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GPollableInputStream

GPollableInputStream — Interface for pollable input streams

Object Hierarchy

    GInterface
    ╰── GPollableInputStream

Prerequisites

GPollableInputStream requires GInputStream.

Known Implementations

GPollableInputStream is implemented by GConverterInputStream, GMemoryInputStream and GUnixInputStream.

Includes

#include <gio/gio.h>

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.

Functions

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.

Parameters

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.

Parameters

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.

Parameters

stream

a GPollableInputStream.

 

cancellable

a GCancellable, or NULL.

[nullable]

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 count,
                                GCancellable *cancellable,
                                GError **error);

Attempts to read up to count 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

Parameters

stream

a GPollableInputStream

 

buffer

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

[array length=count][element-type guint8]

count

the number of bytes you want to read

 

cancellable

a GCancellable, or NULL.

[nullable]

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).

Types and Values

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                  count,
				    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.

Members

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

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