[glib/wip/Jehan/issue-2096-SHGetFileInfoW: 1/2] Issue #2096: SHGetFileInfoW() is not reliable (time-wise).

[Jehan <jehanp src gnome org>]

commit b899e3532ca40874fad1095f82208e961061ba5d
Author: Jehan <jehan girinstud io>
Date:   Mon Apr 27 22:14:31 2020 +0200

    Issue #2096: SHGetFileInfoW() is not reliable (time-wise).
    
    Microsoft docs clearly states:
    > You should call this function from a background thread. Failure to do
    > so could cause the UI to stop responding.
    
    We experienced this exact issue in GIMP for Windows. Some people have
    been complaining about file dialogs taking up to minutes to appear
    (while freezing the whole GUI) because of problematic mounts.
    The chosen solution is to only run SHGetFileInfoW() when the info is
    needed, i.e. when g_win32_mount_get_name() is called (not when
    allocating any GMount), and do it in a thread. So the initially returned
    name is the mount path (which on Windows will be like "X:" and is a
    perfectly fine name already). The pretty name can be updated later,
    particularly by connecting to the "changed" signal.

 gio/gmount.c      | 10 ++++++++-
 gio/gwin32mount.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 63 insertions(+), 11 deletions(-)
---
diff --git a/gio/gmount.c b/gio/gmount.c
index 8dfa1d7c2..667f9ce7d 100644
--- a/gio/gmount.c
+++ b/gio/gmount.c
@@ -176,7 +176,15 @@ g_mount_get_default_location (GMount *mount)
  * @mount: a #GMount.
  * 
  * Gets the name of @mount.
- * 
+ *
+ * Note that on some system (Windows at least), the returned value may not be
+ * the nicest display name, but calling g_mount_get_name() will trigger the
+ * name request in a thread (as it can be very slow in some cases, such as
+ * unresponsive or network mounts). If the name is a GUI-facing text and you
+ * care for the best display name, you may want to initially use the returned
+ * string, and connect to the "changed" signal to update the widget later with
+ * the better name.
+ *
  * Returns: the name for the given @mount. 
  *     The returned string should be freed with g_free()
  *     when no longer needed.
diff --git a/gio/gwin32mount.c b/gio/gwin32mount.c
index 5b4847a9d..4d50f4ded 100644
--- a/gio/gwin32mount.c
+++ b/gio/gwin32mount.c
@@ -33,6 +33,7 @@
 #include "gmount.h"
 #include "gfile.h"
 #include "gmountprivate.h"
+#include "gtask.h"
 #include "gvolumemonitor.h"
 #include "gthemedicon.h"
 #include "glibintl.h"
@@ -103,17 +104,39 @@ g_win32_mount_init (GWin32Mount *win32_mount)
 {
 }
 
-static gchar *
-_win32_get_displayname (const char *drive)
+static void
+_win32_get_displayname (GTask        *task,
+                        gpointer      source_object,
+                        gpointer      task_data,
+                        GCancellable *cancellable)
 {
-  gunichar2 *wdrive = g_utf8_to_utf16 (drive, -1, NULL, NULL, NULL);
-  gchar *name = NULL;
-  SHFILEINFOW sfi;
-  if (SHGetFileInfoW(wdrive, 0, &sfi, sizeof(sfi), SHGFI_DISPLAYNAME))
+  const char  *drive = task_data;
+  gunichar2   *wdrive = g_utf8_to_utf16 (drive, -1, NULL, NULL, NULL);
+  gchar       *name = NULL;
+  SHFILEINFOW  sfi;
+
+  if (SHGetFileInfoW (wdrive, 0, &sfi, sizeof (sfi), SHGFI_DISPLAYNAME))
     name = g_utf16_to_utf8 (sfi.szDisplayName, -1, NULL, NULL, NULL);
 
   g_free (wdrive);
-  return name ? name : g_strdup (drive);
+
+  g_task_return_pointer (task, name, g_free);
+}
+
+static void
+_win32_get_displayname_finish (GObject      *source_object,
+                               GAsyncResult *res,
+                               gpointer      user_data)
+{
+  GWin32Mount *mount = G_WIN32_MOUNT (source_object);
+  gchar       *name  = g_task_propagate_pointer (G_TASK (res), NULL);
+
+  if (name && g_strcmp0 (name, mount->name) != 0)
+    {
+      g_clear_pointer (&mount->name, g_free);
+      mount->name = name;
+      g_signal_emit_by_name (mount, "changed");
+    }
 }
 
 /*
@@ -143,7 +166,7 @@ _g_win32_mount_new (GVolumeMonitor  *volume_monitor,
   mount->mount_path = g_strdup (path);
   mount->drive_type = GetDriveType (drive);
   mount->can_eject = FALSE; /* TODO */
-  mount->name = _win32_get_displayname (drive);
+  mount->name = NULL;
 
   /* need to do this last */
   mount->volume = volume;
@@ -260,8 +283,29 @@ static char *
 g_win32_mount_get_name (GMount *mount)
 {
   GWin32Mount *win32_mount = G_WIN32_MOUNT (mount);
-  
-  return g_strdup (win32_mount->name);
+  gchar       *name        = win32_mount->name;
+
+  if (! name)
+    {
+      GTask *task;
+
+      /* On Windows, this request can be expensive, especially with remote
+       * mounts, or worse unresponsive mounts.
+       * So only request the display name when the info is needed and run it in
+       * a thread.
+       */
+      task = g_task_new (mount, NULL, _win32_get_displayname_finish, NULL);
+      g_task_set_priority (task, G_PRIORITY_LOW);
+      g_task_set_source_tag (task, g_win32_mount_get_name);
+      g_task_set_task_data (task, g_strdup (win32_mount->mount_path), g_free);
+      g_task_run_in_thread (task, _win32_get_displayname);
+      g_object_unref (task);
+
+      /* Still return something usable for now. */
+      name = g_strdup (win32_mount->mount_path);
+    }
+
+  return name;
 }
 
 static GDrive *