Double Lock Checker

[Tengfei1010]

Double lock:

Phase 1: A function acquires a lock twice!

func f1() {
    .....
    r.Lock() // rw.Rlock()
    .....  # no unlock and they may be not in same block.
    r.Lock() // rw.Lock()
}

Phase 2: Another double lock:
The parent function has already acquired the lock and the child function wants to acquire the lock.

func f1() {
    r.Lock()
    .....   // no unlock
    call f2()  // may be call f1->f3->......->f2
    ....
}

func f2() {
   ......   
   r.Lock()
   ......
}

Phase 3: Third double lock:
The lock in a loop.....

func f1() {
   for {
      r.lock()
      .......
  }
}

[Tengfei1010]

Finish the Phase 1