From 57c20c2733dff45ebb5ab529ac9771b2e24f1d5e Mon Sep 17 00:00:00 2001
From: Nikhil Garg <nikhilgarg28@gmail.com>
Date: Wed, 29 Jul 2015 07:37:46 -0700
Subject: [PATCH] bitset: add binlog generation for replication

---
 bitset.go      | 100 +++++++++++++++++++++++++++++++++++++++++++++++--
 bitset_test.go |  13 ++++---
 2 files changed, 103 insertions(+), 10 deletions(-)

diff --git a/bitset.go b/bitset.go
index 9f0b2de..fdd99ac 100644
--- a/bitset.go
+++ b/bitset.go
@@ -1,20 +1,109 @@
 package bitset
 
+import (
+	"bufio"
+	"encoding/binary"
+	"fmt"
+	"os"
+	"time"
+)
+
 const word = uint64(64)
 const logword = uint(6)
+const bufsize = 1 << 16
+
+// each channel write is 9 bytes, so if we were to write full disk sector
+// of 64K bytes at once, we'd flush ~7112 writes
+const channelsize = 7200
+
+const (
+	new = iota
+	set
+	clear
+	flip
+)
+
+type command struct {
+	code  uint8
+	index uint64
+}
 
 type BitSet struct {
-	length uint64
-	bits   []uint64
+	length     uint64
+	bits       []uint64
+	writes     chan command
+	binlogfile string
 }
 
 func getSize(length uint64) uint64 {
 	return uint64((length + word - 1) / word)
 }
 
-func New(length uint64) *BitSet {
+func flush(filename string, writes chan command) {
+	f, err := os.Create(filename)
+	if err != nil {
+		panic(err)
+	}
+
+	defer func() {
+		if err := f.Close(); err != nil {
+			panic(err)
+		}
+	}()
+
+	// make a buffered writer
+	w := bufio.NewWriterSize(f, bufsize)
+
+	ticker := time.NewTimer(time.Second)
+
+	buf := make([]byte, bufsize)
+	long := make([]byte, 8)
+
+	put := func(w *command) {
+		binary.BigEndian.PutUint64(long, w.index)
+		buf = append(buf, w.code)
+		buf = append(buf, long...)
+	}
+
+	for t := range ticker.C {
+		_ = t
+		b := 0
+
+	drain:
+		for b+9 < bufsize {
+			select {
+			case write := <-writes:
+				put(&write)
+				b += 9
+			default:
+				break drain
+			}
+		}
+
+		if b > 0 {
+			// write a chunk
+			if _, err := w.Write(buf[:b]); err != nil {
+				panic(err)
+			}
+
+			if err = w.Flush(); err != nil {
+				panic(err)
+			}
+		}
+	}
+}
+
+func New(length uint64, binlogfile string) *BitSet {
 	size := getSize(length)
-	return &BitSet{length, make([]uint64, size)}
+	ret := &BitSet{
+		length,
+		make([]uint64, size),
+		make(chan command, channelsize),
+		binlogfile,
+	}
+	ret.writes <- command{new, length}
+	go flush(binlogfile, ret.writes)
+	return ret
 }
 
 func getIndex(pos uint64) (q uint64, r uint) {
@@ -37,6 +126,7 @@ func (b *BitSet) Set(pos uint64) bool {
 	current := b.Get(pos)
 	q, r := getIndex(pos)
 	b.bits[q] |= (1 << r)
+	b.writes <- command{set, pos}
 	return current
 }
 
@@ -44,6 +134,7 @@ func (b *BitSet) Clear(pos uint64) bool {
 	current := b.Get(pos)
 	q, r := getIndex(pos)
 	b.bits[q] &= ^(1 << r)
+	b.writes <- command{clear, pos}
 	return current
 }
 
@@ -51,5 +142,6 @@ func (b *BitSet) Flip(pos uint64) bool {
 	current := b.Get(pos)
 	q, r := getIndex(pos)
 	b.bits[q] ^= (1 << r)
+	b.writes <- command{flip, pos}
 	return current
 }
diff --git a/bitset_test.go b/bitset_test.go
index 2a3c75b..fc64d64 100644
--- a/bitset_test.go
+++ b/bitset_test.go
@@ -2,10 +2,11 @@ package bitset
 
 import (
 	"testing"
+	"time"
 )
 
 func TestInit(t *testing.T) {
-	bs := New(1000)
+	bs := New(1000, "/tmp/bitset.log")
 	// initially all bits should be zero
 	for i := uint64(0); i < 1000; i++ {
 		if bs.Get(i) {
@@ -15,7 +16,7 @@ func TestInit(t *testing.T) {
 }
 
 func TestGetSet(t *testing.T) {
-	bs := New(1000)
+	bs := New(1000, "/tmp/bitset.log")
 	if bs.Set(0) == true {
 		t.Error("Set on bit %d returned true when it should return false", 0)
 	}
@@ -31,7 +32,7 @@ func TestGetSet(t *testing.T) {
 
 func TestLargeSetGet(t *testing.T) {
 	size := uint64(1) << 35
-	bs := New(size)
+	bs := New(size, "/tmp/bitset.log")
 
 	positions := []uint64{0, 1, 10, 1000, 1 << 32, size - 1}
 	for _, position := range positions {
@@ -51,7 +52,7 @@ func TestLength(t *testing.T) {
 
 	sizes := []uint64{0, 1, 10, 1000, 1 << 32, 1 << 33}
 	for _, size := range sizes {
-		bs := New(size)
+		bs := New(size, "/tmp/bitset.log")
 		if bs.Length() != size {
 			t.Errorf("Length should be %d", size)
 		}
@@ -59,7 +60,7 @@ func TestLength(t *testing.T) {
 }
 
 func TestClear(t *testing.T) {
-	bs := New(1000)
+	bs := New(1000, "/tmp/bitset.log")
 	pos := uint64(1)
 	bs.Set(pos)
 
@@ -77,7 +78,7 @@ func TestClear(t *testing.T) {
 }
 
 func TestFlip(t *testing.T) {
-	bs := New(1000)
+	bs := New(1000, "/tmp/bitset.log")
 	pos := uint64(1)
 
 	if bs.Get(pos) {