From 1d1f10b4fe217b89ff79edf8a7c82c47ecdf64a5 Mon Sep 17 00:00:00 2001
From: Matthew Wild <mwild1@gmail.com>
Date: Thu, 17 Mar 2016 19:08:42 +0000
Subject: [PATCH] util.cache: Change behaviour of on_evict (and tests). Now
 accepts false instead of a function (never evict), or on_evict can return
 false to prevent eviction.

---
 tests/test_util_cache.lua | 38 +++++++++++++++++++++++++++++---------
 util/cache.lua            | 10 +++++-----
 2 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/tests/test_util_cache.lua b/tests/test_util_cache.lua
index ecdc2dc0..155b154d 100644
--- a/tests/test_util_cache.lua
+++ b/tests/test_util_cache.lua
@@ -222,22 +222,21 @@ function new(new)
 	local c3 = new(1, function (_key, _value, c3)
 		evicted_key, evicted_value = _key, _value;
 		if _key == "a" then
-			-- Put it back in...
-			-- Check that the newest key/value was set before on_evict was called
-			assert_equal(c3:get("b"), 2);
 			-- Sanity check for what we're evicting
 			assert_equal(_key, "a");
 			assert_equal(_value, 1);
-			-- Re-insert the evicted key (causes this evict function to run again with "b",2)
-			c3:set(_key, _value)
-			assert_equal(c3:get(_key), _value)
+			-- We're going to block eviction of this key/value, so set to nil...
+			evicted_key, evicted_value = nil, nil;
+			-- Returning false to block eviction
+			return false
 		end
 	end);
 	local function set(k, v, should_evict_key, should_evict_value)
 		evicted_key, evicted_value = nil, nil;
-		c3:set(k, v);
+		local ret = c3:set(k, v);
 		assert_equal(evicted_key, should_evict_key);
 		assert_equal(evicted_value, should_evict_value);
+		return ret;
 	end
 	set("a", 1)
 	set("a", 1)
@@ -245,10 +244,31 @@ function new(new)
 	set("a", 1)
 	set("a", 1)
 
-	-- The evict handler re-inserts "a"->1, so "b" gets evicted:
-	set("b", 2, "b", 2)
+	-- Our on_evict prevents "a" from being evicted, causing this to fail...
+	assert_equal(set("b", 2), false, "Failed to prevent eviction, or signal result");
+	
+	expect_kv("a", 1, c3:head());
+	expect_kv("a", 1, c3:tail());
+	
 	-- Check the final state is what we expect
 	assert_equal(c3:get("a"), 1);
 	assert_equal(c3:get("b"), nil);
 	assert_equal(c3:count(), 1);
+
+
+	local c4 = new(3, false);
+	
+	assert_equal(c4:set("a", 1), true);
+	assert_equal(c4:set("a", 1), true);
+	assert_equal(c4:set("a", 1), true);
+	assert_equal(c4:set("a", 1), true);
+	assert_equal(c4:set("b", 2), true);
+	assert_equal(c4:set("c", 3), true);
+	assert_equal(c4:set("d", 4), false);
+	assert_equal(c4:set("d", 4), false);
+	assert_equal(c4:set("d", 4), false);
+
+	expect_kv("c", 3, c4:head());
+	expect_kv("a", 1, c4:tail());
+
 end
diff --git a/util/cache.lua b/util/cache.lua
index e53bf4bf..074916cd 100644
--- a/util/cache.lua
+++ b/util/cache.lua
@@ -51,10 +51,13 @@ function cache_methods:set(k, v)
 		return true;
 	end
 	-- Check whether we need to remove oldest k/v
-	local on_evict, evicted_key, evicted_value;
 	if self._count == self.size then
 		local tail = self._tail;
-		on_evict, evicted_key, evicted_value = self._on_evict, tail.key, tail.value;
+		local on_evict, evicted_key, evicted_value = self._on_evict, tail.key, tail.value;
+		if on_evict ~= nil and (on_evict == false or on_evict(evicted_key, evicted_value) == false) then
+			-- Cache is full, and we're not allowed to evict
+			return false;
+		end
 		_remove(self, tail);
 		self._data[evicted_key] = nil;
 	end
@@ -62,9 +65,6 @@ function cache_methods:set(k, v)
 	m = { key = k, value = v, prev = nil, next = nil };
 	self._data[k] = m;
 	_insert(self, m);
-	if on_evict and evicted_key then
-		on_evict(evicted_key, evicted_value, self);
-	end
 	return true;
 end
 
-- 
2.30.2