add task queues

1 files changed, 42 insertions, 0 deletions

diff --git a/source/queue.c b/source/queue.c
new file mode 100644
index 0000000..519aa1f
--- /dev/null
+++ b/source/queue.c
@@ -0,0 +1,42 @@
+
+#include "kpl.h"
+
+void kpl_task_queue_init(kpl_task_queue *task_queue) {
+    __atomic_store_n(&task_queue->dummy.next, NULL, __ATOMIC_RELAXED);
+    __atomic_store_n(&task_queue->head, &task_queue->dummy, __ATOMIC_RELAXED);
+    task_queue->tail = (kpl_task*) &task_queue->dummy;
+}
+
+void kpl_task_queue_add(kpl_task_queue *task_queue, kpl_task *task) {
+    __atomic_store_n(&task->next, NULL, __ATOMIC_RELAXED);
+    kpl_task *head = __atomic_exchange_n(&task_queue->head, task, __ATOMIC_SEQ_CST);
+    __atomic_store_n(&head->next, task, __ATOMIC_RELEASE);
+}
+
+kpl_task *kpl_task_queue_next(kpl_task_queue *task_queue) {
+    kpl_task *task = NULL;
+    for (;;) {
+        kpl_task *tail = task_queue->tail, *next = __atomic_load_n(&tail->next, __ATOMIC_ACQUIRE);
+        if (tail == (kpl_task*) &task_queue->dummy) {
+            if (!next)
+                break;
+            tail = task_queue->tail = next;
+            next = __atomic_load_n(&tail->next, __ATOMIC_ACQUIRE);
+        }
+        if (!next) {
+            kpl_task *head = __atomic_load_n(&task_queue->head, __ATOMIC_ACQUIRE);
+            if (tail != head)
+                continue;
+            kpl_task_queue_add(task_queue, (kpl_task*) &task_queue->dummy);
+            next = __atomic_load_n(&tail->next, __ATOMIC_ACQUIRE);
+        }
+        if (next) {
+            task_queue->tail = next;
+            task = tail;
+            break;
+        }
+    }
+    if (task)
+        __atomic_store_n(&task->next, NULL, __ATOMIC_RELAXED);
+    return task;
+}