From bed2971bf0ca7a258ac0822332ab8c32ec3f6d1a Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Wed, 30 Jan 2019 15:11:01 +0000
Subject: [PATCH] lib/pool: a buffer recycling library which can be optionally
 be used with mmap

---
 lib/pool/pool.go      | 118 ++++++++++++++++++++++++++++++++++++++++++
 lib/pool/pool_test.go |  92 ++++++++++++++++++++++++++++++++
 2 files changed, 210 insertions(+)
 create mode 100644 lib/pool/pool.go
 create mode 100644 lib/pool/pool_test.go

diff --git a/lib/pool/pool.go b/lib/pool/pool.go
new file mode 100644
index 000000000..acd44a12c
--- /dev/null
+++ b/lib/pool/pool.go
@@ -0,0 +1,118 @@
+// Package pool implements a memory pool similar in concept to
+// sync.Pool but with more determinism.
+package pool
+
+import (
+	"fmt"
+	"log"
+	"sync/atomic"
+	"time"
+
+	"github.com/ncw/rclone/lib/mmap"
+)
+
+// Pool of internal buffers
+type Pool struct {
+	cache      chan []byte
+	bufferSize int
+	timer      *time.Timer
+	inUse      int32
+	flushTime  time.Duration
+	alloc      func(int) ([]byte, error)
+	free       func([]byte) error
+}
+
+// New makes a buffer pool
+//
+// flushTime is the interval the buffer pools is flushed
+// bufferSize is the size of the allocations
+// poolSize is the maximum number of free buffers in the pool
+// useMmap should be set to use mmap allocations
+func New(flushTime time.Duration, bufferSize, poolSize int, useMmap bool) *Pool {
+	bp := &Pool{
+		cache:      make(chan []byte, poolSize),
+		flushTime:  flushTime,
+		bufferSize: bufferSize,
+	}
+	if useMmap {
+		bp.alloc = mmap.Alloc
+		bp.free = mmap.Free
+	} else {
+		bp.alloc = func(size int) ([]byte, error) {
+			return make([]byte, size), nil
+		}
+		bp.free = func([]byte) error {
+			return nil
+		}
+	}
+	bp.timer = time.AfterFunc(flushTime, bp.Flush)
+	return bp
+}
+
+// Flush the entire buffer pool
+func (bp *Pool) Flush() {
+	for {
+		select {
+		case b := <-bp.cache:
+			bp.freeBuffer(b)
+		default:
+			return
+		}
+	}
+}
+
+// InUse returns the approximate number of buffers in use which
+// haven't been returned to the pool.
+func (bp *Pool) InUse() int {
+	return int(atomic.LoadInt32(&bp.inUse))
+}
+
+// starts or resets the buffer flusher timer
+func (bp *Pool) kickFlusher() {
+	bp.timer.Reset(bp.flushTime)
+}
+
+// Get a buffer from the pool or allocate one
+func (bp *Pool) Get() []byte {
+	select {
+	case b := <-bp.cache:
+		return b
+	default:
+	}
+	mem, err := bp.alloc(bp.bufferSize)
+	if err != nil {
+		log.Printf("Failed to get memory for buffer, waiting for a freed one: %v", err)
+		return <-bp.cache
+	}
+	atomic.AddInt32(&bp.inUse, 1)
+	return mem
+}
+
+// freeBuffer returns mem to the os if required
+func (bp *Pool) freeBuffer(mem []byte) {
+	err := bp.free(mem)
+	if err != nil {
+		log.Printf("Failed to free memory: %v", err)
+	} else {
+		atomic.AddInt32(&bp.inUse, -1)
+	}
+}
+
+// Put returns the buffer to the buffer cache or frees it
+//
+// Note that if you try to return a buffer of the wrong size to Put it
+// will panic.
+func (bp *Pool) Put(mem []byte) {
+	mem = mem[0:cap(mem)]
+	if len(mem) != bp.bufferSize {
+		panic(fmt.Sprintf("Returning buffer sized %d but expecting %d", len(mem), bp.bufferSize))
+	}
+	select {
+	case bp.cache <- mem:
+		bp.kickFlusher()
+		return
+	default:
+	}
+	bp.freeBuffer(mem)
+	mem = nil
+}
diff --git a/lib/pool/pool_test.go b/lib/pool/pool_test.go
new file mode 100644
index 000000000..7f9ceb4f9
--- /dev/null
+++ b/lib/pool/pool_test.go
@@ -0,0 +1,92 @@
+package pool
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func testGetPut(t *testing.T, useMmap bool) {
+	bp := New(60*time.Second, 4096, 2, useMmap)
+
+	assert.Equal(t, 0, bp.InUse())
+
+	b1 := bp.Get()
+	assert.Equal(t, 1, bp.InUse())
+
+	b2 := bp.Get()
+	assert.Equal(t, 2, bp.InUse())
+
+	b3 := bp.Get()
+	assert.Equal(t, 3, bp.InUse())
+
+	bp.Put(b1)
+	assert.Equal(t, 3, bp.InUse())
+
+	bp.Put(b2)
+	assert.Equal(t, 3, bp.InUse())
+
+	bp.Put(b3)
+	assert.Equal(t, 2, bp.InUse())
+
+	b1a := bp.Get()
+	assert.Equal(t, b1, b1a)
+	assert.Equal(t, 2, bp.InUse())
+
+	b2a := bp.Get()
+	assert.Equal(t, b1, b2a)
+	assert.Equal(t, 2, bp.InUse())
+
+	bp.Put(b1a)
+	bp.Put(b2a)
+	assert.Equal(t, 2, bp.InUse())
+
+	bp.Flush()
+	assert.Equal(t, 0, bp.InUse())
+}
+
+func testFlusher(t *testing.T, useMmap bool) {
+	bp := New(50*time.Millisecond, 4096, 2, useMmap)
+
+	b1 := bp.Get()
+	b2 := bp.Get()
+	b3 := bp.Get()
+	bp.Put(b1)
+	bp.Put(b2)
+	bp.Put(b3)
+	assert.Equal(t, 2, bp.InUse())
+
+	checkFlushHasHappened := func() {
+		var n int
+		for i := 0; i < 10; i++ {
+			time.Sleep(100 * time.Millisecond)
+			n = bp.InUse()
+			if n == 0 {
+				break
+			}
+		}
+		assert.Equal(t, 0, n)
+	}
+
+	checkFlushHasHappened()
+
+	b1 = bp.Get()
+	bp.Put(b1)
+	assert.Equal(t, 1, bp.InUse())
+
+	checkFlushHasHappened()
+}
+
+func TestPool(t *testing.T) {
+	for _, useMmap := range []bool{false, true} {
+		name := "make"
+		if useMmap {
+			name = "mmap"
+		}
+		t.Run(name, func(t *testing.T) {
+			t.Run("GetPut", func(t *testing.T) { testGetPut(t, useMmap) })
+			t.Run("Flusher", func(t *testing.T) { testFlusher(t, useMmap) })
+		})
+	}
+}