem {
-       const struct git_attr *attr;
-       const char *value;
-};
-
 struct git_attr_check {
        int finalized;
        int check_nr;
        int check_alloc;
-       struct git_attr_check_elem *check;
+       const struct git_attr **attr;
 };
+#define GIT_ATTR_CHECK_INIT {0, 0, 0, NULL}
 
-extern struct git_attr_check *git_attr_check_initl(const char *, ...);
-extern int git_check_attr(const char *path, struct git_attr_check *);
+struct git_attr_result {
+       int check_nr;
+       int check_alloc;
+       const char **value;
+};
+#define GIT_ATTR_RESULT_INIT {0, 0, NULL}
 
+/*
+ * Initialize the `git_attr_check` via one of the following three functions:
+ *
+ * git_attr_check_alloc  allocates an empty check,
+ * git_attr_check_append add an attribute to the given git_attr_check
+ * git_attr_result_init  prepare the result struct for a given check struct
+ *
+ * git_all_attrs         allocates a check and fills in all attributes that
+ *                       are set for the given path.
+ * git_attr_check_initl  takes a pointer to where the check will be 
initialized,
+ *                       followed by all attributes that are to be checked.
+ *                       This makes it potentially thread safe as it could
+ *                       internally have a mutex for that memory location.
+ *                       Currently it is not thread safe!
+ */
 extern struct git_attr_check *git_attr_check_alloc(void);
-extern struct git_attr_check_elem *git_attr_check_append(struct git_attr_check 
*, const struct git_attr *);
+extern void git_attr_check_append(struct git_attr_check *,
+                                 const struct git_attr *);
+extern void git_attr_check_initl(struct git_attr_check **,
+                                const char *, ...);
 
-extern void git_attr_check_clear(struct git_attr_check *);
-extern void git_attr_check_free(struct git_attr_check *);
+extern void git_attr_result_init(struct git_attr_result *,
+                                struct git_attr_check *);
 
-/*
- * Return the name of the attribute represented by the argument.  The
- * return value is a pointer to a null-delimited string that is part
- * of the internal data structure; it should not be modified or freed.
- */
-extern const char *git_attr_name(const struct git_attr *);
+extern void git_all_attrs(const char *path,
+                         struct git_attr_check *,
+                         struct git_attr_result *);
 
-/*
- * Retrieve all attributes that apply to the specified path.
- * check holds the attributes and their values.
+/* Query a path for its attributes */
+extern int git_check_attr(const char *path,
+                         struct git_attr_check *,
+                         struct git_attr_result *);
+
+
+
+/**
+ * Free or clear the result struct. The underlying strings are not free'd
+ * as they are globally known.
  */
-void git_all_attrs(const char *path, struct git_attr_check *check);
+extern void git_attr_result_free(struct git_attr_result *);
+extern void git_attr_result_clear(struct git_attr_result *);
+
+extern void git_attr_check_clear(struct git_attr_check *);
+
 
 enum git_attr_direction {
        GIT_ATTR_CHECKIN,
diff --git a/builtin/check-attr.c b/builtin/check-attr.c
index ec61476..5e78d5d 100644
--- a/builtin/check-attr.c
+++ b/builtin/check-attr.c
@@ -24,13 +24,17 @@ static const struct option check_attr_options[] = {
        OPT_END()
 };
 
-static void output_attr(struct git_attr_check *check, const char *file)
+static void output_attr(struct git_attr_check *check,
+                       struct git_attr_result *result, const char *file)
 {
        int j;
        int cnt = check->check_nr;
 
+       if (check->check_nr != result->check_nr)
+               die("BUG: confused check and result internally");
+
        for (j = 0; j < cnt; j++) {
-               const char *value = check->check[j].value;
+               const char *value = result->value[j];
 
                if (ATTR_TRUE(value))
                        value = "set";
@@ -44,11 +48,11 @@ static void output_attr(struct git_attr_check *check, const 
char *file)
                               "%s%c" /* attrname */
                               "%s%c" /* attrvalue */,
                               file, 0,
-                              git_attr_name(check->check[j].attr), 0, value, 
0);
+                              git_attr_name(check->attr[j]), 0, value, 0);
                } else {
                        quote_c_style(file, NULL, stdout, 0);
                        printf(": %s: %s\n",
-                              git_attr_name(check->check[j].attr), value);
+                              git_attr_name(check->attr[j]), value);
                }
        }
 }
@@ -59,16 +63,21 @@ static void check_attr(const char *prefix,
 {
        char *full_path =
                prefix_path(prefix, prefix ? strlen(prefix) : 0, file);
+       struct git_attr_result result = GIT_ATTR_RESULT_INIT;
+       struct git_attr_check local_check = GIT_ATTR_CHECK_INIT;
+
        if (check != NULL) {
-               if (git_check_attr(full_path, check))
-                       die("git_check_attr died");
-               output_attr(check, file);
+               git_attr_result_init(&result, check);
+               git_check_attr(full_path, check, &result);
        } else {
-               check = git_attr_check_alloc();
-               git_all_attrs(full_path, check);
-               output_attr(check, file);
-               git_attr_check_free(check);
+               git_all_attrs(full_path, &local_check, &result);
+               check = &local_check;
        }
+
+       output_attr(check, &result, file);
+
+       git_attr_result_clear(&result);
+       git_attr_check_clear(&local_check);
        free(full_path);
 }
 
