From 6bd0a4b29753570a2c20b61b5ad2c0068567b7b6 Mon Sep 17 00:00:00 2001
From: Philip Withnall <pwithnall@endlessos.org>
Date: Mon, 16 Nov 2020 16:44:29 +0000
Subject: [PATCH 25/29] gthread: Use g_atomic() primitives correctly in
 destructor list
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In the Windows destructor list, consistently access
`g_private_destructors` using atomic primitives.

`g_atomic_pointer_compare_and_exchange()` should be equivalent to
`InterlockedCompareExchangePointer()`, but is a bit more understandable
in a general GLib context, and pairs with `g_atomic_pointer_get()`. (I
can’t find a Windows API equivalent for that.)

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

Helps: #600
Upstream-Status: Backport [https://gitlab.gnome.org/GNOME/glib/-/merge_requests/1719]
---
 glib/gthread-win32.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/glib/gthread-win32.c b/glib/gthread-win32.c
index 0c37dc6c1..20aca6fa1 100644
--- a/glib/gthread-win32.c
+++ b/glib/gthread-win32.c
@@ -301,7 +301,7 @@ struct _GPrivateDestructor
   GPrivateDestructor *next;
 };
 
-static GPrivateDestructor * volatile g_private_destructors;
+static GPrivateDestructor *g_private_destructors;  /* (atomic) prepend-only */
 static CRITICAL_SECTION g_private_lock;
 
 static DWORD
@@ -329,7 +329,7 @@ g_private_get_impl (GPrivate *key)
                 g_thread_abort (errno, "malloc");
               destructor->index = impl;
               destructor->notify = key->notify;
-              destructor->next = g_private_destructors;
+              destructor->next = g_atomic_pointer_get (&g_private_destructors);
 
               /* We need to do an atomic store due to the unlocked
                * access to the destructor list from the thread exit
@@ -337,13 +337,14 @@ g_private_get_impl (GPrivate *key)
                *
                * It can double as a sanity check...
                */
-              if (InterlockedCompareExchangePointer (&g_private_destructors, destructor,
-                                                     destructor->next) != destructor->next)
+              if (!g_atomic_pointer_compare_and_exchange (&g_private_destructors,
+                                                          destructor->next,
+                                                          destructor))
                 g_thread_abort (0, "g_private_get_impl(1)");
             }
 
           /* Ditto, due to the unlocked access on the fast path */
-          if (InterlockedCompareExchangePointer (&key->p, impl, NULL) != NULL)
+          if (!g_atomic_pointer_compare_and_exchange (&key->p, NULL, impl))
             g_thread_abort (0, "g_private_get_impl(2)");
         }
       LeaveCriticalSection (&g_private_lock);
@@ -635,7 +636,7 @@ g_thread_win32_thread_detach (void)
        */
       dtors_called = FALSE;
 
-      for (dtor = g_private_destructors; dtor; dtor = dtor->next)
+      for (dtor = g_atomic_pointer_get (&g_private_destructors); dtor; dtor = dtor->next)
         {
           gpointer value;
 
-- 
2.30.1