src/runtime/testdata/testprog/lockosthread.go - go - Git at Google

 // Copyright 2017 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package main

 import (
 	"os"
 	"runtime"
 	"sync"
 	"time"
 )

 var mainTID int

 func init() {
 	registerInit("LockOSThreadMain", func() {
 		// init is guaranteed to run on the main thread.
 		mainTID = gettid()
 	})
 	register("LockOSThreadMain", LockOSThreadMain)

 	registerInit("LockOSThreadAlt", func() {
 		// Lock the OS thread now so main runs on the main thread.
 		runtime.LockOSThread()
 	})
 	register("LockOSThreadAlt", LockOSThreadAlt)

 	registerInit("LockOSThreadAvoidsStatePropagation", func() {
 		// Lock the OS thread now so main runs on the main thread.
 		runtime.LockOSThread()
 	})
 	register("LockOSThreadAvoidsStatePropagation", LockOSThreadAvoidsStatePropagation)
 	register("LockOSThreadTemplateThreadRace", LockOSThreadTemplateThreadRace)
 }

 func LockOSThreadMain() {
 	// gettid only works on Linux, so on other platforms this just
 	// checks that the runtime doesn't do anything terrible.

 	// This requires GOMAXPROCS=1 from the beginning to reliably
 	// start a goroutine on the main thread.
 	if runtime.GOMAXPROCS(-1) != 1 {
 		println("requires GOMAXPROCS=1")
 		os.Exit(1)
 	}

 	ready := make(chan bool, 1)
 	go func() {
 		// Because GOMAXPROCS=1, this *should* be on the main
 		// thread. Stay there.
 		runtime.LockOSThread()
 		if mainTID != 0 && gettid() != mainTID {
 			println("failed to start goroutine on main thread")
 			os.Exit(1)
 		}
 		// Exit with the thread locked, which should exit the
 		// main thread.
 		ready <- true
 	}()
 	<-ready
 	time.Sleep(1 * time.Millisecond)
 	// Check that this goroutine is still running on a different
 	// thread.
 	if mainTID != 0 && gettid() == mainTID {
 		println("goroutine migrated to locked thread")
 		os.Exit(1)
 	}
 	println("OK")
 }

 func LockOSThreadAlt() {
 	// This is running locked to the main OS thread.

 	var subTID int
 	ready := make(chan bool, 1)
 	go func() {
 		// This goroutine must be running on a new thread.
 		runtime.LockOSThread()
 		subTID = gettid()
 		ready <- true
 		// Exit with the thread locked.
 	}()
 	<-ready
 	runtime.UnlockOSThread()
 	for i := 0; i < 100; i++ {
 		time.Sleep(1 * time.Millisecond)
 		// Check that this goroutine is running on a different thread.
 		if subTID != 0 && gettid() == subTID {
 			println("locked thread reused")
 			os.Exit(1)
 		}
 		exists, supported := tidExists(subTID)
 		if !supported || !exists {
 			goto ok
 		}
 	}
 	println("sub thread", subTID, "still running")
 	return
 ok:
 	println("OK")
 }

 func LockOSThreadAvoidsStatePropagation() {
 	// This test is similar to LockOSThreadAlt in that it will detect if a thread
 	// which should have died is still running. However, rather than do this with
 	// thread IDs, it does this by unsharing state on that thread. This way, it
 	// also detects whether new threads were cloned from the dead thread, and not
 	// from a clean thread. Cloning from a locked thread is undesirable since
 	// cloned threads will inherit potentially unwanted OS state.
 	//
 	// unshareFs, getcwd, and chdir("/tmp") are only guaranteed to work on
 	// Linux, so on other platforms this just checks that the runtime doesn't
 	// do anything terrible.
 	//
 	// This is running locked to the main OS thread.

 	// GOMAXPROCS=1 makes this fail much more reliably if a tainted thread is
 	// cloned from.
 	if runtime.GOMAXPROCS(-1) != 1 {
 		println("requires GOMAXPROCS=1")
 		os.Exit(1)
 	}

 	if err := chdir("/"); err != nil {
 		println("failed to chdir:", err.Error())
 		os.Exit(1)
 	}
 	// On systems other than Linux, cwd == "".
 	cwd, err := getcwd()
 	if err != nil {
 		println("failed to get cwd:", err.Error())
 		os.Exit(1)
 	}
 	if cwd != "" && cwd != "/" {
 		println("unexpected cwd", cwd, " wanted /")
 		os.Exit(1)
 	}

 	ready := make(chan bool, 1)
 	go func() {
 		// This goroutine must be running on a new thread.
 		runtime.LockOSThread()

 		// Unshare details about the FS, like the CWD, with
 		// the rest of the process on this thread.
 		// On systems other than Linux, this is a no-op.
 		if err := unshareFs(); err != nil {
 			if err == errNotPermitted {
 				println("unshare not permitted")
 				os.Exit(0)
 			}
 			println("failed to unshare fs:", err.Error())
 			os.Exit(1)
 		}
 		// Chdir to somewhere else on this thread.
 		// On systems other than Linux, this is a no-op.
 		if err := chdir("/tmp"); err != nil {
 			println("failed to chdir:", err.Error())
 			os.Exit(1)
 		}

