From: David Kerkeslager <kerkeslager@gmail.com>
Date: Mon, 25 Jul 2016 05:45:41 +0000 (+0000)
Subject: Wrote a multiple-producer single-consumer lockless queue
X-Git-Url: https://code.kerkeslager.com/?p=sandbox;a=commitdiff_plain;h=172acc477af67e9383db1b347b68f804b42642cf

Wrote a multiple-producer single-consumer lockless queue
---

diff --git a/lockless/mpsc_queue.c b/lockless/mpsc_queue.c
new file mode 100644
index 0000000..d4969a8
--- /dev/null
+++ b/lockless/mpsc_queue.c
@@ -0,0 +1,74 @@
+#include <assert.h>
+#include <stdlib.h>
+
+struct Queue;
+typedef struct Queue Queue;
+
+struct QueueNode;
+typedef struct QueueNode QueueNode;
+
+struct Queue
+{
+  QueueNode* head;
+  QueueNode* tail;
+};
+
+struct QueueNode
+{
+  void* item;
+  QueueNode* next;
+};
+
+void initQueue(Queue* queue)
+{
+  QueueNode* fake = malloc(sizeof(QueueNode));
+
+  fake->next = NULL;
+
+  queue->head = fake;
+  queue->tail = fake;
+}
+
+void enqueue(Queue* queue, void* item)
+{
+  // Create the node
+  QueueNode* node = malloc(sizeof(QueueNode));
+  node->item = item;
+  node->next = NULL;
+
+  // Append the node
+  while(!__sync_bool_compare_and_swap(&(queue->tail->next), NULL, node));
+
+  // Reuse the node variable to update the tail
+  while((node = queue->tail)->next != NULL)
+  {
+    __sync_bool_compare_and_swap(&(queue->tail), node, node->next);
+  }
+}
+
+void* dequeue(Queue* queue, void* defaultResult)
+{
+  if(queue->head == queue->tail) return defaultResult;
+
+  assert(queue->head->next != NULL);
+
+  QueueNode* previous = queue->head;
+  queue->head = previous->next;
+  free(previous);
+  return queue->head->item;
+}
+
+void freeQueue(Queue* queue)
+{
+  QueueNode* node = queue->head;
+  free(queue);
+
+  while(node != NULL)
+  {
+    QueueNode* temp = node;
+    node = temp->next;
+    free(temp);
+  }
+}
+
+int main() { }