const RW = require('read-write-mutexify')
const rw =new RW()
// read locks waits for writer locks to be released
await rw.read.lock()
await rw.read.lock() // make as many as you want
// unlock with unlock
rw.read.unlock()
rw.read.unlock()
// only one writer can have the write lock and it waits
// for any read lock to be released
await rw.write.lock()
// unlock with unlock
rw.write.unlock()