new: read db_files and db_subdirs only if mtime changed

The db_files and db_subdirs are unnecessary for unchanged directories.

maildir with 10000 e-mails:

old version:
	$ time ./notmuch new
	No new mail.

	real    0m0.053s
	user    0m0.028s
	sys     0m0.026s

new version:
	$ time ./notmuch new
	No new mail.

	real    0m0.032s
	user    0m0.009s
	sys     0m0.023s

Signed-off-by: Karel Zak <kzak@redhat.com>
Reviewed-by:  Austin Clements <amdragon@mit.edu>
Looks good (faster than, but provably equivalent to the original code!
notmuch_directory_get_child_* are side-effect free,
db_files/db_subdirs aren't used between where they were set in the old
code and where they are set in the new code, and db_files/db_subdirs
are initialized to NULL when declared).

Another timing data point:
Old code: ./notmuch new  0.77s user 0.28s system 99% cpu 1.051 total
New code: ./notmuch new  0.09s user 0.27s system 98% cpu 0.368 total

diff --git a/notmuch-new.c b/notmuch-new.c
index 941f9d615a44ce07521395db331a9c6b7d11b6c4..31d45532aa0494934ec545c77ff40130bc27b007 100644 (file)
--- a/notmuch-new.c
+++ b/notmuch-new.c
@@ -247,15 +247,7 @@ add_files_recursive (notmuch_database_t *notmuch,
     directory = notmuch_database_get_directory (notmuch, path);
     db_mtime = notmuch_directory_get_mtime (directory);
 
-    if (db_mtime == 0) {
-       new_directory = TRUE;
-       db_files = NULL;
-       db_subdirs = NULL;
-    } else {
-       new_directory = FALSE;
-       db_files = notmuch_directory_get_child_files (directory);
-       db_subdirs = notmuch_directory_get_child_directories (directory);
-    }
+    new_directory = db_mtime ? FALSE : TRUE;
 
     /* If the database knows about this directory, then we sort based
      * on strcmp to match the database sorting. Otherwise, we can do
@@ -328,6 +320,11 @@ add_files_recursive (notmuch_database_t *notmuch,
     if (fs_mtime == db_mtime)
        goto DONE;
 
+    if (!new_directory) {
+       db_files = notmuch_directory_get_child_files (directory);
+       db_subdirs = notmuch_directory_get_child_directories (directory);
+    }
+
     /* Pass 2: Scan for new files, removed files, and removed directories. */
     for (i = 0; i < num_fs_entries; i++)
     {