GPollableInputStream

typedef struct _GPollableInputStream GPollableInputStream;

An interface for a GInputStream that can be polled for readability.

Since 2.28

struct GPollableInputStreamInterface

struct GPollableInputStreamInterface {
  GTypeInterface g_iface;

  /* Virtual Table */
  gboolean     (*can_poll)         (GPollableInputStream  *stream);

  gboolean     (*is_readable)      (GPollableInputStream  *stream);
  GSource *    (*create_source)    (GPollableInputStream  *stream,
				    GCancellable          *cancellable);
  gssize       (*read_nonblocking) (GPollableInputStream  *stream,
				    void                  *buffer,
				    gsize                  size,
				    GError               **error);
};

The interface for pollable input streams.

The default implementation of can_poll always returns TRUE.

The default implementation of read_nonblocking calls g_pollable_input_stream_is_readable(), and then calls g_input_stream_read() if it returns TRUE. This means you only need to override it if it is possible that your is_readable implementation may return TRUE when the stream is not actually readable.

Since 2.28

g_pollable_input_stream_can_poll ()

gboolean            g_pollable_input_stream_can_poll    (GPollableInputStream *stream);

Checks if stream is actually pollable. Some classes may implement GPollableInputStream but have only certain instances of that class be pollable. If this method returns FALSE, then the behavior of other GPollableInputStream methods is undefined.

For any given stream, the value returned by this method is constant; a stream cannot switch from pollable to non-pollable or vice versa.

Since 2.28

g_pollable_input_stream_is_readable ()

gboolean            g_pollable_input_stream_is_readable (GPollableInputStream *stream);

Checks if stream can be read.

Note that some stream types may not be able to implement this 100% reliably, and it is possible that a call to g_input_stream_read() after this returns TRUE would still block. To guarantee non-blocking behavior, you should always use g_pollable_input_stream_read_nonblocking(), which will return a G_IO_ERROR_WOULD_BLOCK error rather than blocking.

Since 2.28

g_pollable_input_stream_create_source ()

GSource *           g_pollable_input_stream_create_source
                                                        (GPollableInputStream *stream,
                                                         GCancellable *cancellable);

Creates a GSource that triggers when stream can be read, or cancellable is triggered or an error occurs. The callback on the source is of the GPollableSourceFunc type.

As with g_pollable_input_stream_is_readable(), it is possible that the stream may not actually be readable even after the source triggers, so you should use g_pollable_input_stream_read_nonblocking() rather than g_input_stream_read() from the callback.

Since 2.28

g_pollable_input_stream_read_nonblocking ()

gssize              g_pollable_input_stream_read_nonblocking
                                                        (GPollableInputStream *stream,
                                                         void *buffer,
                                                         gsize size,
                                                         GCancellable *cancellable,
                                                         GError **error);

Attempts to read up to size bytes from stream into buffer, as with g_input_stream_read(). If stream is not currently readable, this will immediately return G_IO_ERROR_WOULD_BLOCK, and you can use g_pollable_input_stream_create_source() to create a GSource that will be triggered when stream is readable.

Note that since this method never blocks, you cannot actually use cancellable to cancel it. However, it will return an error if cancellable has already been cancelled when you call, which may happen if you call this method after a source triggers due to having been cancelled.

Virtual: read_nonblocking

GPollableSourceFunc ()

gboolean            (*GPollableSourceFunc)              (GObject *pollable_stream,
                                                         gpointer user_data);

This is the function type of the callback used for the GSource returned by g_pollable_input_stream_create_source() and g_pollable_output_stream_create_source().

Since 2.28

g_pollable_source_new ()

GSource *           g_pollable_source_new               (GObject *pollable_stream);

Utility method for GPollableInputStream and GPollableOutputStream implementations. Creates a new GSource that expects a callback of type GPollableSourceFunc. The new source does not actually do anything on its own; use g_source_add_child_source() to add other sources to it to cause it to trigger.

Since 2.28