[Java multithreading] volatile keyword correct use method

Volatile variables have synchronized the visibility characteristics, but do not have atomic characteristics, that is, in a multithreaded environment, variables using the volatile keyword can only ensure that different threads read variables, you can read the latest modified variable value, but modify the value of the variable, but there is no guarantee of thread safety ( There may be write-value overrides). The following test code shows a few ways to use the volatile keyword.

1 /**2 * <b>volatile keyword correct usage </b><br>3  * @authorGaylen4  * @versionV1.1.05 * History6 * 1.1.0, November 20, 2014 Gaylen FE7  * @sinceJava 6.08  */9  Public classTestvolatile {Ten  One     /**volatile + atomic guarantees read and write security*/ A      Public Static volatileAtomicinteger count1 =NewAtomicinteger (0); -  -     /**volatile for read security, but no guarantee of write security*/ the      Public Static volatile intCount2 = 0; -  -     /**volatile + synchronized for read and write security*/ -      Public Static volatile intCount3 = 0; +  -     /**static only guarantees global uniqueness, but does not guarantee read and write security*/ +      Public Static intCOUNT4 = 0; A  at      Public Static synchronized voidcount3increment () { -testvolatile.count3++; -     } -  -     /**number of test threads*/ -      Public Static Final intNumofthread = 1000; in  -     /**thread helper class to ensure all threads are executed*/ to     Private StaticCountdownlatch Countdownlatch =NewCountdownlatch (numofthread); +  -      Public Static voidincrement () { the         Try { *Thread.Sleep (1); $}Catch(interruptedexception e) {Panax Notoginseng         } - count1.getandincrement (); thecount2++; + count3increment (); Acount4++; the     } +  -     /** $ * Output Results $ * Wait for all threads to finish executing, output result -      */ -      Public Static voidprint () { the         Try { - countdownlatch.await ();Wuyi}Catch(interruptedexception e) { the e.printstacktrace (); -         } WuSYSTEM.OUT.PRINTLN ("Run Result: count1=" +TestVolatile.count1.get ()); -SYSTEM.OUT.PRINTLN ("Run Result: count2=" +testvolatile.count2); AboutSYSTEM.OUT.PRINTLN ("Run Result: count3=" +testvolatile.count3); $SYSTEM.OUT.PRINTLN ("Run Result: count4=" +testvolatile.count4); -System.out.println ("---------------------------------------"); -  -     } A  +     /** the * <b> Program Entry </b><br> - * Start 1000 threads at the same time to increase operation $      * @paramargs the      */ the      Public Static voidMain (string[] args) { the          for(inti = 0; i < Numofthread; i++) { the             NewThread (NewRunnable () { -  in @Override the                  Public voidrun () { the                      for(intindex = 0; Index < 1000; index++) { About testvolatile.increment (); the                     } the Countdownlatch.countdown (); the                 } + }). Start (); -         } the print ();Bayi     } the}

The test program output results are as follows:

Running Result: count1=1000000
Running Result: count2=998528
Running Result: count3=1000000
Running Result: count4=999892
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The test program shows that using volatile + synchronized or volatile + atom variables can guarantee the safe variable reading and writing in multi-threaded environment.

[Java multithreading] volatile keyword correct use method