[glib] Add internal helper GContextSpecificGroup

[Ryan Lortie <desrt src gnome org>]

commit c90b083fa8fd3da88086e634b45a190c0e4ba165
Author: Ryan Lortie <desrt desrt ca>
Date:   Wed Jan 7 23:09:30 2015 -0500

    Add internal helper GContextSpecificGroup
    
    Add a new internal helper called GContextSpecificGroup.
    
    This is a mechanism for helping to maintain a group of context-specific
    monitor objects (eg: GAppInfoMonitor, GUnixMountMonitor).
    
    https://bugzilla.gnome.org/show_bug.cgi?id=742599

 gio/Makefile.am             |    2 +
 gio/gcontextspecificgroup.c |  258 +++++++++++++++++++++++++++++++++++++++++++
 gio/gcontextspecificgroup.h |   47 ++++++++
 3 files changed, 307 insertions(+), 0 deletions(-)
---
diff --git a/gio/Makefile.am b/gio/Makefile.am
index 27369c8..d0b8d10 100644
--- a/gio/Makefile.am
+++ b/gio/Makefile.am
@@ -350,6 +350,8 @@ libgio_2_0_la_SOURCES =             \
        gbytesicon.c            \
        gcancellable.c          \
        gcharsetconverter.c     \
+       gcontextspecificgroup.c \
+       gcontextspecificgroup.h \
        gconverter.c            \
        gconverterinputstream.c \
        gconverteroutputstream.c        \
diff --git a/gio/gcontextspecificgroup.c b/gio/gcontextspecificgroup.c
new file mode 100644
index 0000000..849b0a4
--- /dev/null
+++ b/gio/gcontextspecificgroup.c
@@ -0,0 +1,258 @@
+/*
+ * Copyright © 2015 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 licence, 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, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Ryan Lortie <desrt desrt ca>
+ */
+
+#include "config.h"
+
+#include "gcontextspecificgroup.h"
+
+#include <glib-object.h>
+#include "glib-private.h"
+
+typedef struct
+{
+  GSource   source;
+
+  GMutex    lock;
+  gpointer  instance;
+  GQueue    pending;
+} GContextSpecificSource;
+
+static gboolean
+g_context_specific_source_dispatch (GSource     *source,
+                                    GSourceFunc  callback,
+                                    gpointer     user_data)
+{
+  GContextSpecificSource *css = (GContextSpecificSource *) source;
+  guint signal_id;
+
+  g_mutex_lock (&css->lock);
+
+  g_assert (!g_queue_is_empty (&css->pending));
+  signal_id = GPOINTER_TO_UINT (g_queue_pop_head (&css->pending));
+
+  if (g_queue_is_empty (&css->pending))
+    g_source_set_ready_time (source, -1);
+
+  g_mutex_unlock (&css->lock);
+
+  g_signal_emit (css->instance, signal_id, 0);
+
+  return TRUE;
+}
+
+static void
+g_context_specific_source_finalize (GSource *source)
+{
+  GContextSpecificSource *css = (GContextSpecificSource *) source;
+
+  g_mutex_clear (&css->lock);
+  g_queue_clear (&css->pending);
+}
+
+static GContextSpecificSource *
+g_context_specific_source_new (const gchar *name,
+                               gpointer     instance)
+{
+  static GSourceFuncs source_funcs = {
+    NULL,
+    NULL,
+    g_context_specific_source_dispatch,
+    g_context_specific_source_finalize
+  };
+  GContextSpecificSource *css;
+  GSource *source;
+
+  source = g_source_new (&source_funcs, sizeof (GContextSpecificSource));
+  css = (GContextSpecificSource *) source;
+
+  g_source_set_name (source, name);
+
+  g_mutex_init (&css->lock);
+  g_queue_init (&css->pending);
+  css->instance = instance;
+
+  return css;
+}
+
+typedef struct
+{
+  GCallback callback;
+  GMutex    mutex;
+  GCond     cond;
+} Closure;
+
+static gboolean
+g_context_specific_group_invoke_closure (gpointer user_data)
+{
+  Closure *closure = user_data;
+
+  (* closure->callback) ();
+
+  g_mutex_lock (&closure->mutex);
+
+  closure->callback = NULL;
+
+  g_cond_broadcast (&closure->cond);
+
+  g_mutex_unlock (&closure->mutex);
+
+  return FALSE;
+}
+
+/* this is not the most elegant way to deal with this, but it's probably
+ * the best.  there are only two other things we could do, really:
+ *
+ *  - run the start function (but not the stop function) from the user's
+ *    thread under some sort of lock.  we don't run the stop function
+ *    from the user's thread to avoid the destroy-while-emitting problem
+ *
+ *  - have some check-and-compare functionality similar to what
+ *    gsettings does where we send an artificial event in case we notice
+ *    a change during the potential race period (using stat, for
+ *    example)
+ */
+static void
+g_context_specific_group_wait_for_callback (GCallback callback)
+{
+  Closure closure;
+
+  g_mutex_init (&closure.mutex);
+  g_cond_init (&closure.cond);
+
+  closure.callback = callback;
+
+  g_main_context_invoke (GLIB_PRIVATE_CALL(g_get_worker_context) (),
+                         g_context_specific_group_invoke_closure, &closure);
