sd_bus_wait - Wait for I/O on a bus connection
int sd_bus_wait(sd_bus *bus, uint64_t timeout_usec);
sd_bus_wait() synchronously waits for I/O on the specified bus connection object. This function is supposed to be called whenever sd_bus_process(3) returns zero, indicating that no work is pending on the connection. Internally, this call invokes ppoll(2), to wait for I/O on the bus connection. If the timeout_sec parameter is specified, the call will block at most for the specified amount of time in µs. Pass UINT64_MAX to permit it to sleep indefinitely.
After each invocation of sd_bus_wait() the sd_bus_process() call should be invoked in order to process any now pending I/O work.
Note that sd_bus_wait() is suitable only for simple programs as it does not permit waiting for other I/O events. For more complex programs either connect the bus connection object to an external event loop using sd_bus_get_fd(3) or to an sd-event(3) event loop using sd_bus_attach_event(3).
If any I/O was seen, a positive value is returned, zero otherwise. If an error occurs, a negative errno-style error code is returned.
Returned errors may indicate the following problems:
An invalid bus object was passed.
The bus connection was allocated in a parent process and is being reused in a child process after fork().
The bus connection has been terminated already.
These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.