GPollableInputStream

GPollableInputStream — Interface for pollable input streams

Synopsis

#include <gio/gio.h>

                    GPollableInputStream;
struct              GPollableInputStreamInterface;

gboolean            g_pollable_input_stream_can_poll    (GPollableInputStream *stream);
gboolean            g_pollable_input_stream_is_readable (GPollableInputStream *stream);
GSource *           g_pollable_input_stream_create_source
                                                        (GPollableInputStream *stream,
                                                         GCancellable *cancellable);
gssize              g_pollable_input_stream_read_nonblocking
                                                        (GPollableInputStream *stream,
                                                         void *buffer,
                                                         gsize size,
                                                         GCancellable *cancellable,
                                                         GError **error);

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

Object Hierarchy

  GInterface
   +----GPollableInputStream

Prerequisites

GPollableInputStream requires GInputStream.

Known Implementations

GPollableInputStream is implemented by GUnixInputStream.

Description

GPollableInputStream is implemented by GInputStreams that can be polled for readiness to read. This can be used when interfacing with a non-GIO API that expects UNIX-file-descriptor-style asynchronous I/O rather than GIO-style.

Details

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.

GTypeInterface g_iface;

The parent interface.

can_poll ()

Checks if the GPollableInputStream instance is actually pollable

is_readable ()

Checks if the stream is readable

create_source ()

Creates a GSource to poll the stream

read_nonblocking ()

Does a non-blocking read or returns G_IO_ERROR_WOULD_BLOCK

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.

stream :

a GPollableInputStream.

Returns :

TRUE if stream is pollable, FALSE if not.

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.

stream :

a GPollableInputStream.

Returns :

TRUE if stream is readable, FALSE if not. If an error has occurred on stream, this will result in g_pollable_input_stream_is_readable() returning TRUE, and the next attempt to read will return the error.

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.

stream :

a GPollableInputStream.

cancellable :

a GCancellable, or NULL. [allow-none]

Returns :

a new GSource. [transfer full]

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

stream :

a GPollableInputStream

buffer :

a buffer to read data into (which should be at least size bytes long).

size :

the number of bytes you want to read

cancellable :

a GCancellable, or NULL. [allow-none]

error :

GError for error reporting, or NULL to ignore.

Returns :

the number of bytes read, or -1 on error (including G_IO_ERROR_WOULD_BLOCK).

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().

pollable_stream :

the GPollableInputStream or GPollableOutputStream

user_data :

data passed in by the user.

Returns :

it should return FALSE if the source should be removed.

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.

pollable_stream :

the stream associated with the new source

Returns :

the new GSource. [transfer full]

Since 2.28

See Also

GInputStream, GPollableOutputStream, GFileDescriptorBased