From c35a2c748c6ad053344c9f15f6f86246e48628e0 Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Fri, 2 Oct 2020 17:35:11 +1000
Subject: Only wake Tx if they're still reading a modified value

---
 funcs.go | 2 ++
 tx.go    | 2 ++
 var.go   | 8 +++++---
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/funcs.go b/funcs.go
index 91d6bc8..80c25b1 100644
--- a/funcs.go
+++ b/funcs.go
@@ -71,7 +71,9 @@ retry:
 			time.Sleep(time.Duration(ns))
 		}
 	}
+	tx.mu.Lock()
 	ret, retry := catchRetry(op, tx)
+	tx.mu.Unlock()
 	if retry {
 		expvars.Add("retries", 1)
 		// wait for one of the variables we read to change before retrying
diff --git a/tx.go b/tx.go
index 3a1506c..c064f76 100644
--- a/tx.go
+++ b/tx.go
@@ -121,12 +121,14 @@ func (tx *Tx) Assert(p bool) {
 }
 
 func (tx *Tx) reset() {
+	tx.mu.Lock()
 	for k := range tx.reads {
 		delete(tx.reads, k)
 	}
 	for k := range tx.writes {
 		delete(tx.writes, k)
 	}
+	tx.mu.Unlock()
 	tx.removeRetryProfiles()
 	tx.resetLocks()
 }
diff --git a/var.go b/var.go
index f3b8d40..3f43096 100644
--- a/var.go
+++ b/var.go
@@ -27,9 +27,11 @@ func (v *Var) wakeWatchers(new VarValue) {
 		// We have to lock here to ensure that the Tx is waiting before we signal it. Otherwise we
 		// could signal it before it goes to sleep and it will miss the notification.
 		tx.mu.Lock()
-		tx.cond.Broadcast()
-		for !tx.waiting && !tx.completed {
-			tx.cond.Wait()
+		if read := tx.reads[v]; read != nil && read.Changed(new) {
+			tx.cond.Broadcast()
+			for !tx.waiting && !tx.completed {
+				tx.cond.Wait()
+			}
 		}
 		tx.mu.Unlock()
 		return !v.value.Load().(VarValue).Changed(new)
-- 
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