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[glib] Add GAppInfoMonitor

commit e55d33edc1336ddc6d5cdfa0e3003a69a5812d26
Author: Ryan Lortie <desrt desrt ca>
Date:   Wed Sep 25 09:19:43 2013 -0400

    Add GAppInfoMonitor
    
    This is a simple object that emits a "change" signal when the installed
    applications may have changed in some way.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=711556

 docs/reference/gio/gio-docs.xml     |    1 +
 docs/reference/gio/gio-sections.txt |   13 ++
 docs/reference/gio/gio.types        |    1 +
 gio/gappinfo.c                      |  225 +++++++++++++++++++++++++++++++++++
 gio/gappinfo.h                      |   14 ++
 gio/gappinfoprivate.h               |   28 +++++
 gio/gdesktopappinfo.c               |    4 +
 7 files changed, 286 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/gio/gio-docs.xml b/docs/reference/gio/gio-docs.xml
index 1d65a11..46b8bb8 100644
--- a/docs/reference/gio/gio-docs.xml
+++ b/docs/reference/gio/gio-docs.xml
@@ -83,6 +83,7 @@
         <title>File types and applications</title>
         <xi:include href="xml/gcontenttype.xml"/>
         <xi:include href="xml/gappinfo.xml"/>
+        <xi:include href="xml/gappinfomonitor.xml"/>
         <xi:include href="xml/gdesktopappinfo.xml"/>
     </chapter>
     <chapter id="volume_mon">
diff --git a/docs/reference/gio/gio-sections.txt b/docs/reference/gio/gio-sections.txt
index 67afe3e..22dc8fd 100644
--- a/docs/reference/gio/gio-sections.txt
+++ b/docs/reference/gio/gio-sections.txt
@@ -1399,6 +1399,19 @@ GAppLaunchContextPrivate
 </SECTION>
 
 <SECTION>
+<FILE>gappinfomonitor</FILE>
+<TITLE>GAppInfoMonitor</TITLE>
+GAppInfoMonitor
+g_app_info_monitor_get
+<SUBSECTION Standard>
+GAppInfoMonitor
+G_APP_INFO_MONITOR
+G_IS_APP_INFO_MONITOR
+<SUBSECTION Private>
+g_app_info_monitor_get_type
+</SECTION>
+
+<SECTION>
 <FILE>gmountoperation</FILE>
 <TITLE>GMountOperation</TITLE>
 GAskPasswordFlags
diff --git a/docs/reference/gio/gio.types b/docs/reference/gio/gio.types
index 73e09a2..9d43905 100644
--- a/docs/reference/gio/gio.types
+++ b/docs/reference/gio/gio.types
@@ -4,6 +4,7 @@ g_action_group_get_type
 g_action_map_get_type
 g_simple_action_group_get_type
 g_app_info_get_type
+g_app_info_monitor_get_type
 g_app_launch_context_get_type
 g_application_get_type
 g_async_initable_get_type
diff --git a/gio/gappinfo.c b/gio/gappinfo.c
index 2d0b58c..941015c 100644
--- a/gio/gappinfo.c
+++ b/gio/gappinfo.c
@@ -21,7 +21,10 @@
  */
 
 #include "config.h"
+
 #include "gappinfo.h"
+#include "gappinfoprivate.h"
+
 #include "glibintl.h"
 #include <gioerror.h>
 #include <gfile.h>
@@ -31,6 +34,7 @@
  * SECTION:gappinfo
  * @short_description: Application information and launch contexts
  * @include: gio/gio.h
+ * @see_also: #GAppInfoMonitor
  * 
  * #GAppInfo and #GAppLaunchContext are used for describing and launching
  * applications installed on the system.
@@ -1025,3 +1029,224 @@ g_app_launch_context_launch_failed (GAppLaunchContext *context,
 
