[evolution-data-server/pohly-gnome-2-32: 2/10] addressbook file backend: use 32 bit integers as IDs

[Patrick Ohly <pohly src gnome org>]

commit 248427f9dff63852c42e5db404cf93c3b082cf98
Author: Patrick Ohly <patrick ohly intel com>
Date:   Fri Mar 18 16:07:23 2011 +0100

    addressbook file backend: use 32 bit integers as IDs
    
    The motiviation for this change is primarily that it'll simplify
    wrapping EDS in QtContacts, which only supports 32 bit integers for
    the storages that it wraps.
    
    Previously the ID was generated as a combination of time and running
    counter, without checking for conflicts. This patch changes this such
    that the ID is only a running counter. ID conflicts are detected during
    an attempt to save, leading to retries with the next counter value.
    
    The "for future use" members of _EBookBackendFilePrivate are removed
    because they serve no useful purpose in a structure which is allocated
    and used only locally.

 addressbook/backends/file/e-book-backend-file.c |   48 +++++++++++++++-------
 1 files changed, 33 insertions(+), 15 deletions(-)
---
diff --git a/addressbook/backends/file/e-book-backend-file.c b/addressbook/backends/file/e-book-backend-file.c
index dc6a703..d21c527 100644
--- a/addressbook/backends/file/e-book-backend-file.c
+++ b/addressbook/backends/file/e-book-backend-file.c
@@ -77,11 +77,7 @@ struct _EBookBackendFilePrivate {
 	DB       *file_db;
 	DB_ENV   *env;
 	EBookBackendSummary *summary;
-	/* for future use */
-	gpointer reserved1;
-	gpointer reserved2;
-	gpointer reserved3;
-	gpointer reserved4;
+	guint     id;
 };
 
 G_LOCK_DEFINE_STATIC (global_env);
@@ -169,13 +165,13 @@ build_summary (EBookBackendFilePrivate *bfpriv)
 }
 
 static gchar *
-e_book_backend_file_create_unique_id (void)
+e_book_backend_file_create_next_id (EBookBackendFile *bf)
 {
-	/* use a 32 counter and the 32 bit timestamp to make an id.
-	   it's doubtful 2^32 id's will be created in a second, so we
-	   should be okay. */
-	static guint c = 0;
-	return g_strdup_printf (PAS_ID_PREFIX "%08lX%08X", time(NULL), c++);
+	/* use a 32 counter, avoid 0; collision checks must be done by caller */
+	++bf->priv->id;
+	if (!bf->priv->id)
+		bf->priv->id = 1;
+	return g_strdup_printf (PAS_ID_PREFIX "%04X", bf->priv->id);
 }
 
 static void
@@ -210,7 +206,8 @@ do_create(EBookBackendFile  *bf,
 	g_assert (vcard_req);
 	g_assert (contact);
 
-	id = e_book_backend_file_create_unique_id ();
+ retry:
+	id = e_book_backend_file_create_next_id (bf);
 
 	string_to_dbt (id, &id_dbt);
 
@@ -224,9 +221,10 @@ do_create(EBookBackendFile  *bf,
 
 	string_to_dbt (vcard, &vcard_dbt);
 
-	db_error = db->put (db, NULL, &id_dbt, &vcard_dbt, 0);
+	db_error = db->put (db, NULL, &id_dbt, &vcard_dbt, DB_NOOVERWRITE);
 
 	g_free (vcard);
+	g_free (id);
 
 	if (0 == db_error) {
 		db_error = db->sync (db, 0);
@@ -234,12 +232,16 @@ do_create(EBookBackendFile  *bf,
 			g_warning ("db->sync failed with %s", db_strerror (db_error));
 		}
 	} else {
-		g_warning (G_STRLOC ": db->put failed with %s", db_strerror (db_error));
 		g_object_unref (*contact);
 		*contact = NULL;
+		if (DB_KEYEXIST == db_error) {
+			/* did not guess a new ID, try again */
+			goto retry;
+		} else {
+			g_warning (G_STRLOC ": db->put failed with %s", db_strerror (db_error));
+		}
 	}
 
-	g_free (id);
 	db_error_to_gerror (db_error, perror);
 
 	return db_error == 0;
@@ -1108,6 +1110,7 @@ e_book_backend_file_load_source (EBookBackend           *backend,
 	DB_ENV *env;
 	time_t db_mtime;
 	struct stat sb;
+	DB_HASH_STAT *hashstat;
 
 	dirname = e_book_backend_file_extract_path_from_source (source);
 	filename = g_build_filename (dirname, "addressbook.db", NULL);
@@ -1290,6 +1293,21 @@ e_book_backend_file_load_source (EBookBackend           *backend,
 	}
 	db_mtime = sb.st_mtime;
 
+	/*
+	 * Picking the number of records as base for the next ID avoids trying out
+	 * lots of already used IDs in a database with few deleted contacts.
+	 * Optional optimization, if this fails or returns no information, we simply
+	 * start with zero.
+	 *
+	 * Note that DB_FAST_STAT is not used, because without it we won't get
+	 * hash_nkeys. This makes the stat call slower, but should be worth it
+	 * because we need to access the content sooner or later.
+	 */
+	if (!bf->priv->file_db->stat(bf->priv->file_db, NULL, &hashstat, 0)) {
+		bf->priv->id = hashstat->hash_nkeys;
+		g_free(hashstat);
+	}
+
 	g_free (bf->priv->summary_filename);
 	bf->priv->summary_filename = g_strconcat (bf->priv->filename, ".summary", NULL);
 	bf->priv->summary = e_book_backend_summary_new (bf->priv->summary_filename, SUMMARY_FLUSH_TIMEOUT);