Playing with concurrency: what are the ways of communication between threads?

Shared memory

volatile keyword

Wait for a notice

wait,notify Why do we have to synchronized Use it together ？

When there is no resource for the thread to obtain , Thread needs to wait , Because there may be multiple threads waiting , So you need to put it into the synchronization queue of resources . When resources meet , Need to wake up the thread in the waiting queue . When multiple threads operate on a synchronized queue , To ensure thread safety , So it needs to be locked

sleep and wait What are the differences ？

although sleep and wait All the behaviors are waiting , But absolutely 2 There are two unrelated methods .

1. sleep It's a simple waiting method , and wait Is a method for thread communication , When resources are not satisfied, we have to wait . So this 2 Methods are placed in different classes ,sleep yes Thread Class method ,wait yes Object Class method .
2. sleep Method can be used anywhere ,wait Only in synchronized Method or synchronized Block the use of
3. Thread.sleep Just give up CPU, Object locks are not released
4. Object.wait Not only give up CPU, It also releases the object lock . Only call... For this object notify() It's time or method , To execute... Again

wait Why release the lock when

When a thread a Get into synchronized(obj) In block , That's right obj be locked , Call at this time wait It will be blocked , If the lock is not released at this time , Then other threads will not enter synchronized In block , Naturally, you can't call notify Method , This will cause deadlock