鍗曚緥妯″紡鏄竴縐嶄負(fù)綾?鎻愪緵鍞竴瀹炰緥鐨勮璁℃ā寮忋傚崟渚嬫ā寮忕殑鐩殑鏄負(fù)浜嗘帶鍒跺璞＄殑鍒涘緩錛屽畠鍙互闄愬埗鍒涘緩鐨勬暟鐩負(fù)涓錛屼絾鍦ㄦ儏鍐墊敼鍙樼殑鏃跺欙紝涔熷厑璁哥伒媧誨湴鍒涘緩鏇村鐨勫璞°傚洜涓哄彧鏈変竴涓疄渚嬶紝鎵浠ヤ篃鍙湁涓濂楀疄渚嬬殑綾誨彉閲忕殑鎷瘋礉錛岃繖寰堝儚 static 鍙橀噺銆?br />
鍦?JAVA 涓紝鍗曚緥妯″紡涓嶅簲璇ヨ褰撲綔涓縐嶅疄鐜板叏灞鍙橀噺鐨勬柟娉曘傛洿澶氱殑錛屽鍚屽伐鍘傛ā寮忥紝鍗曚緥妯″紡鍏佽浣犻氳繃 紜鏌愪簺鍏堝喅鏉′歡鏄惁婊¤凍 鎴栬?浠?lazily 鏂瑰紡鎸夐渶鍒涘緩鐨勬柟寮?鏉ュ皝瑁呭拰鎺у埗鍒涘緩榪囩▼銆?br />
浜?緙栫▼瀹炵幇
1 楗ラタ妯″紡 Eager Singleton
public class MySingleton {
private static MySingleton fInstance = new MySingleton(); 
private MySingleton(){
// Construct object 
} public static MySingleton getInstance(){ reutnr fInstance; }
}2 鎳掓眽妯″紡 Lazy Singleton
public class MySingleton { private static MySingleton fInstance; private MySingleton(){ // construct object } public static synchronized MySingleton getInstance(){ if (fInstance == null){ fInstance = new MySingleton(); } return fInstance; }}鐢變簬鍙湁涓涓鏈夋瀯閫犲櫒錛屾墍浠ュ崟渚嬬被鏄棤娉曡闆嗘垚鐨勩傚熀浜庤繖涓鐐癸紝鍗曚緥妯″紡騫朵笉鏄竴涓潰鍚戝璞℃ā寮忥紝浠呬粎鏄竴涓熀浜庡璞＄殑妯″紡銆?br />
3 楗ラタ妯″紡鍩烘湰娌℃湁闂錛屾噿姹夋ā寮忓垯瀹規(guī)槗鍑虹幇涓浜涢敊璇殑緙栫▼鏂規(guī)硶
1)
// error, no synchronization on method
public static MySingleton getInstance() {
if (fInstance==null) {
fInstance = new MySingleton();
}
return fInstance;
}
2)
// Also an error, synchronization does not prevent // two calls of constructor. public static MySingleton getInstance() { if (fInstance==null) { synchronized (MySingleton.class) { fInstance = new MySingleton(); } } return fInstance; } 3) Double-checked locking 涓嶈浣跨敤
public static MySingleton getInstance(){ if (fInstance == null ){ synchronized (MySingleton.class) { if(fInstance == null){ fInstance = new MySingleton(); } } }}涓轟簡閬垮厤姣忔璋冪敤 getInstance鏂規(guī)硶鏄姄鍙栧悓姝ラ攣鐨勬秷鑰楋紝鏈変漢鍙戞槑浜?Double-checked locking 銆備絾涓嶈浣跨敤錛屽洜涓鴻繖鏍風(fēng)殑浠ｇ爜灝嗘棤娉曞湪緙栬瘧鍣ㄤ紭鍖栧拰澶氬鐞嗗櫒鍏變韓鍐呭瓨鐨勬儏鍐典笅宸ヤ綔銆傝嫢鎯寵緇嗕簡瑙ｏ紝闄勫綍涓湁瀵規(guī)鍋氳緇嗘弿榪扮殑閾炬帴銆?br />
涓?鎬葷粨
1 鍗曚緥妯″紡涓嶅簲琚互鐢紝姣斿涓嶈兘涓轟簡寰楀埌涓涓叏灞鍙橀噺鑰屽垱寤哄崟渚嬶紝鍗曚緥鏄敤浜庢帶鍒跺璞＄殑鍒涘緩榪囩▼鐨勩傚彧鏈夌湡姝ｇ殑鐩殑鏄帶鍒跺璞″垱寤虹殑榪囩▼鎴栨暟閲忔椂錛屾墠鑳借冭檻浣跨敤鍗曚緥銆傚湪澶ч儴鍒嗘儏鍐典笅錛屽崟渚嬫ā寮忔槸鏈変唬鏇挎柟妗堢殑銆傛瘮濡傜粡鍏哥殑鏁版嵁搴撹繛鎺ョ被琚互鍗曚緥瀹炵幇錛屽叾瀹炲彲浠ヤ互瀵硅薄姹犳ā寮忓疄鐜般?br />
2 浣跨敤鍗曚緥妯″紡錛屽敖閲忎嬌鐢ㄩゥ楗挎ā寮?錛屽彧鏈変綘鑳介嫻嬭繖涓被涓瀹氫細(xì)琚垱寤猴紝閭ｄ箞灝卞彲浠ヤ嬌鐢ㄩゥ楗挎ā寮忋傚鏋滐紝涓瀹氶渶瑕佹帹榪熷璞＄殑鍒涘緩鏃墮棿銆傞偅涔堜笉瑕佷嬌鐢?Double-checked locking 涔嬬被鐨勬柟娉曠殑鏉ユ彁楂樻晥鐜囷紝榪欏皢寰椾笉鍋垮け銆?br />
[1] DoubleCheckedLocking
http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
]]>