From 0ebeb1e6433147faf1b52c0ec636e5fc3cc99ac0 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Sun, 23 Oct 2016 04:45:52 -0700
Subject: [PATCH] lru: atomic batches.

---
 lib/utils/lru.js | 120 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)

diff --git a/lib/utils/lru.js b/lib/utils/lru.js
index 82065f74..839d6aec 100644
--- a/lib/utils/lru.js
+++ b/lib/utils/lru.js
@@ -30,6 +30,7 @@ function LRU(maxSize, getSize) {
   this.size = 0;
   this.head = null;
   this.tail = null;
+  this.pending = null;
 }
 
 /**
@@ -325,6 +326,74 @@ LRU.prototype.toArray = function toArray() {
   return items;
 };
 
+/**
+ * Create an atomic batch for the lru
+ * (used for caching database writes).
+ * @returns {LRUBatch}
+ */
+
+LRU.prototype.batch = function batch() {
+  return new LRUBatch(this);
+};
+
+/**
+ * Start the pending LRU batch.
+ */
+
+LRU.prototype.start = function start() {
+  assert(!this.pending);
+  this.pending = this.batch();
+};
+
+/**
+ * Clear the pending LRU batch.
+ */
+
+LRU.prototype.clear = function clear() {
+  assert(this.pending);
+  this.pending = this.batch();
+};
+
+/**
+ * Drop the pending LRU batch.
+ */
+
+LRU.prototype.drop = function drop() {
+  assert(this.pending);
+  this.pending = null;
+};
+
+/**
+ * Commit the pending LRU batch.
+ */
+
+LRU.prototype.commit = function commit() {
+  assert(this.pending);
+  this.pending.commit();
+  this.pending = null;
+};
+
+/**
+ * Push an item onto the pending LRU batch.
+ * @param {String} key
+ * @param {Object} value
+ */
+
+LRU.prototype.push = function push(key, value) {
+  assert(this.pending);
+  this.pending.set(key, value);
+};
+
+/**
+ * Push a removal onto the pending LRU batch.
+ * @param {String} key
+ */
+
+LRU.prototype.unpush = function unpush(key) {
+  assert(this.pending);
+  this.pending.remove(key);
+};
+
 /**
  * Represents an LRU item.
  * @constructor
@@ -340,6 +409,50 @@ function LRUItem(key, value) {
   this.prev = null;
 }
 
+/**
+ * LRU Batch
+ * @constructor
+ */
+
+function LRUBatch(lru) {
+  this.lru = lru;
+  this.ops = [];
+}
+
+LRUBatch.prototype.set = function set(key, value) {
+  this.ops.push(new LRUOp(false, key, value));
+};
+
+LRUBatch.prototype.remove = function remove(key) {
+  this.ops.push(new LRUOp(true, key));
+};
+
+LRUBatch.prototype.commit = function commit() {
+  var i, op;
+
+  for (i = 0; i < this.ops.length; i++) {
+    op = this.ops[i];
+    if (op.remove) {
+      this.lru.remove(op.key);
+      continue;
+    }
+    this.lru.set(op.key, op.value);
+  }
+
+  this.ops.length = 0;
+};
+
+/**
+ * LRU Op
+ * @constructor
+ */
+
+function LRUOp(remove, key, value) {
+  this.remove = remove;
+  this.key = key;
+  this.value = value;
+}
+
 /**
  * A null cache. Every method is a NOP.
  * @constructor
@@ -356,6 +469,13 @@ NullCache.prototype.reset = function reset() {};
 NullCache.prototype.keys = function keys(key) { return []; };
 NullCache.prototype.values = function values(key) { return []; };
 NullCache.prototype.toArray = function toArray(key) { return []; };
+NullCache.prototype.batch = function batch() { return new LRUBatch(this); };
+NullCache.prototype.start = function start() {};
+NullCache.prototype.clear = function clear() {};
+NullCache.prototype.drop = function drop() {};
+NullCache.prototype.commit = function commit() {};
+NullCache.prototype.push = function push(key, value) {};
+NullCache.prototype.unpush = function unpush(key) {};
 
 /*
  * Expose