[glib] GInputStream: Add g_input_stream_async_read_is_via_threads()

[Dan Winship <danw src gnome org>]

commit 94a232a4ed6245d0189f7de182f10a7c3825dc73
Author: Mike Ruprecht <mike ruprecht collabora co uk>
Date:   Sat Feb 23 17:32:31 2013 -0600

    GInputStream: Add g_input_stream_async_read_is_via_threads()
    
    In implementing a better g_output_stream_splice_async() and possibly
    other situtations it's helpful to know whether the input stream's
    read function internally uses threads. If it and the output stream's
    write async functions use threads, then the splice function could
    spawn a single thread for better efficiency.
    
    This patch adds a function to determine whether an input stream's
    g_input_stream_read_async() function internally uses threads.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=691581

 gio/Makefile.am    |    1 +
 gio/ginputstream.c |   32 +++++++++++++++++++++++++-------
 gio/gioprivate.h   |   32 ++++++++++++++++++++++++++++++++
 3 files changed, 58 insertions(+), 7 deletions(-)
---
diff --git a/gio/Makefile.am b/gio/Makefile.am
index 717419f..3661686 100644
--- a/gio/Makefile.am
+++ b/gio/Makefile.am
@@ -381,6 +381,7 @@ libgio_2_0_la_SOURCES =             \
        giomodule-priv.h        \
        gioscheduler.c          \
        giostream.c             \
+       gioprivate.h            \
        gloadableicon.c         \
        gmount.c                \
        gmemoryinputstream.c    \
diff --git a/gio/ginputstream.c b/gio/ginputstream.c
index 6c7cd60..c35dd0d 100644
--- a/gio/ginputstream.c
+++ b/gio/ginputstream.c
@@ -25,6 +25,7 @@
 #include "glibintl.h"
 
 #include "ginputstream.h"
+#include "gioprivate.h"
 #include "gseekable.h"
 #include "gcancellable.h"
 #include "gasyncresult.h"
@@ -1041,6 +1042,28 @@ g_input_stream_clear_pending (GInputStream *stream)
   stream->priv->pending = FALSE;
 }
 
+/**
+ * g_input_stream_async_read_is_via_threads:
+ * @stream: input stream
+ *
+ * Checks if an input stream's read_async function uses threads.
+ *
+ * Returns: %TRUE if @stream's read_async function uses threads.
+ **/
+gboolean
+g_input_stream_async_read_is_via_threads (GInputStream *stream)
+{
+  GInputStreamClass *class;
+
+  g_return_val_if_fail (G_IS_INPUT_STREAM (stream), FALSE);
+
+  class = G_INPUT_STREAM_GET_CLASS (stream);
+
+  return (class->read_async == g_input_stream_real_read_async &&
+      !(G_IS_POLLABLE_INPUT_STREAM (stream) &&
+        g_pollable_input_stream_can_poll (G_POLLABLE_INPUT_STREAM (stream))));
+}
+
 /********************************************
  *   Default implementation of async ops    *
  ********************************************/
@@ -1128,10 +1151,6 @@ read_async_pollable (GPollableInputStream *stream,
   /* g_input_stream_real_read_async() unrefs task */
 }
 
-#define CAN_DO_NONBLOCKING_READS(stream) \
-  (G_IS_POLLABLE_INPUT_STREAM (stream) && \
-   g_pollable_input_stream_can_poll (G_POLLABLE_INPUT_STREAM (stream)))
-
 
 static void
 g_input_stream_real_read_async (GInputStream        *stream,
@@ -1152,7 +1171,7 @@ g_input_stream_real_read_async (GInputStream        *stream,
   op->buffer = buffer;
   op->count = count;
 
-  if (CAN_DO_NONBLOCKING_READS (stream))
+  if (!g_input_stream_async_read_is_via_threads (stream))
     read_async_pollable (G_POLLABLE_INPUT_STREAM (stream), task);
   else
     g_task_run_in_thread (task, read_async_thread);
@@ -1260,8 +1279,7 @@ g_input_stream_real_skip_async (GInputStream        *stream,
   task = g_task_new (stream, cancellable, callback, user_data);
   g_task_set_priority (task, io_priority);
 
-  if (class->read_async == g_input_stream_real_read_async &&
-      !CAN_DO_NONBLOCKING_READS (stream))
+  if (g_input_stream_async_read_is_via_threads (stream))
     {
       /* Read is thread-using async fallback.
        * Make skip use threads too, so that we can use a possible sync skip
diff --git a/gio/gioprivate.h b/gio/gioprivate.h
new file mode 100644
index 0000000..fc0fc5c
--- /dev/null
+++ b/gio/gioprivate.h
@@ -0,0 +1,32 @@
+/* GIO - GLib Input, Output and Streaming Library
+ *
+ * Copyright (C) 2013 Collabora Ltd.
+ *
+ * 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.
+ */
+
+#ifndef __G_IO_PRIVATE_H__
+#define __G_IO_PRIVATE_H__
+
+#include "ginputstream.h"
+
+G_BEGIN_DECLS
+
+gboolean g_input_stream_async_read_is_via_threads (GInputStream *stream);
+
+G_END_DECLS
+
+#endif /* __G_IO_PRIVATE__ */