X-Git-Url: https://code.kerkeslager.com/?a=blobdiff_plain;f=vm%2Fvm.c;fp=vm%2Fvm.c;h=0000000000000000000000000000000000000000;hb=ca2eb68dcd347c8c5b0bf8f5ba1c4eec7d303c14;hp=bc6588ca8ad8211638e8084031d692ca7b8329cc;hpb=efb0b2fb4d5d3e8feff70e10f273dbdd175ef504;p=sandbox

diff --git a/vm/vm.c b/vm/vm.c
deleted file mode 100644
index bc6588c..0000000
--- a/vm/vm.c
+++ /dev/null
@@ -1,123 +0,0 @@
-#include <stdbool.h>
-#include <stdlib.h>
-
-struct Queue;
-typedef struct Queue Queue;
-struct QueueNode;
-typedef struct QueueNode QueueNode;
-
-void initializeQueue(Queue* queue);
-void enqueue(Queue* queue, void* item);
-void* dequeue(Queue* queue);
-void freeQueue(Queue* queue, void (*itemFreer)(void*));
-
-struct Queue
-{
-  // This implements a multiple-producer, single-consumer lockless concurrent
-  // queue.
-  //
-  // After initialization, `head` and `tail` always points to a valid memory
-  // location--they are never `NULL`. To achieve this we initialize `head` and
-  // `tail` with a dummy node. This has two negative implications:
-  //
-  // 1. Unintuitively, `head->item` actually represents the item most recently
-  //    dequeued. In fact, `head->item` may have been freed after it was
-  //    dequeued, so we should never dereference it.
-  // 2. At initialization, no item has been dequeued yet, so we must allocate
-  //    an extra `QueueNode` at initialization which will never be used to
-  //    store an item.
-  //
-  // However, this extra memory allocation at initialization means that we
-  // never have to check whether `head` or `tail` are `NULL`, or initialize
-  // these variables concurrently, which are expensive operations.
-  QueueNode* head;
-  QueueNode* tail;
-};
-
-struct QueueNode
-{
-  // This implements a singly-linked list.
-  void* item;
-  QueueNode* next;
-};
-
-void initializeQueue(Queue* queue)
-{
-  // Initialize the queue with a node that fakes the previously dequeued item.
-  // We don't have to initialize `dummyNode->item` because it will never be
-  // used.
-  QueueNode* dummyNode = malloc(sizeof(QueueNode));
-  dummyNode->next = NULL;
-  queue->head = dummyNode;
-  queue->tail = dummyNode;
-}
-
-bool isEmpty(Queue* queue)
-{
-  // In a normal singly-linked list, the list is empty when the `head` is
-  // `NULL`, but here the queue is empty when the `head` is the same as the
-  // `tail`.
-  return queue->head == queue->tail;
-}
-
-void enqueue(Queue* queue, void* item)
-{
-  // Create the node that will be the new tail.
-  QueueNode* node = malloc(sizeof(QueueNode));
-  node->item = item;
-  node->next = NULL;
-
-  // Append the node to the list. Note that this is blocked as long as
-  // `queue->tail` is not actually pointing to the last node in the list
-  // because then `queue->tail->next` will not be `NULL`. This situation
-  // occurs when another thread has called `enqueue` and appended a node to
-  // the list, but hasn't yet updated `queue->tail`.
-  while(!__sync_bool_compare_and_swap(&(queue->tail->next), NULL, node));
-
-  // Move `queue->tail` forward until it points to the end of the list.
-  // Other threads attempting to eqneue will be unable to do so until this
-  // is complete. Additionally, other threads attempting to dequeue will be
-  // blocked until `queue->tail` has advanced by at least one node.
-  //
-  // We don't have to worry that another thread might have appended more
-  // nodes; advancing `queue->tail` to the end of the linked list is always
-  // the correct thing to do.
-  QueueNode* tail;
-  while((tail = queue->tail)->next != NULL)
-  {
-    __sync_val_compare_and_swap(&(queue->tail), tail, tail->next);
-  }
-}
-
-void* dequeue(Queue* queue)
-{
-  if(isEmpty(queue))
-  {
-    return NULL; // TODO Provide ability to return a defined default.
-  }
-
-  QueueNode* oldHead = queue->head;
-  queue->head = oldHead->next;
-  free(oldHead);
-
-  return queue->head->item;
-}
-
-void freeQueue(Queue* queue, void (*itemFreer)(void*))
-{
-  QueueNode* current = queue->head;
-  free(queue);
-
-  while(current != NULL)
-  {
-    itemFreer(current->item);
-    QueueNode* temp = current->next;
-    free(current);
-    current = temp;
-  }
-}
-
-int main(int argc, char** argv)
-{
-  return EXIT_SUCCESS;
-}