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- 閿佺殑闃熷垪灏佽瀹氫箟锛氫富瑕佹槸鎸囩瓑寰呴槦鍒楀拰鏉′欢闃熷垪锛屾槸鍚﹂渶瑕佹潯浠堕槦鍒楁垨鑰呯瓑寰呴槦鍒楀畾涔夛紵
- 閿佺殑搴曞眰瀹炵幇鎿嶄綔锛?涓昏鏄寚搴曞眰CL閿佸拰CAS鎿嶄綔锛屾槸鍚﹂渶瑕佽€冭檻鑷棆閿佹垨鑰匔AS鎿嶄綔瀹炰緥瀵硅薄鏂规硶锛?/li>
- 閿佺殑缁勫悎瀹炵幇鏂伴攣锛?涓昏鏄熀浜庣嫭鍗犻攣鍜屽叡浜攣锛屾槸鍚﹁€冭檻瀵瑰簲API鑷畾涔夋搷浣滃疄鐜帮紵
缁间笂鎵€杩帮紝澶ц嚧鍙互鏍规嵁涓婅堪杩欎簺鏂瑰悜锛屾垜浠究鍙互娓呮馃墣锔忕煡閬揓ava棰嗗煙涓悇绉嶉攣瀹炵幇鐨勫熀鏈悊璁烘椂鍜屽疄鐜版€濇兂銆?/p>
鍥?ReentrantReadWriteLock(璇诲啓閿?鐨勮璁′笌瀹炵幇
鍦↗ava棰嗗煙涓紝ReentrantReadWriteLock(璇诲啓閿?鏄拡瀵逛簬Java澶氱嚎绋嬪苟鍙戞帶鍒朵腑寮曞叆涓€涓叡浜攣瀹氫箟璇绘搷浣滀笌鐙崰閿佸畾涔夎鎿嶄綔绛夊満鏅叡鍚岀粍鍚堟瀯鎴愪竴鎶婇攣鏉ユ彁楂樺苟鍙戯紝涓昏鏄熀浜庡唴缃殑AQS鍩虹鎶借薄闃熷垪鍚屾鍣ㄥ疄鐜扮殑涓€绉嶅苟鍙戞帶鍒跺伐鍏风被銆?/p>
<br />閫氳繃ReentrantReadWriteLock绫昏兘鑾峰彇璇婚攣鍜屽啓閿侊紝瀹冪殑璇婚攣鏄彲浠ュ绾跨▼鍏变韩鐨勫叡浜攣锛岃€屽畠鐨勫啓閿佹槸鎺掍粬閿侊紝鍦ㄨ鍗犳椂涓嶅厑璁稿叾浠栫嚎绋嬪啀鎶㈠崰鎿嶄綔銆?/p>
1. 璁捐鎬濇兂
<br />涓€鑸潵璇达紝鍦ㄤ竴浜涚壒娈婄殑鍦烘櫙涓紝姣斿瀵逛簬鏁版嵁鐨勮鍜屽啓鎿嶄綔锛屼负鎻愰珮骞跺彂鎬ц兘锛屾€讳細寮曞叆鍏变韩閿佸拰鐙韩閿佹潵鍏卞悓缁勬垚涓€鎶婇攣锛岄€氬父鎯呭喌涓嬶紝鎴戜滑鎶婅繖绫婚攣鎴愪负璇诲啓閿?ReadWriteLock) 銆?lt;br />绠€鍗曟潵璇达紝灏辨槸涓昏鑰冭檻璇诲拰鍐欐搷浣滐紝璇绘搷浣滀笉浼氫慨鏀规暟鎹紝鍙互鍒╃敤澶氫釜绾跨▼杩涜璇绘搷浣滐紝涓€鑸噰鐢ㄥ叡浜攣瀹炵幇锛涜€屽啓鎿嶄綔浼氭敼鍙樻暟鎹湰韬紝鍙兘鍏佽涓€涓嚎绋嬭繘琛屾搷浣滐紝鍥犳閲囩敤鐙韩閿佸疄鐜般€?lt;br />璇诲啓閿?ReadWriteLock) 鏈€澶х殑涓€涓壒鐐瑰氨鏄湪鍐呴儴缁存姢涓€瀵归攣锛屼竴鎶婅閿?ReadLock) 锛屼竴鎶婂啓閿?WriteLock) 銆傚叾涓紝瀵逛簬绾跨▼鎸佹湁鐨勬儏鍐垫潵璇达紝绠€鍗曞彲浠ユ€荤粨涓衡€滆鍏变韩锛屽啓鐙崰鈥濄€?/p>
1.1 璇诲啓閿佺殑鍩烘湰鐞嗚
铏界劧璇诲啓閿?ReadWriteLock) 涔嬮棿鏄湁鍏崇郴鐨勶細鍚屼竴鏃跺埢涓嶅厑璁歌閿佸拰鍐欓攣鍚屾椂琚姠鍗狅紝浜岃€呬箣闂存槸浜掓枼鐨勩€?lt;br />鍋囪鐜板湪鏈塏涓嚎绋嬶紝涓昏浠嶵(1),T(2)锛?..锛屼竴鐩村埌T(N)涓嚎绋嬶紝鍦ㄨ鍐欓攣鐨勬搷浣滄儏鍐靛涓嬶紝鍏朵腑锛?/p>
- 澶氳妯″紡(澶氳鍏变韩)锛歍(N) 涓嚎绋嬪彲浠ュ悓鏃舵妸鎸佸苟鑾峰彇璇婚攣锛屽亣璁綯(1)绾跨▼鎴愬姛鑾峰彇骞舵寔鏈夎閿侊紝T(2)绾跨▼鍜屽悗缁殑T(N)涓嚎绋嬩緷鐒跺彲浠ユ垚鍔熻幏鍙栬閿侊紝鍗充娇T(1)绾跨▼娌℃湁閲婃斁鎸佹湁鐨勮閿併€?/li>
- 璇诲啓妯″紡(璇诲啓浜掓枼)锛氬亣璁綯(1)绾跨▼鎴愬姛鑾峰彇骞舵寔鏈夎閿侊紝T(2)绾跨▼鍜屽悗缁殑T(N)涓嚎绋嬩究涓嶈兘鎴愬姛鑾峰彇涓旀寔鏈夊啓閿侊紝闄ら潪T(1)绾跨▼宸茬粡閲婃斁鎸佹湁鐨勮閿併€?/li>
- 鐙啓妯″紡(鍗曞啓鐙崰)锛氬亣璁綯(1)绾跨▼鎴愬姛鑾峰彇骞舵寔鏈夊啓閿侊紝T(2)绾跨▼鍜屽悗缁殑T(N)涓嚎绋嬩究涓嶈兘鎴愬姛鑾峰彇涓旀寔鏈夎閿佸拰鍐欓攣锛屽彧鑳界瓑寰呯瓑寰匱(1)绾跨▼閲婃斁瀹屾寔鏈夌殑鍐欓攣锛屾墠鑳界户缁線涓嬫墽琛屻€?/li>
浠庝竴瀹氭剰涔変笂璁诧紝鏍规嵁璇诲啓閿佹搷浣滅殑鎯呭喌鐨勬€ц川鍒嗘瀽锛岃幏鍙栬閿佸拰鍐欓攣鐨勬潯浠跺彲浠ュぇ鑷存€荤粨涓猴細
- 鑾峰彇璇婚攣鐨勬潯浠讹細褰撳墠浠讳綍绾跨▼娌℃湁鎴愬姛鑾峰彇涓斿凡缁忔寔鏈夊啓閿佺殑鎯呭喌锛屾墠鍙兘鑾峰彇骞舵寔鏈夎閿併€?/li>
- 鑾峰彇鍐欓攣鐨勬潯浠讹細褰撳墠浠讳綍绾跨▼娌℃湁鎴愬姛鑾峰彇涓斿凡缁忔寔鏈夊啓閿佸拰璇婚攣鐨勬儏鍐碉紝鎵嶅彲鑳借幏鍙栧苟鎸佹湁鍐欓攣銆?/li>
浣嗘槸鍦ㄦ煇浜涙儏鍐典笅锛屽彲鑳藉瓨鍦ㄦ煇涓嚎绋嬪凡缁忚幏鍙栧苟鎸佹湁璇婚攣锛屽笇鏈涜兘澶熻幏鍙栧啓閿侊紝骞朵笖鍦ㄥ凡缁忛噴鏀捐閿佹椂锛岄€氬父鎯呭喌涓嬫垜浠О涔嬩负璇诲啓閿佺殑鍗囩骇銆?lt;br />褰撶劧锛屾湁鍗囩骇灏变細鏈夐檷绾э紝涓庝箣瀵瑰簲鐨勫氨鏄鍐欓攣鐨勯檷绾э紝涓昏鎻忚堪鐨勬槸鏌愪釜绾跨▼宸茬粡鑾峰彇骞舵寔鏈夊啓閿侊紝甯屾湜鑳藉鑾峰彇璇婚攣锛屽苟涓斿凡缁忛噴鏀惧啓閿併€?lt;br />涓€鑸潵璇达紝瀵逛簬璇诲啓閿佺殑鍗囩骇涓庨檷绾э紝鎴戜滑涓€鑸渶瑕佹敞鎰忕殑浠ヤ笅涓や釜闂锛屽叾涓細
- 璇诲啓閿佺殑鍗囩骇锛氭寚鐨勬槸璇婚攣鍗囩骇涓哄啓閿佺殑鎯呭喌锛岄渶瑕佹弧瓒虫煇涓嚎绋嬪繀椤绘槸鍞竴鎷ユ湁璇婚攣鐨勭嚎绋嬬殑鏉′欢锛屽惁鍒欐棤娉曞崌绾с€?/li>
- 璇诲啓閿佺殑闄嶇骇锛氭寚鐨勬槸鍐欓攣闄嶇骇涓鸿閿佺殑鎯呭喌锛屾病鏈変粈涔堟潯浠堕檺鍒讹紝鍐欓攣鏄嫭鍗犻攣锛屽叾鎸佹湁绾跨▼鏄敮涓€鐨勪笖涓嶄細瀛樺湪璇婚攣鎸佹湁绾跨▼鐨勬儏鍐碉紝鍙互鐩存帴骞虫粦鍗囩骇璇婚攣銆?/li>
1.2 璇诲啓閿佺殑瀹炵幇鎬濇兂
ReentrantReadWriteLock鏈€鏃╂槸鍦↗DK1.5鐗堟湰涓彁渚涚殑锛屼粠璁捐鎬濇兂涓婃潵鐪嬶紝涓昏鍖呮嫭鍚屾鍣ㄧ殑宸ヤ綔妯″紡锛岃閿佸拰鍐欓攣绛?涓牳蹇冭绱犮€傚叾涓細
- 瀹炵幇ReadWriteLock鎺ュ彛 锛氫富瑕佸熀浜嶳eadWriteLock鎺ュ彛API瀹炵幇瀵瑰簲鏂规硶锛屼富瑕佹槸瀹炵幇writeLock()鏂规硶鍜宺eadLock() 鏂规硶锛屽叾涓瓀riteLock()鏂规硶琛ㄧず鑾峰彇鍐欓攣锛宺eadLock() 鏂规硶琛ㄧず鑾峰彇璇婚攣銆?/li>
- 鍚屾鍣ㄧ殑宸ヤ綔妯″紡锛氬熀浜嶢QS鍩虹鎶借薄闃熷垪鍚屾鍣ㄥ皝瑁呭唴缃疄鐜颁竴涓潤鎬佺殑鍐呯疆鍚屾鍣ㄦ娊璞＄被锛岀劧鍚庡熀浜庤繖涓娊璞＄被鍒嗗埆瀹炵幇浜嗗叕骞冲悓姝ュ櫒鍜岄潪鍏钩鍚屾鍣紝鐢ㄦ潵鎸囧畾鍜屾弿杩板悓姝ュ櫒宸ヤ綔妯″紡鏄叕骞虫ā寮忚繕鏄潪鍏钩妯″紡銆?/li>
- 鍏钩/闈炲叕骞虫ā寮忥細涓昏鎻忚堪鐨勬槸澶氫釜绾跨▼鍦ㄥ悓鏃惰幏鍙栭攣鏃舵槸鍚︽寜鐓у厛鍒板厛寰楃殑椤哄簭鑾峰彇閿侊紝濡傛灉鏄垯涓哄叕骞虫ā寮忥紝鍚﹀垯涓洪潪鍏钩妯″紡銆?/li>
- 鍐呯疆涓や釜闈欐€佸叕鏈夊唴閮ㄧ被锛氬畾涔変簡璇婚攣鍜屽啓閿侀潤鎬佸叕鏈夊唴閮ㄧ被锛屽苟涓旈兘鏀寔鍏钩/闈炲叕骞虫ā寮忥紝鏈川閮芥槸鍩轰簬AQS鍩虹鎶借薄闃熷垪鍚屾鍣ㄥ疄鐜般€?/li>
- 缁存姢鍏变韩鐘舵€佸彉閲忥細 涓昏鏄熀浜庝竴涓狝QS鍩虹鎶借薄闃熷垪鍚屾鍣ㄦ潵瀹炵幇璇婚攣鍜屽啓閿侊紝瑕佹眰鍏辩敤涓€涓叡浜姸鎬佸彉閲忋€?/li>
2. 鍩烘湰瀹炵幇
鍦≧eentrantReadWriteLock绫诲湪JDK1.8鐗堟湰涓紝瀵逛簬ReentrantReadWriteLock鐨勫熀鏈疄鐜板涓嬶細
public class ReentrantReadWriteLock
implements ReadWriteLock, java.io.Serializable {
private static final long serialVersionUID = -6992448646407690164L;
/** ReentrantReadWriteLock閿?鍐呴儴ReadLock绫?*/
private final ReentrantReadWriteLock.ReadLock readerLock;
/** ReentrantReadWriteLock閿?鍐呴儴WriteLock绫?*/
private final ReentrantReadWriteLock.WriteLock writerLock;
/** ReentrantReadWriteLock閿?鍐呴儴鍚屾鍣?*/
final Sync sync;
/** ReentrantReadWriteLock閿?鍩轰簬AQS灏佽鍐呴儴鍚屾鍣?*/
abstract static class Sync extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 6317671515068378041L;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?begin*/
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍏变韩鐘舵€佺Щ鍔ㄤ綅鏁?6 */
static final int SHARED_SHIFT = 16;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣姣忔鍔犻攣鐨勭姸鎬佸ぇ灏?/
static final int SHARED_UNIT = (1 << SHARED_SHIFT);
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣姣忔鍔犻攣鐨勬渶澶ф鏁?/
static final int MAX_COUNT = (1 << SHARED_SHIFT) - 1;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍐欓攣鐨勬帺鐮?/
static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鏈湴瀛樺偍璇婚攣娆℃暟*/
private transient ThreadLocalHoldCounter readHolds;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣鐨勭姸鎬佺爜鍊?/
private transient HoldCounter cachedHoldCounter;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?绾跨▼鍙橀噺*/
private transient Thread firstReader = null;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?棣栨璇婚攣娆℃暟*/
private transient int firstReaderHoldCount;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?end*/
Sync() {
readHolds = new ThreadLocalHoldCounter();
setState(getState()); // ensures visibility of readHolds
}
/** ReentrantReadWriteLock閿?璇婚攣鏍囪*/
abstract boolean readerShouldBlock();
/** ReentrantReadWriteLock閿?璇婚攣鏍囪*/
abstract boolean writerShouldBlock();
//... 鍏朵粬浠ｇ爜
}
/** ReentrantReadWriteLock閿?鏃犲弬鏁版瀯閫?榛樿闈炲叕骞虫ā寮? */
public ReentrantReadWriteLock() {
this(false);
}
/** ReentrantReadWriteLock閿?鏈夊弬鏁版瀯閫?鍙€夊叕骞?闈炲叕骞虫ā寮? */
public ReentrantReadWriteLock(boolean fair) {
sync = fair new FairSync() : new NonfairSync();
readerLock = new ReadLock(this);
writerLock = new WriteLock(this);