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 3918c07..14b764a 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -900,13 +900,19 @@ static int no_try_delta(const char *path)
 {
        static struct git_attr_check *check;
 
-       if (!check)
-               check = git_attr_check_initl("delta", NULL);
-       if (git_check_attr(path, check))
-               return 0;
-       if (ATTR_FALSE(check->check[0].value))
-               return 1;
-       return 0;
+       struct git_attr_result result = GIT_ATTR_RESULT_INIT;
+       int ret = 0;
+
+       git_attr_check_initl(&check, "delta", NULL);
+       git_attr_result_init(&result, check);
+
+       if (!git_check_attr(path, check, &result)) {
+               if (ATTR_FALSE(result.value[0]))
+                       ret = 1;
+       }
+
+       git_attr_result_clear(&result);
+       return ret;
 }
 
 /*
diff --git a/convert.c b/convert.c
index bb2435a..01de8ef 100644
--- a/convert.c
+++ b/convert.c
@@ -718,10 +718,8 @@ static int ident_to_worktree(const char *path, const char 
*src, size_t len,
        return 1;
 }
 
-static enum crlf_action git_path_check_crlf(struct git_attr_check_elem *check)
+static enum crlf_action git_path_check_crlf(const char *value)
 {
-       const char *value = check->value;
-
        if (ATTR_TRUE(value))
                return CRLF_TEXT;
        else if (ATTR_FALSE(value))
@@ -735,10 +733,8 @@ static enum crlf_action git_path_check_crlf(struct 
git_attr_check_elem *check)
        return CRLF_UNDEFINED;
 }
 
-static enum eol git_path_check_eol(struct git_attr_check_elem *check)
+static enum eol git_path_check_eol(const char *value)
 {
-       const char *value = check->value;
-
        if (ATTR_UNSET(value))
                ;
        else if (!strcmp(value, "lf"))
@@ -748,9 +744,8 @@ static enum eol git_path_check_eol(struct 
git_attr_check_elem *check)
        return EOL_UNSET;
 }
 
-static struct convert_driver *git_path_check_convert(struct 
git_attr_check_elem *check)
+static struct convert_driver *git_path_check_convert(const char *value)
 {
-       const char *value = check->value;
        struct convert_driver *drv;
 
        if (ATTR_TRUE(value) || ATTR_FALSE(value) || ATTR_UNSET(value))
@@ -761,10 +756,8 @@ static struct convert_driver 
*git_path_check_convert(struct git_attr_check_elem
        return NULL;
 }
 
-static int git_path_check_ident(struct git_attr_check_elem *check)
+static int git_path_check_ident(const char *value)
 {
-       const char *value = check->value;
-
        return !!ATTR_TRUE(value);
 }
 
@@ -778,25 +771,29 @@ struct conv_attrs {
 static void convert_attrs(struct conv_attrs *ca, const char *path)
 {
        static struct git_attr_check *check;
+       static int init_user_convert_tail;
 
-       if (!check) {
-               check = git_attr_check_initl("crlf", "ident",
-                                            "filter", "eol", "text",
-                                            NULL);
+       struct git_attr_result result = GIT_ATTR_RESULT_INIT;
+
+       git_attr_check_initl(&check, "crlf", "ident", "filter",
+                            "eol", "text", NULL);
+       git_attr_result_init(&result, check);
+
+       if (!init_user_convert_tail) {
                user_convert_tail = &user_convert;
                git_config(read_convert_config, NULL);
+               init_user_convert_tail = 1;
        }
 
-       if (!git_check_attr(path, check)) {
-               struct git_attr_check_elem *ccheck = check->check;
-               ca->crlf_action = git_path_check_crlf(ccheck + 4);
+       if (!git_check_attr(path, check, &result)) {
+               ca->crlf_action = git_path_check_crlf(result.value[4]);
                if (ca->crlf_action == CRLF_UNDEFINED)
-                       ca->crlf_action = git_path_check_crlf(ccheck + 0);
+                       ca->crlf_action = git_path_check_crlf(result.value[0]);
                ca->attr_action = ca->crlf_action;
-               ca->ident = git_path_check_ident(ccheck + 1);
-               ca->drv = git_path_check_convert(ccheck + 2);
+               ca->ident = git_path_check_ident(result.value[1]);
+               ca->drv = git_path_check_convert(result.value[2]);
                if (ca->crlf_action != CRLF_BINARY) {
-                       enum eol eol_attr = git_path_check_eol(ccheck + 3);
+                       enum eol eol_attr = git_path_check_eol(result.value[3]);
                        if (ca->crlf_action == CRLF_AUTO && eol_attr == EOL_LF)
                                ca->crlf_action = CRLF_AUTO_INPUT;
                        else if (ca->crlf_action == CRLF_AUTO && eol_attr == 
EOL_CRLF)
@@ -820,6 +817,8 @@ static void convert_attrs(struct conv_attrs *ca, const char 
*path)
                ca->crlf_action = CRLF_AUTO_CRLF;
        if (ca->crlf_action == CRLF_UNDEFINED && auto_crlf == AUTO_CRLF_INPUT)
                ca->crlf_action = CRLF_AUTO_INPUT;
+
+       git_attr_result_clear(&result);
 }
 
