From 098c09334fefc9e061d061ec5cb491b4bbc83a4f Mon Sep 17 00:00:00 2001
From: Colin Cross <ccross@android.com>
Date: Thu, 26 Oct 2023 14:02:58 -0700
Subject: [PATCH] Remove unnecessary locking in fs

osFs.acquire and osFs.release are surprisingly expensive, using a
combined 345.7s of runtime in an AOSP aosp_cf_x86_64_phone-userdebug
build.  They are used to ensure we don't use too many simultaneous
open files, but many of the functions they are called from don't
actually open a file.  Remove them from all the stat-based functions
(Exists, IsDir, IsSymlink, Lstat, Stat), and from ReadLink.  After
this change the time spent in acquire and release is effectively
zero.

Test: SOONG_PROFILE_CPU=/tmp/cpu.pprof m nothing
Change-Id: Ie5e22e33c61794354821f05ab79ceb4efc3b276c
---
 pathtools/fs.go | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/pathtools/fs.go b/pathtools/fs.go
index b959289..25e295f 100644
--- a/pathtools/fs.go
+++ b/pathtools/fs.go
@@ -204,8 +204,6 @@ func (fs *osFs) Open(name string) (ReaderAtSeekerCloser, error) {
 }
 
 func (fs *osFs) Exists(name string) (bool, bool, error) {
-	fs.acquire()
-	defer fs.release()
 	stat, err := os.Stat(fs.toAbs(name))
 	if err == nil {
 		return true, stat.IsDir(), nil
@@ -217,8 +215,6 @@ func (fs *osFs) Exists(name string) (bool, bool, error) {
 }
 
 func (fs *osFs) IsDir(name string) (bool, error) {
-	fs.acquire()
-	defer fs.release()
 	info, err := os.Stat(fs.toAbs(name))
 	if err != nil {
 		return false, err
@@ -227,8 +223,6 @@ func (fs *osFs) IsDir(name string) (bool, error) {
 }
 
 func (fs *osFs) IsSymlink(name string) (bool, error) {
-	fs.acquire()
-	defer fs.release()
 	if info, err := os.Lstat(fs.toAbs(name)); err != nil {
 		return false, err
 	} else {
@@ -249,14 +243,10 @@ func (fs *osFs) glob(pattern string) ([]string, error) {
 }
 
 func (fs *osFs) Lstat(path string) (stats os.FileInfo, err error) {
-	fs.acquire()
-	defer fs.release()
 	return os.Lstat(fs.toAbs(path))
 }
 
 func (fs *osFs) Stat(path string) (stats os.FileInfo, err error) {
-	fs.acquire()
-	defer fs.release()
 	return os.Stat(fs.toAbs(path))
 }
 
@@ -284,8 +274,6 @@ func (fs *osFs) ReadDirNames(name string) ([]string, error) {
 }
 
 func (fs *osFs) Readlink(name string) (string, error) {
-	fs.acquire()
-	defer fs.release()
 	return os.Readlink(fs.toAbs(name))
 }