}
/** ReentrantReadWriteLock閿?鑾峰彇鍐欓攣 */
public ReentrantReadWriteLock.WriteLock writeLock() { return writerLock; }
/** ReentrantReadWriteLock閿?鑾峰彇璇婚攣 */
public ReentrantReadWriteLock.ReadLock readLock() { return readerLock; }
/** ReentrantReadWriteLock閿?瀹炰緥鍖朥nsafe鏀寔 */
private static final sun.misc.Unsafe UNSAFE;
/** ReentrantReadWriteLock閿?绾跨▼鍋忕Щ閲?*/
private static final long TID_OFFSET;
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
static final long getThreadId(Thread thread) {
return UNSAFE.getLongVolatile(thread, TID_OFFSET);
}
/** ReentrantReadWriteLock閿?鍙嶅皠鏈哄埗瀹炰緥鍖朥nsafe */
static {
try {
UNSAFE = sun.misc.Unsafe.getUnsafe();
Class<?> tk = Thread.class;
TID_OFFSET = UNSAFE.objectFieldOffset
(tk.getDeclaredField("tid"));
} catch (Exception e) {
throw new Error(e);
}
}
}
- 鍐呴儴鍚屾鍣細鍩轰簬AQS鍩虹鍚屾鍣ㄥ皝瑁呭拰瀹氫箟浜嗕竴涓潤鎬佸唴閮⊿ync鎶借薄绫?/li>
- 鍚屾鍣ㄥ伐浣滄ā寮忥細鎻愪緵浜?2涓瀯閫犳柟娉曪紝鍏朵腑鏃犲弬鏁版瀯閫犳柟娉曡〃绀虹殑鏄粯璁ょ殑宸ヤ綔妯″紡锛屾湁鍙傛暟鏋勯€犳柟娉曚富瑕佷緷鎹弬鏁版潵瀹炵幇鎸囧畾鐨勫伐浣滄ā寮?/li>
- 鍏钩/闈炲叕骞虫ā寮忥細涓昏鏄熀浜嶴ync鎶借薄绫诲皝瑁匩onfairSync闈炲叕骞冲悓姝ュ櫒鍜屽皝瑁匩onfairSync闈炲叕骞冲悓姝ュ櫒鏉ュ疄鐜般€?/li>
- 鍐呯疆涓や釜鍐呴儴绫伙細涓昏鏄疄鐜颁簡ReadLock绫诲拰WriteLock绫伙紝鍏朵腑ReadLock绫诲搴旂潃璇婚攣锛學riteLock绫诲搴旂潃鍐欓攣銆?/li>
2.1 鍩轰簬AQS鍚屾鍣ㄥ皝瑁呴潤鎬佸唴閮⊿ync鎶借薄绫?/h4>
/** ReentrantReadWriteLock閿?鍩轰簬AQS灏佽鍐呴儴鍚屾鍣?*/
abstract static class Sync extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 6317671515068378041L;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?begin */
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍏变韩鐘舵€佺Щ鍔ㄤ綅鏁?6 */
static final int SHARED_SHIFT = 16;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣姣忔鍔犻攣鐨勭姸鎬佸ぇ灏?/
static final int SHARED_UNIT = (1 << SHARED_SHIFT);
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣姣忔鍔犻攣鐨勬渶澶ф鏁?/
static final int MAX_COUNT = (1 << SHARED_SHIFT) - 1;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍐欓攣鐨勬帺鐮?/
static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鏈湴瀛樺偍璇婚攣娆℃暟*/
private transient ThreadLocalHoldCounter readHolds;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣鐨勭姸鎬佺爜鍊?/
private transient HoldCounter cachedHoldCounter;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?绾跨▼鍙橀噺*/
private transient Thread firstReader = null;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?棣栨璇婚攣娆℃暟*/
private transient int firstReaderHoldCount;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?end*/
Sync() {
readHolds = new ThreadLocalHoldCounter();
setState(getState()); // ensures visibility of readHolds
}
/** ReentrantReadWriteLock閿?璇婚攣鏍囪*/
abstract boolean readerShouldBlock();
/** ReentrantReadWriteLock閿?璇婚攣鏍囪*/
abstract boolean writerShouldBlock();
/** ReentrantReadWriteLock閿?鐙崰妯″紡鑾峰彇璇婚攣*/
protected final boolean tryRelease(int releases) {
if (!isHeldExclusively())
throw new IllegalMonitorStateException();
int nextc = getState() - releases;
boolean free = exclusiveCount(nextc) == 0;
if (free)
setExclusiveOwnerThread(null);
setState(nextc);
return free;
}
/** ReentrantReadWriteLock閿?鐙崰妯″紡閲婃斁閿?/
protected final boolean tryAcquire(int acquires) {
Thread current = Thread.currentThread();
int c = getState();
int w = exclusiveCount(c);
if (c != 0) {
// (Note: if c != 0 and w == 0 then shared count != 0)
if (w == 0 || current != getExclusiveOwnerThread())
return false;
if (w + exclusiveCount(acquires) > MAX_COUNT)
throw new Error("Maximum lock count exceeded");
// Reentrant acquire
setState(c + acquires);
return true;
}
if (writerShouldBlock() ||
!compareAndSetState(c, c + acquires))
return false;
setExclusiveOwnerThread(current);
return true;
}
/** ReentrantReadWriteLock閿?鍏变韩妯″紡閲婃斁閿?/
protected final boolean tryReleaseShared(int unused) {
Thread current = Thread.currentThread();
if (firstReader == current) {
// assert firstReaderHoldCount > 0;
if (firstReaderHoldCount == 1)
firstReader = null;
else
firstReaderHoldCount--;
} else {
HoldCounter rh = cachedHoldCounter;
if (rh == null || rh.tid != getThreadId(current))
rh = readHolds.get();
int count = rh.count;
if (count <= 1) {
readHolds.remove();
if (count <= 0)
throw unmatchedUnlockException();
}
--rh.count;
}
for (;;) {
int c = getState();
int nextc = c - SHARED_UNIT;
if (compareAndSetState(c, nextc))
return nextc == 0;
}
}
/** ReentrantReadWriteLock閿?鍏变韩妯″紡鑾峰彇閿?/
protected final int tryAcquireShared(int unused) {
Thread current = Thread.currentThread();
int c = getState();
if (exclusiveCount(c) != 0 &&
getExclusiveOwnerThread() != current)
return -1;
int r = sharedCount(c);
if (!readerShouldBlock() &&
r < MAX_COUNT &&
compareAndSetState(c, c + SHARED_UNIT)) {
if (r == 0) {
firstReader = current;
firstReaderHoldCount = 1;
} else if (firstReader == current) {
firstReaderHoldCount++;
} else {
HoldCounter rh = cachedHoldCounter;
if (rh == null || rh.tid != getThreadId(current))
cachedHoldCounter = rh = readHolds.get();
else if (rh.count == 0)
readHolds.set(rh);
rh.count++;
}
return 1;
}
return fullTryAcquireShared(current);
}
/** ReentrantReadWriteLock閿?鍏变韩妯″紡鑾峰彇閿?/
final int fullTryAcquireShared(Thread current) {
HoldCounter rh = null;
for (;;) {
int c = getState();
if (exclusiveCount(c) != 0) {
if (getExclusiveOwnerThread() != current)
return -1;
// else we hold the exclusive lock; blocking here
// would cause deadlock.
