From 1220fe96505bcd117efa840ad1c82fe39e87d5a7 Mon Sep 17 00:00:00 2001
From: greatroar <61184462+greatroar@users.noreply.github.com>
Date: Sat, 17 Sep 2022 19:37:09 +0200
Subject: [PATCH 1/2] internal/cache: Concurrent use of cache not working on
 Windows

---
 internal/cache/file_test.go | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/internal/cache/file_test.go b/internal/cache/file_test.go
index 388d7d4f7..87664f014 100644
--- a/internal/cache/file_test.go
+++ b/internal/cache/file_test.go
@@ -6,6 +6,7 @@ import (
 	"io/ioutil"
 	"math/rand"
 	"os"
+	"runtime"
 	"testing"
 	"time"
 
@@ -204,7 +205,19 @@ func TestFileLoad(t *testing.T) {
 }
 
 // Simulate multiple processes writing to a cache, using goroutines.
+//
+// The possibility of sharing a cache between multiple concurrent restic
+// processes isn't guaranteed in the docs and doesn't always work on Windows
+// due to the Go runtime opening files without FILE_SHARE_DELETE, hence the
+// check on GOOS. This is considered a "nice to have" on POSIX, for now.
+//
+// See https://devblogs.microsoft.com/oldnewthing/20211022-00/?p=105822
+// for hints on how to fix this properly.
 func TestFileSaveConcurrent(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("may not work due to FILE_SHARE_DELETE issue")
+	}
+
 	const nproc = 40
 
 	c, cleanup := TestNewCache(t)

From 7fc178aaf48453f42c0ce33663c2f14a56f5a7e1 Mon Sep 17 00:00:00 2001
From: Michael Eischer <michael.eischer@fau.de>
Date: Sat, 24 Sep 2022 13:07:01 +0200
Subject: [PATCH 2/2] internal/cache: extend description of cache sharing test
 failure

---
 internal/cache/file_test.go | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/internal/cache/file_test.go b/internal/cache/file_test.go
index 87664f014..3e92c1d96 100644
--- a/internal/cache/file_test.go
+++ b/internal/cache/file_test.go
@@ -207,10 +207,13 @@ func TestFileLoad(t *testing.T) {
 // Simulate multiple processes writing to a cache, using goroutines.
 //
 // The possibility of sharing a cache between multiple concurrent restic
-// processes isn't guaranteed in the docs and doesn't always work on Windows
-// due to the Go runtime opening files without FILE_SHARE_DELETE, hence the
-// check on GOOS. This is considered a "nice to have" on POSIX, for now.
+// processes isn't guaranteed in the docs and doesn't always work on Windows, hence the
+// check on GOOS. Cache sharing is considered a "nice to have" on POSIX, for now.
 //
+// The cache first creates a temporary file and then renames it to its final name.
+// On Windows renaming internally creates a file handle with a shareMode which
+// includes FILE_SHARE_DELETE. The Go runtime opens files without FILE_SHARE_DELETE,
+// thus Open(fn) will fail until the file handle used for renaming was closed.
 // See https://devblogs.microsoft.com/oldnewthing/20211022-00/?p=105822
 // for hints on how to fix this properly.
 func TestFileSaveConcurrent(t *testing.T) {