GIOStream

GIOStream — Base class for implementing read/write streams

Types and Values

Object Hierarchy

    GObject
    ╰── GIOStream
        ├── GFileIOStream
        ├── GSimpleIOStream
        ├── GSocketConnection
        ╰── GTlsConnection

Includes

#include <gio/gio.h>

Description

GIOStream represents an object that has both read and write streams. Generally the two streams act as separate input and output streams, but they share some common resources and state. For instance, for seekable streams, both streams may use the same position.

Examples of GIOStream objects are GSocketConnection, which represents a two-way network connection; and GFileIOStream, which represents a file handle opened in read-write mode.

To do the actual reading and writing you need to get the substreams with g_io_stream_get_input_stream() and g_io_stream_get_output_stream().

The GIOStream object owns the input and the output streams, not the other way around, so keeping the substreams alive will not keep the GIOStream object alive. If the GIOStream object is freed it will be closed, thus closing the substreams, so even if the substreams stay alive they will always return G_IO_ERROR_CLOSED for all operations.

To close a stream use g_io_stream_close() which will close the common stream object and also the individual substreams. You can also close the substreams themselves. In most cases this only marks the substream as closed, so further I/O on it fails but common state in the GIOStream may still be open. However, some streams may support "half-closed" states where one direction of the stream is actually shut down.

Operations on GIOStreams cannot be started while another operation on the GIOStream or its substreams is in progress. Specifically, an application can read from the GInputStream and write to the GOutputStream simultaneously (either in separate threads, or as asynchronous operations in the same thread), but an application cannot start any GIOStream operation while there is a GIOStream, GInputStream or GOutputStream operation in progress, and an application can’t start any GInputStream or GOutputStream operation while there is a GIOStream operation in progress.

This is a product of individual stream operations being associated with a given GMainContext (the thread-default context at the time the operation was started), rather than entire streams being associated with a single GMainContext.

GIO may run operations on GIOStreams from other (worker) threads, and this may be exposed to application code in the behaviour of wrapper streams, such as GBufferedInputStream or GTlsConnection. With such wrapper APIs, application code may only run operations on the base (wrapped) stream when the wrapper stream is idle. Note that the semantics of such operations may not be well-defined due to the state the wrapper stream leaves the base stream in (though they are guaranteed not to crash).

Functions

g_io_stream_get_input_stream ()

GInputStream *
g_io_stream_get_input_stream (GIOStream *stream);

Gets the input stream for this object. This is used for reading.

Parameters

stream

a GIOStream

 

Returns

a GInputStream, owned by the GIOStream. Do not free.

[transfer none]

Since: 2.22


g_io_stream_get_output_stream ()

GOutputStream *
g_io_stream_get_output_stream (GIOStream *stream);

Gets the output stream for this object. This is used for writing.

Parameters

stream

a GIOStream

 

Returns

a GOutputStream, owned by the GIOStream. Do not free.

[transfer none]

Since: 2.22


g_io_stream_splice_async ()

void
g_io_stream_splice_async (GIOStream *stream1,
                          GIOStream *stream2,
                          GIOStreamSpliceFlags flags,
                          int io_priority,
                          GCancellable *cancellable,
                          GAsyncReadyCallback callback,
                          gpointer user_data);

Asyncronously splice the output stream of stream1 to the input stream of stream2 , and splice the output stream of stream2 to the input stream of stream1 .

When the operation is finished callback will be called. You can then call g_io_stream_splice_finish() to get the result of the operation.

Parameters

stream1

a GIOStream.

 

stream2

a GIOStream.

 

flags

a set of GIOStreamSpliceFlags.

 

io_priority

the io priority of the request.

 

cancellable

optional GCancellable object, NULL to ignore.

[nullable]

callback

a GAsyncReadyCallback.

[scope async]

user_data

user data passed to callback .

[closure]

Since: 2.28


g_io_stream_splice_finish ()

gboolean
g_io_stream_splice_finish (GAsyncResult *result,
                           GError **error);

Finishes an asynchronous io stream splice operation.

Parameters

result

a GAsyncResult.

 

error

a GError location to store the error occurring, or NULL to ignore.

 

Returns

TRUE on success, FALSE otherwise.

Since: 2.28


g_io_stream_close ()

gboolean
g_io_stream_close (GIOStream *stream,
                   GCancellable *cancellable,
                   GError **error);

Closes the stream, releasing resources related to it. This will also close the individual input and output streams, if they are not already closed.

