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public synchronized void increase() { inc++; } public static void main(String[] args) { final Test test = new Test(); for(int i=0;i<10;i++){ new Thread(){ public void run() { for(int j=0;j<1000;j++) test.increase(); }; }.start(); } while(Thread.activeCount()>1) //±£Ö¤Ç°ÃæµÄÏ̶߳¼Ö´ÐÐÍê Thread.yield(); System.out.println(test.inc); } } ²ÉÓÃLock£º public class Test { public int inc = 0; Lock lock = new ReentrantLock(); public void increase() { lock.lock(); try { inc++; } finally{ lock.unlock(); } } public static void main(String[] args) { final Test test = new Test(); for(int i=0;i<10;i++){ new Thread(){ public void run() { for(int j=0;j<1000;j++) test.increase(); }; }.start(); } while(Thread.activeCount()>1) //±£Ö¤Ç°ÃæµÄÏ̶߳¼Ö´ÐÐÍê Thread.yield(); System.out.println(test.inc); } } ²ÉÓÃAtomicInteger£º public class Test { public AtomicInteger inc = new AtomicInteger(); public void increase() { inc.getAndIncrement(); } public static void main(String[] args) { final Test test = new Test(); for(int i=0;i<10;i++){ new Thread(){ public void run() { for(int j=0;j<1000;j++) test.increase(); }; }.start(); } while(Thread.activeCount()>1) //±£Ö¤Ç°ÃæµÄÏ̶߳¼Ö´ÐÐÍê Thread.yield(); System.out.println(test.inc); } } ÔÚjava 1.5µÄjava.util.concurrent.atomic°üÏÂÌṩÁËһЩԭ×Ó²Ù×÷À࣬¼´¶Ô»ù±¾Êý¾ÝÀàÐ굀 ×ÔÔö(¼Ó1²Ù×÷)£¬×Ô¼õ(¼õ1²Ù×÷)¡¢ÒÔ¼°¼Ó·¨²Ù×÷(¼ÓÒ»¸öÊý)£¬¼õ·¨²Ù×÷(¼õÒ»¸öÊý)½øÐÐÁË·â×°£¬±£Ö¤ÕâЩ²Ù×÷ÊÇÔ­×ÓÐÔ²Ù×÷¡£atomicÊÇÀûÓÃCASÀ´ÊµÏÖÔ­×ÓÐÔ²Ù×÷µÄ(Compare And