} else if (readerShouldBlock()) {
// Make sure we're not acquiring read lock reentrantly
if (firstReader == current) {
// assert firstReaderHoldCount > 0;
} else {
if (rh == null) {
rh = cachedHoldCounter;
if (rh == null || rh.tid != getThreadId(current)) {
rh = readHolds.get();
if (rh.count == 0)
readHolds.remove();
}
}
if (rh.count == 0)
return -1;
}
}
if (sharedCount(c) == MAX_COUNT)
throw new Error("Maximum lock count exceeded");
if (compareAndSetState(c, c + SHARED_UNIT)) {
if (sharedCount(c) == 0) {
firstReader = current;
firstReaderHoldCount = 1;
} else if (firstReader == current) {
firstReaderHoldCount++;
} else {
if (rh == null)
rh = cachedHoldCounter;
if (rh == null || rh.tid != getThreadId(current))
rh = readHolds.get();
else if (rh.count == 0)
readHolds.set(rh);
rh.count++;
cachedHoldCounter = rh; // cache for release
}
return 1;
}
}
}
/** ReentrantReadWriteLock閿?鍒ゆ柇鏄惁鐙崰妯″紡*/
protected final boolean isHeldExclusively() {
return getExclusiveOwnerThread() == Thread.currentThread();
}
// Methods relayed to outer class
/** ReentrantReadWriteLock閿?瀹氫箟鏉′欢鍙橀噺*/
final ConditionObject newCondition() {
return new ConditionObject();
}
/** ReentrantReadWriteLock閿?鑾峰彇褰撳墠閿佺殑鎸佹湁鑰?/
final Thread getOwner() {
// Must read state before owner to ensure memory consistency
return ((exclusiveCount(getState()) == 0) ?
null :
getExclusiveOwnerThread());
}
/** ReentrantReadWriteLock閿?鑾峰彇璇婚攣娆℃暟缁熻*/
final int getReadLockCount() {
return sharedCount(getState());
}
/** ReentrantReadWriteLock閿?鍒ゆ柇鏄惁鏄啓閿?/
final boolean isWriteLocked() {
return exclusiveCount(getState()) != 0;
}
/** ReentrantReadWriteLock閿?鑾峰彇鍐欓攣鎸佹湁娆℃暟缁熻*/
final int getWriteHoldCount() {
return isHeldExclusively() exclusiveCount(getState()) : 0;
}
/** ReentrantReadWriteLock閿?鑾峰彇璇婚攣娆℃寔鏈夋暟缁熻*/
final int getReadHoldCount() {
if (getReadLockCount() == 0)
return 0;
Thread current = Thread.currentThread();
if (firstReader == current)
return firstReaderHoldCount;
HoldCounter rh = cachedHoldCounter;
if (rh != null && rh.tid == getThreadId(current))
return rh.count;
int count = readHolds.get().count;
if (count == 0) readHolds.remove();
return count;
}
/** ReentrantReadWriteLock閿?鑾峰彇璇婚攣*/
final boolean tryReadLock() {
Thread current = Thread.currentThread();
for (;;) {
int c = getState();
if (exclusiveCount(c) != 0 &&
getExclusiveOwnerThread() != current)
return false;
int r = sharedCount(c);
if (r == MAX_COUNT)
throw new Error("Maximum lock count exceeded");
if (compareAndSetState(c, c + SHARED_UNIT)) {
if (r == 0) {
firstReader = current;
firstReaderHoldCount = 1;
} else if (firstReader == current) {
firstReaderHoldCount++;
} else {
HoldCounter rh = cachedHoldCounter;
if (rh == null || rh.tid != getThreadId(current))
cachedHoldCounter = rh = readHolds.get();
else if (rh.count == 0)
readHolds.set(rh);
rh.count++;
}
return true;
}
}
}
/** ReentrantReadWriteLock閿?鑾峰彇鍐欓攣*/
final boolean tryWriteLock() {
Thread current = Thread.currentThread();
int c = getState();
if (c != 0) {
int w = exclusiveCount(c);
if (w == 0 || current != getExclusiveOwnerThread())
return false;
if (w == MAX_COUNT)
throw new Error("Maximum lock count exceeded");
}
if (!compareAndSetState(c, c + 1))
return false;
setExclusiveOwnerThread(current);
return true;
}
/** ReentrantReadWriteLock閿?娴佸鐞?/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
readHolds = new ThreadLocalHoldCounter();
setState(0); // reset to unlocked state
}
/** ReentrantReadWriteLock閿?鑾峰彇鐘舵€?/
final int getCount() { return getState(); }
}
- 瀹炵幇鏂瑰紡锛?涓昏鏄熀浜嶢QS鍩虹鍚屾鍣ㄦ潵瀹炵幇锛屽叾涓皝瑁呮娊璞′簡readerShouldBlock()鏂规硶鍜寃riterShouldBlock()鏂规硶锛岀敤浜庢爣璁板綋鍓嶈姹傜殑绾跨▼鏄幏鍙栦粈涔堢被鍨嬬殑閿併€傚叾涓細
- readerShouldBlock()鏂规硶锛氫緷鎹爣璁拌繑鍥炵殑鏄痶rue锛屾爣璁扮嚎绋嬭幏鍙栫殑鏄疪eadLock閿?/li>
- writerShouldBlock()鏂规硶锛氫緷鎹爣璁拌繑鍥炵殑鏄痶rue锛屾爣璁扮嚎绋嬭幏鍙栫殑鏄疻riteLock閿?/li>
- 缁存姢鍏辩敤鐘舵€佸彉閲? 瀵逛簬鍏变韩鐘舵€佸彉閲忕殑瀹炵幇锛屼富瑕佹槸鍦ㄥ唴閮ㄧ殑鍚屾鍣ㄤ腑Sync绫讳腑瀹氫箟HoldCounter绫诲拰ThreadLocalHoldCounter绫诲疄鐜扮殑锛屽叾涓畾涔変簡涓€鍫嗗父閲忥紝缁熻璇诲啓閿佺姸鎬佸€肩殑sharedCount()鏂规硶鍜宔xclusiveCount()鏂规硶銆?/li>
- 璇诲啓閿佺殑涓昏鏂规硶锛?涓昏鏄彁渚涗簡tryReadLock()鏂规硶鍜宼ryWriteLock()鏂规硶锛屽叾涓細
- tryReadLock()鏂规硶锛氳幏鍙栬閿佹柟娉曪紝鏍稿績澶勭悊鏄嚜鏃?compareAndSetState()鏂规硶鏉ュ鐞?/li>
- tryWriteLock()鏂规硶锛氳幏鍙栧啓閿佹柟娉曪紝鏍稿績澶勭悊鏄€氳繃compareAndSetState()鏂规硶鏉ュ鐞?/li>
- 璇诲啓閿佺殑鑾峰彇鏂瑰紡锛氬熀浜嶢QS鍩虹鍚屾鍣ㄦ潵瀹炵幇瀵逛簬鍏变韩妯″紡鍜岀嫭浜ā寮忎袱绉嶆儏鍐碉紝閮芥彁渚涗簡瀵瑰簲鐨勬柟娉曘€傚叾涓細
- tryAcquire()鏂规硶锛氱嫭浜ā寮忚幏鍙栭攣鏂规硶锛岃繖閲屼富瑕侀拡瀵筗riteLock閿侊紝鏍稿績澶勭悊鏄€氳繃AQS鍩虹鍚屾鍣ㄤ腑compareAndSetState()鏂规硶鏉ュ鐞嗭紝瀹炵幇鐘舵€佸彉閲忕殑鎿嶄綔
- tryAcquireShared() 鏂规硶锛氬叡浜ā寮忚幏鍙栭攣鏂规硶锛岃繖閲屼富瑕佸搴擱eadLock閿侊紝鏍稿績澶勭悊鏄€氳繃AQS鍩虹鍚屾鍣ㄤ腑compareAndSetState()鏂规硶鏉ュ鐞嗭紝瀹炵幇鐘舵€佸彉閲忕殑鎿嶄綔
- 璇诲啓閿佺殑閲婃斁鏂瑰紡锛氬熀浜嶢QS鍩虹鍚屾鍣ㄦ潵瀹炵幇瀵逛簬鍏变韩妯″紡鍜岀嫭浜ā寮忎袱绉嶆儏鍐碉紝閮芥彁渚涗簡瀵瑰簲鐨勬柟娉曘€傚叾涓細
- tryRelease(int releases) 鏂规硶锛氱嫭浜ā寮忛噴鏀鹃攣鏂规硶
- tryReleaseShared(int unused) 鏂规硶锛氬叡浜ā寮忛噴鏀鹃攣鏂规硶锛屾牳蹇冨鐞嗘槸鑷棆+compareAndSetState()鏂规硶鏉ュ鐞?/li>
- 鍏朵粬鏂规硶锛氫富瑕佽繕鎻愪緵浜嗕竴浜涙瘮杈冨父瑙勭殑鏂规硶锛屽叾涓細
- getCount() 鏂规硶锛氫富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄦ潵鑾峰彇鐘舵€佸彉閲?/li>
- getOwner()鏂规硶锛氫富瑕佹槸鐢ㄤ簬鑾峰彇褰撳墠閿佺殑鎸佹湁鑰咃紝涓€鑸槸绾跨▼瀵硅薄锛屾牴鎹?em>exclusiveCount(getState()) == 0鏉ュ垽鏂紝鏉′欢鎴愮珛灏遍粯璁や负null; 鍚﹀垯锛岄€氳繃AQS鍩虹鍚屾鍣ㄤ腑鐨刧etExclusiveOwnerThread()鏂规硶鏉ヨ幏鍙栥€?/li>
- getReadLockCount() 鏂规硶锛氱敤浜庤幏鍙栨煇涓嚎绋嬪浜嶳eadLock閿佺殑鏁伴噺锛屼富瑕佹槸缁熻娆℃暟
- isWriteLocked() 鏂规硶锛氱敤浜庡垽鏂嚎绋嬫槸鍚﹀凡缁忚幏鍙栧苟鎸佹湁WriteLock閿?/li>
- getWriteHoldCount()鏂规硶锛氱敤浜庤幏鍙栫嚎绋嬪浜嶹riteLock閿佺殑鎸佹湁鎯呭喌锛屼富瑕佹槸缁熻娆℃暟
- getReadHoldCount() 鏂规硶锛氱敤浜庤幏鍙栫嚎绋嬪浜嶹riteLock閿佺殑鎸佹湁鎯呭喌锛屼富瑕佹槸缁熻娆℃暟
- isHeldExclusively() 鏂规硶锛氱敤浜庡垽鏂槸鍚︾嫭鍗犳ā寮?/li>
- unmatchedUnlockException()鏂规硶锛氬皝瑁呬竴涓紓甯稿鐞嗕俊鎭紝涓昏鏄寚瀹欼llegalMonitorStateException
2.2 鍩轰簬Sync鎶借薄绫诲皝瑁呭叡浜姸鎬佸彉閲?/h4>
/** ReentrantReadWriteLock閿?鍩轰簬AQS灏佽鍐呴儴鍚屾鍣?*/
abstract static class Sync extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 6317671515068378041L;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?begin*/
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍏变韩鐘舵€佺Щ鍔ㄤ綅鏁?6 */
static final int SHARED_SHIFT = 16;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣姣忔鍔犻攣鐨勭姸鎬佸ぇ灏?/
static final int SHARED_UNIT = (1 << SHARED_SHIFT);
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣姣忔鍔犻攣鐨勬渶澶ф鏁?/
static final int MAX_COUNT = (1 << SHARED_SHIFT) - 1;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍐欓攣鐨勬帺鐮?/
static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鏈湴瀛樺偍璇婚攣娆℃暟*/
private transient ThreadLocalHoldCounter readHolds;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣鐨勭姸鎬佺爜鍊?/
private transient HoldCounter cachedHoldCounter;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?绾跨▼鍙橀噺*/
private transient Thread firstReader = null;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?棣栨璇婚攣娆℃暟*/
private transient int firstReaderHoldCount;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?end*/
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鏋勯€犳柟娉?/
Sync() {
readHolds = new ThreadLocalHoldCounter();
setState(getState()); // ensures visibility of readHolds
}
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣鐨勭姸鎬佺爜鍊?/
static int sharedCount(int c) { return c >>> SHARED_SHIFT; }
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍐欓攣鐨勭姸鎬佺爜鍊?/
static int exclusiveCount(int c) { return c & EXCLUSIVE_MASK; }
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲?缁熻璁℃暟鍣?*/
static final class HoldCounter {
int count = 0;
// Use id, not reference, to avoid garbage retention
final long tid = getThreadId(Thread.currentThread());
}
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲?鏈湴瀛樺偍缁熻鍓湰 */
static final class ThreadLocalHoldCounter
extends ThreadLocal<HoldCounter> {
public HoldCounter initialValue() {
return new HoldCounter();
}
}
//... 鍏朵粬浠ｇ爜
}
- 瀹炵幇鏂瑰紡锛?涓昏鏄湪鍐呴儴鐨勫悓姝ュ櫒涓璖ync绫讳腑瀹氫箟HoldCounter绫诲拰ThreadLocalHoldCounter绫诲疄鐜扮殑銆傚叾涓細
- HoldCounter绫伙細涓昏鏄畾涔変簡涓€涓鏁板櫒count鍜屼竴涓嚎绋嬬紪鍙穞id鍙橀噺锛屽叾涓鏁板櫒count榛樿鍊间负0锛岃€岀嚎绋嬬紪鍙穞id閫氳繃getThreadId(Thread.currentThread())鏂规硶鏉ヨ幏鍙栥€?/li>
- ThreadLocalHoldCounter绫伙細鍩轰簬ThreadLocal鍜孒oldCounter鏉ユ彁渚涗簡initialValue()鏂规硶锛屼富瑕佹槸瀹炰緥璇濆寲HoldCounter绫汇€?/li>
- 鍏辩敤鐘舵€佸父閲忥細涓昏鏄湪鍐呴儴鐨勫悓姝ュ櫒涓璖ync绫讳腑瀹氫箟浜嗙浉鍏冲父閲忥紝鍏朵腑锛?
