// silently unlocked. So a second RLock must block instead of proceeding.
		lockF2 := mustBlock(t, "RLock", f2)
		unlock(t, f)
		lockF2(t)
	default:
		rLock(t, f2)
		doUnlockTF = true
	}

	other := mustOpen(t, f.Name())
	defer other.Close()
	lockOther := mustBlock(t, "Lock", other)

	unlock(t, f2)
	if doUnlockTF {
		unlock(t, f)
	}
	lockOther(t)
	unlock(t, other)

	}
	if n == 0 {
		return
	}
	c.file.register(c)

	state := c.state.load()
	for ; ; state = c.state.load() {
		switch {
		case !state.locked() && state.havePtr():
			if !c.state.update(&state, state.incReader()) {
				continue
			}
			// Counter unlocked or counter shared; has an initialized count pointer; acquired shared lock.
			if c.ptr.count == nil {
				for !c.state.update(&state, state.addExtra(uint64(n))) {

		t.Logf("unlock2()")
		unlock2()
	})

	t.Logf("unlock()")
	unlock()
	wait(t)
}

func TestReadWaitsForLock(t *testing.T) {
	t.Parallel()

	dir, remove := mustTempDir(t)
	defer remove()

	path := filepath.Join(dir, "timestamp.txt")

	f, err := lockedfile.Create(path)
	if err != nil {
		t.Fatalf("Create: %v", err)
	}
	defer f.Close()

	const (

	// 	P.1 unlocks file A.
	// 	Q.3 unblocks and locks file A.
	// 	Q.3 unlocks files A and B.
	// 	P.2 wakes up and locks file B.
	// 	P.2 unlocks file B.
	//
	// We know that the retry loop will not introduce a *spurious* livelock
	// because, according to the POSIX specification, EDEADLK is only to be
	// returned when “the lock is blocked by a lock from another process”.

*/
import "C"
import (
	"os"
	"os/signal"
	"syscall"
	"testing"
)

var blocked bool

//export IntoGoAndBack
func IntoGoAndBack() {
	// Verify that SIGIO stays blocked on the C thread
	// even when unblocked for signal.Notify().
	signal.Notify(make(chan os.Signal), syscall.SIGIO)
	blocked = C.CheckBlocked() != 0
}

func testSigprocmask(t *testing.T) {
	if r := C.RunSigThread(); r != 0 {

//
//   - "open/create -- file is locked" (cwfs, kfs)
//   - "exclusive lock" (fossil)
//   - "exclusive use file already open" (ramfs)
var lockedErrStrings = [...]string{
	"file is locked",
	"exclusive lock",
	"exclusive use file already open",
}

// Even though plan9 doesn't support the Lock/RLock/Unlock functions to
// manipulate already-open files, IsLocked is still meaningful: os.OpenFile

// and orthogonal to syscallEnd; both must be called if the syscall blocked. This sets up an instant
// to emit a flow event from, indicating explicitly that this goroutine was unblocked by the system.
func (gs *gState[R]) blockedSyscallEnd(ts trace.Time, stack trace.Stack, ctx *traceContext) {
	name := "exit blocked syscall"
	gs.setStartCause(ts, name, trace.SyscallP, stack)

	}

	if from == trace.GoWaiting {
		// Goroutine unblocked.
		gs.unblock(ev.Time(), ev.Stack(), ev.Goroutine(), ctx)
	}
	if from == trace.GoNotExist && to == trace.GoRunnable {
		// Goroutine was created.
		gs.created(ev.Time(), ev.Goroutine(), ev.Stack())
	}
	if from == trace.GoSyscall && to != trace.GoRunning {
		// Exiting blocked syscall.
		gs.syscallEnd(ev.Time(), true, ctx)

		if from == trace.GoUndetermined {
			// Back-date the event to the start of the trace.
			start = ctx.startTime
		}
		gs.start(start, ev.Thread(), ctx)
	}

	if from == trace.GoWaiting {
		// Goroutine was unblocked.
		gs.unblock(ev.Time(), ev.Stack(), ev.Thread(), ctx)
	}
	if from == trace.GoNotExist && to == trace.GoRunnable {
		// Goroutine was created.
		gs.created(ev.Time(), ev.Thread(), ev.Stack())
	}

		// is safe.
		if ii.combinesBackward() {
			cccB := b[k-1].ccc
			cccC := ii.ccc
			blocked := false // b[i] blocked by starter or greater or equal CCC?
			if cccB == 0 {
				s = k - 1
			} else {
				blocked = s != k-1 && cccB >= cccC
			}
			if !blocked {
				combined := combine(rb.runeAt(s), rb.runeAt(i))
				if combined != 0 {
					rb.assignRune(s, combined)
					continue