 		// The state on this thread is now considered "tainted", but it
 		// should no longer be observable in any other context.

 		ready <- true
 		// Exit with the thread locked.
 	}()
 	<-ready

 	// Spawn yet another goroutine and lock it. Since GOMAXPROCS=1, if
 	// for some reason state from the (hopefully dead) locked thread above
 	// propagated into a newly created thread (via clone), or that thread
 	// is actually being re-used, then we should get scheduled on such a
 	// thread with high likelihood.
 	done := make(chan bool)
 	go func() {
 		runtime.LockOSThread()

 		// Get the CWD and check if this is the same as the main thread's
 		// CWD. Every thread should share the same CWD.
 		// On systems other than Linux, wd == "".
 		wd, err := getcwd()
 		if err != nil {
 			println("failed to get cwd:", err.Error())
 			os.Exit(1)
 		}
 		if wd != cwd {
 			println("bad state from old thread propagated after it should have died")
 			os.Exit(1)
 		}
 		<-done

 		runtime.UnlockOSThread()
 	}()
 	done <- true
 	runtime.UnlockOSThread()
 	println("OK")
 }

 func LockOSThreadTemplateThreadRace() {
 	// This test attempts to reproduce the race described in
 	// golang.org/issue/38931. To do so, we must have a stop-the-world
 	// (achieved via ReadMemStats) racing with two LockOSThread calls.
 	//
 	// While this test attempts to line up the timing, it is only expected
 	// to fail (and thus hang) around 2% of the time if the race is
 	// present.

 	// Ensure enough Ps to actually run everything in parallel. Though on
 	// <4 core machines, we are still at the whim of the kernel scheduler.
 	runtime.GOMAXPROCS(4)

 	go func() {
 		// Stop the world; race with LockOSThread below.
 		var m runtime.MemStats
 		for {
 			runtime.ReadMemStats(&m)
 		}
 	}()

 	// Try to synchronize both LockOSThreads.
 	start := time.Now().Add(10 * time.Millisecond)

 	var wg sync.WaitGroup
 	wg.Add(2)

 	for i := 0; i < 2; i++ {
 		go func() {
 			for time.Now().Before(start) {
 			}

 			// Add work to the local runq to trigger early startm
 			// in handoffp.
 			go func() {}()

 			runtime.LockOSThread()
 			runtime.Gosched() // add a preemption point.
 			wg.Done()
 		}()
 	}

 	wg.Wait()
 	// If both LockOSThreads completed then we did not hit the race.
 	println("OK")
 }
	// Copyright 2017 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package main

	import (
	"os"
	"runtime"
	"sync"
	"time"
	)

	var mainTID int

	func init() {
	registerInit("LockOSThreadMain", func() {
	// init is guaranteed to run on the main thread.
	mainTID = gettid()
	})
	register("LockOSThreadMain", LockOSThreadMain)

	registerInit("LockOSThreadAlt", func() {
	// Lock the OS thread now so main runs on the main thread.
	runtime.LockOSThread()
	})
	register("LockOSThreadAlt", LockOSThreadAlt)

	registerInit("LockOSThreadAvoidsStatePropagation", func() {
	// Lock the OS thread now so main runs on the main thread.
	runtime.LockOSThread()
	})
	register("LockOSThreadAvoidsStatePropagation", LockOSThreadAvoidsStatePropagation)
	register("LockOSThreadTemplateThreadRace", LockOSThreadTemplateThreadRace)
	}

	func LockOSThreadMain() {
	// gettid only works on Linux, so on other platforms this just
	// checks that the runtime doesn't do anything terrible.

	// This requires GOMAXPROCS=1 from the beginning to reliably
	// start a goroutine on the main thread.
	if runtime.GOMAXPROCS(-1) != 1 {
	println("requires GOMAXPROCS=1")
	os.Exit(1)
	}

	ready := make(chan bool, 1)
	go func() {
	// Because GOMAXPROCS=1, this should be on the main
	// thread. Stay there.
	runtime.LockOSThread()
	if mainTID != 0 && gettid() != mainTID {
	println("failed to start goroutine on main thread")
	os.Exit(1)
	}
	// Exit with the thread locked, which should exit the
	// main thread.
	ready <- true
	}()
	<-ready
	time.Sleep(1 * time.Millisecond)
	// Check that this goroutine is still running on a different
	// thread.
	if mainTID != 0 && gettid() == mainTID {
	println("goroutine migrated to locked thread")
	os.Exit(1)
	}
	println("OK")
	}

	func LockOSThreadAlt() {
	// This is running locked to the main OS thread.

