在thread2进入method2之后，运行thread1以完成method1的信号

Question

I have 2 methods which need to function as below.

method1 {
  1. run logic and insert into table1
}

method2 {
  1. wait till other threads finish method1
  2. block future threads from starting method1
  3. update table1
}

The easiest solution would be to synchronize both method1 and method2. Another point of consideration is that method1 can be invoked by multiple threads (>10) and is common operation, while method2 is called very very rarely. So, synchronizing method1 will seriously hamper multiprocessing capability.

I explored the possibility of using ReadWriteLock, with a readLock in method1 and writeLock in method2. But that doesn't help me with #1 in method2, ie. after a writeLock is acquired in method2, I want running threads in method1 to complete before I proceed method2.

Answer 1

This is a classic usage of ReadWriteLock .

See Java Concurrency with ReadWriteLock

The read lock may be held simultaneously by multiple reader threads, so long as there are no writers. The write lock is exclusive .

So when you request a write lock in #1 of method2 it will wait until a time when all read locks have been released by anyone calling method1 before taking the lock and returning.

Taking a write lock essentially performs both #1 and #2 of method2 .