sd_bus_send - Man Page

#include <systemd/sd-bus​.h>

int sd_bus_send(sd_bus *bus, sd_bus_message *m, uint64_t *cookie);

int sd_bus_send_to(sd_bus *bus, sd_bus_message *m, const char *destination, uint64_t *cookie);

int sd_bus_message_send(sd_bus_message *m);

sd_bus_send() queues the bus message object m for transfer​. If bus is NULL, the bus that m is attached to is used​. bus only needs to be set when the message is sent to a different bus than the one it is attached to, for example when forwarding messages​. If the output parameter cookie is not NULL, it is set to the message identifier​. This value can later be used to match incoming replies to their corresponding messages​. If cookie is set to NULL and the message is not sealed, sd_bus_send() assumes the message m does not expect a reply and adds the necessary headers to indicate this​.

Note that in most scenarios, sd_bus_send() should not be called directly​. Instead, use higher level functions such as sd_bus_call_method(3) and sd_bus_reply_method_return(3) which call sd_bus_send() internally​.

sd_bus_send_to() is a shorthand for sending a message to a specific destination​. It's main use case is to simplify sending unicast signal messages (signals that only have a single receiver)​. It's behavior is similar to calling sd_bus_message_set_destination(3) followed by calling sd_bus_send()​.

sd_bus_send()/sd_bus_send_to() will write the message directly to the underlying transport (e​.g​. kernel socket buffer) if possible​. If the connection is not set up fully yet the message is queued locally​. If the transport buffers are congested any unwritten message data is queued locally, too​. If the connection has been closed or is currently being closed the call fails​. sd_bus_process(3) should be invoked to write out any queued message data to the transport​.

sd_bus_message_send() is the same as sd_bus_send() but without the first and last argument​. sd_bus_message_send(m) is equivalent to sd_bus_send(sd_bus_message_get_bus(m), m, NULL)​.

On success, these functions return a non-negative integer​. On failure, they return a negative errno-style error code​.

Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemd ​pkg-config(1) file​.

All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time​. Different threads may access the same object at different times​. Multiple independent objects may be used from different threads in parallel​.

The code described here uses getenv(3), which is declared to be not multi-thread-safe​. This means that the code calling the functions described here must not call setenv(3) from a parallel thread​. It is recommended to only do calls to setenv() from an early phase of the program when no other threads have been started​.

sd_bus_send() and sd_bus_send_to() were added in version 246​.

systemd(1), sd-bus(3), sd_bus_call_method(3), sd_bus_message_set_destination(3), sd_bus_reply_method_return(3), sd_bus_process(3)