GIOStream

gio.iostream.IOStream 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 gio.iostream.IOStream objects are gio.socket_connection.SocketConnection, which represents a two-way network connection; and gio.file_iostream.FileIOStream, which represents a file handle opened in read-write mode.

To do the actual reading and writing you need to get the substreams with gio.iostream.IOStream.getInputStream and gio.iostream.IOStream.getOutputStream.

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

To close a stream use gio.iostream.IOStream.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 gio.iostream.IOStream may still be open. However, some streams may support ‘half-closed’ states where one direction of the stream is actually shut down.

Operations on gio.iostream.IOStreams cannot be started while another operation on the gio.iostream.IOStream or its substreams is in progress. Specifically, an application can read from the gio.input_stream.InputStream and write to the gio.output_stream.OutputStream simultaneously (either in separate threads, or as asynchronous operations in the same thread), but an application cannot start any gio.iostream.IOStream operation while there is a gio.iostream.IOStream, gio.input_stream.InputStream or gio.output_stream.OutputStream operation in progress, and an application can’t start any gio.input_stream.InputStream or gio.output_stream.OutputStream operation while there is a gio.iostream.IOStream operation in progress.

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

GIO may run operations on gio.iostream.IOStreams from other (worker) threads, and this may be exposed to application code in the behaviour of wrapper streams, such as gio.buffered_input_stream.BufferedInputStream or gio.tls_connection.TlsConnection. 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).