Once the stream is closed, all other operations will return G_IO_ERROR_CLOSED. Closing a stream multiple times will not return an error.

Closing a stream will automatically flush any outstanding buffers in the stream.

Streams will be automatically closed when the last reference is dropped, but you might want to call this function to make sure resources are released as early as possible.

Some streams might keep the backing store of the stream (e.g. a file descriptor) open after the stream is closed. See the documentation for the individual stream for details.

On failure the first error that happened will be reported, but the close operation will finish as much as possible. A stream that failed to close will still return G_IO_ERROR_CLOSED for all operations. Still, it is important to check and report the error to the user, otherwise there might be a loss of data as all data might not be written.

If cancellable is not NULL, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error G_IO_ERROR_CANCELLED will be returned. Cancelling a close will still leave the stream closed, but some streams can use a faster close that doesn't block to e.g. check errors.

The default implementation of this method just calls close on the individual input/output streams.

Parameters

stream

a GIOStream

 

cancellable

optional GCancellable object, NULL to ignore.

[nullable]

error

location to store the error occurring, or NULL to ignore

 

Returns

TRUE on success, FALSE on failure

Since: 2.22


g_io_stream_close_async ()

void
g_io_stream_close_async (GIOStream *stream,
                         int io_priority,
                         GCancellable *cancellable,
                         GAsyncReadyCallback callback,
                         gpointer user_data);

Requests an asynchronous close of the stream, releasing resources related to it. When the operation is finished callback will be called. You can then call g_io_stream_close_finish() to get the result of the operation.

For behaviour details see g_io_stream_close().

The asynchronous methods have a default fallback that uses threads to implement asynchronicity, so they are optional for inheriting classes. However, if you override one you must override all.

Parameters

stream

a GIOStream

 

io_priority

the io priority of the request

 

cancellable

optional cancellable object.

[nullable]

callback

callback to call when the request is satisfied.

[scope async]

user_data

the data to pass to callback function.

[closure]

Since: 2.22


g_io_stream_close_finish ()

gboolean
g_io_stream_close_finish (GIOStream *stream,
                          GAsyncResult *result,
                          GError **error);

Closes a stream.

Parameters

stream

a GIOStream

 

result

a GAsyncResult

 

error

a GError location to store the error occurring, or NULL to ignore

 

Returns

TRUE if stream was successfully closed, FALSE otherwise.

Since: 2.22


g_io_stream_is_closed ()

gboolean
g_io_stream_is_closed (GIOStream *stream);

Checks if a stream is closed.

Parameters

stream

a GIOStream

 

Returns

TRUE if the stream is closed.

Since: 2.22


g_io_stream_has_pending ()

gboolean
g_io_stream_has_pending (GIOStream *stream);

Checks if a stream has pending actions.

Parameters

stream

a GIOStream

 

Returns

TRUE if stream has pending actions.

Since: 2.22


g_io_stream_set_pending ()

gboolean
g_io_stream_set_pending (GIOStream *stream,
                         GError **error);

Sets stream to have actions pending. If the pending flag is already set or stream is closed, it will return FALSE and set error .

Parameters

stream

a GIOStream

 

error

a GError location to store the error occurring, or NULL to ignore

 

Returns

TRUE if pending was previously unset and is now set.

Since: 2.22


g_io_stream_clear_pending ()

void
g_io_stream_clear_pending (GIOStream *stream);

Clears the pending flag on stream .

Parameters

stream

a GIOStream

 

Since: 2.22

Types and Values

enum GIOStreamSpliceFlags

GIOStreamSpliceFlags determine how streams should be spliced.

Members

G_IO_STREAM_SPLICE_NONE

Do not close either stream.

 

G_IO_STREAM_SPLICE_CLOSE_STREAM1

Close the first stream after the splice.

 

G_IO_STREAM_SPLICE_CLOSE_STREAM2

Close the second stream after the splice.

 

G_IO_STREAM_SPLICE_WAIT_FOR_BOTH

Wait for both splice operations to finish before calling the callback.

 

Since: 2.28


GIOStream

typedef struct _GIOStream GIOStream;

Base class for read-write streams.

Property Details

The “closed” property

  “closed”                   gboolean

Is the stream closed.

Flags: Read

Default value: FALSE


The “input-stream” property

  “input-stream”             GInputStream *

The GInputStream to read from.

Flags: Read


The “output-stream” property

  “output-stream”            GOutputStream *

The GOutputStream to write to.

Flags: Read