[evolution-data-server] ebook: avoid repeatedly creating GSettings in e_book_client_is_self

[Patrick Ohly <pohly src gnome org>]

commit e93c32af909da3794b176caca3c823d162ba7ea0
Author: Patrick Ohly <patrick ohly intel com>
Date:   Thu Feb 14 16:04:14 2013 +0100

    ebook: avoid repeatedly creating GSettings in e_book_client_is_self
    
    When receiving the complete address book, a client has to use
    e_book_client_is_self() on every EContact to find the one which is the
    "self" contact. Calling e_book_client_get_self() instead does not
    work, because that would create the self contact if none exists (not
    desired for an app which just reads!).
    
    The problem with e_book_client_is_self() is that it creates and
    destroys a GSettings instance for the self UID each time the method is
    called. In addition to reading the value over and over again, this
    also triggers two D-Bus messages (AddMatch and RemoveMatch) - clearly
    bad for performance.
    
    To solve this problem, this patch caches the GSettings instance in a
    static variable. It is protected by a mutex, to keep the function
    thread-safe. The downside is that the instance is never going to be
    freed.
    
    It would be better to attach the GSettings instance to the EBookClient
    instance, but because e_book_client_is_self() doesn't get a pointer to
    that, this is not possible without an API change.

 addressbook/libebook/e-book-client.c |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)
---
diff --git a/addressbook/libebook/e-book-client.c b/addressbook/libebook/e-book-client.c
index 4841447..0244841 100644
--- a/addressbook/libebook/e-book-client.c
+++ b/addressbook/libebook/e-book-client.c
@@ -1564,15 +1564,23 @@ e_book_client_set_self (EBookClient *client,
 gboolean
 e_book_client_is_self (EContact *contact)
 {
-       GSettings *settings;
+       static GSettings *settings;
+       static GMutex mutex;
        gchar *uid;
        gboolean is_self;
 
        g_return_val_if_fail (contact && E_IS_CONTACT (contact), FALSE);
 
-       settings = g_settings_new (SELF_UID_PATH_ID);
+       /*
+        * It would be nice to attach this instance to the EBookClient
+        * instance so that it can be free again later, but
+        * unfortunately the API doesn't allow that.
+        */
+       g_mutex_lock (&mutex);
+       if (!settings)
+               settings = g_settings_new (SELF_UID_PATH_ID);
        uid = g_settings_get_string (settings, SELF_UID_KEY);
-       g_object_unref (settings);
+       g_mutex_unlock (&mutex);
 
        is_self = uid && !g_strcmp0 (uid, e_contact_get_const (contact, E_CONTACT_UID));