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Commit 1f46a91b authored by George Burgess IV's avatar George Burgess IV
Browse files

build: limit concurrency of updateSymlinks 

In rare cases, the unbounded concurrency here may lead to Go runtime
panics, due to the runtime spawning >10K threads.

Bug: 376466642
Test: `m` generates build files properly
Change-Id: Ib2e812b2fd56ebcee16154c69927821a4f379a87
parent 25777477

ui/build/soong.go

+18 −3
Original line number Diff line number Diff line
@@ -433,13 +433,13 @@ func checkEnvironmentFile(ctx Context, currentEnv *Environment, envFile string) 
	}

}



func updateSymlinks(ctx Context, dir, prevCWD, cwd string) error {

func updateSymlinks(ctx Context, dir, prevCWD, cwd string, updateSemaphore chan struct{}) error {

	defer symlinkWg.Done()



	visit := func(path string, d fs.DirEntry, err error) error {

		if d.IsDir() && path != dir {

			symlinkWg.Add(1)

			go updateSymlinks(ctx, path, prevCWD, cwd)

			go updateSymlinks(ctx, path, prevCWD, cwd, updateSemaphore)

			return filepath.SkipDir

		}

		f, err := d.Info()
@@ -470,12 +470,27 @@ func updateSymlinks(ctx Context, dir, prevCWD, cwd string) error { 
		return nil

	}



	<-updateSemaphore

	defer func() { updateSemaphore <- struct{}{} }()

	if err := filepath.WalkDir(dir, visit); err != nil {

		return err

	}

	return nil

}



// b/376466642: If the concurrency of updateSymlinks is unbounded, Go's runtime spawns a

// theoretically unbounded number of threads to handle blocking syscalls. This causes the runtime to

// panic due to hitting thread limits in rare cases. Limiting to GOMAXPROCS concurrent symlink

// updates should make this a non-issue.

func newUpdateSemaphore() chan struct{} {

	numPermits := runtime.GOMAXPROCS(0)

	c := make(chan struct{}, numPermits)

	for i := 0; i < numPermits; i++ {

		c <- struct{}{}

	}

	return c

}



func fixOutDirSymlinks(ctx Context, config Config, outDir string) error {

	cwd, err := os.Getwd()

	if err != nil {
@@ -508,7 +523,7 @@ func fixOutDirSymlinks(ctx Context, config Config, outDir string) error { 
	}



	symlinkWg.Add(1)

	if err := updateSymlinks(ctx, outDir, prevCWD, cwd); err != nil {

	if err := updateSymlinks(ctx, outDir, prevCWD, cwd, newUpdateSemaphore()); err != nil {

		return err

	}

	symlinkWg.Wait()