plumbing: add buffer cache and use it in packfile parser

It uses less memory and is faster as slices don't have to be converted
from/to MemoryObject and they are indexed by offset.

Signed-off-by: Javi Fontan <jfontan@gmail.com>

1 files changed, 128 insertions, 0 deletions

diff --git a/plumbing/cache/buffer_test.go b/plumbing/cache/buffer_test.go
new file mode 100644
index 0000000..262138a
--- /dev/null
+++ b/plumbing/cache/buffer_test.go
@@ -0,0 +1,128 @@
+package cache
+
+import (
+	"sync"
+
+	. "gopkg.in/check.v1"
+)
+
+type BufferSuite struct {
+	c       map[string]Buffer
+	aBuffer []byte
+	bBuffer []byte
+	cBuffer []byte
+	dBuffer []byte
+	eBuffer []byte
+}
+
+var _ = Suite(&BufferSuite{})
+
+func (s *BufferSuite) SetUpTest(c *C) {
+	s.aBuffer = []byte("a")
+	s.bBuffer = []byte("bbb")
+	s.cBuffer = []byte("c")
+	s.dBuffer = []byte("d")
+	s.eBuffer = []byte("ee")
+
+	s.c = make(map[string]Buffer)
+	s.c["two_bytes"] = NewBufferLRU(2 * Byte)
+	s.c["default_lru"] = NewBufferLRUDefault()
+}
+
+func (s *BufferSuite) TestPutSameBuffer(c *C) {
+	for _, o := range s.c {
+		o.Put(1, s.aBuffer)
+		o.Put(1, s.aBuffer)
+		_, ok := o.Get(1)
+		c.Assert(ok, Equals, true)
+	}
+}
+
+func (s *BufferSuite) TestPutBigBuffer(c *C) {
+	for _, o := range s.c {
+		o.Put(1, s.bBuffer)
+		_, ok := o.Get(2)
+		c.Assert(ok, Equals, false)
+	}
+}
+
+func (s *BufferSuite) TestPutCacheOverflow(c *C) {
+	// this test only works with an specific size
+	o := s.c["two_bytes"]
+
+	o.Put(1, s.aBuffer)
+	o.Put(2, s.cBuffer)
+	o.Put(3, s.dBuffer)
+
+	obj, ok := o.Get(1)
+	c.Assert(ok, Equals, false)
+	c.Assert(obj, IsNil)
+	obj, ok = o.Get(2)
+	c.Assert(ok, Equals, true)
+	c.Assert(obj, NotNil)
+	obj, ok = o.Get(3)
+	c.Assert(ok, Equals, true)
+	c.Assert(obj, NotNil)
+}
+
+func (s *BufferSuite) TestEvictMultipleBuffers(c *C) {
+	o := s.c["two_bytes"]
+
+	o.Put(1, s.cBuffer)
+	o.Put(2, s.dBuffer) // now cache is full with two objects
+	o.Put(3, s.eBuffer) // this put should evict all previous objects
+
+	obj, ok := o.Get(1)
+	c.Assert(ok, Equals, false)
+	c.Assert(obj, IsNil)
+	obj, ok = o.Get(2)
+	c.Assert(ok, Equals, false)
+	c.Assert(obj, IsNil)
+	obj, ok = o.Get(3)
+	c.Assert(ok, Equals, true)
+	c.Assert(obj, NotNil)
+}
+
+func (s *BufferSuite) TestClear(c *C) {
+	for _, o := range s.c {
+		o.Put(1, s.aBuffer)
+		o.Clear()
+		obj, ok := o.Get(1)
+		c.Assert(ok, Equals, false)
+		c.Assert(obj, IsNil)
+	}
+}
+
+func (s *BufferSuite) TestConcurrentAccess(c *C) {
+	for _, o := range s.c {
+		var wg sync.WaitGroup
+
+		for i := 0; i < 1000; i++ {
+			wg.Add(3)
+			go func(i int) {
+				o.Put(int64(i), []byte{00})
+				wg.Done()
+			}(i)
+
+			go func(i int) {
+				if i%30 == 0 {
+					o.Clear()
+				}
+				wg.Done()
+			}(i)
+
+			go func(i int) {
+				o.Get(int64(i))
+				wg.Done()
+			}(i)
+		}
+
+		wg.Wait()
+	}
+}
+
+func (s *BufferSuite) TestDefaultLRU(c *C) {
+	defaultLRU := s.c["default_lru"].(*BufferLRU)
+
+	c.Assert(defaultLRU.MaxSize, Equals, DefaultMaxSize)
+}