1 files changed, 136 insertions, 0 deletions
diff --git a/servers/lloadd/tier_roundrobin.c b/servers/lloadd/tier_roundrobin.c
new file mode 100644
index 0000000..d299fb9
--- /dev/null
+++ b/servers/lloadd/tier_roundrobin.c
@@ -0,0 +1,136 @@
+/* $OpenLDAP$ */
+/* This work is part of OpenLDAP Software <http://www.openldap.org/>.
+ *
+ * Copyright 1998-2022 The OpenLDAP Foundation.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted only as authorized by the OpenLDAP
+ * Public License.
+ *
+ * A copy of this license is available in the file LICENSE in the
+ * top-level directory of the distribution or, alternatively, at
+ * <http://www.OpenLDAP.org/license.html>.
+ */
+
+#include "portable.h"
+
+#include "lload.h"
+
+static LloadTierInit roundrobin_init;
+static LloadTierBackendCb roundrobin_add_backend;
+static LloadTierBackendCb roundrobin_remove_backend;
+static LloadTierSelect roundrobin_select;
+
+struct lload_tier_type roundrobin_tier;
+
+static LloadTier *
+roundrobin_init( void )
+{
+    LloadTier *tier;
+
+    tier = ch_calloc( 1, sizeof(LloadTier) );
+
+    tier->t_type = roundrobin_tier;
+    ldap_pvt_thread_mutex_init( &tier->t_mutex );
+    LDAP_CIRCLEQ_INIT( &tier->t_backends );
+
+    return tier;
+}
+
+static int
+roundrobin_add_backend( LloadTier *tier, LloadBackend *b )
+{
+    assert( b->b_tier == tier );
+    LDAP_CIRCLEQ_INSERT_TAIL( &tier->t_backends, b, b_next );
+    if ( !tier->t_private ) {
+        tier->t_private = b;
+    }
+    tier->t_nbackends++;
+    return LDAP_SUCCESS;
+}
+
+static int
+roundrobin_remove_backend( LloadTier *tier, LloadBackend *b )
+{
+    LloadBackend *next = LDAP_CIRCLEQ_LOOP_NEXT( &tier->t_backends, b, b_next );
+
+    assert_locked( &tier->t_mutex );
+    assert_locked( &b->b_mutex );
+
+    assert( b->b_tier == tier );
+
+    LDAP_CIRCLEQ_REMOVE( &tier->t_backends, b, b_next );
+    if ( b == tier->t_private ) {
+        if ( tier->t_nbackends ) {
+            tier->t_private = next;
+        } else {
+            assert( b == next );
+            tier->t_private = NULL;
+        }
+    }
+    tier->t_nbackends--;
+    return LDAP_SUCCESS;
+}
+
+static int
+roundrobin_select(
+        LloadTier *tier,
+        LloadOperation *op,
+        LloadConnection **cp,
+        int *res,
+        char **message )
+{
+    LloadBackend *b, *first, *next;
+    int rc = 0;
+
+    checked_lock( &tier->t_mutex );
+    first = b = tier->t_private;
+    checked_unlock( &tier->t_mutex );
+
+    if ( !first ) return rc;
+
+    do {
+        int result;
+
+        checked_lock( &b->b_mutex );
+        next = LDAP_CIRCLEQ_LOOP_NEXT( &tier->t_backends, b, b_next );
+
+        result = backend_select( b, op, cp, res, message );
+        checked_unlock( &b->b_mutex );
+
+        rc |= result;
+        if ( result && *cp ) {
+            /*
+             * Round-robin step:
+             * Rotate the queue to put this backend at the end. The race here
+             * is acceptable.
+             */
+            checked_lock( &tier->t_mutex );
+            tier->t_private = next;
+            checked_unlock( &tier->t_mutex );
+            return rc;
+        }
+
+        b = next;
+    } while ( b != first );
+
+    return rc;
+}
+
+struct lload_tier_type roundrobin_tier = {
+        .tier_name = "roundrobin",
+
+        .tier_init = roundrobin_init,
+        .tier_startup = tier_startup,
+        .tier_reset = tier_reset,
+        .tier_destroy = tier_destroy,
+
+        .tier_oc = BER_BVC("olcBkLloadTierConfig"),
+        .tier_backend_oc = BER_BVC("olcBkLloadBackendConfig"),
+
+        .tier_add_backend = roundrobin_add_backend,
+        .tier_remove_backend = roundrobin_remove_backend,
+
+        .tier_select = roundrobin_select,
+};