- SHARED_SHIFT锛?涓昏鐢ㄤ簬鏍囪浣嶇Щ鐨勪綅鏁帮紝榛樿閲囩敤 鏁村瀷16浣?/li>
- SHARED_UNIT锛氳〃绀鸿閿佸姞閿佹搷浣滄椂姣忔瀵瑰簲鐨勭姸鎬佸€煎ぇ灏忥紝灏?宸︾Щ鍔?6浣嶆濂藉搴旈珮16浣嶇殑1.
- MAX_COUNT锛氳〃绀鸿閿佽兘鎵ц鍔犻攣鎿嶄綔鐨勬渶澶ф鏁帮紝涓€鑸负16涓簩杩涘埗鐨?
- EXCLUSIVE_MASK锛氬啓閿佺殑鎺╃爜,涓€鑸负16涓簩杩涘埗鐨?
- 涓昏鏂规硶锛氫富瑕佹彁渚涗簡缁熻璇诲啓閿佺姸鎬佸€肩殑sharedCount()鏂规硶鍜宔xclusiveCount()鏂规硶锛屽叾涓細
- sharedCount()鏂规硶锛氳幏鍙栬閿佺殑鐘舵€佺爜鍊硷紝鏍规嵁鐩爣鍙傛暟(targetParam)宸︾Щ16浣嶅嵆鍙緱鍒?/li>
- exclusiveCount()鏂规硶锛氳幏鍙栧啓閿佺殑鐘舵€佺爜鍊硷紝鏍规嵁鐩爣鍙傛暟(targetParam)鍚屽啓閿佺殑鎺╃爜鍋氶€昏緫涓?&)杩愮畻渚垮彲寰楀埌銆?/li>
/** ReentrantReadWriteLock閿?鍩轰簬AQS灏佽鍐呴儴鍚屾鍣?*/
abstract static class Sync extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 6317671515068378041L;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?begin */
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍏变韩鐘舵€佺Щ鍔ㄤ綅鏁?6 */
static final int SHARED_SHIFT = 16;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣姣忔鍔犻攣鐨勭姸鎬佸ぇ灏?/
static final int SHARED_UNIT = (1 << SHARED_SHIFT);
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣姣忔鍔犻攣鐨勬渶澶ф鏁?/
static final int MAX_COUNT = (1 << SHARED_SHIFT) - 1;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍐欓攣鐨勬帺鐮?/
static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鏈湴瀛樺偍璇婚攣娆℃暟*/
private transient ThreadLocalHoldCounter readHolds;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣鐨勭姸鎬佺爜鍊?/
private transient HoldCounter cachedHoldCounter;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?绾跨▼鍙橀噺*/
private transient Thread firstReader = null;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?棣栨璇婚攣娆℃暟*/
private transient int firstReaderHoldCount;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?end*/
Sync() {
readHolds = new ThreadLocalHoldCounter();
setState(getState()); // ensures visibility of readHolds
}
/** ReentrantReadWriteLock閿?璇婚攣鏍囪*/
abstract boolean readerShouldBlock();
/** ReentrantReadWriteLock閿?璇婚攣鏍囪*/
abstract boolean writerShouldBlock();
/** ReentrantReadWriteLock閿?鐙崰妯″紡鑾峰彇璇婚攣*/
protected final boolean tryRelease(int releases) {
if (!isHeldExclusively())
throw new IllegalMonitorStateException();
int nextc = getState() - releases;
boolean free = exclusiveCount(nextc) == 0;
if (free)
setExclusiveOwnerThread(null);
setState(nextc);
return free;
}
/** ReentrantReadWriteLock閿?鐙崰妯″紡閲婃斁閿?/
protected final boolean tryAcquire(int acquires) {
Thread current = Thread.currentThread();
int c = getState();
int w = exclusiveCount(c);
if (c != 0) {
// (Note: if c != 0 and w == 0 then shared count != 0)
if (w == 0 || current != getExclusiveOwnerThread())
return false;
if (w + exclusiveCount(acquires) > MAX_COUNT)
throw new Error("Maximum lock count exceeded");
// Reentrant acquire
setState(c + acquires);
return true;
}
if (writerShouldBlock() ||
!compareAndSetState(c, c + acquires))
return false;
setExclusiveOwnerThread(current);
return true;
}
/** ReentrantReadWriteLock閿?鍏变韩妯″紡閲婃斁閿?/
protected final boolean tryReleaseShared(int unused) {
Thread current = Thread.currentThread();
if (firstReader == current) {
// assert firstReaderHoldCount > 0;
if (firstReaderHoldCount == 1)
firstReader = null;
else
firstReaderHoldCount--;
} else {
HoldCounter rh = cachedHoldCounter;
if (rh == null || rh.tid != getThreadId(current))
rh = readHolds.get();
int count = rh.count;
if (count <= 1) {
readHolds.remove();
if (count <= 0)
throw unmatchedUnlockException();
}
--rh.count;
}
for (;;) {
int c = getState();
int nextc = c - SHARED_UNIT;
if (compareAndSetState(c, nextc))
return nextc == 0;
}
}
/** ReentrantReadWriteLock閿?鍏变韩妯″紡鑾峰彇閿?/
protected final int tryAcquireShared(int unused) {
Thread current = Thread.currentThread();
int c = getState();
if (exclusiveCount(c) != 0 &&
getExclusiveOwnerThread() != current)
return -1;
int r = sharedCount(c);
if (!readerShouldBlock() &&
r < MAX_COUNT &&
compareAndSetState(c, c + SHARED_UNIT)) {
if (r == 0) {
firstReader = current;
firstReaderHoldCount = 1;
} else if (firstReader == current) {
firstReaderHoldCount++;
} else {
HoldCounter rh = cachedHoldCounter;
if (rh == null || rh.tid != getThreadId(current))
cachedHoldCounter = rh = readHolds.get();
else if (rh.count == 0)
readHolds.set(rh);
rh.count++;
}
return 1;
}
return fullTryAcquireShared(current);
}
/** ReentrantReadWriteLock閿?鍏变韩妯″紡鑾峰彇閿?/
final int fullTryAcquireShared(Thread current) {
HoldCounter rh = null;
for (;;) {
int c = getState();
if (exclusiveCount(c) != 0) {
if (getExclusiveOwnerThread() != current)
return -1;
// else we hold the exclusive lock; blocking here
// would cause deadlock.
} else if (readerShouldBlock()) {
// Make sure we're not acquiring read lock reentrantly
if (firstReader == current) {
// assert firstReaderHoldCount > 0;
} else {
if (rh == null) {
rh = cachedHoldCounter;
if (rh == null || rh.tid != getThreadId(current)) {
rh = readHolds.get();
if (rh.count == 0)
readHolds.remove();
}
}
if (rh.count == 0)
return -1;
}
}
if (sharedCount(c) == MAX_COUNT)
throw new Error("Maximum lock count exceeded");
if (compareAndSetState(c, c + SHARED_UNIT)) {
if (sharedCount(c) == 0) {
firstReader = current;
firstReaderHoldCount = 1;
} else if (firstReader == current) {
firstReaderHoldCount++;
} else {
if (rh == null)
rh = cachedHoldCounter;
if (rh == null || rh.tid != getThreadId(current))
rh = readHolds.get();
else if (rh.count == 0)
readHolds.set(rh);
rh.count++;
cachedHoldCounter = rh; // cache for release
}
return 1;
}
}
}
/** ReentrantReadWriteLock閿?鍒ゆ柇鏄惁鐙崰妯″紡*/
protected final boolean isHeldExclusively() {
return getExclusiveOwnerThread() == Thread.currentThread();
}
// Methods relayed to outer class
/** ReentrantReadWriteLock閿?瀹氫箟鏉′欢鍙橀噺*/
final ConditionObject newCondition() {
return new ConditionObject();
}
/** ReentrantReadWriteLock閿?鑾峰彇褰撳墠閿佺殑鎸佹湁鑰?/
final Thread getOwner() {
// Must read state before owner to ensure memory consistency
return ((exclusiveCount(getState()) == 0) ?
