MonetDB: default - Use atomic pointer variable.

[Sjoerd Mullender]

Changeset: bfcea6701f71 for MonetDB
URL: https://dev.monetdb.org/hg/MonetDB?cmd=changeset;node=bfcea6701f71
Modified Files:
        gdk/gdk_utils.c
Branch: default
Log Message:

Use atomic pointer variable.


diffs (92 lines):

diff --git a/gdk/gdk_utils.c b/gdk/gdk_utils.c
--- a/gdk/gdk_utils.c
+++ b/gdk/gdk_utils.c
@@ -699,28 +699,29 @@ GDKexiting(void)
        return (bool) (ATOMIC_GET(&GDKstopped) > 0);
 }
 
-static struct serverthread {
+struct serverthread {
        struct serverthread *next;
        MT_Id pid;
-} *serverthread;
+};
+static ATOMIC_PTR_TYPE serverthread = ATOMIC_PTR_VAR_INIT(NULL);
 
 void
 GDKprepareExit(void)
 {
+       struct serverthread *st;
+
        if (ATOMIC_ADD(&GDKstopped, 1) > 0)
                return;
 
        THRDDEBUG dump_threads();
-       MT_lock_set(&GDKthreadLock);
-       while (serverthread != NULL) {
-               struct serverthread *st = serverthread;
-               serverthread = st->next;
-               MT_lock_unset(&GDKthreadLock);
+       /* we're saved from the ABA problem in this code because it is
+        * only executed by one thread */
+       while ((st = ATOMIC_PTR_GET(&serverthread)) != NULL) {
+               while (!ATOMIC_PTR_CAS(&serverthread, &st, st->next))
+                       ;
                MT_join_thread(st->pid);
                GDKfree(st);
-               MT_lock_set(&GDKthreadLock);
        }
-       MT_lock_unset(&GDKthreadLock);
        join_detached_threads();
 }
 
@@ -734,15 +735,15 @@ GDKregister(MT_Id pid)
        if ((st = GDKmalloc(sizeof(struct serverthread))) == NULL)
                return;
        st->pid = pid;
-       MT_lock_set(&GDKthreadLock);
-       st->next = serverthread;
-       serverthread = st;
-       MT_lock_unset(&GDKthreadLock);
+       st->next = ATOMIC_PTR_GET(&serverthread);
+       while (!ATOMIC_PTR_CAS(&serverthread, &st->next, st))
+               ;
 }
 
 void
 GDKreset(int status)
 {
+       struct serverthread *st;
        MT_Id pid = MT_getpid();
 
        assert(GDKexiting());
@@ -756,23 +757,21 @@ GDKreset(int status)
                GDKval = NULL;
        }
 
-       MT_lock_set(&GDKthreadLock);
-       while (serverthread != NULL) {
-               struct serverthread *st = serverthread;
-               serverthread = st->next;
-               MT_lock_unset(&GDKthreadLock);
+       /* we're saved from the ABA problem in this code because it is
+        * only executed by one thread */
+       while ((st = ATOMIC_PTR_GET(&serverthread)) != NULL) {
+               while (!ATOMIC_PTR_CAS(&serverthread, &st, st->next))
+                       ;
                MT_join_thread(st->pid);
                GDKfree(st);
-               MT_lock_set(&GDKthreadLock);
        }
-       MT_lock_unset(&GDKthreadLock);
        join_detached_threads();
 
        if (status == 0) {
                /* they had their chance, now kill them */
                bool killed = false;
                MT_lock_set(&GDKthreadLock);
-               assert(serverthread == NULL);
+               assert(ATOMIC_PTR_GET(&serverthread) == NULL);
                for (Thread t = GDKthreads; t < GDKthreads + THREADS; t++) {
                        MT_Id victim;
                        if ((victim = (MT_Id) ATOMIC_GET(&t->pid)) != 0) {
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