Module: Gio::DatagramBased
- Defined in:
- (unknown)
Overview
Interface for socket-like objects with datagram semantics.
A GDatagramBased is a networking interface for representing datagram-based
communications. It is a more or less direct mapping of the core parts of the
BSD socket API in a portable GObject interface. It is implemented by
[classGio.Socket], which wraps the UNIX socket API on UNIX and winsock2 on Windows.
GDatagramBased is entirely platform independent, and is intended to be used
alongside higher-level networking APIs such as [classGio.IOStream].
It uses vectored scatter/gather I/O by default, allowing for many messages
to be sent or received in a single call. Where possible, implementations of
the interface should take advantage of vectored I/O to minimise processing
or system calls. For example, GSocket uses recvmmsg() and sendmmsg()
where possible. Callers should take advantage of scatter/gather I/O (the use of
multiple buffers per message) to avoid unnecessary copying of data to
assemble or disassemble a message.
Each GDatagramBased operation has a timeout parameter which may be negative
for blocking behaviour, zero for non-blocking behaviour, or positive for
timeout behaviour. A blocking operation blocks until finished or there is an
error. A non-blocking operation will return immediately with a
G_IO_ERROR_WOULD_BLOCK error if it cannot make progress. A timeout operation
will block until the operation is complete or the timeout expires; if the
timeout expires it will return what progress it made, or
G_IO_ERROR_TIMED_OUT if no progress was made. To know when a call would
successfully run you can call [methodGio.DatagramBased.condition_check] or
[methodGio.DatagramBased.condition_wait]. You can also use
[methodGio.DatagramBased.create_source] and attach it to a [structGLib.MainContext]
to get callbacks when I/O is possible.
When running a non-blocking operation applications should always be able to
handle getting a G_IO_ERROR_WOULD_BLOCK error even when some other function
said that I/O was possible. This can easily happen in case of a race
condition in the application, but it can also happen for other reasons. For
instance, on Windows a socket is always seen as writable until a write
returns G_IO_ERROR_WOULD_BLOCK.
As with GSocket, GDatagramBaseds can be either connection oriented (for
example, SCTP) or connectionless (for example, UDP). GDatagramBaseds must be
datagram-based, not stream-based. The interface does not cover connection
establishment — use methods on the underlying type to establish a connection
before sending and receiving data through the GDatagramBased API. For
connectionless socket types the target/source address is specified or
received in each I/O operation.
Like most other APIs in GLib, GDatagramBased is not inherently thread safe.
To use a GDatagramBased concurrently from multiple threads, you must
implement your own locking.
Instance Method Summary collapse
-
#condition_check(condition) ⇒ GLib::IOCondition
Checks on the readiness of datagram_based to perform operations.
-
#condition_wait(condition, timeout, cancellable) ⇒ Boolean
Waits for up to timeout microseconds for condition to become true on datagram_based.
-
#create_source(condition, cancellable) ⇒ GLib::Source
Creates a #GSource that can be attached to a GMain::Context to monitor for the availability of the specified condition on the GDatagram::Based.
-
#receive_messages(messages, num_messages, flags, timeout, cancellable) ⇒ Integer
Receive one or more data messages from datagram_based in one go.
-
#send_messages(messages, num_messages, flags, timeout, cancellable) ⇒ Integer
Send one or more data messages from datagram_based in one go.
Instance Method Details
#condition_check(condition) ⇒ GLib::IOCondition
Checks on the readiness of datagram_based to perform operations. The
operations specified in condition are checked for and masked against the
currently-satisfied conditions on datagram_based. The result is returned.
%G_IO_IN will be set in the return value if data is available to read with
g_datagram_based_receive_messages(), or if the connection is closed remotely
(EOS); and if the datagram_based has not been closed locally using some
implementation-specific method (such as g_socket_close() or
g_socket_shutdown() with shutdown_read set, if it’s a #GSocket).
If the connection is shut down or closed (by calling g_socket_close() or
g_socket_shutdown() with shutdown_read set, if it’s a #GSocket, for
example), all calls to this function will return %G_IO_ERROR_CLOSED.
%G_IO_OUT will be set if it is expected that at least one byte can be sent
using g_datagram_based_send_messages() without blocking. It will not be set
if the datagram_based has been closed locally.
%G_IO_HUP will be set if the connection has been closed locally.
%G_IO_ERR will be set if there was an asynchronous error in transmitting data
previously enqueued using g_datagram_based_send_messages().
Note that on Windows, it is possible for an operation to return
%G_IO_ERROR_WOULD_BLOCK even immediately after
g_datagram_based_condition_check() has claimed that the GDatagram::Based is
ready for writing. Rather than calling g_datagram_based_condition_check() and
then writing to the GDatagram::Based if it succeeds, it is generally better to
simply try writing right away, and try again later if the initial attempt
returns %G_IO_ERROR_WOULD_BLOCK.
It is meaningless to specify %G_IO_ERR or %G_IO_HUP in condition; these
conditions will always be set in the output if they are true. Apart from
these flags, the output is guaranteed to be masked by condition.
This call never blocks.