null :
getExclusiveOwnerThread());
}
/** ReentrantReadWriteLock閿?鑾峰彇璇婚攣娆℃暟缁熻*/
final int getReadLockCount() {
return sharedCount(getState());
}
/** ReentrantReadWriteLock閿?鍒ゆ柇鏄惁鏄啓閿?/
final boolean isWriteLocked() {
return exclusiveCount(getState()) != 0;
}
/** ReentrantReadWriteLock閿?鑾峰彇鍐欓攣鎸佹湁娆℃暟缁熻*/
final int getWriteHoldCount() {
return isHeldExclusively() exclusiveCount(getState()) : 0;
}
/** ReentrantReadWriteLock閿?鑾峰彇璇婚攣娆℃寔鏈夋暟缁熻*/
final int getReadHoldCount() {
if (getReadLockCount() == 0)
return 0;
Thread current = Thread.currentThread();
if (firstReader == current)
return firstReaderHoldCount;
HoldCounter rh = cachedHoldCounter;
if (rh != null && rh.tid == getThreadId(current))
return rh.count;
int count = readHolds.get().count;
if (count == 0) readHolds.remove();
return count;
}
/** ReentrantReadWriteLock閿?鑾峰彇璇婚攣*/
final boolean tryReadLock() {
Thread current = Thread.currentThread();
for (;;) {
int c = getState();
if (exclusiveCount(c) != 0 &&
getExclusiveOwnerThread() != current)
return false;
int r = sharedCount(c);
if (r == MAX_COUNT)
throw new Error("Maximum lock count exceeded");
if (compareAndSetState(c, c + SHARED_UNIT)) {
if (r == 0) {
firstReader = current;
firstReaderHoldCount = 1;
} else if (firstReader == current) {
firstReaderHoldCount++;
} else {
HoldCounter rh = cachedHoldCounter;
if (rh == null || rh.tid != getThreadId(current))
cachedHoldCounter = rh = readHolds.get();
else if (rh.count == 0)
readHolds.set(rh);
rh.count++;
}
return true;
}
}
}
/** ReentrantReadWriteLock閿?鑾峰彇鍐欓攣*/
final boolean tryWriteLock() {
Thread current = Thread.currentThread();
int c = getState();
if (c != 0) {
int w = exclusiveCount(c);
if (w == 0 || current != getExclusiveOwnerThread())
return false;
if (w == MAX_COUNT)
throw new Error("Maximum lock count exceeded");
}
if (!compareAndSetState(c, c + 1))
return false;
setExclusiveOwnerThread(current);
return true;
}
/** ReentrantReadWriteLock閿?娴佸鐞?/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
readHolds = new ThreadLocalHoldCounter();
setState(0); // reset to unlocked state
}
/** ReentrantReadWriteLock閿?鑾峰彇鐘舵€?/
final int getCount() { return getState(); }
}
- readerShouldBlock()鏂规硶锛氫緷鎹爣璁拌繑鍥炵殑鏄痶rue锛屾爣璁扮嚎绋嬭幏鍙栫殑鏄疪eadLock閿?/li>
- writerShouldBlock()鏂规硶锛氫緷鎹爣璁拌繑鍥炵殑鏄痶rue锛屾爣璁扮嚎绋嬭幏鍙栫殑鏄疻riteLock閿?/li>
- tryReadLock()鏂规硶锛氳幏鍙栬閿佹柟娉曪紝鏍稿績澶勭悊鏄嚜鏃?compareAndSetState()鏂规硶鏉ュ鐞?/li>
- tryWriteLock()鏂规硶锛氳幏鍙栧啓閿佹柟娉曪紝鏍稿績澶勭悊鏄€氳繃compareAndSetState()鏂规硶鏉ュ鐞?/li>
- tryAcquire()鏂规硶锛氱嫭浜ā寮忚幏鍙栭攣鏂规硶锛岃繖閲屼富瑕侀拡瀵筗riteLock閿侊紝鏍稿績澶勭悊鏄€氳繃AQS鍩虹鍚屾鍣ㄤ腑compareAndSetState()鏂规硶鏉ュ鐞嗭紝瀹炵幇鐘舵€佸彉閲忕殑鎿嶄綔
- tryAcquireShared() 鏂规硶锛氬叡浜ā寮忚幏鍙栭攣鏂规硶锛岃繖閲屼富瑕佸搴擱eadLock閿侊紝鏍稿績澶勭悊鏄€氳繃AQS鍩虹鍚屾鍣ㄤ腑compareAndSetState()鏂规硶鏉ュ鐞嗭紝瀹炵幇鐘舵€佸彉閲忕殑鎿嶄綔
- tryRelease(int releases) 鏂规硶锛氱嫭浜ā寮忛噴鏀鹃攣鏂规硶
- tryReleaseShared(int unused) 鏂规硶锛氬叡浜ā寮忛噴鏀鹃攣鏂规硶锛屾牳蹇冨鐞嗘槸鑷棆+compareAndSetState()鏂规硶鏉ュ鐞?/li>
- getCount() 鏂规硶锛氫富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄦ潵鑾峰彇鐘舵€佸彉閲?/li>
- getOwner()鏂规硶锛氫富瑕佹槸鐢ㄤ簬鑾峰彇褰撳墠閿佺殑鎸佹湁鑰咃紝涓€鑸槸绾跨▼瀵硅薄锛屾牴鎹?em>exclusiveCount(getState()) == 0鏉ュ垽鏂紝鏉′欢鎴愮珛灏遍粯璁や负null; 鍚﹀垯锛岄€氳繃AQS鍩虹鍚屾鍣ㄤ腑鐨刧etExclusiveOwnerThread()鏂规硶鏉ヨ幏鍙栥€?/li>
- getReadLockCount() 鏂规硶锛氱敤浜庤幏鍙栨煇涓嚎绋嬪浜嶳eadLock閿佺殑鏁伴噺锛屼富瑕佹槸缁熻娆℃暟
- isWriteLocked() 鏂规硶锛氱敤浜庡垽鏂嚎绋嬫槸鍚﹀凡缁忚幏鍙栧苟鎸佹湁WriteLock閿?/li>
- getWriteHoldCount()鏂规硶锛氱敤浜庤幏鍙栫嚎绋嬪浜嶹riteLock閿佺殑鎸佹湁鎯呭喌锛屼富瑕佹槸缁熻娆℃暟
- getReadHoldCount() 鏂规硶锛氱敤浜庤幏鍙栫嚎绋嬪浜嶹riteLock閿佺殑鎸佹湁鎯呭喌锛屼富瑕佹槸缁熻娆℃暟
- isHeldExclusively() 鏂规硶锛氱敤浜庡垽鏂槸鍚︾嫭鍗犳ā寮?/li>
- unmatchedUnlockException()鏂规硶锛氬皝瑁呬竴涓紓甯稿鐞嗕俊鎭紝涓昏鏄寚瀹欼llegalMonitorStateException
/** ReentrantReadWriteLock閿?鍩轰簬AQS灏佽鍐呴儴鍚屾鍣?*/
abstract static class Sync extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 6317671515068378041L;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?begin*/
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍏变韩鐘舵€佺Щ鍔ㄤ綅鏁?6 */
static final int SHARED_SHIFT = 16;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣姣忔鍔犻攣鐨勭姸鎬佸ぇ灏?/
static final int SHARED_UNIT = (1 << SHARED_SHIFT);
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣姣忔鍔犻攣鐨勬渶澶ф鏁?/
static final int MAX_COUNT = (1 << SHARED_SHIFT) - 1;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍐欓攣鐨勬帺鐮?/
static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鏈湴瀛樺偍璇婚攣娆℃暟*/
private transient ThreadLocalHoldCounter readHolds;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣鐨勭姸鎬佺爜鍊?/
private transient HoldCounter cachedHoldCounter;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?绾跨▼鍙橀噺*/
private transient Thread firstReader = null;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?棣栨璇婚攣娆℃暟*/
private transient int firstReaderHoldCount;
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?end*/
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鏋勯€犳柟娉?/
Sync() {
readHolds = new ThreadLocalHoldCounter();
setState(getState()); // ensures visibility of readHolds
}
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?璇婚攣鐨勭姸鎬佺爜鍊?/
static int sharedCount(int c) { return c >>> SHARED_SHIFT; }
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲忓皝瑁?鍐欓攣鐨勭姸鎬佺爜鍊?/
static int exclusiveCount(int c) { return c & EXCLUSIVE_MASK; }
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲?缁熻璁℃暟鍣?*/
static final class HoldCounter {
int count = 0;
// Use id, not reference, to avoid garbage retention
final long tid = getThreadId(Thread.currentThread());
}
/** ReentrantReadWriteLock閿?鍏辩敤鐘舵€佸彉閲?鏈湴瀛樺偍缁熻鍓湰 */
static final class ThreadLocalHoldCounter
extends ThreadLocal<HoldCounter> {
public HoldCounter initialValue() {
return new HoldCounter();
}
}
//... 鍏朵粬浠ｇ爜
}
- 瀹炵幇鏂瑰紡锛?涓昏鏄湪鍐呴儴鐨勫悓姝ュ櫒涓璖ync绫讳腑瀹氫箟HoldCounter绫诲拰ThreadLocalHoldCounter绫诲疄鐜扮殑銆傚叾涓細
- HoldCounter绫伙細涓昏鏄畾涔変簡涓€涓鏁板櫒count鍜屼竴涓嚎绋嬬紪鍙穞id鍙橀噺锛屽叾涓鏁板櫒count榛樿鍊间负0锛岃€岀嚎绋嬬紪鍙穞id閫氳繃getThreadId(Thread.currentThread())鏂规硶鏉ヨ幏鍙栥€?/li>
- ThreadLocalHoldCounter绫伙細鍩轰簬ThreadLocal鍜孒oldCounter鏉ユ彁渚涗簡initialValue()鏂规硶锛屼富瑕佹槸瀹炰緥璇濆寲HoldCounter绫汇€?/li>
- 鍏辩敤鐘舵€佸父閲忥細涓昏鏄湪鍐呴儴鐨勫悓姝ュ櫒涓璖ync绫讳腑瀹氫箟浜嗙浉鍏冲父閲忥紝鍏朵腑锛?
- SHARED_SHIFT锛?涓昏鐢ㄤ簬鏍囪浣嶇Щ鐨勪綅鏁帮紝榛樿閲囩敤 鏁村瀷16浣?/li>
- SHARED_UNIT锛氳〃绀鸿閿佸姞閿佹搷浣滄椂姣忔瀵瑰簲鐨勭姸鎬佸€煎ぇ灏忥紝灏?宸︾Щ鍔?6浣嶆濂藉搴旈珮16浣嶇殑1.
- MAX_COUNT锛氳〃绀鸿閿佽兘鎵ц鍔犻攣鎿嶄綔鐨勬渶澶ф鏁帮紝涓€鑸负16涓簩杩涘埗鐨?
- EXCLUSIVE_MASK锛氬啓閿佺殑鎺╃爜,涓€鑸负16涓簩杩涘埗鐨?
