1 files changed, 61 insertions, 0 deletions
diff --git a/libpager/queue.h b/libpager/queue.h
new file mode 100644
index 00000000..d3cf738e
--- /dev/null
+++ b/libpager/queue.h
@@ -0,0 +1,61 @@
+/* A FIFO queue with constant-time enqueue and dequeue operations.
+
+   Copyright (C) 2014 Free Software Foundation, Inc.
+
+   Written by Justus Winter <4winter@informatik.uni-hamburg.de>
+
+   This file is part of the GNU Hurd.
+
+   The GNU Hurd is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2, or (at
+   your option) any later version.
+
+   The GNU Hurd is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with the GNU Hurd.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* A FIFO queue with constant-time enqueue and dequeue operations.  */
+struct item {
+  struct item *next;
+};
+
+struct queue {
+  struct item *head;
+  struct item **tail;
+};
+
+static inline void
+queue_init (struct queue *q)
+{
+  q->head = NULL;
+  q->tail = &q->head;
+}
+
+static inline void
+queue_enqueue (struct queue *q, struct item *r)
+{
+  *q->tail = r;
+  q->tail = &r->next;
+  r->next = NULL;
+}
+
+static inline void *
+queue_dequeue (struct queue *q)
+{
+  struct item *r = q->head;
+  if (r == NULL)
+    return NULL;
+
+  /* Pop the first item off.  */
+  if ((q->head = q->head->next) == NULL)
+    /* The queue is empty, fix tail pointer.  */
+    q->tail = &q->head;
+
+  r->next = NULL;
+  return r;
+}