+
+  g_mutex_lock (&closure.mutex);
+  while (closure.callback)
+    g_cond_wait (&closure.cond, &closure.mutex);
+  g_mutex_unlock (&closure.mutex);
+
+  g_mutex_clear (&closure.mutex);
+  g_cond_clear (&closure.cond);
+}
+
+gpointer
+g_context_specific_group_get (GContextSpecificGroup *group,
+                              GType                  type,
+                              goffset                context_offset,
+                              GCallback              start_func)
+{
+  GContextSpecificSource *css;
+  GMainContext *context;
+
+  context = g_main_context_get_thread_default ();
+  if (!context)
+    context = g_main_context_default ();
+
+  g_mutex_lock (&group->lock);
+
+  if (!group->table)
+    group->table = g_hash_table_new (NULL, NULL);
+
+  /* start only if there are no others */
+  if (start_func && g_hash_table_size (group->table) == 0)
+    g_context_specific_group_wait_for_callback (start_func);
+
+  css = g_hash_table_lookup (group->table, context);
+
+  if (!css)
+    {
+      gpointer instance;
+
+      instance = g_object_new (type, NULL);
+      css = g_context_specific_source_new (g_type_name (type), instance);
+      G_STRUCT_MEMBER (GMainContext *, instance, context_offset) = g_main_context_ref (context);
+      g_source_attach ((GSource *) css, context);
+
+      g_hash_table_insert (group->table, context, css);
+    }
+  else
+    g_object_ref (css->instance);
+
+  g_mutex_unlock (&group->lock);
+
+  return css->instance;
+}
+
+void
+g_context_specific_group_remove (GContextSpecificGroup *group,
+                                 GMainContext          *context,
+                                 gpointer               instance,
+                                 GCallback              stop_func)
+{
+  GContextSpecificSource *css;
+
+  if (!context)
+    {
+      g_critical ("Removing %s with NULL context.  This object was probably directly constructed from a "
+                  "dynamic language.  This is not a valid use of the API.", G_OBJECT_TYPE_NAME (instance));
+      return;
+    }
+
+  g_mutex_lock (&group->lock);
+  css = g_hash_table_lookup (group->table, context);
+  g_hash_table_remove (group->table, context);
+  g_assert (css);
+
+  /* stop only if we were the last one */
+  if (stop_func && g_hash_table_size (group->table) == 0)
+    g_context_specific_group_wait_for_callback (stop_func);
+
+  g_mutex_unlock (&group->lock);
+
+  g_assert (css->instance == instance);
+
+  g_source_unref ((GSource *) css);
+  g_main_context_unref (context);
+}
+
+void
+g_context_specific_group_emit (GContextSpecificGroup *group,
+                               guint                  signal_id)
+{
+  g_mutex_lock (&group->lock);
+
+  if (group->table)
+    {
+      GHashTableIter iter;
+      gpointer value;
+      gpointer ptr;
+
+      ptr = GUINT_TO_POINTER (signal_id);
+
+      g_hash_table_iter_init (&iter, group->table);
+      while (g_hash_table_iter_next (&iter, NULL, &value))
+        {
+          GContextSpecificSource *css = value;
+
+          g_mutex_lock (&css->lock);
+
+          g_queue_remove (&css->pending, ptr);
+          g_queue_push_tail (&css->pending, ptr);
+
+          g_source_set_ready_time ((GSource *) css, 0);
+
+          g_mutex_unlock (&css->lock);
+        }
+    }
+
+  g_mutex_unlock (&group->lock);
+}
diff --git a/gio/gcontextspecificgroup.h b/gio/gcontextspecificgroup.h
new file mode 100644
index 0000000..b77134b
--- /dev/null
+++ b/gio/gcontextspecificgroup.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright © 2015 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 licence, 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, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Ryan Lortie <desrt desrt ca>
+ */
+
+#ifndef __G_CONTEXT_SPECIFIC_GROUP_H__
+#define __G_CONTEXT_SPECIFIC_GROUP_H__
+
+#include <glib-object.h>
+
+typedef struct
+{
+  GHashTable *table;
+  GMutex      lock;
+} GContextSpecificGroup;
+
+gpointer
+g_context_specific_group_get (GContextSpecificGroup *group,
+                              GType                  type,
+                              goffset                context_offset,
+                              GCallback              start_func);
+
+void
+g_context_specific_group_remove (GContextSpecificGroup *group,
+                                 GMainContext          *context,
+                                 gpointer               instance,
+                                 GCallback              stop_func);
+
+void
+g_context_specific_group_emit (GContextSpecificGroup *group,
+                               guint                  signal_id);
+
+#endif /* __G_CONTEXT_SPECIFIC_GROUP_H__ */