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authorLennart Poettering <lennart@poettering.net>2015-11-27 19:13:45 +0100
committerLennart Poettering <lennart@poettering.net>2015-11-27 19:19:36 +0100
commit4afd3348c7506dd1d36305b7bcb9feb8952b9d6b (patch)
tree778068851852e18794eb3351d0cb250cd3911f10 /man/sd_bus_new.xml
parentf5edf80e297e4ba499db57779af2f121922f372a (diff)
tree-wide: expose "p"-suffix unref calls in public APIs to make gcc cleanup easy
GLIB has recently started to officially support the gcc cleanup attribute in its public API, hence let's do the same for our APIs. With this patch we'll define an xyz_unrefp() call for each public xyz_unref() call, to make it easy to use inside a __attribute__((cleanup())) expression. Then, all code is ported over to make use of this. The new calls are also documented in the man pages, with examples how to use them (well, I only added docs where the _unref() call itself already had docs, and the examples, only cover sd_bus_unrefp() and sd_event_unrefp()). This also renames sd_lldp_free() to sd_lldp_unref(), since that's how we tend to call our destructors these days. Note that this defines no public macro that wraps gcc's attribute and makes it easier to use. While I think it's our duty in the library to make our stuff easy to use, I figure it's not our duty to make gcc's own features easy to use on its own. Most likely, client code which wants to make use of this should define its own: #define _cleanup_(function) __attribute__((cleanup(function))) Or similar, to make the gcc feature easier to use. Making this logic public has the benefit that we can remove three header files whose only purpose was to define these functions internally. See #2008.
Diffstat (limited to 'man/sd_bus_new.xml')
-rw-r--r--man/sd_bus_new.xml48
1 files changed, 40 insertions, 8 deletions
diff --git a/man/sd_bus_new.xml b/man/sd_bus_new.xml
index e1cab6e567..d281b5dd44 100644
--- a/man/sd_bus_new.xml
+++ b/man/sd_bus_new.xml
@@ -46,6 +46,7 @@
<refname>sd_bus_new</refname>
<refname>sd_bus_ref</refname>
<refname>sd_bus_unref</refname>
+ <refname>sd_bus_unrefp</refname>
<refpurpose>Create a new bus object and create or destroy references to it</refpurpose>
</refnamediv>
@@ -68,6 +69,11 @@
<funcdef>sd_bus *<function>sd_bus_unref</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
</funcprototype>
+
+ <funcprototype>
+ <funcdef>void <function>sd_bus_unrefp</function></funcdef>
+ <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
+ </funcprototype>
</funcsynopsis>
</refsynopsisdiv>
@@ -93,14 +99,40 @@
only allocate a bus object but also start the connection to a
well-known bus in a single function invocation.</para>
- <para><function>sd_bus_ref()</function> creates a new reference to
- <parameter>bus</parameter>.</para>
+ <para><function>sd_bus_ref()</function> increases the reference
+ counter of <parameter>bus</parameter> by one.</para>
- <para><function>sd_bus_unref()</function> destroys a reference to
- <parameter>bus</parameter>. Once the reference count has dropped
- to zero, <parameter>bus</parameter> cannot be used anymore, so
- further calls to <function>sd_bus_ref()</function> or
+ <para><function>sd_bus_unref()</function> decreases the reference
+ counter of <parameter>bus</parameter> by one. Once the reference
+ count has dropped to zero, <parameter>bus</parameter> is destroyed
+ and cannot be used anymore, so further calls to
+ <function>sd_bus_ref()</function> or
<function>sd_bus_unref()</function> are illegal.</para>
+
+ <para><function>sd_bus_unrefp()</function> is similar to
+ <function>sd_bus_unref()</function> but takes a pointer to a
+ pointer to an <type>sd_bus</type> object. This call is useful in
+ conjunction with GCC's and LLVM's <ulink
+ url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
+ Variable Attribute</ulink>. Note that this function is defined as
+ inline function. Use a declaration like the following, in order to
+ allocate a bus object that is freed automatically as the code
+ block is left:</para>
+
+ <programlisting>{
+ __attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
+ int r;
+ …
+ r = sd_bus_default(&amp;bus);
+ if (r &lt; 0)
+ fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
+ …
+}</programlisting>
+
+ <para><function>sd_bus_ref()</function>,
+ <function>sd_bus_unref()</function> and
+ <function>sd_bus_unrefp()</function> execute no operation if the
+ passed in bus object is <constant>NULL</constant>.</para>
</refsect1>
<refsect1>
@@ -110,10 +142,10 @@
positive integer. On failure, it returns a negative errno-style
error code.</para>
- <para><function>sd_bus_ref</function> always returns the argument.
+ <para><function>sd_bus_ref()</function> always returns the argument.
</para>
- <para><function>sd_bus_unref</function> always returns
+ <para><function>sd_bus_unref()</function> always returns
<constant>NULL</constant>.</para>
</refsect1>