GPollableOutputStream

typedef struct _GPollableOutputStream GPollableOutputStream;

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

Since 2.28

struct GPollableOutputStreamInterface

struct GPollableOutputStreamInterface {
  GTypeInterface g_iface;

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

  gboolean     (*is_writable)       (GPollableOutputStream  *stream);
  GSource *    (*create_source)     (GPollableOutputStream  *stream,
				     GCancellable           *cancellable);
  gssize       (*write_nonblocking) (GPollableOutputStream  *stream,
				     const void             *buffer,
				     gsize                   count,
				     GError                **error);
};

The interface for pollable output streams.

The default implementation of can_poll always returns TRUE.

The default implementation of write_nonblocking calls g_pollable_output_stream_is_writable(), and then calls g_output_stream_write() if it returns TRUE. This means you only need to override it if it is possible that your is_writable implementation may return TRUE when the stream is not actually writable.

Since 2.28

g_pollable_output_stream_can_poll ()

gboolean            g_pollable_output_stream_can_poll   (GPollableOutputStream *stream);

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

gboolean            g_pollable_output_stream_is_writable
                                                        (GPollableOutputStream *stream);

Checks if stream can be written.

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

Since 2.28

g_pollable_output_stream_create_source ()

GSource *           g_pollable_output_stream_create_source
                                                        (GPollableOutputStream *stream,
                                                         GCancellable *cancellable);

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

As with g_pollable_output_stream_is_writable(), it is possible that the stream may not actually be writable even after the source triggers, so you should use g_pollable_output_stream_write_nonblocking() rather than g_output_stream_write() from the callback.

Since 2.28

g_pollable_output_stream_write_nonblocking ()

gssize              g_pollable_output_stream_write_nonblocking
                                                        (GPollableOutputStream *stream,
                                                         const void *buffer,
                                                         gsize count,
                                                         GCancellable *cancellable,
                                                         GError **error);

Attempts to write up to count bytes from buffer to stream, as with g_output_stream_write(). If stream is not currently writable, this will immediately return G_IO_ERROR_WOULD_BLOCK, and you can use g_pollable_output_stream_create_source() to create a GSource that will be triggered when stream is writable.

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: write_nonblocking