From d6711ea6dec3d49b182dbe60a1e1db6c148adede Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Mon, 31 Aug 2020 14:06:50 +1000
Subject: Add exponentially longer sleeping between transaction attempts

---
 funcs.go | 15 +++++++++++++++
 tx.go    | 18 ++++++++++--------
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/funcs.go b/funcs.go
index aad9c90..650a559 100644
--- a/funcs.go
+++ b/funcs.go
@@ -1,8 +1,10 @@
 package stm
 
 import (
+	"math/rand"
 	"runtime/pprof"
 	"sync"
+	"time"
 )
 
 var (
@@ -43,8 +45,21 @@ func Atomically(op Operation) interface{} {
 	expvars.Add("atomically", 1)
 	// run the transaction
 	tx := newTx()
+	tx.tries = 0
 retry:
+	tx.tries++
 	tx.reset()
+	shift := int64(tx.tries - 1)
+	const maxShift = 30
+	if shift > maxShift {
+		shift = maxShift
+	}
+	ns := int64(1) << shift
+	ns = rand.Int63n(ns)
+	if ns > 0 {
+		tx.updateWatchers()
+		time.Sleep(time.Duration(ns))
+	}
 	ret, retry := catchRetry(op, tx)
 	if retry {
 		expvars.Add("retries", 1)
diff --git a/tx.go b/tx.go
index 0f8a449..6e8b06f 100644
--- a/tx.go
+++ b/tx.go
@@ -15,6 +15,7 @@ type Tx struct {
 	locks    txLocks
 	mu       sync.Mutex
 	cond     sync.Cond
+	tries    int
 }
 
 // Check that none of the logged values have changed since the transaction began.
@@ -35,11 +36,7 @@ func (tx *Tx) commit() {
 	}
 }
 
-// wait blocks until another transaction modifies any of the Vars read by tx.
-func (tx *Tx) wait() {
-	if len(tx.reads) == 0 {
-		panic("not waiting on anything")
-	}
+func (tx *Tx) updateWatchers() {
 	for v := range tx.watching {
 		if _, ok := tx.reads[v]; !ok {
 			delete(tx.watching, v)
@@ -52,6 +49,14 @@ func (tx *Tx) wait() {
 			tx.watching[v] = struct{}{}
 		}
 	}
+}
+
+// wait blocks until another transaction modifies any of the Vars read by tx.
+func (tx *Tx) wait() {
+	if len(tx.reads) == 0 {
+		panic("not waiting on anything")
+	}
+	tx.updateWatchers()
 	tx.mu.Lock()
 	firstWait := true
 	for tx.verify() {
@@ -63,9 +68,6 @@ func (tx *Tx) wait() {
 		firstWait = false
 	}
 	tx.mu.Unlock()
-	//for v := range tx.reads {
-	//	v.watchers.Delete(tx)
-	//}
 }
 
 // Get returns the value of v as of the start of the transaction.
-- 
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