pkg syscall (freebsd-386), const SIGLIBRT = 33
pkg syscall (freebsd-386), const SIGLIBRT Signal
pkg syscall (freebsd-386), const SOCK_CLOEXEC = 268435456
pkg syscall (freebsd-386), const SOCK_CLOEXEC ideal-int
pkg syscall (freebsd-386), const SOCK_NONBLOCK = 536870912
pkg syscall (freebsd-386), const SOCK_NONBLOCK ideal-int
pkg syscall (freebsd-386), const SO_VENDOR = 2147483648
pkg syscall (freebsd-386), const SO_VENDOR ideal-int

	// callback(x) calls goCallback(x)
	callbackMutex.Lock()
	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()
}

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.