close_lock_file(): new function in the lockfile API

The lockfile API is a handy way to obtain a file that is cleaned
up if you die().  But sometimes you would need this sequence to
work:

 1. hold_lock_file_for_update() to get a file descriptor for
    writing;

 2. write the contents out, without being able to decide if the
    results should be committed or rolled back;

 3. do something else that makes the decision --- and this
    "something else" needs the lockfile not to have an open file
    descriptor for writing (e.g. Windows do not want a open file
    to be renamed);

 4. call commit_lock_file() or rollback_lock_file() as
    appropriately.

This adds close_lock_file() you can call between step 2 and 3 in
the above sequence.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/api-lockfile.txt

@@ -37,7 +37,8 @@ commit_lock_file::
 	Take a pointer to the `struct lock_file` initialized
 	with an earlier call to `hold_lock_file_for_update()`,
 	close the file descriptor and rename the lockfile to its
-	final destination.
+	final destination.  Returns 0 upon success, a negative
+	value on failure to close(2) or rename(2).
 
 rollback_lock_file::
 
@@ -45,6 +46,12 @@ rollback_lock_file::
 	with an earlier call to `hold_lock_file_for_update()`,
 	close the file descriptor and remove the lockfile.
 
+close_lock_file::
+	Take a pointer to the `struct lock_file` initialized
+	with an earlier call to `hold_lock_file_for_update()`,
+	and close the file descriptor.  Returns 0 upon success,
+	a negative value on failure to close(2).
+
 Because the structure is used in an `atexit(3)` handler, its
 storage has to stay throughout the life of the program.  It
 cannot be an auto variable allocated on the stack.
@@ -54,8 +61,10 @@ done writing to the file descriptor.  If you do not call either
 and simply `exit(3)` from the program, an `atexit(3)` handler
 will close and remove the lockfile.
 
-You should not close the file descriptor you obtained from
-`hold_lock_file_for_update` function yourself.  The `struct
+If you need to close the file descriptor you obtained from
+`hold_lock_file_for_update` function yourself, do so by calling
+`close_lock_file()`.  You should never call `close(2)` yourself!
+Otherwise the `struct
 lock_file` structure still remembers that the file descriptor
 needs to be closed, and a later call to `commit_lock_file()` or
 `rollback_lock_file()` will result in duplicate calls to

cache.h

@@ -308,7 +308,7 @@ extern int commit_lock_file(struct lock_file *);
 extern int hold_locked_index(struct lock_file *, int);
 extern int commit_locked_index(struct lock_file *);
 extern void set_alternate_index_output(const char *);
-
+extern int close_lock_file(struct lock_file *);
 extern void rollback_lock_file(struct lock_file *);
 extern int delete_ref(const char *, const unsigned char *sha1);
 

lockfile.c

@@ -13,7 +13,8 @@ static void remove_lock_file(void)
 	while (lock_file_list) {
 		if (lock_file_list->owner == me &&
 		    lock_file_list->filename[0]) {
-			close(lock_file_list->fd);
+			if (lock_file_list->fd >= 0)
+				close(lock_file_list->fd);
 			unlink(lock_file_list->filename);
 		}
 		lock_file_list = lock_file_list->next;
@@ -159,17 +160,26 @@ int hold_lock_file_for_update(struct lock_file *lk, const char *path, int die_on
 	return fd;
 }
 
+int close_lock_file(struct lock_file *lk)
+{
+	int fd = lk->fd;
+	lk->fd = -1;
+	return close(fd);
+}
+
 int commit_lock_file(struct lock_file *lk)
 {
 	char result_file[PATH_MAX];
-	int i;
-	close(lk->fd);
+	size_t i;
+	if (lk->fd >= 0 && close_lock_file(lk))
+		return -1;
 	strcpy(result_file, lk->filename);
 	i = strlen(result_file) - 5; /* .lock */
 	result_file[i] = 0;
-	i = rename(lk->filename, result_file);
+	if (rename(lk->filename, result_file))
+		return -1;
 	lk->filename[0] = 0;
-	return i;
+	return 0;
 }
 
 int hold_locked_index(struct lock_file *lk, int die_on_error)
@@ -185,9 +195,12 @@ void set_alternate_index_output(const char *name)
 int commit_locked_index(struct lock_file *lk)
 {
 	if (alternate_index_output) {
-		int result = rename(lk->filename, alternate_index_output);
+		if (lk->fd >= 0 && close_lock_file(lk))
+			return -1;
+		if (rename(lk->filename, alternate_index_output))
+			return -1;
 		lk->filename[0] = 0;
-		return result;
+		return 0;
 	}
 	else
 		return commit_lock_file(lk);
@@ -196,7 +209,8 @@ int commit_locked_index(struct lock_file *lk)
 void rollback_lock_file(struct lock_file *lk)
 {
 	if (lk->filename[0]) {
-		close(lk->fd);
+		if (lk->fd >= 0)
+			close(lk->fd);
 		unlink(lk->filename);
 	}
 	lk->filename[0] = 0;