   g_signal_emit (context, signals[LAUNCH_FAILED], 0, startup_notify_id);
 }
+
+
+/**
+ * SECTION:gappinfomonitor
+ * @short_description: Monitor application information for changes
+ *
+ * #GAppInfoMonitor is a very simple object used for monitoring the app
+ * info database for changes (ie: newly installed or removed
+ * applications).
+ *
+ * Call g_app_info_monitor_get() to get a #GAppInfoMonitor and connect
+ * to the "changed" signal.
+ *
+ * In the usual case, applications should try to make note of the change
+ * (doing things like invalidating caches) but not act on it.  In
+ * particular, applications should avoid making calls to #GAppInfo APIs
+ * in response to the change signal, deferring these until the time that
+ * the data is actually required.  The exception to this case is when
+ * application information is actually being displayed on the screen
+ * (eg: during a search or when the list of all applications is shown).
+ * The reason for this is that changes to the list of installed
+ * applications often come in groups (like during system updates) and
+ * rescanning the list on every change is pointless and expensive.
+ *
+ * Since: 2.40
+ **/
+
+/**
+ * GAppInfoMonitor:
+ *
+ * The only thing you can do with this is to get it via
+ * g_app_info_monitor_get() and connect to the "changed" signal.
+ *
+ * Since: 2.40
+ **/
+
+/* We have one of each of these per main context and hand them out
+ * according to the thread default main context at the time of the call
+ * to g_app_info_monitor_get().
+ *
+ * g_object_unref() is only ever called from the same context, so we
+ * effectively have a single-threaded scenario for each GAppInfoMonitor.
+ *
+ * We use a hashtable to cache the per-context monitor (but we do not
+ * hold a ref).  During finalize, we remove it.  This is possible
+ * because we don't have to worry about the usual races due to the
+ * single-threaded nature of each object.
+ *
+ * We keep a global list of all contexts that have a monitor for them,
+ * which we have to access under a lock.  When we dispatch the events to
+ * be handled in each context, we don't pass the monitor, but the
+ * context itself.
+ *
+ * We dispatch from the GLib worker context, so if we passed the
+ * monitor, we would need to take a ref on it (in case it was destroyed
+ * in its own thread meanwhile).  The monitor holds a ref on a context
+ * and the dispatch would mean that the context would hold a ref on the
+ * monitor.  If someone stopped iterating the context at just this
+ * moment both the context and monitor would leak.
+ *
+ * Instead, we dispatch the context to itself.  We don't hold a ref.
+ * There is the danger that the context will be destroyed during the
+ * dispatch, but if that is the case then we just won't receive our
+ * callback.
+ *
+ * When the dispatch occurs we just lookup the monitor in the hashtable,
+ * by context.  We can now add and remove refs, since the context will
+ * have been acquired.
+ */
+
+typedef struct _GAppInfoMonitorClass GAppInfoMonitorClass;
+
+struct _GAppInfoMonitor
+{
+  GObject parent_instance;
+  GMainContext *context;
+};
+
+struct _GAppInfoMonitorClass
+{
+  GObjectClass parent_class;
+};
+
+static GHashTable *g_app_info_monitors;
+static GMutex      g_app_info_monitor_lock;
+static guint       g_app_info_monitor_changed_signal;
+
+G_DEFINE_TYPE (GAppInfoMonitor, g_app_info_monitor, G_TYPE_OBJECT)
+
+static void
+g_app_info_monitor_finalize (GObject *object)
+{
+  GAppInfoMonitor *monitor = G_APP_INFO_MONITOR (object);
+
+  g_mutex_lock (&g_app_info_monitor_lock);
+  g_hash_table_remove (g_app_info_monitors, monitor->context);
+  g_mutex_unlock (&g_app_info_monitor_lock);
+
+  G_OBJECT_CLASS (g_app_info_monitor_parent_class)->finalize (object);
+}
+
+static void
+g_app_info_monitor_init (GAppInfoMonitor *monitor)
+{
+}
+
+static void
+g_app_info_monitor_class_init (GAppInfoMonitorClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+
+  g_app_info_monitor_changed_signal = g_signal_new ("changed", G_TYPE_APP_INFO_MONITOR, G_SIGNAL_RUN_FIRST,
+                                                    0, NULL, NULL, g_cclosure_marshal_VOID__VOID, 
G_TYPE_NONE, 0);
+
+  object_class->finalize = g_app_info_monitor_finalize;
+}
+
+/**
+ * g_app_info_monitor_get:
+ *
+ * Gets the #GAppInfoMonitor for the current thread-default main
+ * context.
+ *
+ * The #GAppInfoMonitor will emit a "changed" signal in the
+ * thread-default main context whenever the list of installed
+ * applications (as reported by g_app_info_get_all()) may have changed.
+ *
+ * You must only call g_object_unref() on the return value from under
+ * the same main context as you created it.
+ *
+ * Returns: (transfer full): a reference to a #GAppInfoMonitor
+ *
+ * Since: 2.40
+ **/
+GAppInfoMonitor *
+g_app_info_monitor_get (void)
+{
+  GAppInfoMonitor *monitor;
+  GMainContext *context;
+
+  context = g_main_context_get_thread_default ();
+  if (!context)
+    context = g_main_context_default ();
+
+  g_return_val_if_fail (g_main_context_acquire (context), NULL);
+
+  g_mutex_lock (&g_app_info_monitor_lock);
+  if (!g_app_info_monitors)
+    g_app_info_monitors = g_hash_table_new (NULL, NULL);
+
+  monitor = g_hash_table_lookup (g_app_info_monitors, context);
+  g_mutex_unlock (&g_app_info_monitor_lock);
+
+  if (!monitor)
+    {
+      monitor = g_object_new (G_TYPE_APP_INFO_MONITOR, NULL);
+      monitor->context = g_main_context_ref (context);
+
+      g_mutex_lock (&g_app_info_monitor_lock);
+      g_hash_table_insert (g_app_info_monitors, context, monitor);
+      g_mutex_unlock (&g_app_info_monitor_lock);
+    }
+  else
+    g_object_ref (monitor);
+
+  g_main_context_release (context);
+
+  return monitor;
+}
+
+static gboolean
+g_app_info_monitor_emit (gpointer user_data)
+{
+  GMainContext *context = user_data;
+  GAppInfoMonitor *monitor;
+
+  g_mutex_lock (&g_app_info_monitor_lock);
+  monitor = g_hash_table_lookup (g_app_info_monitors, context);
+  g_mutex_unlock (&g_app_info_monitor_lock);
+
+  /* It is possible that the monitor was already destroyed by the time
+   * we get here, so make sure it's not NULL.
+   */
+  if (monitor != NULL)
+    {
+      /* We don't have to worry about another thread disposing the
+       * monitor but we do have to worry about the possibility that one
+       * of the attached handlers may do so.
+       *
+       * Take a ref so that the monitor doesn't disappear in the middle
+       * of the emission.
+       */
+      g_object_ref (monitor);
+      g_signal_emit (monitor, g_app_info_monitor_changed_signal, 0);
+      g_object_unref (monitor);
+    }
+
+  return FALSE;
+}
+
+void
+g_app_info_monitor_fire (void)
+{
+  GHashTableIter iter;
+  gpointer context;
+
+  g_mutex_lock (&g_app_info_monitor_lock);
+
+  g_hash_table_iter_init (&iter, g_app_info_monitors);
+  while (g_hash_table_iter_next (&iter, &context, NULL))
+    {
+      GSource *idle;
+
+      idle = g_idle_source_new ();
+      g_source_set_callback (idle, g_app_info_monitor_emit, context, NULL);
+      g_source_attach (idle, context);
+      g_source_unref (idle);
+    }
+
+  g_mutex_unlock (&g_app_info_monitor_lock);
+}
diff --git a/gio/gappinfo.h b/gio/gappinfo.h
index baed4c4..8b793ce 100644
--- a/gio/gappinfo.h
+++ b/gio/gappinfo.h
@@ -296,6 +296,20 @@ GLIB_AVAILABLE_IN_ALL
 void               g_app_launch_context_launch_failed         (GAppLaunchContext *context,
                                                                const char *       startup_notify_id);
 
