Module: Gio::DatagramBased
- Defined in:
- (unknown)
Overview
A GDatagram::Based 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 #GSocket, which wraps the UNIX socket API on UNIX and winsock2 on Windows.
GDatagram::Based is entirely platform independent, and is intended to be used alongside higher-level networking APIs such as #GIOStream.
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 GDatagram::Based 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 g_datagram_based_condition_check() or g_datagram_based_condition_wait(). You can also use g_datagram_based_create_source() and attach it to a GMain::Context 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, GDatagram::Baseds can be either connection oriented (for example, SCTP) or connectionless (for example, UDP). GDatagram::Baseds 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 GDatagram::Based API. For connectionless socket types the target/source address is specified or received in each I/O operation.
Like most other APIs in GLib, GDatagram::Based is not inherently thread safe. To use a GDatagram::Based concurrently from multiple threads, you must implement your own locking.
Instance Method Summary collapse
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#condition_check(condition) ⇒ GLib::IOCondition
Checks on the readiness of datagram_based to perform operations.
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#condition_wait(condition, timeout, cancellable) ⇒ TrueClass
Waits for up to timeout microseconds for condition to become true on datagram_based.
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#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.
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#receive_messages(messages, num_messages, flags, timeout, cancellable) ⇒ Integer
Receive one or more data messages from datagram_based in one go.
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#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) ⇒ TrueClass
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.