From 13f110e5c84469f8eb2be750b2a3b7ef71625afd Mon Sep 17 00:00:00 2001
From: Sergey Matveev <stargrave@stargrave.org>
Date: Sat, 7 Oct 2023 20:14:22 +0300
Subject: [PATCH] Protect concurrent map r/w

---
 ifchange.go |  2 +-
 tgt.go      | 21 +++++++++++++--------
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/ifchange.go b/ifchange.go
index a55120e..374adcf 100644
--- a/ifchange.go
+++ b/ifchange.go
@@ -80,7 +80,7 @@ func buildDependants(tgts []*Tgt) map[string]*Tgt {
 			}
 		}
 	}
-	TgtCache = nil
+	TgtCache = make(map[string]*Tgt)
 	IfchangeCache = nil
 	if len(seen) == 0 {
 		return seen
diff --git a/tgt.go b/tgt.go
index 3fa14a0..1cba1e6 100644
--- a/tgt.go
+++ b/tgt.go
@@ -3,9 +3,13 @@ package main
 import (
 	"path"
 	"path/filepath"
+	"sync"
 )
 
-var TgtCache = make(map[string]*Tgt)
+var (
+	TgtCache  = make(map[string]*Tgt)
+	TgtCacheM sync.RWMutex
+)
 
 func mustAbs(pth string) string {
 	pth, err := filepath.Abs(pth)
@@ -43,10 +47,11 @@ type Tgt struct {
 
 func NewTgt(tgt string) *Tgt {
 	a := mustAbs(tgt)
-	if TgtCache != nil {
-		if t := TgtCache[a]; t != nil {
-			return t
-		}
+	TgtCacheM.RLock()
+	cached := TgtCache[a]
+	TgtCacheM.RUnlock()
+	if cached != nil {
+		return cached
 	}
 	h, t := pathSplit(a)
 	res := Tgt{
@@ -54,9 +59,9 @@ func NewTgt(tgt string) *Tgt {
 		rel: mustRel(Cwd, a),
 		dep: path.Join(h, RedoDir, t+DepSuffix),
 	}
-	if TgtCache != nil {
-		TgtCache[a] = &res
-	}
+	TgtCacheM.Lock()
+	TgtCache[a] = &res
+	TgtCacheM.Unlock()
 	return &res
 }
 
-- 
2.44.0