+#define G_TYPE_APP_INFO_MONITOR                             (g_app_info_monitor_get_type ())
+#define G_APP_INFO_MONITOR(inst)                            (G_TYPE_CHECK_INSTANCE_CAST ((inst),             
        \
+                                                             G_TYPE_APP_INFO_MONITOR, GAppInfoMonitor))
+#define G_IS_APP_INFO_MONITOR(inst)                         (G_TYPE_CHECK_INSTANCE_TYPE ((inst),             
        \
+                                                             G_TYPE_APP_INFO_MONITOR))
+
+typedef struct _GAppInfoMonitor                             GAppInfoMonitor;
+
+GLIB_AVAILABLE_IN_2_40
+GType                   g_app_info_monitor_get_type                     (void);
+
+GLIB_AVAILABLE_IN_2_40
+GAppInfoMonitor *       g_app_info_monitor_get                          (void);
+
 G_END_DECLS
 
 #endif /* __G_APP_INFO_H__ */
diff --git a/gio/gappinfoprivate.h b/gio/gappinfoprivate.h
new file mode 100644
index 0000000..c987977
--- /dev/null
+++ b/gio/gappinfoprivate.h
@@ -0,0 +1,28 @@
+/* GIO - GLib Input, Output and Streaming Library
+ *
+ * Copyright © 2013 Canonical Limited
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General
+ * Public License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+ * Boston, MA 02111-1307, USA.
+ *
+ * Author: Ryan Lortie <desrt desrt ca>
+ */
+
+#ifndef __G_APP_INFO_PRIVATE_H__
+#define __G_APP_INFO_PRIVATE_H__
+
+void g_app_info_monitor_fire (void);
+
+#endif /* __G_APP_INFO_PRIVATE_H__ */
diff --git a/gio/gdesktopappinfo.c b/gio/gdesktopappinfo.c
index c67186f..a76369c 100644
--- a/gio/gdesktopappinfo.c
+++ b/gio/gdesktopappinfo.c
@@ -47,6 +47,7 @@
 #include "glibintl.h"
 #include "giomodule-priv.h"
 #include "gappinfo.h"
+#include "gappinfoprivate.h"
 #include "glocaldirectorymonitor.h"
 
 
@@ -179,6 +180,9 @@ desktop_file_dir_changed (GFileMonitor      *monitor,
   desktop_file_dir_reset (dir);
 
   g_mutex_unlock (&desktop_file_dir_lock);
+
+  /* Notify anyone else who may be interested */
+  g_app_info_monitor_fire ();
 }
 
 /* Internal utility functions {{{2 */
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