From 597720941a528be2e43789a10781346a6dff7607 Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Fri, 28 Aug 2020 10:43:34 +1000
Subject: Reduce more allocations

---
 funcs.go |  5 +++--
 tx.go    | 34 ++++++++++++++++++++++++----------
 2 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/funcs.go b/funcs.go
index b13a917..aad9c90 100644
--- a/funcs.go
+++ b/funcs.go
@@ -9,8 +9,9 @@ var (
 	txPool = sync.Pool{New: func() interface{} {
 		expvars.Add("new txs", 1)
 		tx := &Tx{
-			reads:  make(map[*Var]uint64),
-			writes: make(map[*Var]interface{}),
+			reads:    make(map[*Var]uint64),
+			writes:   make(map[*Var]interface{}),
+			watching: make(map[*Var]struct{}),
 		}
 		tx.cond.L = &tx.mu
 		return tx
diff --git a/tx.go b/tx.go
index 2d16549..0f8a449 100644
--- a/tx.go
+++ b/tx.go
@@ -9,11 +9,12 @@ import (
 
 // A Tx represents an atomic transaction.
 type Tx struct {
-	reads  map[*Var]uint64
-	writes map[*Var]interface{}
-	locks  txLocks
-	mu     sync.Mutex
-	cond   sync.Cond
+	reads    map[*Var]uint64
+	writes   map[*Var]interface{}
+	watching map[*Var]struct{}
+	locks    txLocks
+	mu       sync.Mutex
+	cond     sync.Cond
 }
 
 // Check that none of the logged values have changed since the transaction began.
@@ -39,8 +40,17 @@ func (tx *Tx) wait() {
 	if len(tx.reads) == 0 {
 		panic("not waiting on anything")
 	}
+	for v := range tx.watching {
+		if _, ok := tx.reads[v]; !ok {
+			delete(tx.watching, v)
+			v.watchers.Delete(tx)
+		}
+	}
 	for v := range tx.reads {
-		v.watchers.Store(tx, nil)
+		if _, ok := tx.watching[v]; !ok {
+			v.watchers.Store(tx, nil)
+			tx.watching[v] = struct{}{}
+		}
 	}
 	tx.mu.Lock()
 	firstWait := true
@@ -53,9 +63,9 @@ func (tx *Tx) wait() {
 		firstWait = false
 	}
 	tx.mu.Unlock()
-	for v := range tx.reads {
-		v.watchers.Delete(tx)
-	}
+	//for v := range tx.reads {
+	//	v.watchers.Delete(tx)
+	//}
 }
 
 // Get returns the value of v as of the start of the transaction.
@@ -104,6 +114,10 @@ func (tx *Tx) reset() {
 }
 
 func (tx *Tx) recycle() {
+	for v := range tx.watching {
+		delete(tx.watching, v)
+		v.watchers.Delete(tx)
+	}
 	txPool.Put(tx)
 }
 
@@ -134,7 +148,7 @@ func (tx *Tx) collectAllLocks() {
 }
 
 func (tx *Tx) sortLocks() {
-	sort.Sort(tx.locks)
+	sort.Sort(&tx.locks)
 }
 
 func (tx *Tx) lock() {
-- 
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