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GMemoryOutputStream: docs and whitespace fixes

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Document the difference between resizable and fixed-sized streams,
particularly with regards to sizing and seeking.

https://bugzilla.gnome.org/show_bug.cgi?id=684842
This commit is contained in:
Ryan Lortie 2013-10-22 15:51:15 -04:00
parent 1d1c17d9ee
commit 38dc8d4cd3
1 changed files with 64 additions and 34 deletions
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98
gio/gmemoryoutputstream.c
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@ -42,8 +42,8 @@
* #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
@ -57,8 +57,8 @@ enum {
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 */
@ -114,7 +114,7 @@ static gboolean g_memory_output_stream_truncate (GSeekable *see
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);
@ -341,10 +341,33 @@ g_memory_output_stream_init (GMemoryOutputStream *stream)
*
* 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 */
@ -416,16 +439,20 @@ g_memory_output_stream_get_data (GMemoryOutputStream *ostream)
* @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()).
*
* Note that for growable streams the returned size may become invalid on
* the next write or truncate operation on the stream.
* 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.
*
* If you want the number of bytes currently written to the stream, use
* g_memory_output_stream_get_data_size().
* 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.
*
* 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
*/
@ -441,9 +468,8 @@ g_memory_output_stream_get_size (GMemoryOutputStream *ostream)
* 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
*
@ -506,11 +532,11 @@ g_memory_output_stream_steal_as_bytes (GMemoryOutputStream *ostream)
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;
}
@ -606,10 +632,14 @@ g_memory_output_stream_write (GOutputStream *stream,
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
@ -703,10 +733,10 @@ g_memory_output_stream_can_seek (GSeekable *seekable)
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;
@ -783,6 +813,7 @@ g_memory_output_stream_can_truncate (GSeekable *seekable)
ostream = G_MEMORY_OUTPUT_STREAM (seekable);
priv = ostream->priv;
/* We do not allow truncation of fixed-sized streams */
return priv->realloc_fn != NULL;
}
@ -808,13 +839,12 @@ g_memory_output_stream_is_writable (GPollableOutputStream *stream)
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;