 int would_convert_to_git_filter_fd(const char *path)
diff --git a/ll-merge.c b/ll-merge.c
index bc6479c..3abc77a 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -355,6 +355,7 @@ int ll_merge(mmbuffer_t *result_buf,
 {
        static struct git_attr_check *check;
        static const struct ll_merge_options default_opts;
+       static struct git_attr_result result;
        const char *ll_driver_name = NULL;
        int marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
        const struct ll_merge_driver *driver;
@@ -368,13 +369,15 @@ int ll_merge(mmbuffer_t *result_buf,
                normalize_file(theirs, path);
        }
 
-       if (!check)
-               check = git_attr_check_initl("merge", "conflict-marker-size", 
NULL);
+       if (!check) {
+               git_attr_check_initl(&check, "merge", "conflict-marker-size", 
NULL);
+               git_attr_result_init(&result, check);
+       }
 
-       if (!git_check_attr(path, check)) {
-               ll_driver_name = check->check[0].value;
-               if (check->check[1].value) {
-                       marker_size = atoi(check->check[1].value);
+       if (!git_check_attr(path, check, &result)) {
+               ll_driver_name = result.value[0];
+               if (result.value[1]) {
+                       marker_size = atoi(result.value[1]);
                        if (marker_size <= 0)
                                marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
                }
@@ -394,14 +397,19 @@ int ll_merge(mmbuffer_t *result_buf,
 int ll_merge_marker_size(const char *path)
 {
        static struct git_attr_check *check;
+
+       struct git_attr_result result = GIT_ATTR_RESULT_INIT;
        int marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
 
-       if (!check)
-               check = git_attr_check_initl("conflict-marker-size", NULL);
-       if (!git_check_attr(path, check) && check->check[0].value) {
-               marker_size = atoi(check->check[0].value);
+       git_attr_check_initl(&check, "conflict-marker-size", NULL);
+       git_attr_result_init(&result, check);
+
+       if (!git_check_attr(path, check, &result) && result.value[0]) {
+               marker_size = atoi(result.value[0]);
                if (marker_size <= 0)
                        marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
        }
+       git_attr_result_clear(&result);
+
        return marker_size;
 }
diff --git a/userdiff.c b/userdiff.c
index 46dfd32..62b1ed6 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -264,20 +264,30 @@ struct userdiff_driver *userdiff_find_by_path(const char 
*path)
 {
        static struct git_attr_check *check;
 
-       if (!check)
-               check = git_attr_check_initl("diff", NULL);
+       struct git_attr_result result = GIT_ATTR_RESULT_INIT;
+       const char *value;
+
        if (!path)
                return NULL;
-       if (git_check_attr(path, check))
+
+       git_attr_check_initl(&check, "diff", NULL);
+       git_attr_result_init(&result, check);
+
+       if (git_check_attr(path, check, &result)) {
+               git_attr_result_clear(&result);
                return NULL;
+       }
+
+       value = result.value[0];
+       git_attr_result_clear(&result);
 
-       if (ATTR_TRUE(check->check[0].value))
+       if (ATTR_TRUE(value))
                return &driver_true;
-       if (ATTR_FALSE(check->check[0].value))
+       if (ATTR_FALSE(value))
                return &driver_false;
-       if (ATTR_UNSET(check->check[0].value))
+       if (ATTR_UNSET(value))
                return NULL;
-       return userdiff_find_by_name(check->check[0].value);
+       return userdiff_find_by_name(value);
 }
 
 struct userdiff_driver *userdiff_get_textconv(struct userdiff_driver *driver)
diff --git a/ws.c b/ws.c
index bb3270c..5e30fef 100644
--- a/ws.c
+++ b/ws.c
@@ -73,15 +73,20 @@ unsigned parse_whitespace_rule(const char *string)
 
 unsigned whitespace_rule(const char *pathname)
 {
-       static struct git_attr_check *attr_whitespace_rule;
+       static struct git_attr_check *check;
 
-       if (!attr_whitespace_rule)
-               attr_whitespace_rule = git_attr_check_initl("whitespace", NULL);
+       struct git_attr_result result = GIT_ATTR_RESULT_INIT;
+       const char *value;
+       int r;
 
-       if (!git_check_attr(pathname, attr_whitespace_rule)) {
-               const char *value;
+       git_attr_check_initl(&check, "whitespace", NULL);
+       git_attr_result_init(&result, check);
 
-               value = attr_whitespace_rule->check[0].value;
+       r = git_check_attr(pathname, check, &result);
+       value = result.value[0];
+       git_attr_result_clear(&result);
+
+       if (!r) {
                if (ATTR_TRUE(value)) {
                        /* true (whitespace) */
                        unsigned all_rule = ws_tab_width(whitespace_rule_cfg);
-- 
2.10.1.432.g8a36cd8.dirty

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