- 涓昏鏂规硶锛氫富瑕佹彁渚涗簡缁熻璇诲啓閿佺姸鎬佸€肩殑sharedCount()鏂规硶鍜宔xclusiveCount()鏂规硶锛屽叾涓細
- sharedCount()鏂规硶锛氳幏鍙栬閿佺殑鐘舵€佺爜鍊硷紝鏍规嵁鐩爣鍙傛暟(targetParam)宸︾Щ16浣嶅嵆鍙緱鍒?/li>
- exclusiveCount()鏂规硶锛氳幏鍙栧啓閿佺殑鐘舵€佺爜鍊硷紝鏍规嵁鐩爣鍙傛暟(targetParam)鍚屽啓閿佺殑鎺╃爜鍋氶€昏緫涓?&)杩愮畻渚垮彲寰楀埌銆?/li>
涓€鑸潵璇达紝AQS鍩虹鍚屾鍣ㄧ殑鍏变韩鐘舵€佸彉閲忔槸鏁村瀷鐨?2浣嶏紝瑕佸熀浜庝竴涓狝QS鍩虹鍚屾鍣ㄥ疄鐜拌鍐欓攣鐨勫叡浜竴涓叡浜彉閲忋€?lt;br />鍏朵腑锛屾渶鍏钩鐨勬柟寮忚璁℃柟寮忓氨鏄閿佷笌鍐欓攣鍚勮嚜鍗犵敤16浣嶏紝灏辨剰鍛崇潃璇婚攣鍗犵敤鐨勬槸楂?6浣嶏紝鍐欓攣鍗犵敤鐨勬槸浣?6浣嶇殑銆?/p>
浣嗘槸锛屽湪鑾峰彇璇诲啓閿佺殑鐘舵€佸€肩殑鏃跺€欙紝杩樹細娑夊強涓€浜涢澶栫殑璁＄畻锛岃繖鏍风殑璁捐鏂瑰紡鍙兘浼氶渶瑕佺敤鍒颁綅绉诲拰閫昏緫涓庢搷浣滅瓑銆?/p>
2.3 鍩轰簬Sync鎶借薄绫诲皝瑁匜airSync鍏钩鍚屾鍣?/h4>
/** ReentrantReadWriteLock閿?鍩轰簬Sync鎶借薄绫诲皝瑁匜airSync鍏钩鍚屾鍣?*/
static final class FairSync extends Sync {
private static final long serialVersionUID = -2274990926593161451L;
/** ReentrantReadWriteLock閿? 瀹炵幇writerShouldBlock鏂规硶*/
final boolean writerShouldBlock() {
return hasQueuedPredecessors();
}
/** ReentrantReadWriteLock閿? 瀹炵幇readerShouldBlock鏂规硶*/
final boolean readerShouldBlock() {
return hasQueuedPredecessors();
}
}
- 瀹炵幇鏂瑰紡锛氬熀浜嶴ync鎶借薄绫诲皝瑁匜airSync鍏钩鍚屾鍣紝琛ㄧず鏀寔鍏钩妯″紡
- 涓昏鏂规硶锛氫富瑕佸疄鐜板疄鐜皐riterShouldBlock()鏂规硶鍜宺eaderShouldBlock()鏂规硶,鍏朵腑锛?
- writerShouldBlock()鏂规硶锛氶€氳繃hasQueuedPredecessors()瀹炵幇
- readerShouldBlock()鏂规硶锛氶€氳繃apparentlyFirstQueuedIsExclusive()瀹炵幇
2.4 鍩轰簬Sync鎶借薄绫诲皝瑁匩onfairSync闈炲叕骞冲悓姝ュ櫒
/** ReentrantReadWriteLock閿?鍩轰簬Sync鎶借薄绫诲皝瑁匜airSync鍏钩鍚屾鍣?*/
static final class NonfairSync extends Sync {
private static final long serialVersionUID = -8159625535654395037L;
/** ReentrantReadWriteLock閿? 瀹炵幇writerShouldBlock鏂规硶*/
final boolean writerShouldBlock() {
return false; // writers can always barge
}
/** ReentrantReadWriteLock閿? 瀹炵幇readerShouldBlock鏂规硶*/
final boolean readerShouldBlock() {
return apparentlyFirstQueuedIsExclusive();
}
}
- 瀹炵幇鏂瑰紡锛氬熀浜嶴ync鎶借薄绫诲皝瑁匩onfairSync闈炲叕骞冲悓姝ュ櫒锛岃〃绀烘敮鎸侀潪鍏钩妯″紡
- 涓昏鏂规硶锛氫富瑕佸疄鐜板疄鐜皐riterShouldBlock()鏂规硶鍜宺eaderShouldBlock()鏂规硶,鍏朵腑锛?
- writerShouldBlock()鏂规硶锛氶粯璁よ繑鍥瀎alse
- readerShouldBlock()鏂规硶锛氶€氳繃apparentlyFirstQueuedIsExclusive()瀹炵幇
2.5 鍩轰簬Lock鎺ュ彛瀹炵幇ReadLock璇婚攣鍐呴儴绫?/h4>
/** ReentrantReadWriteLock閿?鍩轰簬Lock鎺ュ彛瀹炵幇ReadLock璇婚攣鍐呴儴绫?/
public static class ReadLock implements Lock, java.io.Serializable {
private static final long serialVersionUID = -5992448646407690164L;
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?鍚屾鍣?*/
private final Sync sync;
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?鍐呴儴鏋勯€犳柟娉?/
protected ReadLock(ReentrantReadWriteLock lock) {
sync = lock.sync;
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?鑾峰彇閿佹柟娉?榛樿鍏变韩妯″紡)*/
public void lock() {
sync.acquireShared(1);
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?鑾峰彇閿佹柟娉?鏀寔涓柇鏈哄埗)*/
public void lockInterruptibly() throws InterruptedException {
sync.acquireSharedInterruptibly(1);
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?灏濊瘯鑾峰彇閿?涓€鑸ā寮?*/
public boolean tryLock() {
return sync.tryReadLock();
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?灏濊瘯鑾峰彇閿?鏀寔瓒呮椂鏈哄埗)*/
public boolean tryLock(long timeout, TimeUnit unit)
throws InterruptedException {
return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?閲婃斁閿?/
public void unlock() {
sync.releaseShared(1);
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?鏉′欢鍙橀噺*/
public Condition newCondition() {
throw new UnsupportedOperationException();
}
public String toString() {
int r = sync.getReadLockCount();
return super.toString() +
"[Read locks = " + r + "]";
}
}
- 瀹炵幇鏂瑰紡锛氫富瑕佹槸鍩轰簬Lock鎺ュ彛鏉ュ疄鐜扮殑ReadLock閿侊紝鍚屾椂閫氳繃鏋勯€犳柟娉曟寚瀹氫簡涓€涓唴閮ㄥ悓姝ュ櫒Sync锛屽叾瀵瑰簲鐨勬柟娉曢兘鏄熀浜嶢QS鍩虹鍚屾鍣ㄧ殑鍏变韩妯″紡鏉ュ疄鐜扮殑銆?/li>
- 鑾峰彇閿佹柟寮忥細涓昏鎻愪緵浜?涓柟娉曟潵瀹炵幇閿佺殑鑾峰彇锛屽叾涓細
- 鏃犲弬鏁扮殑lock()鏂规硶锛?鑾峰彇閿佺殑涓€鑸ā寮忥紝涓昏鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨刟cquireShared(int arg)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄痙oAcquireShared(int arg)鏂规硶
- 鏃犲弬鏁扮殑lockInterruptibly()鏂规硶锛氳幏鍙栧彲涓柇閿佺殑妯″紡锛屼富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄤ腑鐨刟cquireSharedInterruptibly(int arg)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄痙oAcquireSharedInterruptibly(int arg)鏂规硶
- 鏃犲弬鏁扮殑tryLock()鏂规硶锛氬皾璇曡幏鍙朢eadLock閿侊紝涓昏鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨則ryReadLock()鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄嚜鏃?compareAndSetState()鏂规硶鐨勫姞鎸丆AS鎿嶄綔鐨勩€?/li>
- 鏈夊弬鏁扮殑ryLock()鏂规硶锛氬皾璇曡幏鍙朢eadLock閿侊紝鏀寔瓒呮椂鏈哄埗锛屼富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄤ腑鐨則ryAcquireSharedNanos(int arg, long nanosTimeout)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄湪doAcquireSharedNanos(int arg, long nanosTimeout)鏂规硶锛屼富瑕佹槸鑷棆+shouldParkAfterFailedAcquire()鏂规硶鐨勫姞鎸丆AS鎿嶄綔鐨勩€?/li>
- 閲婃斁閿佹柟寮忥細涓昏鎻愪緵浜嗕竴涓猽nlock()鏂规硶鏉ュ疄鐜癛eadLock 鐨勯噴鏀撅紝鍏朵腑鏈川鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨剅eleaseShared(int arg) 鏂规硶锛屽叾涓牳蹇冨鐞嗛€昏緫鏄痙oReleaseShared()鐨勬柟娉曪紝鍏舵牳蹇冨鐞嗘槸鑷棆+compareAndSetWaitStatus()鏂规硶鏉ュ姞鎸丆AS鎿嶄綔鐨勩€?/li>
2.6 鍩轰簬Lock鎺ュ彛瀹炵幇WriteLock鍐欓攣鍐呴儴绫?/h4>
/** ReentrantReadWriteLock閿?鍩轰簬Lock鎺ュ彛瀹炵幇WriteLock鍐欓攣鍐呴儴绫?/
public static class WriteLock implements Lock, java.io.Serializable {
private static final long serialVersionUID = -4992448646407690164L;
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鍚屾鍣?/
private final Sync sync;
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鍐呴儴鏋勯€犳柟娉?/
protected WriteLock(ReentrantReadWriteLock lock) {
sync = lock.sync;
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?鐙崰妯″紡)*/
public void lock() {
sync.acquire(1);
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?鍙腑鏂?*/
public void lockInterruptibly() throws InterruptedException {
sync.acquireInterruptibly(1);
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?涓€鑸ā寮?*/
public boolean tryLock( ) {
return sync.tryWriteLock();
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?鏀寔瓒呮椂鏈哄埗)*/
public boolean tryLock(long timeout, TimeUnit unit)
throws InterruptedException {
return sync.tryAcquireNanos(1, unit.toNanos(timeout));
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?閲婃斁閿?/
public void unlock() {
sync.release(1);
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鏉′欢鍙橀噺*/
public Condition newCondition() {
return sync.newCondition();
}
public String toString() {
Thread o = sync.getOwner();
return super.toString() + ((o == null) ?
