Java Concurrency: Read-write lock Readwritelock

In the absence of a write operation, two threads read one resource at a time without any problems, allowing multiple threads to read shared resources at the same time.

However, if a thread wants to write these shared resources, there should be no other thread reading or writing the resource.

Simply put, when multiple threads operate the same resource simultaneously, read-only coexistence, write-write does not coexist, and read and write do not coexist.

The lock rules for read and write locks are as follows:
After a read lock is obtained, other threads can obtain a read lock and cannot acquire a write lock
When a write lock is obtained, no other thread can obtain a read lock or a write lock

.

ImportJava.util.concurrent.locks.ReadWriteLock;ImportJava.util.concurrent.locks.ReentrantReadWriteLock;/*** Read/write lock. */ Public classReadwritelockdemo { Public Static voidMain (string[] args) {ReadWrite ReadWrite=NewReadWrite ();  for(inti=0;i<5;i++) {              NewThread (NewRunnable () {@Override Public voidrun () {readwrite.get ();              }}). Start (); NewThread (NewRunnable () {@Override Public voidrun () {readwrite.set ();          }}). Start (); }    }}   classReadWrite {PrivateReadwritelock readwritelock=NewReentrantreadwritelock (); /*** Perform a "read" Operation*/       Public voidget () {Try{readwritelock.readlock (). Lock (); System.out.println ("Thread" +thread.currentthread (). GetName () + "to read. "); Thread.Sleep (2*1000); }Catch(interruptedexception e) {e.printstacktrace (); }finally{readwritelock.readlock (). Unlock (); System.out.println ("Thread" +thread.currentthread (). GetName () + "finished reading. "); }      }       /*** "Write" Operation*/       Public  voidset () {Try{readwritelock.writelock (). Lock (); System.out.println ("Thread" +thread.currentthread (). GetName () + "write. "); Thread.Sleep (2*1000); }Catch(interruptedexception e) {e.printstacktrace (); }finally{readwritelock.writelock (). Unlock (); System.out.println ("Thread" +thread.currentthread (). GetName () + "write complete. "); }      }   }

The sample results are as follows:

 thread Thread-0 to read. Threads thread -0 Read finished. Threads thread -1 writes. Threads thread -1 write complete. Threads thread -5 writes. Threads thread -5 write complete. Threads thread -3 writes. Threads thread -3 write complete. Threads thread -7 writes. Threads thread -7 write complete. Threads thread -9 writes. Threads thread -9 write complete. Threads thread -2 for reading. Threads thread -4 for reading. Threads thread -6 for reading. Threads thread -8 for reading. Threads thread -2 Read finished. Threads thread -6 Read finished. Threads thread -8 Read finished. Thread -4 read completed. 

Java Concurrency: Read-write lock Readwritelock