#condition_wait(condition, timeout, cancellable) ⇒ Boolean
Waits for up to timeout microseconds for condition to become true on
datagram_based. If the condition is met, true is returned.
If cancellable is cancelled before the condition is met, or if timeout is
reached before the condition is met, then false is returned and error is
set appropriately (%G_IO_ERROR_CANCELLED or %G_IO_ERROR_TIMED_OUT).
#create_source(condition, cancellable) ⇒ GLib::Source
Creates a #GSource that can be attached to a GMain::Context to monitor for
the availability of the specified condition on the GDatagram::Based. The
#GSource keeps a reference to the datagram_based.
The callback on the source is of the GDatagram::BasedSourceFunc type.
It is meaningless to specify %G_IO_ERR or %G_IO_HUP in condition; these
conditions will always be reported in the callback if they are true.
If non-nil, cancellable can be used to cancel the source, which will
cause the source to trigger, reporting the current condition (which is
likely 0 unless cancellation happened at the same time as a condition
change). You can check for this in the callback using
g_cancellable_is_cancelled().
#receive_messages(messages, num_messages, flags, timeout, cancellable) ⇒ Integer
Receive one or more data messages from datagram_based in one go.
messages must point to an array of GInput::Message structs and
num_messages must be the length of this array. Each GInput::Message
contains a pointer to an array of GInput::Vector structs describing the
buffers that the data received in each message will be written to.
flags modify how all messages are received. The commonly available
arguments for this are available in the GSocket::MsgFlags enum, but the
values there are the same as the system values, and the flags
are passed in as-is, so you can pass in system-specific flags too. These
flags affect the overall receive operation. Flags affecting individual
messages are returned in GInput::Message.flags.
The other members of GInput::Message are treated as described in its
documentation.
If timeout is negative the call will block until num_messages have been
received, the connection is closed remotely (EOS), cancellable is cancelled,
or an error occurs.
If timeout is 0 the call will return up to num_messages without blocking,
or %G_IO_ERROR_WOULD_BLOCK if no messages are queued in the operating system
to be received.
If timeout is positive the call will block on the same conditions as if
timeout were negative. If the timeout is reached
before any messages are received, %G_IO_ERROR_TIMED_OUT is returned,
otherwise it will return the number of messages received before timing out.
(Note: This is effectively the behaviour of MSG_WAITFORONE with
recvmmsg().)
To be notified when messages are available, wait for the %G_IO_IN condition.
Note though that you may still receive %G_IO_ERROR_WOULD_BLOCK from
g_datagram_based_receive_messages() even if you were previously notified of a
%G_IO_IN condition.
If the remote peer closes the connection, any messages queued in the
underlying receive buffer will be returned, and subsequent calls to
g_datagram_based_receive_messages() will return 0 (with no error set).
If the connection is shut down or closed (by calling g_socket_close() or
g_socket_shutdown() with shutdown_read set, if it’s a #GSocket, for
example), all calls to this function will return %G_IO_ERROR_CLOSED.
On error -1 is returned and error is set accordingly. An error will only
be returned if zero messages could be received; otherwise the number of
messages successfully received before the error will be returned. If
cancellable is cancelled, %G_IO_ERROR_CANCELLED is returned as with any
other error.
#send_messages(messages, num_messages, flags, timeout, cancellable) ⇒ Integer
Send one or more data messages from datagram_based in one go.
messages must point to an array of GOutput::Message structs and
num_messages must be the length of this array. Each GOutput::Message
contains an address to send the data to, and a pointer to an array of
GOutput::Vector structs to describe the buffers that the data to be sent
for each message will be gathered from.
flags modify how the message is sent. The commonly available arguments
for this are available in the GSocket::MsgFlags enum, but the
values there are the same as the system values, and the flags
are passed in as-is, so you can pass in system-specific flags too.
The other members of GOutput::Message are treated as described in its
documentation.
If timeout is negative the call will block until num_messages have been
sent, cancellable is cancelled, or an error occurs.
If timeout is 0 the call will send up to num_messages without blocking,
or will return %G_IO_ERROR_WOULD_BLOCK if there is no space to send messages.
If timeout is positive the call will block on the same conditions as if
timeout were negative. If the timeout is reached before any messages are
sent, %G_IO_ERROR_TIMED_OUT is returned, otherwise it will return the number
of messages sent before timing out.
To be notified when messages can be sent, wait for the %G_IO_OUT condition.
Note though that you may still receive %G_IO_ERROR_WOULD_BLOCK from
g_datagram_based_send_messages() even if you were previously notified of a
%G_IO_OUT condition. (On Windows in particular, this is very common due to
the way the underlying APIs work.)
If the connection is shut down or closed (by calling g_socket_close() or
g_socket_shutdown() with shutdown_write set, if it’s a #GSocket, for
example), all calls to this function will return %G_IO_ERROR_CLOSED.
On error -1 is returned and error is set accordingly. An error will only
be returned if zero messages could be sent; otherwise the number of messages
successfully sent before the error will be returned. If cancellable is
cancelled, %G_IO_ERROR_CANCELLED is returned as with any other error.