From 318ad3ab3a83041f83f824de2568b332407d0f37 Mon Sep 17 00:00:00 2001
From: Maas-Maarten Zeeman <mmzeeman@xs4all.nl>
Date: Tue, 18 Oct 2011 10:43:48 +0200
Subject: [PATCH] Work in progress

---
 c_src/queue.c | 207 ++++++++++++++++++++++++++++++++++++++++++++++++++
 c_src/queue.h |  24 ++++++
 2 files changed, 231 insertions(+)
 create mode 100644 c_src/queue.c
 create mode 100644 c_src/queue.h

diff --git a/c_src/queue.c b/c_src/queue.c
new file mode 100644
index 0000000..7214ec6
--- /dev/null
+++ b/c_src/queue.c
@@ -0,0 +1,207 @@
+// This file is part of Emonk released under the MIT license. 
+// See the LICENSE file for more information.
+
+/* Adapted by: Maas-Maarten Zeeman <mmzeeman@xs4all.nl */
+
+#include <assert.h>
+#include <stdio.h>
+
+#include "queue.h"
+
+struct qitem_t
+{
+    struct qitem_t*     next;
+    void*               data;
+};
+
+typedef struct qitem_t qitem;
+
+struct queue_t
+{
+    ErlNifMutex *lock;
+    ErlNifCond *cond;
+    qitem *head;
+    qitem *tail;
+    void *message;
+    int length;
+};
+
+queue *
+queue_create()
+{
+    queue *ret;
+
+    ret = (queue *) enif_alloc(sizeof(struct queue_t));
+    if(ret == NULL) 
+      goto error;
+
+    ret->lock = NULL;
+    ret->cond = NULL;
+    ret->head = NULL;
+    ret->tail = NULL;
+    ret->message = NULL;
+    ret->length = 0;
+
+    ret->lock = enif_mutex_create("queue_lock");
+    if(ret->lock == NULL) 
+      goto error;
+    
+    ret->cond = enif_cond_create("queue_cond");
+    if(ret->cond == NULL) 
+      goto error;
+
+    return ret;
+
+error:
+    if(ret->lock != NULL) 
+      enif_mutex_destroy(ret->lock);
+    if(ret->cond != NULL) 
+      enif_cond_destroy(ret->cond);
+    if(ret != NULL) 
+      enif_free(ret);
+    return NULL;
+}
+
+void
+queue_destroy(queue *queue)
+{
+    ErlNifMutex *lock;
+    ErlNifCond *cond;
+    int length;
+
+    enif_mutex_lock(queue->lock);
+    lock = queue->lock;
+    cond = queue->cond;
+    length = queue->length;
+
+    queue->lock = NULL;
+    queue->cond = NULL;
+    queue->head = NULL;
+    queue->tail = NULL;
+    queue->length = -1;
+    enif_mutex_unlock(lock);
+
+    assert(length == 0 && "Attempting to destroy a non-empty queue.");
+    enif_cond_destroy(cond);
+    enif_mutex_destroy(lock);
+    enif_free(queue);
+}
+
+int
+queue_has_item(queue *queue)
+{
+    int ret;
+
+    enif_mutex_lock(queue->lock);
+    ret = (queue->head != NULL);
+    enif_mutex_unlock(queue->lock);
+    
+    return ret;
+}
+
+int
+queue_push(queue *queue, void *item)
+{
+    qitem * entry = (qitem *) enif_alloc(sizeof(struct qitem_t));
+    if(entry == NULL) 
+      return 0;
+
+    entry->data = item;
+    entry->next = NULL;
+
+    enif_mutex_lock(queue->lock);
+
+    assert(queue->length >= 0 && "Invalid queue size at push");
+    
+    if(queue->tail != NULL)
+    {
+        queue->tail->next = entry;
+    }
+
+    queue->tail = entry;
+
+    if(queue->head == NULL)
+    {
+        queue->head = queue->tail;
+    }
+
+    queue->length += 1;
+
+    enif_cond_signal(queue->cond);
+    enif_mutex_unlock(queue->lock);
+
+    return 1;
+}
+
+void*
+queue_pop(queue *queue)
+{
+    qitem *entry;
+    void* item;
+
+    enif_mutex_lock(queue->lock);
+    
+    /* Wait for an item to become available.
+     */
+    while(queue->head == NULL)
+    {
+        enif_cond_wait(queue->cond, queue->lock);
+    }
+    
+    assert(queue->length >= 0 && "Invalid queue size at pop.");
+
+    /* Woke up because queue->head != NULL
+     * Remove the entry and return the payload.
+     */
+    entry = queue->head;
+    queue->head = entry->next;
+    entry->next = NULL;
+
+    if(queue->head == NULL)
+    {
+        assert(queue->tail == entry && "Invalid queue state: Bad tail.");
+        queue->tail = NULL;
+    }
+
+    queue->length -= 1;
+
+    enif_mutex_unlock(queue->lock);
+
+    item = entry->data;
+    enif_free(entry);
+
+    return item;
+}
+
+int
+queue_send(queue *queue, void *item)
+{
+    enif_mutex_lock(queue->lock);
+    assert(queue->message == NULL && "Attempting to send multiple messages.");
+    queue->message = item;
+    enif_cond_signal(queue->cond);
+    enif_mutex_unlock(queue->lock);
+    return 1;
+}
+
+void *
+queue_receive(queue *queue)
+{
+    void *item;
+
+    enif_mutex_lock(queue->lock);
+    
+    /* Wait for an item to become available.
+     */
+    while(queue->message == NULL)
+    {
+        enif_cond_wait(queue->cond, queue->lock);
+    }
+
+    item = queue->message;
+    queue->message = NULL;
+    
+    enif_mutex_unlock(queue->lock);
+    
+    return item;
+}
diff --git a/c_src/queue.h b/c_src/queue.h
new file mode 100644
index 0000000..5ac597d
--- /dev/null
+++ b/c_src/queue.h
@@ -0,0 +1,24 @@
+// This file is part of Emonk released under the MIT license. 
+// See the LICENSE file for more information.
+
+/* adapted by: Maas-Maarten Zeeman <mmzeeman@xs4all.nl */
+
+#ifndef ESQLITE_QUEUE_H
+#define ESQLITE_QUEUE_H
+
+#include "erl_nif.h"
+
+typedef struct queue_t queue;
+
+queue * queue_create();
+void queue_destroy(queue *queue);
+
+int queue_has_item(queue *queue);
+
+int queue_push(queue *queue, void* item);
+void* queue_pop(queue *queue);
+
+int queue_send(queue *queue, void* item);
+void* queue_receive(queue *);
+
+#endif