sd_bus_ref(3)

1SD_BUS_NEW(3)                     sd_bus_new                     SD_BUS_NEW(3)
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NAME

6       sd_bus_new, sd_bus_ref, sd_bus_unref, sd_bus_unrefp - Create a new bus
7       object and create or destroy references to it
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SYNOPSIS

10       #include <systemd/sd-bus.h>
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12       int sd_bus_new(sd_bus **bus);
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14       sd_bus *sd_bus_ref(sd_bus *bus);
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16       sd_bus *sd_bus_unref(sd_bus *bus);
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18       void sd_bus_unrefp(sd_bus **bus);
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DESCRIPTION

21       sd_bus_new() creates a new bus object. This object is
22       reference-counted, and will be destroyed when all references are gone.
23       Initially, the caller of this function owns the sole reference and the
24       bus object will not be connected to any bus. To connect it to a bus,
25       make sure to set an address with sd_bus_set_address(3) or a related
26       call, and then start the connection with sd_bus_start(3).
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28       In most cases, it is a better idea to invoke sd_bus_default_user(3),
29       sd_bus_default_system(3) or related calls instead of the more low-level
30       sd_bus_new() and sd_bus_start(). The higher-level calls not only
31       allocate a bus object but also start the connection to a well-known bus
32       in a single function invocation.
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34       sd_bus_ref() increases the reference counter of bus by one.
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36       sd_bus_unref() decreases the reference counter of bus by one. Once the
37       reference count has dropped to zero, bus is destroyed and cannot be
38       used anymore, so further calls to sd_bus_ref() or sd_bus_unref() are
39       illegal.
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41       sd_bus_unrefp() is similar to sd_bus_unref() but takes a pointer to a
42       pointer to an sd_bus object. This call is useful in conjunction with
43       GCC's and LLVM's Clean-up Variable Attribute[1]. Note that this
44       function is defined as inline function. Use a declaration like the
45       following, in order to allocate a bus object that is freed
46       automatically as the code block is left:
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48           {
49                   __attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
50                   int r;
51                   ...
52                   r = sd_bus_default(&bus);
53                   if (r < 0)
54                           fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
55                   ...
56           }
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58       sd_bus_ref(), sd_bus_unref() and sd_bus_unrefp() execute no operation
59       if the passed in bus object is NULL.
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RETURN VALUE

62       On success, sd_bus_new() returns 0 or a positive integer. On failure,
63       it returns a negative errno-style error code.
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65       sd_bus_ref() always returns the argument.
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67       sd_bus_unref() always returns NULL.
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ERRORS

70       Returned errors may indicate the following problems:
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72       -ENOMEM
73           Memory allocation failed.
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NOTES

76       These APIs are implemented as a shared library, which can be compiled
77       and linked to with the libsystemd pkg-config(1) file.
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NOTES

84        1. Clean-up Variable Attribute
85           https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
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89systemd 239                                                      SD_BUS_NEW(3)