From a739c973048b7e5b968f3b2c8bd0417a2fb01f99 Mon Sep 17 00:00:00 2001
From: "Bryan C. Mills" <bcmills@google.com>
Date: Fri, 28 Jan 2022 10:26:33 -0500
Subject: [PATCH] internal/lsp/fake: retry ioutil.ReadFile on plan9 if it fails
 due to exclusive use

Fixes golang/go#50840.
(Maybe.)

Change-Id: I22d217f3706308b51d5b2ac84a781c50a6a41336
Reviewed-on: https://go-review.googlesource.com/c/tools/+/381734
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
---
 internal/lsp/fake/workdir.go | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/internal/lsp/fake/workdir.go b/internal/lsp/fake/workdir.go
index c95fbe7165..8e28c020cd 100644
--- a/internal/lsp/fake/workdir.go
+++ b/internal/lsp/fake/workdir.go
@@ -12,6 +12,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"sync"
 	"time"
@@ -152,11 +153,21 @@ func toURI(fp string) protocol.DocumentURI {
 
 // ReadFile reads a text file specified by a workdir-relative path.
 func (w *Workdir) ReadFile(path string) (string, error) {
-	b, err := ioutil.ReadFile(w.AbsPath(path))
-	if err != nil {
-		return "", err
+	backoff := 1 * time.Millisecond
+	for {
+		b, err := ioutil.ReadFile(w.AbsPath(path))
+		if err != nil {
+			if runtime.GOOS == "plan9" && strings.HasSuffix(err.Error(), " exclusive use file already open") {
+				// Plan 9 enforces exclusive access to locked files.
+				// Give the owner time to unlock it and retry.
+				time.Sleep(backoff)
+				backoff *= 2
+				continue
+			}
+			return "", err
+		}
+		return string(b), nil
 	}
-	return string(b), nil
 }
 
 func (w *Workdir) RegexpRange(path, re string) (Pos, Pos, error) {