"[Unlocked]" :
"[Locked by thread " + o.getName() + "]");
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鏄惁鐙崰鍒ゆ柇*/
public boolean isHeldByCurrentThread() {
return sync.isHeldExclusively();
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?缁熻鏁伴噺*/
public int getHoldCount() {
return sync.getWriteHoldCount();
}
}
- 瀹炵幇鏂瑰紡锛氫富瑕佹槸鍩轰簬Lock鎺ュ彛鏉ュ疄鐜扮殑WriteLock閿侊紝鍚屾椂閫氳繃鏋勯€犳柟娉曟寚瀹氫簡涓€涓唴閮ㄥ悓姝ュ櫒Sync锛屽叾瀵瑰簲鐨勬柟娉曢兘鏄熀浜嶢QS鍩虹鍚屾鍣ㄧ殑鐙崰妯″紡鏉ュ疄鐜扮殑銆?/li>
- 鑾峰彇閿佸紡锛氫富瑕佹彁渚涗簡4涓柟娉曟潵瀹炵幇閿佺殑鑾峰彇锛屽叾涓細
- 鏃犲弬鏁扮殑lock()鏂规硶锛?鑾峰彇WriteLock閿佺殑涓€鑸ā寮忥紝涓昏鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨刟cquire(int arg)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄痑cquireQueued(final Node node, int arg)鏂规硶
- 鏃犲弬鏁扮殑lockInterruptibly()鏂规硶锛氳幏鍙朩riteLock閿佸彲涓柇閿佺殑妯″紡锛屼富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄤ腑鐨刟cquireInterruptibly(int arg)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄痙oAcquireInterruptibly(int arg)鏂规硶
- 鏃犲弬鏁扮殑tryLock()鏂规硶锛氬皾璇曡幏鍙朩riteLock閿侊紝涓昏鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨則ryReadLock()鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄嚜鏃?compareAndSetState()鏂规硶鐨勫姞鎸丆AS鎿嶄綔鐨勩€?/li>
- 鏈夊弬鏁扮殑ryLock()鏂规硶锛氬皾璇曡幏鍙朩riteLock閿侊紝鏀寔瓒呮椂鏈哄埗锛屼富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄤ腑鐨則ryAcquireNanos(int arg, long nanosTimeout)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄湪doAcquireNanos(int arg, long nanosTimeout)鏂规硶锛屼富瑕佹槸鑷棆+shouldParkAfterFailedAcquire()鏂规硶鐨勫姞鎸丆AS鎿嶄綔鐨勩€?/li>
- 閲婃斁閿佹柟寮忥細涓昏鎻愪緵浜嗕竴涓猽nlock()鏂规硶鏉ュ疄鐜癛eadLock 鐨勯噴鏀撅紝鍏朵腑鏈川鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑unparkSuccessor(Node node)鏂规硶锛屼富瑕佹槸閫氳繃compareAndSetWaitStatus()鏂规硶鏉ュ姞鎸丆AS鎿嶄綔鐨勩€?/li>
3. 鍏蜂綋瀹炵幇
public class ReentrantReadWriteLock
implements ReadWriteLock, java.io.Serializable {
private static final long serialVersionUID = -6992448646407690164L;
/** ReentrantReadWriteLock閿?鍐呴儴ReadLock绫?*/
private final ReentrantReadWriteLock.ReadLock readerLock;
/** ReentrantReadWriteLock閿?鍐呴儴WriteLock绫?*/
private final ReentrantReadWriteLock.WriteLock writerLock;
/** ReentrantReadWriteLock閿?鍐呴儴鍚屾鍣?*/
final Sync sync;
/** ReentrantReadWriteLock閿?瀹炰緥鍖朥nsafe鏀寔 */
private static final sun.misc.Unsafe UNSAFE;
/** ReentrantReadWriteLock閿?绾跨▼鍋忕Щ閲?*/
private static final long TID_OFFSET;
/** ReentrantReadWriteLock閿?鍩轰簬AQS灏佽鍐呴儴鍚屾鍣?*/
abstract static class Sync extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 6317671515068378041L;
static final int SHARED_SHIFT = 16;
static final int SHARED_UNIT = (1 << SHARED_SHIFT);
static final int MAX_COUNT = (1 << SHARED_SHIFT) - 1;
static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;
private transient ThreadLocalHoldCounter readHolds;
private transient HoldCounter cachedHoldCounter;
private transient Thread firstReader = null;
private transient int firstReaderHoldCount;
Sync() {
readHolds = new ThreadLocalHoldCounter();
setState(getState()); // ensures visibility of readHolds
}
abstract boolean readerShouldBlock();
abstract boolean writerShouldBlock();
//... 鍏朵粬浠ｇ爜
}
/** ReentrantReadWriteLock閿?鏃犲弬鏁版瀯閫?榛樿闈炲叕骞虫ā寮? */
public ReentrantReadWriteLock() {
this(false);
}
/** ReentrantReadWriteLock閿?鏈夊弬鏁版瀯閫?鍙€夊叕骞?闈炲叕骞虫ā寮? */
public ReentrantReadWriteLock(boolean fair) {
sync = fair new FairSync() : new NonfairSync();
readerLock = new ReadLock(this);
writerLock = new WriteLock(this);
}
/** ReentrantReadWriteLock閿?鑾峰彇鍐欓攣 */
public ReentrantReadWriteLock.WriteLock writeLock() { return writerLock; }
/** ReentrantReadWriteLock閿?鑾峰彇璇婚攣 */
public ReentrantReadWriteLock.ReadLock readLock() { return readerLock; }
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final boolean isFair() {
return sync instanceof FairSync;
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Thread getOwner() {
return sync.getOwner();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getReadLockCount() {
return sync.getReadLockCount();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public boolean isWriteLocked() {
return sync.isWriteLocked();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public boolean isWriteLockedByCurrentThread() {
return sync.isHeldExclusively();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getWriteHoldCount() {
return sync.getWriteHoldCount();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getReadHoldCount() {
return sync.getReadHoldCount();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getQueuedWriterThreads() {
return sync.getExclusiveQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getQueuedReaderThreads() {
return sync.getSharedQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final boolean hasQueuedThreads() {
return sync.hasQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final boolean hasQueuedThread(Thread thread) {
return sync.isQueued(thread);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final int getQueueLength() {
return sync.getQueueLength();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getQueuedThreads() {
return sync.getQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public boolean hasWaiters(Condition condition) {
if (condition == null)
throw new NullPointerException();
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
throw new IllegalArgumentException("not owner");
return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getWaitingThreads(Condition condition) {
if (condition == null)
throw new NullPointerException();
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
throw new IllegalArgumentException("not owner");
return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getWaitQueueLength(Condition condition) {
if (condition == null)
throw new NullPointerException();
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
throw new IllegalArgumentException("not owner");
return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
static final long getThreadId(Thread thread) {
return UNSAFE.getLongVolatile(thread, TID_OFFSET);
}
/** ReentrantReadWriteLock閿?鍙嶅皠鏈哄埗瀹炰緥鍖朥nsafe */
static {
try {
UNSAFE = sun.misc.Unsafe.getUnsafe();
Class<?> tk = Thread.class;
TID_OFFSET = UNSAFE.objectFieldOffset
(tk.getDeclaredField("tid"));
} catch (Exception e) {
throw new Error(e);
}
}
}
- 璇诲啓閿佸悓姝ュ櫒锛氫富瑕佹彁渚涗簡2涓瀯閫犳柟娉曟潵瀹炵幇璇诲啓閿佺殑绠＄悊锛屽叾涓細
- 鏃犲弬鏁版瀯閫犳柟娉曪細榛樿闈炲叕骞虫ā寮忥紝涓昏鏄€氳繃this鍏抽敭瀛楁潵鎸囧畾鐨?/li>
- 鏈夊弬鏁版瀯閫犳柟娉曪細鍙€夊叕骞?闈炲叕骞虫ā寮忥紝渚濇嵁鎸囧畾浼犲叆鍏钩鏍囪fair鏉ュ疄渚嬪寲NonfairSync闈炲叕骞冲悓姝ュ櫒鍜孎airSync鍏钩鍚屾鍣紝鍏朵腑锛屽綋fair=true鏃讹紝鏄叕骞冲钩妯″紡锛涘惁鍒欙紝褰揻air=false鏃朵负闈炲叕骞虫ā寮忋€傚悓鏃讹紝瀹炰緥鍖朢eadLock鍜學riteLock瀵硅薄銆?/li>
- 璇婚攣涓昏鏂规硶锛氬浜庤閿佺殑鎿嶄綔锛屼竴鑸垜浠彧闇€瑕佸叧娉╮eadLock()鏂规硶鍜岀被浼糶etReadXX() 鏂规硶锛屽叾涓細
- readLock()鏂规硶锛氫富瑕佺敤浜庤幏鍙栧拰瀹炵幇璇婚攣ReadLock
- getReadHoldCount() 鏂规硶锛氫富瑕佺敤浜庣粺璁℃煇涓嚎绋嬪浜庤閿佺殑鎸佹湁鎯呭喌
- getReadLockCount() 鏂规硶锛氫富瑕佺敤浜庣粺璁℃煇涓嚎绋嬪浜庤閿佺殑鑾峰彇鐨勬鏁?/li>
- 鍐欓攣涓昏鏂规硶锛氬浜庤閿佺殑鎿嶄綔锛屼竴鑸垜浠彧闇€瑕佸叧娉╮eadLock()鏂规硶鍜岀被浼煎寘鍚玿WriteXX() 鏂规硶锛屽叾涓細
- writeLock() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栧拰瀹炵幇鍐欓攣WriteLock
- getWriteHoldCount()鏂规硶锛氫富瑕佺敤浜庣粺璁″綋鍓嶇嚎绋嬪浜庡啓閿乄riteLock鐨勬寔鏈夋儏鍐?/li>
- isWriteLocked()鏂规硶锛氫富瑕佺敤浜庡垽鏂煇涓嚎绋嬪浜庡啓閿乄riteLock鐨勬槸鍚﹀姞閿?/li>
- isWriteLockedByCurrentThread() 鏂规硶锛氫富瑕佺敤浜庡垽鏂綋鍓嶇嚎绋嬪浜庡啓閿乄riteLock鐨勬槸鍚﹀姞閿?/li>
- 鏉′欢闃熷垪鎿嶄綔鏂规硶锛氳繕鎻愪緵浜嗕竴绯诲垪鐨勫浜庢潯浠跺彉閲忛槦鍒楁搷浣滄柟娉曪紝鍏朵腑锛?
- getQueuedWriterThreads() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栧啓閿乄riteLock鐨勬儏鍐?/li>
- getQueuedReaderThreads() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栬閿丷eadLock鐨勬儏鍐?/li>
- getQueuedThreads()鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栬閿丷eadLock鍜屽啓閿乄riteLock鐨勬儏鍐?/li>
- getQueueLength() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栬閿丷eadLock鍜屽啓閿乄riteLock鐨勪釜鏁?/li>
- 绛夊緟闃熷垪鎿嶄綔鏂规硶锛?杩樻彁渚涗簡涓€绯诲垪鐨勫浜庣瓑寰呴槦鍒楁搷浣滄柟娉曪紝鍏朵腑锛?
