A. Read-write lock is how to achieve?
AQS succession, then the AQS by converting binary state, is divided into upper 16 bits and lower 16 bits to distinguish. High 16 indicates a read state, the lower 16 bits write state.
II. Analytical representation (level 16)
Assuming a state value S
a. Write Lock
When a write lock is determined by K = S & 0X0000FFFF, it will erase all high, then only the lower 16 bits, and then determines whether or not K is greater than 0, K> 0, represents write locks, not vice versa.
b. a read lock
When a read lock, by K = S >>> 16, we can see that an unsigned right shift (int are signed, one is to prevent the upper, right upper S.1), this time to the right, high bit 0 , the lower 16 bits of write lock determination removed. Then it is determined whether K is greater than 0, K> 0, there is a read lock, not vice versa.
The figure is operation when the acquired read-write lock. Methods of tryAcquire and tryAcquireShare.