Swap)£¬CASʵ¼ÊÉÏÊÇÀûÓô¦ÀíÆ÷ÌṩµÄCMPXCHGÖ¸ÁîʵÏֵģ¬¶ø´¦ÀíÆ÷Ö´ÐÐCMPXCHGÖ¸ÁîÊÇÒ»¸öÔ­×ÓÐÔ²Ù×÷¡£ 5.3 volatileÄܱ£Ö¤ÓÐÐòÐÔÂð? volatileÄÜÔÚÒ»¶¨³Ì¶ÈÉϱ£Ö¤ÓÐÐòÐÔ¡£ volatile¹Ø¼ü×Ö½ûÖ¹Ö¸ÁîÖØÅÅÐòÓÐÁ½²ãÒâ˼£º 1)µ±³ÌÐòÖ´Ðе½volatile±äÁ¿µÄ¶Á²Ù×÷»òÕßд²Ù×÷ʱ£¬ÔÚÆäÇ°ÃæµÄ²Ù×÷µÄ¸ü¸Ä¿Ï¶¨È«²¿ÒѾ­½øÐУ¬ÇÒ½á¹ûÒѾ­¶ÔºóÃæµÄ²Ù×÷¿É¼û;ÔÚÆäºóÃæµÄ²Ù×÷¿Ï¶¨»¹Ã»ÓнøÐÐ; 2)ÔÚ½øÐÐÖ¸ÁîÓÅ»¯Ê±£¬²»Äܽ«ÔÚ¶Ôvolatile±äÁ¿·ÃÎʵÄÓï¾ä·ÅÔÚÆäºóÃæÖ´ÐУ¬Ò²²»ÄÜ°Ñvolatile±äÁ¿ºóÃæµÄÓï¾ä·Åµ½ÆäÇ°ÃæÖ´ÐС£ ¾Ù¸öÀý×Ó£º //x¡¢yΪ·Çvolatile±äÁ¿ //flagΪvolatile±äÁ¿ x = 2; //Óï¾ä1 y = 0; //Óï¾ä2 flag = true; //Óï¾ä3 x = 4; //Óï¾ä4 y = -1; //Óï¾ä5 ÓÉÓÚflag±äÁ¿Îªvolatile±äÁ¿£¬ÄÇôÔÚ½øÐÐÖ¸ÁîÖØÅÅÐòµÄ¹ý³ÌµÄʱºò£¬²»»á½«Óï¾ä3·Åµ½Óï¾ä1¡¢Óï¾ä2Ç°Ã棬Ҳ²»»á½²Óï¾ä3·Åµ½Óï¾ä4¡¢Óï¾ä5ºóÃæ¡£µ«ÊÇҪעÒâÓï¾ä1ºÍÓï¾ä2µÄ˳Ðò¡¢Óï¾ä4ºÍÓï¾ä5µÄ˳ÐòÊDz»×÷Èκα£Ö¤µÄ¡£ ²¢ÇÒvolatile¹Ø¼ü×ÖÄܱ£Ö¤£¬Ö´Ðе½Óï¾ä3ʱ£¬Óï¾ä1ºÍÓï¾ä2±Ø¶¨ÊÇÖ´ÐÐÍê±ÏÁ˵ģ¬ÇÒÓï¾ä1ºÍÓï¾ä2µÄÖ´Ðнá¹û¶ÔÓï¾ä3¡¢Óï¾ä4¡¢Óï¾ä5ÊǿɼûµÄ¡£ 5.4 volatileµÄÔ­ÀíºÍʵÏÖ»úÖÆ ÕâÀï̽ÌÖÒ»ÏÂvolatileµ½µ×ÈçºÎ±£Ö¤¿É¼ûÐԺͽûÖ¹Ö¸ÁîÖØÅÅÐòµÄ¡£ ÏÂÃæÕâ¶Î»°Õª×Ô¡¶ÉîÈëÀí½âJavaÐéÄâ»ú¡·£º ¡°¹Û²ì¼ÓÈëvolatile¹Ø¼ü×ÖºÍûÓмÓÈëvolatile¹Ø¼ü×ÖʱËùÉú³ÉµÄ»ã±à´úÂë·¢ÏÖ£¬¼ÓÈëvolatile¹Ø¼ü×Öʱ£¬»á¶à³öÒ»¸ölockǰ׺ָÁ lockǰ׺ָÁîʵ¼ÊÉÏÏ൱ÓÚÒ»¸öÄÚ´æÆÁÕÏ(Ò²³ÉÄÚ´æÕ¤À¸)£¬ÄÚ´æÆÁÕÏ»áÌṩ3¸ö¹¦ÄÜ£º ËüÈ·±£Ö¸ÁîÖØÅÅÐòʱ²»»á°ÑÆäºóÃæµÄÖ¸ÁîÅŵ½ÄÚ´æÆÁÕÏ֮ǰµÄλÖã¬Ò²²»»á°ÑÇ°ÃæµÄÖ¸ÁîÅŵ½ÄÚ´æÆÁÕϵĺóÃæ;¼´ÔÚÖ´Ðе½ÄÚ´æÆÁÕÏÕâ¾äÖ¸Áîʱ£¬ÔÚËüÇ°ÃæµÄ²Ù×÷ÒѾ­È«²¿Íê³É; 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private Singleton() { } public static Singleton getInstance() { if(instance==null) { synchronized (Singleton.class) { if(instance==null) instance = new Singleton(); } } return instance; } }