同步和异步有何异同（What are the similarities and differences between synchronous and asynchronous）.docVIP

同步和异步有何异同（What are the similarities and differences between synchronous and asynchronous） If the data will be shared between threads. For example, after the data is being written by another thread may be read, or reading data may have been written by another thread, then these data is shared, the need for simultaneous access. When the application uses a method to take a long time to execute on the object, and do not want to return to the program waits for method, you should use asynchronous programming, using asynchronous way are much more efficient in many cases. Java synchronization: Basic concept: Each Object will have 1 locks Synchronization is the serial use of some resources (Note: here are some examples that omit unnecessary code in order to highlight the importance of eliminating some member variables, i.e., objects that need synchronization 1. synchronize the shared, mutable data in multiple threads There is no need to synchronize for local variables in a function There is no need to synchronize for immutable data It is necessary to access shared mutable data in multithreaded applications 2., you can use synchronized in a single thread and can be nested, but meaningless Class Test { Public, static, void, main (String[], args) { Test t = new, Test (); Synchronized (T) { Synchronized (T) { System.out.println (OK!); } } } } 3. locks for object instances Class Test{ Public, synchronized, void, F1 () { //do something here } Public, void, F2 () { Synchronized (this) { //do something here } } } The F1 () above is consistent with the F2 () effect, and the lock that synchronized obtains is a lock of a Test (this) For example: Test, t = new, Test (); When thread A calls t.f2 (), thread B cannot enter t.f1 () until t.f2 () ends Role: synchronous method for accessing the same instance of Test in multi thread 4. class lock Class Test{ Final, static, Object, o=, new, Object (); Public, static, synchronized, void, F1 () { //do something here } Public, static, void, F2 ()