1 files changed, 112 insertions, 0 deletions
diff --git a/lib/isc/counter.c b/lib/isc/counter.c
new file mode 100644
index 0000000..0c0ccd6
--- /dev/null
+++ b/lib/isc/counter.c
@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+/*! \file */
+
+#include <stdbool.h>
+#include <stddef.h>
+
+#include <isc/atomic.h>
+#include <isc/counter.h>
+#include <isc/magic.h>
+#include <isc/mem.h>
+#include <isc/refcount.h>
+#include <isc/util.h>
+
+#define COUNTER_MAGIC	 ISC_MAGIC('C', 'n', 't', 'r')
+#define VALID_COUNTER(r) ISC_MAGIC_VALID(r, COUNTER_MAGIC)
+
+struct isc_counter {
+	unsigned int magic;
+	isc_mem_t *mctx;
+	isc_refcount_t references;
+	atomic_uint_fast32_t limit;
+	atomic_uint_fast32_t used;
+};
+
+isc_result_t
+isc_counter_create(isc_mem_t *mctx, int limit, isc_counter_t **counterp) {
+	isc_counter_t *counter;
+
+	REQUIRE(counterp != NULL && *counterp == NULL);
+
+	counter = isc_mem_get(mctx, sizeof(*counter));
+
+	counter->mctx = NULL;
+	isc_mem_attach(mctx, &counter->mctx);
+
+	isc_refcount_init(&counter->references, 1);
+	atomic_init(&counter->limit, limit);
+	atomic_init(&counter->used, 0);
+
+	counter->magic = COUNTER_MAGIC;
+	*counterp = counter;
+	return (ISC_R_SUCCESS);
+}
+
+isc_result_t
+isc_counter_increment(isc_counter_t *counter) {
+	uint32_t used = atomic_fetch_add_relaxed(&counter->used, 1) + 1;
+	uint32_t limit = atomic_load_acquire(&counter->limit);
+
+	if (limit != 0 && used >= limit) {
+		return (ISC_R_QUOTA);
+	}
+
+	return (ISC_R_SUCCESS);
+}
+
+unsigned int
+isc_counter_used(isc_counter_t *counter) {
+	REQUIRE(VALID_COUNTER(counter));
+
+	return (atomic_load_acquire(&counter->used));
+}
+
+void
+isc_counter_setlimit(isc_counter_t *counter, int limit) {
+	REQUIRE(VALID_COUNTER(counter));
+
+	atomic_store(&counter->limit, limit);
+}
+
+void
+isc_counter_attach(isc_counter_t *source, isc_counter_t **targetp) {
+	REQUIRE(VALID_COUNTER(source));
+	REQUIRE(targetp != NULL && *targetp == NULL);
+
+	isc_refcount_increment(&source->references);
+
+	*targetp = source;
+}
+
+static void
+destroy(isc_counter_t *counter) {
+	isc_refcount_destroy(&counter->references);
+	counter->magic = 0;
+	isc_mem_putanddetach(&counter->mctx, counter, sizeof(*counter));
+}
+
+void
+isc_counter_detach(isc_counter_t **counterp) {
+	isc_counter_t *counter;
+
+	REQUIRE(counterp != NULL && *counterp != NULL);
+	counter = *counterp;
+	*counterp = NULL;
+	REQUIRE(VALID_COUNTER(counter));
+
+	if (isc_refcount_decrement(&counter->references) == 1) {
+		destroy(counter);
+	}
+}