From 4afd3348c7506dd1d36305b7bcb9feb8952b9d6b Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Fri, 27 Nov 2015 19:13:45 +0100
Subject: 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.
---
 man/sd_event_new.xml | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

(limited to 'man/sd_event_new.xml')

diff --git a/man/sd_event_new.xml b/man/sd_event_new.xml
index 3356faa899..2c23b00a8c 100644
--- a/man/sd_event_new.xml
+++ b/man/sd_event_new.xml
@@ -47,6 +47,7 @@
     <refname>sd_event_default</refname>
     <refname>sd_event_ref</refname>
     <refname>sd_event_unref</refname>
+    <refname>sd_event_unrefp</refname>
     <refname>sd_event_get_tid</refname>
     <refname>sd_event</refname>
 
@@ -79,6 +80,11 @@
         <paramdef>sd_event *<parameter>event</parameter></paramdef>
       </funcprototype>
 
+      <funcprototype>
+        <funcdef>void <function>sd_event_unrefp</function></funcdef>
+        <paramdef>sd_event **<parameter>event</parameter></paramdef>
+      </funcprototype>
+
       <funcprototype>
         <funcdef>int <function>sd_event_get_tid</function></funcdef>
         <paramdef>sd_event *<parameter>event</parameter></paramdef>
@@ -139,8 +145,29 @@
     all remaining event sources of the event loop also need to be
     freed as each keeps a reference to it.</para>
 
-    <para>Both <function>sd_event_ref()</function> and
-    <function>sd_event_unref()</function> execute no operation if the
+    <para><function>sd_event_unrefp()</function> is similar to
+    <function>sd_event_unref()</function> but takes a pointer to a
+    pointer to an <type>sd_event</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 an event loop object that is freed
+    automatically as the code block is left:</para>
+
+    <programlisting>{
+        __attribute__((cleanup(sd_event_unrefp)) sd_event *event = NULL;
+        int r;
+        …
+        r = sd_event_default(&amp;event);
+        if (r &lt; 0)
+                fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r));
+        …
+}</programlisting>
+
+    <para><function>sd_event_ref()</function>,
+    <function>sd_event_unref()</function> and
+    <function>sd_event_unrefp()</function> execute no operation if the
     passed in event loop object is <constant>NULL</constant>.</para>
 
     <para><function>sd_event_get_tid()</function> retrieves the thread
-- 
cgit v1.2.3-54-g00ecf