	var subTID int
	ready := make(chan bool, 1)
	go func() {
	// This goroutine must be running on a new thread.
	runtime.LockOSThread()
	subTID = gettid()
	ready <- true
	// Exit with the thread locked.
	}()
	<-ready
	runtime.UnlockOSThread()
	for i := 0; i < 100; i++ {
	time.Sleep(1 * time.Millisecond)
	// Check that this goroutine is running on a different thread.
	if subTID != 0 && gettid() == subTID {
	println("locked thread reused")
	os.Exit(1)
	}
	exists, supported := tidExists(subTID)
	if !supported \|\| !exists {
	goto ok
	}
	}
	println("sub thread", subTID, "still running")
	return
	ok:
	println("OK")
	}

	func LockOSThreadAvoidsStatePropagation() {
	// This test is similar to LockOSThreadAlt in that it will detect if a thread
	// which should have died is still running. However, rather than do this with
	// thread IDs, it does this by unsharing state on that thread. This way, it
	// also detects whether new threads were cloned from the dead thread, and not
	// from a clean thread. Cloning from a locked thread is undesirable since
	// cloned threads will inherit potentially unwanted OS state.
	//
	// unshareFs, getcwd, and chdir("/tmp") are only guaranteed to work on
	// Linux, so on other platforms this just checks that the runtime doesn't
	// do anything terrible.
	//
	// This is running locked to the main OS thread.

	// GOMAXPROCS=1 makes this fail much more reliably if a tainted thread is
	// cloned from.
	if runtime.GOMAXPROCS(-1) != 1 {
	println("requires GOMAXPROCS=1")
	os.Exit(1)
	}

	if err := chdir("/"); err != nil {
	println("failed to chdir:", err.Error())
	os.Exit(1)
	}
	// On systems other than Linux, cwd == "".
	cwd, err := getcwd()
	if err != nil {
	println("failed to get cwd:", err.Error())
	os.Exit(1)
	}
	if cwd != "" && cwd != "/" {
	println("unexpected cwd", cwd, " wanted /")
	os.Exit(1)
	}

	ready := make(chan bool, 1)
	go func() {
	// This goroutine must be running on a new thread.
	runtime.LockOSThread()

	// Unshare details about the FS, like the CWD, with
	// the rest of the process on this thread.
	// On systems other than Linux, this is a no-op.
	if err := unshareFs(); err != nil {
	if err == errNotPermitted {
	println("unshare not permitted")
	os.Exit(0)
	}
	println("failed to unshare fs:", err.Error())
	os.Exit(1)
	}
	// Chdir to somewhere else on this thread.
	// On systems other than Linux, this is a no-op.
	if err := chdir("/tmp"); err != nil {
	println("failed to chdir:", err.Error())
	os.Exit(1)
	}

	// The state on this thread is now considered "tainted", but it
	// should no longer be observable in any other context.

	ready <- true
	// Exit with the thread locked.
	}()
	<-ready

	// Spawn yet another goroutine and lock it. Since GOMAXPROCS=1, if
	// for some reason state from the (hopefully dead) locked thread above
	// propagated into a newly created thread (via clone), or that thread
	// is actually being re-used, then we should get scheduled on such a
	// thread with high likelihood.
	done := make(chan bool)
	go func() {
	runtime.LockOSThread()

	// Get the CWD and check if this is the same as the main thread's
	// CWD. Every thread should share the same CWD.
	// On systems other than Linux, wd == "".
	wd, err := getcwd()
	if err != nil {
	println("failed to get cwd:", err.Error())
	os.Exit(1)
	}
	if wd != cwd {
	println("bad state from old thread propagated after it should have died")
	os.Exit(1)
	}
	<-done

	runtime.UnlockOSThread()
	}()
	done <- true
	runtime.UnlockOSThread()
	println("OK")
	}

	func LockOSThreadTemplateThreadRace() {
	// This test attempts to reproduce the race described in
	// golang.org/issue/38931. To do so, we must have a stop-the-world
	// (achieved via ReadMemStats) racing with two LockOSThread calls.
	//
	// While this test attempts to line up the timing, it is only expected
	// to fail (and thus hang) around 2% of the time if the race is
	// present.

	// Ensure enough Ps to actually run everything in parallel. Though on
	// <4 core machines, we are still at the whim of the kernel scheduler.
	runtime.GOMAXPROCS(4)

	go func() {
	// Stop the world; race with LockOSThread below.
	var m runtime.MemStats
	for {
	runtime.ReadMemStats(&m)
	}
	}()

	// Try to synchronize both LockOSThreads.
	start := time.Now().Add(10 * time.Millisecond)

	var wg sync.WaitGroup
	wg.Add(2)

	for i := 0; i < 2; i++ {
	go func() {
	for time.Now().Before(start) {
	}

	// Add work to the local runq to trigger early startm
	// in handoffp.
	go func() {}()

	runtime.LockOSThread()
	runtime.Gosched() // add a preemption point.
	wg.Done()
	}()
	}

	wg.Wait()
	// If both LockOSThreads completed then we did not hit the race.
	println("OK")
	}