From 26afb0040cf728de82db2c1417c5a2973d06f0aa Mon Sep 17 00:00:00 2001
From: Eric Botcazou <ebotcazou@adacore.com>
Date: Fri, 16 Feb 2024 23:57:23 +0100
Subject: [PATCH] ada: Document more details of the implementation of
finalization chains
gcc/ada/
* exp_ch7.adb (Finalization Management): Add a short description of
the implementation of finalization chains.
---
gcc/ada/exp_ch7.adb | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/gcc/ada/exp_ch7.adb b/gcc/ada/exp_ch7.adb
index e978a778f1e5..25a7c0b2b46d 100644
--- a/gcc/ada/exp_ch7.adb
+++ b/gcc/ada/exp_ch7.adb
@@ -100,6 +100,35 @@ package body Exp_Ch7 is
-- have to be detached from the finalization chain, in case (2) they must
-- not and in case (1) this is optional as we are exiting the scope anyway.
+ -- There are two kinds of finalization chain to which objects are attached,
+ -- depending on the way they are created. For objects (statically) declared
+ -- in a scope, the finalization chain is that of the master of the scope,
+ -- which is embodied in a Finalization_Master object. As per RM 7.6.1(11/3)
+ -- the finalization of the master (on scope exit) performs the finalization
+ -- of objects attached to its chain in the reverse order of their creation.
+
+ -- For dynamically allocated objects, the finalization chain is that of the
+ -- finalization collection of the access type through which the objects are
+ -- allocated, which is embodied in a Finalization_Collection object. As per
+ -- RM 7.6.1(11.1/3), the finalization of the collection performs the
+ -- finalization of objects attached to its chain in an arbitrary order.
+
+ -- A Finalization_Collection object is implemented as a controlled object
+ -- and its finalization is therefore driven by the finalization master of
+ -- the scope where it is declared. As per RM 7.6.1(11.2/3), for a named
+ -- access type, the Finalization_Collection object is declared in the list
+ -- of actions of its freeze node.
+
+ -- ??? For an anonymous access type, the implementation deviates from the
+ -- RM 7.6.1 clause as follows: all the anonymous access types with the same
+ -- designated type that are (implicitly) declared in a library unit share a
+ -- single Finalization_Collection object declared in the outermost scope of
+ -- the library unit, except if the designated type is declared in a dynamic
+ -- scope nested in the unit; in this case no Finalization_Collection object
+ -- is created. As a result, in the first case, objects allocated through
+ -- the anonymous access types are finalized when the library unit goes out
+ -- of scope, while in the second case, they are not finalized at all.
+
-- Here is a simple example of the expansion of a controlled block:
-- declare
--
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