sd_bus_pending_method_calls — Return the number of currently pending, outgoing method calls
#include <systemd/sd-bus.h>
| int sd_bus_pending_method_calls( | sd_bus *bus ); | 
sd_bus_pending_method_calls() returns the number of currently pending outgoing
    method calls, i.e. method calls enqueued with
    sd_bus_call_async(3) for
    which no reply has been received yet, and which have not reached a timeout yet.
The bus argument may be NULL, in which case zero is
    returned.
This function returns 0 if there are no pending method calls, or a NULL bus
    object was specified. On failure, a negative errno-style error code is returned.
Functions described here are available as a shared
  library, which can be compiled against and linked to with the
  libsystemd pkg-config(1)
  file.
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.