1 files changed, 161 insertions, 0 deletions
diff --git a/lib/isc/include/isc/queue.h b/lib/isc/include/isc/queue.h
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+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * 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 http://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+
+/*
+ * This is a generic implementation of a two-lock concurrent queue.
+ * There are built-in mutex locks for the head and tail of the queue,
+ * allowing elements to be safely added and removed at the same time.
+ *
+ * NULL is "end of list"
+ * -1 is "not linked"
+ */
+
+#ifndef ISC_QUEUE_H
+#define ISC_QUEUE_H 1
+
+#include <stdbool.h>
+
+#include <isc/assertions.h>
+#include <isc/mutex.h>
+
+#ifdef ISC_QUEUE_CHECKINIT
+#define ISC_QLINK_INSIST(x) ISC_INSIST(x)
+#else
+#define ISC_QLINK_INSIST(x) (void)0
+#endif
+
+#define ISC_QLINK(type) struct { type *prev, *next; }
+
+#define ISC_QLINK_INIT(elt, link) \
+	do { \
+		(elt)->link.next = (elt)->link.prev = (void *)(-1); \
+	} while(0)
+
+#define ISC_QLINK_LINKED(elt, link) ((void*)(elt)->link.next != (void*)(-1))
+
+#define ISC_QUEUE(type) struct { \
+	type *head, *tail; \
+	isc_mutex_t headlock, taillock; \
+}
+
+#define ISC_QUEUE_INIT(queue, link) \
+	do { \
+		(void) isc_mutex_init(&(queue).taillock); \
+		(void) isc_mutex_init(&(queue).headlock); \
+		(queue).tail = (queue).head = NULL; \
+	} while (0)
+
+#define ISC_QUEUE_EMPTY(queue) ((queue).head == NULL)
+
+#define ISC_QUEUE_DESTROY(queue) \
+	do { \
+		ISC_QLINK_INSIST(ISC_QUEUE_EMPTY(queue)); \
+		(void) isc_mutex_destroy(&(queue).taillock); \
+		(void) isc_mutex_destroy(&(queue).headlock); \
+	} while (0)
+
+/*
+ * queues are meant to separate the locks at either end.  For best effect, that
+ * means keeping the ends separate - i.e. non-empty queues work best.
+ *
+ * a push to an empty queue has to take the pop lock to update
+ * the pop side of the queue.
+ * Popping the last entry has to take the push lock to update
+ * the push side of the queue.
+ *
+ * The order is (pop, push), because a pop is presumably in the
+ * latency path and a push is when we're done.
+ *
+ * We do an MT hot test in push to see if we need both locks, so we can
+ * acquire them in order.  Hopefully that makes the case where we get
+ * the push lock and find we need the pop lock (and have to release it) rare.
+ *
+ * > 1 entry - no collision, push works on one end, pop on the other
+ *   0 entry - headlock race
+ *     pop wins - return(NULL), push adds new as both head/tail
+ *     push wins - updates head/tail, becomes 1 entry case.
+ *   1 entry - taillock race
+ *     pop wins - return(pop) sets head/tail NULL, becomes 0 entry case
+ *     push wins - updates {head,tail}->link.next, pop updates head
+ *                 with new ->link.next and doesn't update tail
+ *
+ */
+#define ISC_QUEUE_PUSH(queue, elt, link) \
+	do { \
+		bool headlocked = false; \
+		ISC_QLINK_INSIST(!ISC_QLINK_LINKED(elt, link)); \
+		if ((queue).head == NULL) { \
+			LOCK(&(queue).headlock); \
+			headlocked = true; \
+		} \
+		LOCK(&(queue).taillock); \
+		if ((queue).tail == NULL && !headlocked) { \
+			UNLOCK(&(queue).taillock); \
+			LOCK(&(queue).headlock); \
+			LOCK(&(queue).taillock); \
+			headlocked = true; \
+		} \
+		(elt)->link.prev = (queue).tail; \
+		(elt)->link.next = NULL; \
+		if ((queue).tail != NULL) \
+			(queue).tail->link.next = (elt); \
+		(queue).tail = (elt); \
+		UNLOCK(&(queue).taillock); \
+		if (headlocked) { \
+			if ((queue).head == NULL) \
+				(queue).head = (elt); \
+			UNLOCK(&(queue).headlock); \
+		} \
+	} while (0)
+
+#define ISC_QUEUE_POP(queue, link, ret) \
+	do { \
+		LOCK(&(queue).headlock); \
+		ret = (queue).head; \
+		while (ret != NULL) { \
+			if (ret->link.next == NULL) { \
+				LOCK(&(queue).taillock); \
+				if (ret->link.next == NULL) { \
+					(queue).head = (queue).tail = NULL; \
+					UNLOCK(&(queue).taillock); \
+					break; \
+				}\
+				UNLOCK(&(queue).taillock); \
+			} \
+			(queue).head = ret->link.next; \
+			(queue).head->link.prev = NULL; \
+			break; \
+		} \
+		UNLOCK(&(queue).headlock); \
+		if (ret != NULL) \
+			(ret)->link.next = (ret)->link.prev = (void *)(-1); \
+	} while(0)
+
+#define ISC_QUEUE_UNLINK(queue, elt, link) \
+	do { \
+		ISC_QLINK_INSIST(ISC_QLINK_LINKED(elt, link)); \
+		LOCK(&(queue).headlock); \
+		LOCK(&(queue).taillock); \
+		if ((elt)->link.prev == NULL) \
+			(queue).head = (elt)->link.next; \
+		else \
+			(elt)->link.prev->link.next = (elt)->link.next; \
+		if ((elt)->link.next == NULL) \
+			(queue).tail = (elt)->link.prev; \
+		else \
+			(elt)->link.next->link.prev = (elt)->link.prev; \
+		UNLOCK(&(queue).taillock); \
+		UNLOCK(&(queue).headlock); \
+		(elt)->link.next = (elt)->link.prev = (void *)(-1); \
+	} while(0)
+
+#endif /* ISC_QUEUE_H */