fai.diff

diff --git a/tid/tid.go b/tid/tid.go
index c884924..0aa0674 100644
--- a/tid/tid.go
+++ b/tid/tid.go
@@ -1,11 +1,17 @@
 package tid
 
 import (
+	"sync/atomic"
 	"github.com/goose-lang/std"
 	"github.com/mit-pdos/gokv/grove_ffi"
 	"github.com/mit-pdos/vmvcc/config"
 )
 
+func GenTIDWithFAI(gtidref *uint64) uint64 {
+	tid := atomic.AddUint64(gtidref, 1)
+	return tid
+}
+
 func GenTID(sid uint64) uint64 {
 	var tid uint64
 
diff --git a/txnsite/txnsite.go b/txnsite/txnsite.go
index 91e325d..9c74479 100644
--- a/txnsite/txnsite.go
+++ b/txnsite/txnsite.go
@@ -1,6 +1,7 @@
 package txnsite
 
 import (
+	"sync"
 	"github.com/mit-pdos/vmvcc/tid"
 	"github.com/mit-pdos/vmvcc/cfmutex"
 	"github.com/tchajed/goose/machine"
@@ -14,13 +15,17 @@ type TxnSite struct {
 	// Active transaction IDs.
 	padding [4]uint64
 	// TODO: should only need 3, change it once performance is tested.
+	gtidref *uint64
+	gtidlk  *sync.Mutex
 }
 
-func MkTxnSite(sid uint64) *TxnSite {
+func MkTxnSite(sid uint64, gtidref *uint64, gtidlk *sync.Mutex) *TxnSite {
 	site := new(TxnSite)
 	site.latch = new(cfmutex.CFMutex)
 	site.tids  = make([]uint64, 0, 8)
 	site.sid   = sid
+	site.gtidref = gtidref
+	site.gtidlk  = gtidlk
 
 	return site
 }
@@ -30,7 +35,12 @@ func (site *TxnSite) Activate() uint64 {
 	site.latch.Lock()
 
 	var t uint64
-	t = tid.GenTID(site.sid)
+	// t = tid.GenTID(site.sid)
+	t = tid.GenTIDWithFAI(site.gtidref)
+	// site.gtidlk.Lock()
+	// t = *site.gtidref
+	// *site.gtidref++
+	// site.gtidlk.Unlock()
 	// Assume TID never overflow.
 	primitive.Assume(t < 18446744073709551615)
 
@@ -76,7 +86,13 @@ func (site *TxnSite) GetSafeTS() uint64 {
 	site.latch.Lock()
 
 	var tidnew uint64
-	tidnew = tid.GenTID(site.sid)
+	// tidnew = tid.GenTID(site.sid)
+	tidnew = tid.GenTIDWithFAI(site.gtidref)
+	// site.gtidlk.Lock()
+	// tidnew = *site.gtidref
+	// *site.gtidref++
+	// site.gtidlk.Unlock()
+
 	primitive.Assume(tidnew < 18446744073709551615)
 
 	var tidmin uint64 = tidnew
diff --git a/vmvcc/db.go b/vmvcc/db.go
index 8da24d6..d2ad962 100644
--- a/vmvcc/db.go
+++ b/vmvcc/db.go
@@ -1,6 +1,7 @@
 package vmvcc
 
 import (
+	"sync"
 	"github.com/mit-pdos/vmvcc/config"
 	"github.com/mit-pdos/vmvcc/index"
 	"github.com/mit-pdos/vmvcc/wrbuf"
@@ -15,6 +16,7 @@ type DB struct {
 	latch *cfmutex.CFMutex
 	// Next site ID to assign.
 	sid   uint64
+	gtid  uint64
 	// All transaction sites.
 	sites []*txnsite.TxnSite
 	// Index.
@@ -28,11 +30,13 @@ func MkDB() *DB {
 	db := &DB { proph : proph }
 	db.latch = new(cfmutex.CFMutex)
 	db.sites = make([]*txnsite.TxnSite, config.N_TXN_SITES)
+	db.gtid = 0
 
 	// Call this once to establish invariants.
+	gtidlk := new(sync.Mutex)
 	tid.GenTID(0)
 	for i := uint64(0); i < config.N_TXN_SITES; i++ {
-		site := txnsite.MkTxnSite(i)
+		site := txnsite.MkTxnSite(i, &db.gtid, gtidlk)
 		db.sites[i] = site
 	}
 	db.idx = index.MkIndex()