* #GMemoryOutputStream is a class for using arbitrary
* memory chunks as output for GIO streaming output operations.
*
- * As of GLib 2.34, #GMemoryOutputStream implements
- * #GPollableOutputStream.
+ * As of GLib 2.34, #GMemoryOutputStream trivially implements
+ * #GPollableOutputStream: it always polls as ready.
*/
#define MIN_ARRAY_SIZE 16
PROP_DESTROY_FUNCTION
};
-struct _GMemoryOutputStreamPrivate {
-
+struct _GMemoryOutputStreamPrivate
+{
gpointer data; /* Write buffer */
gsize len; /* Current length of the data buffer. Can change with resizing. */
gsize valid_len; /* The part of data that has been written to */
static gboolean g_memory_output_stream_is_writable (GPollableOutputStream *stream);
static GSource *g_memory_output_stream_create_source (GPollableOutputStream *stream,
- GCancellable *cancellable);
+ GCancellable *cancellable);
static void g_memory_output_stream_pollable_iface_init (GPollableOutputStreamInterface *iface);
*
* Creates a new #GMemoryOutputStream.
*
- * If @data is non-%NULL, the stream will use that for its internal storage.
+ * In most cases this is not the function you want. See
+ * g_memory_output_stream_new_resizable() instead.
+ *
+ * If @data is non-%NULL, the stream will use that for its internal storage.
+ *
* If @realloc_fn is non-%NULL, it will be used for resizing the internal
- * storage when necessary. To construct a fixed-size output stream,
- * pass %NULL as @realloc_fn.
+ * storage when necessary and the stream will be considered resizable.
+ * In that case, the stream will start out being (conceptually) empty.
+ * @size is used only as a hint for how big @data is. Specifically,
+ * seeking to the end of a newly-created stream will seek to zero, not
+ * @size. Seeking past the end of the stream and then writing will
+ * introduce a zero-filled gap.
+ *
+ * If @realloc_fn is %NULL then the stream is fixed-sized. Seeking to
+ * the end will seek to @size exactly. Writing past the end will give
+ * an 'out of space' error. Attempting to seek past the end will fail.
+ * Unlike the resizable case, seeking to an offset within the stream and
+ * writing will preserve the bytes passed in as @data before that point
+ * and will return them as part of g_memory_output_stream_steal_data().
+ * If you intend to seek you should probably therefore ensure that @data
+ * is properly initialised.
+ *
+ * It is probably only meaningful to provide @data and @size in the case
+ * that you want a fixed-sized stream. Put another way: if @realloc_fn
+ * is non-%NULL then it makes most sense to give @data as %NULL and
+ * @size as 0 (allowing #GMemoryOutputStream to do the initial
+ * allocation for itself).
*
* |[
* /* a stream that can grow */
* @ostream: a #GMemoryOutputStream
*
* Gets the size of the currently allocated data area (available from
- * g_memory_output_stream_get_data()). If the stream isn't
- * growable (no realloc was passed to g_memory_output_stream_new()) then
- * this is the maximum size of the stream and further writes
- * will return %G_IO_ERROR_NO_SPACE.
+ * g_memory_output_stream_get_data()).
+ *
+ * You probably don't want to use this function on resizable streams.
+ * See g_memory_output_stream_get_data_size() instead. For resizable
+ * streams the size returned by this function is an implementation
+ * detail and may be change at any time in response to operations on the
+ * stream.
*
- * Note that for growable streams the returned size may become invalid on
- * the next write or truncate operation on the stream.
+ * If the stream is fixed-sized (ie: no realloc was passed to
+ * g_memory_output_stream_new()) then this is the maximum size of the
+ * stream and further writes will return %G_IO_ERROR_NO_SPACE.
*
- * If you want the number of bytes currently written to the stream, use
- * g_memory_output_stream_get_data_size().
+ * In any case, if you want the number of bytes currently written to the
+ * stream, use g_memory_output_stream_get_data_size().
*
* Returns: the number of bytes allocated for the data buffer
*/
* g_memory_output_stream_get_data_size:
* @ostream: a #GMemoryOutputStream
*
- * Returns the number of bytes from the start up
- * to including the last byte written in the stream
- * that has not been truncated away.
+ * Returns the number of bytes from the start up to including the last
+ * byte written in the stream that has not been truncated away.
*
* Returns: the number of bytes written to the stream
*
g_return_val_if_fail (g_output_stream_is_closed (G_OUTPUT_STREAM (ostream)), NULL);
result = g_bytes_new_with_free_func (ostream->priv->data,
- ostream->priv->valid_len,
- ostream->priv->destroy,
- ostream->priv->data);
+ ostream->priv->valid_len,
+ ostream->priv->destroy,
+ ostream->priv->data);
ostream->priv->data = NULL;
-
+
return result;
}
if (priv->pos + count > priv->len)
{
- /* At least enought to fit the write, rounded up
- for greater than linear growth.
- TODO: This wastes a lot of memory at large stream sizes.
- Figure out a more rational allocation strategy. */
+ /* At least enough to fit the write, rounded up for greater than
+ * linear growth.
+ *
+ * Assuming that we're using something like realloc(), the kernel
+ * will overcommit memory to us, so doubling the size each time
+ * will keep the number of realloc calls low without wasting too
+ * much memory.
+ */
new_size = g_nearest_pow (priv->pos + count);
/* Check for overflow again. We have only checked if
pos + count > G_MAXSIZE, but it only catches the case of writing
static gboolean
g_memory_output_stream_seek (GSeekable *seekable,
- goffset offset,
- GSeekType type,
- GCancellable *cancellable,
- GError **error)
+ goffset offset,
+ GSeekType type,
+ GCancellable *cancellable,
+ GError **error)
{
GMemoryOutputStream *stream;
GMemoryOutputStreamPrivate *priv;
ostream = G_MEMORY_OUTPUT_STREAM (seekable);
priv = ostream->priv;
+ /* We do not allow truncation of fixed-sized streams */
return priv->realloc_fn != NULL;
}
static GSource *
g_memory_output_stream_create_source (GPollableOutputStream *stream,
- GCancellable *cancellable)
+ GCancellable *cancellable)
{
GSource *base_source, *pollable_source;
base_source = g_timeout_source_new (0);
- pollable_source = g_pollable_source_new_full (stream, base_source,
- cancellable);
+ pollable_source = g_pollable_source_new_full (stream, base_source, cancellable);
g_source_unref (base_source);
return pollable_source;
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