rw trylock

property
w int
r int
mu sync.Mutex
rwmu sync.RWMutex


rlock 
mu.lock
r++
if w == 0
  rwmu.rlock
  mu.unlock
else
  mu.unlock
  rwmu.rlock


tryrlock 
mu.lock
if w > 0
  mu.unlock
  return false
else
  r++
  rwmu.rlock
  mu.unlock


lock
mu.lock
w++
if r > 0 || w > 1
  mu.unlock
  rwmu.lock
else
  rwmu.lock
  mu.unlock


trylock
mu.lock
if r > 0 || w > 0
  mu.unlock
  return false
else
w++
rwmu.lock
mu.unlock