callbackToken++
	i := callbackToken
	callbackFuncs[i] = f
	callbackMutex.Unlock()

	// Pass the address of i because the C function was written to
	// take a pointer.  We could pass an int if we felt like
	// rewriting the C code.
	C.callback(unsafe.Pointer(&i))

	callbackMutex.Lock()
	delete(callbackFuncs, i)
	callbackMutex.Unlock()
}

//export goCallback
func goCallback(p unsafe.Pointer) {
	i := *(*int)(p)

pkg syscall (darwin-386), func Mlock([]uint8) error
pkg syscall (darwin-386), func Mlockall(int) error
pkg syscall (darwin-386), func Mprotect([]uint8, int) error
pkg syscall (darwin-386), func Munlock([]uint8) error
pkg syscall (darwin-386), func Munlockall() error
pkg syscall (darwin-386), func SendmsgN(int, []uint8, []uint8, Sockaddr, int) (int, error)

of an interface type or of elements of a composite type remains unchanged:
</p>

<pre>
// A Mutex is a data type with two methods, Lock and Unlock.
type Mutex struct         { /* Mutex fields */ }
func (m *Mutex) Lock()    { /* Lock implementation */ }
func (m *Mutex) Unlock()  { /* Unlock implementation */ }

// NewMutex has the same composition as Mutex but its method set is empty.
type NewMutex Mutex

pkg syscall (netbsd-arm64-cgo), const SYS_MSGSND ideal-int
pkg syscall (netbsd-arm64-cgo), const SYS_MUNLOCK = 204
pkg syscall (netbsd-arm64-cgo), const SYS_MUNLOCKALL = 243
pkg syscall (netbsd-arm64-cgo), const SYS_MUNLOCKALL ideal-int
pkg syscall (netbsd-arm64-cgo), const SYS_MUNLOCK ideal-int
pkg syscall (netbsd-arm64-cgo), const SYS_MUNMAP = 73
pkg syscall (netbsd-arm64-cgo), const SYS_MUNMAP ideal-int

The first call to <code>l.Unlock()</code> (in <code>f</code>) is synchronized
before the second call to <code>l.Lock()</code> (in <code>main</code>) returns,
which is sequenced before the <code>print</code>.
</p>

<p class="rule">
For any call to <code>l.RLock</code> on a <code>sync.RWMutex</code> variable <code>l</code>,
there is an <i>n</i> such that the <i>n</i>th call to <code>l.Unlock</code>

	fw *flate.Writer
}

func (w *pooledFlateWriter) Write(p []byte) (n int, err error) {
	w.mu.Lock()
	defer w.mu.Unlock()
	if w.fw == nil {
		return 0, errors.New("Write after Close")
	}
	return w.fw.Write(p)
}

func (w *pooledFlateWriter) Close() error {
	w.mu.Lock()
	defer w.mu.Unlock()
	var err error
	if w.fw != nil {
		err = w.fw.Close()
		flateWriterPool.Put(w.fw)
		w.fw = nil
	}
	return err

// int nts = 0;
// int all_done = 0;
//
// static void *aFn(void *vargp) {
//   int done = 0;
//   while (!done) {
//     usleep(100);
//     pthread_mutex_lock(&mu);
//     done = all_done;
//     pthread_mutex_unlock(&mu);
//   }
//   return NULL;
// }
//
// void trial(int argc) {
//   int i;
//   nts = argc;
//   t = calloc(nts, sizeof(pthread_t));
//   pthread_mutex_init(&mu, NULL);
//   for (i = 0; i < nts; i++) {

pkg syscall (darwin-arm64), const SYS_PSYNCH_RW_RDLOCK = 306
pkg syscall (darwin-arm64), const SYS_PSYNCH_RW_RDLOCK ideal-int
pkg syscall (darwin-arm64), const SYS_PSYNCH_RW_UNLOCK = 308
pkg syscall (darwin-arm64), const SYS_PSYNCH_RW_UNLOCK ideal-int
pkg syscall (darwin-arm64), const SYS_PSYNCH_RW_UNLOCK2 = 309
pkg syscall (darwin-arm64), const SYS_PSYNCH_RW_UNLOCK2 ideal-int

pkg sync, method (*Cond) Wait()
pkg sync, method (*Mutex) Lock()
pkg sync, method (*Mutex) Unlock()
pkg sync, method (*Once) Do(func())
pkg sync, method (*RWMutex) Lock()
pkg sync, method (*RWMutex) RLock()
pkg sync, method (*RWMutex) RLocker() Locker
pkg sync, method (*RWMutex) RUnlock()
pkg sync, method (*RWMutex) Unlock()
pkg sync, method (*WaitGroup) Add(int)
pkg sync, method (*WaitGroup) Done()

}

// url may contain a #fragment, and the fragment is then noted as needing to exist.
func crawl(url string, sourceURL string) {
	if strings.Contains(url, "/devel/release") {
		return
	}
	mu.Lock()
	defer mu.Unlock()
	if u, frag, ok := strings.Cut(url, "#"); ok {
		url = u
		if frag != "" {
			uf := urlFrag{url, frag}
			neededFrags[uf] = append(neededFrags[uf], sourceURL)
		}
	}
	if crawled[url] {
		return
	}