ThreadLocal digs its knowledge points again

• ThreadLocal The stored value is thread closure , Threads are mutually exclusive , It is mainly used to share some data within the thread , Avoid passing... Through parameters 

•  Thread Perspective , Each thread maintains an implicit reference to a copy of its thread local variable , As long as the thread is active and  ThreadLocal  The instance is accessible ; After the thread disappears , All copies of its thread local instances are garbage collected 

•  stay Thread There is one in the class Map, A copy of the variables used to store each thread .

•  For multi-threaded resource sharing , The synchronization mechanism was adopted “ Time for space ” The way , and ThreadLocal Adopted “ Space for time ” The way