- getWaitingThreads() 鏂规硶锛氫富瑕佷緷鎹瓹ondition鏉ョ敤浜庤幏鍙栫瓑寰呴槦鍒椾腑鎵€鏈夌殑绾跨▼鐨勫璞?/li>
- getWaitQueueLength() 鏂规硶锛氫富瑕佷緷鎹瓹ondition鏉ョ敤浜庤幏鍙栫瓑寰呴槦鍒椾腑鎵€鏈夌殑绾跨▼瀵逛簬鍐欓攣WriteLock鐨勭浉鍏崇殑涓暟
- 鍏朵粬鏂规硶锛氶櫎姝や箣澶栵紝杩樻彁渚涗簡涓€浜涢槦鍒楁搷浣滅殑甯歌鏂规硶锛屽叾涓細
- hasQueuedThread() 鏂规硶锛氫富瑕佷緷鎹崟涓猅hread瀵硅薄鐢ㄤ簬鑾峰彇绾跨▼鏄惁鏈夎幏鍙栬閿丷eadLock鍜屽啓閿乄riteLock鐨勬儏鍐?/li>
- hasQueuedThreads() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栧涓嚎绋嬫槸鍚︽湁鑾峰彇璇婚攣ReadLock鍜屽啓閿乄riteLock鐨勬儏鍐?/li>
- hasWaiters()鏂规硶锛氫富瑕佷緷鎹瓹ondition鏉ョ敤浜庡垽鏂瓑寰呴槦鍒椾腑鎵€鏈夌殑绾跨▼瀵逛簬鍐欓攣WriteLock鐨勭浉鍏虫儏鍐?/li>
- isFair() 鏂规硶锛氱敤浜庡垽鏂槸鍚﹀叕骞虫ā寮?/li>
- getThreadId()鏂规硶锛氳幏鍙栫嚎绋嬬紪鍙稩D锛屼富瑕佹槸閫氳繃鎸囧畾UNSAFE.getLongVolatile(thread, TID_OFFSET)瀹炵幇銆?/li>
/** ReentrantReadWriteLock閿?鍩轰簬Sync鎶借薄绫诲皝瑁匜airSync鍏钩鍚屾鍣?*/
static final class FairSync extends Sync {
private static final long serialVersionUID = -2274990926593161451L;
/** ReentrantReadWriteLock閿? 瀹炵幇writerShouldBlock鏂规硶*/
final boolean writerShouldBlock() {
return hasQueuedPredecessors();
}
/** ReentrantReadWriteLock閿? 瀹炵幇readerShouldBlock鏂规硶*/
final boolean readerShouldBlock() {
return hasQueuedPredecessors();
}
}
- writerShouldBlock()鏂规硶锛氶€氳繃hasQueuedPredecessors()瀹炵幇
- readerShouldBlock()鏂规硶锛氶€氳繃apparentlyFirstQueuedIsExclusive()瀹炵幇
/** ReentrantReadWriteLock閿?鍩轰簬Sync鎶借薄绫诲皝瑁匜airSync鍏钩鍚屾鍣?*/
static final class NonfairSync extends Sync {
private static final long serialVersionUID = -8159625535654395037L;
/** ReentrantReadWriteLock閿? 瀹炵幇writerShouldBlock鏂规硶*/
final boolean writerShouldBlock() {
return false; // writers can always barge
}
/** ReentrantReadWriteLock閿? 瀹炵幇readerShouldBlock鏂规硶*/
final boolean readerShouldBlock() {
return apparentlyFirstQueuedIsExclusive();
}
}
- writerShouldBlock()鏂规硶锛氶粯璁よ繑鍥瀎alse
- readerShouldBlock()鏂规硶锛氶€氳繃apparentlyFirstQueuedIsExclusive()瀹炵幇
/** ReentrantReadWriteLock閿?鍩轰簬Lock鎺ュ彛瀹炵幇ReadLock璇婚攣鍐呴儴绫?/
public static class ReadLock implements Lock, java.io.Serializable {
private static final long serialVersionUID = -5992448646407690164L;
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?鍚屾鍣?*/
private final Sync sync;
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?鍐呴儴鏋勯€犳柟娉?/
protected ReadLock(ReentrantReadWriteLock lock) {
sync = lock.sync;
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?鑾峰彇閿佹柟娉?榛樿鍏变韩妯″紡)*/
public void lock() {
sync.acquireShared(1);
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?鑾峰彇閿佹柟娉?鏀寔涓柇鏈哄埗)*/
public void lockInterruptibly() throws InterruptedException {
sync.acquireSharedInterruptibly(1);
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?灏濊瘯鑾峰彇閿?涓€鑸ā寮?*/
public boolean tryLock() {
return sync.tryReadLock();
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?灏濊瘯鑾峰彇閿?鏀寔瓒呮椂鏈哄埗)*/
public boolean tryLock(long timeout, TimeUnit unit)
throws InterruptedException {
return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?閲婃斁閿?/
public void unlock() {
sync.releaseShared(1);
}
/** ReentrantReadWriteLock閿?ReadLock璇婚攣鍐呴儴绫?鏉′欢鍙橀噺*/
public Condition newCondition() {
throw new UnsupportedOperationException();
}
public String toString() {
int r = sync.getReadLockCount();
return super.toString() +
"[Read locks = " + r + "]";
}
}
- 瀹炵幇鏂瑰紡锛氫富瑕佹槸鍩轰簬Lock鎺ュ彛鏉ュ疄鐜扮殑ReadLock閿侊紝鍚屾椂閫氳繃鏋勯€犳柟娉曟寚瀹氫簡涓€涓唴閮ㄥ悓姝ュ櫒Sync锛屽叾瀵瑰簲鐨勬柟娉曢兘鏄熀浜嶢QS鍩虹鍚屾鍣ㄧ殑鍏变韩妯″紡鏉ュ疄鐜扮殑銆?/li>
- 鑾峰彇閿佹柟寮忥細涓昏鎻愪緵浜?涓柟娉曟潵瀹炵幇閿佺殑鑾峰彇锛屽叾涓細
- 鏃犲弬鏁扮殑lock()鏂规硶锛?鑾峰彇閿佺殑涓€鑸ā寮忥紝涓昏鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨刟cquireShared(int arg)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄痙oAcquireShared(int arg)鏂规硶
- 鏃犲弬鏁扮殑lockInterruptibly()鏂规硶锛氳幏鍙栧彲涓柇閿佺殑妯″紡锛屼富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄤ腑鐨刟cquireSharedInterruptibly(int arg)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄痙oAcquireSharedInterruptibly(int arg)鏂规硶
- 鏃犲弬鏁扮殑tryLock()鏂规硶锛氬皾璇曡幏鍙朢eadLock閿侊紝涓昏鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨則ryReadLock()鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄嚜鏃?compareAndSetState()鏂规硶鐨勫姞鎸丆AS鎿嶄綔鐨勩€?/li>
- 鏈夊弬鏁扮殑ryLock()鏂规硶锛氬皾璇曡幏鍙朢eadLock閿侊紝鏀寔瓒呮椂鏈哄埗锛屼富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄤ腑鐨則ryAcquireSharedNanos(int arg, long nanosTimeout)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄湪doAcquireSharedNanos(int arg, long nanosTimeout)鏂规硶锛屼富瑕佹槸鑷棆+shouldParkAfterFailedAcquire()鏂规硶鐨勫姞鎸丆AS鎿嶄綔鐨勩€?/li>
- 閲婃斁閿佹柟寮忥細涓昏鎻愪緵浜嗕竴涓猽nlock()鏂规硶鏉ュ疄鐜癛eadLock 鐨勯噴鏀撅紝鍏朵腑鏈川鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨剅eleaseShared(int arg) 鏂规硶锛屽叾涓牳蹇冨鐞嗛€昏緫鏄痙oReleaseShared()鐨勬柟娉曪紝鍏舵牳蹇冨鐞嗘槸鑷棆+compareAndSetWaitStatus()鏂规硶鏉ュ姞鎸丆AS鎿嶄綔鐨勩€?/li>
2.6 鍩轰簬Lock鎺ュ彛瀹炵幇WriteLock鍐欓攣鍐呴儴绫?/h4>
/** ReentrantReadWriteLock閿?鍩轰簬Lock鎺ュ彛瀹炵幇WriteLock鍐欓攣鍐呴儴绫?/
public static class WriteLock implements Lock, java.io.Serializable {
private static final long serialVersionUID = -4992448646407690164L;
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鍚屾鍣?/
private final Sync sync;
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鍐呴儴鏋勯€犳柟娉?/
protected WriteLock(ReentrantReadWriteLock lock) {
sync = lock.sync;
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?鐙崰妯″紡)*/
public void lock() {
sync.acquire(1);
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?鍙腑鏂?*/
public void lockInterruptibly() throws InterruptedException {
sync.acquireInterruptibly(1);
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?涓€鑸ā寮?*/
public boolean tryLock( ) {
return sync.tryWriteLock();
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?鏀寔瓒呮椂鏈哄埗)*/
public boolean tryLock(long timeout, TimeUnit unit)
throws InterruptedException {
return sync.tryAcquireNanos(1, unit.toNanos(timeout));
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?閲婃斁閿?/
public void unlock() {
sync.release(1);
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鏉′欢鍙橀噺*/
public Condition newCondition() {
return sync.newCondition();
}
public String toString() {
Thread o = sync.getOwner();
return super.toString() + ((o == null) ?
"[Unlocked]" :
"[Locked by thread " + o.getName() + "]");
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鏄惁鐙崰鍒ゆ柇*/
public boolean isHeldByCurrentThread() {
return sync.isHeldExclusively();
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?缁熻鏁伴噺*/
public int getHoldCount() {
return sync.getWriteHoldCount();
}
}
- 瀹炵幇鏂瑰紡锛氫富瑕佹槸鍩轰簬Lock鎺ュ彛鏉ュ疄鐜扮殑WriteLock閿侊紝鍚屾椂閫氳繃鏋勯€犳柟娉曟寚瀹氫簡涓€涓唴閮ㄥ悓姝ュ櫒Sync锛屽叾瀵瑰簲鐨勬柟娉曢兘鏄熀浜嶢QS鍩虹鍚屾鍣ㄧ殑鐙崰妯″紡鏉ュ疄鐜扮殑銆?/li>
- 鑾峰彇閿佸紡锛氫富瑕佹彁渚涗簡4涓柟娉曟潵瀹炵幇閿佺殑鑾峰彇锛屽叾涓細
- 鏃犲弬鏁扮殑lock()鏂规硶锛?鑾峰彇WriteLock閿佺殑涓€鑸ā寮忥紝涓昏鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨刟cquire(int arg)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄痑cquireQueued(final Node node, int arg)鏂规硶
- 鏃犲弬鏁扮殑lockInterruptibly()鏂规硶锛氳幏鍙朩riteLock閿佸彲涓柇閿佺殑妯″紡锛屼富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄤ腑鐨刟cquireInterruptibly(int arg)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄痙oAcquireInterruptibly(int arg)鏂规硶
- 鏃犲弬鏁扮殑tryLock()鏂规硶锛氬皾璇曡幏鍙朩riteLock閿侊紝涓昏鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨則ryReadLock()鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄嚜鏃?compareAndSetState()鏂规硶鐨勫姞鎸丆AS鎿嶄綔鐨勩€?/li>
- 鏈夊弬鏁扮殑ryLock()鏂规硶锛氬皾璇曡幏鍙朩riteLock閿侊紝鏀寔瓒呮椂鏈哄埗锛屼富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄤ腑鐨則ryAcquireNanos(int arg, long nanosTimeout)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄湪doAcquireNanos(int arg, long nanosTimeout)鏂规硶锛屼富瑕佹槸鑷棆+shouldParkAfterFailedAcquire()鏂规硶鐨勫姞鎸丆AS鎿嶄綔鐨勩€?/li>
- 閲婃斁閿佹柟寮忥細涓昏鎻愪緵浜嗕竴涓猽nlock()鏂规硶鏉ュ疄鐜癛eadLock 鐨勯噴鏀撅紝鍏朵腑鏈川鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑unparkSuccessor(Node node)鏂规硶锛屼富瑕佹槸閫氳繃compareAndSetWaitStatus()鏂规硶鏉ュ姞鎸丆AS鎿嶄綔鐨勩€?/li>
3. 鍏蜂綋瀹炵幇
public class ReentrantReadWriteLock
implements ReadWriteLock, java.io.Serializable {
private static final long serialVersionUID = -6992448646407690164L;
/** ReentrantReadWriteLock閿?鍐呴儴ReadLock绫?*/
private final ReentrantReadWriteLock.ReadLock readerLock;
/** ReentrantReadWriteLock閿?鍐呴儴WriteLock绫?*/
private final ReentrantReadWriteLock.WriteLock writerLock;
/** ReentrantReadWriteLock閿?鍐呴儴鍚屾鍣?*/
final Sync sync;
/** ReentrantReadWriteLock閿?瀹炰緥鍖朥nsafe鏀寔 */
private static final sun.misc.Unsafe UNSAFE;
/** ReentrantReadWriteLock閿?绾跨▼鍋忕Щ閲?*/
private static final long TID_OFFSET;
/** ReentrantReadWriteLock閿?鍩轰簬AQS灏佽鍐呴儴鍚屾鍣?*/
abstract static class Sync extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 6317671515068378041L;
static final int SHARED_SHIFT = 16;
static final int SHARED_UNIT = (1 << SHARED_SHIFT);
static final int MAX_COUNT = (1 << SHARED_SHIFT) - 1;
static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;
private transient ThreadLocalHoldCounter readHolds;
private transient HoldCounter cachedHoldCounter;
private transient Thread firstReader = null;
private transient int firstReaderHoldCount;
Sync() {
readHolds = new ThreadLocalHoldCounter();
setState(getState()); // ensures visibility of readHolds
}
abstract boolean readerShouldBlock();
abstract boolean writerShouldBlock();
//... 鍏朵粬浠ｇ爜
}
/** ReentrantReadWriteLock閿?鏃犲弬鏁版瀯閫?榛樿闈炲叕骞虫ā寮? */
public ReentrantReadWriteLock() {
this(false);
}
/** ReentrantReadWriteLock閿?鏈夊弬鏁版瀯閫?鍙€夊叕骞?闈炲叕骞虫ā寮? */
public ReentrantReadWriteLock(boolean fair) {
sync = fair new FairSync() : new NonfairSync();
readerLock = new ReadLock(this);
writerLock = new WriteLock(this);
}
/** ReentrantReadWriteLock閿?鑾峰彇鍐欓攣 */
public ReentrantReadWriteLock.WriteLock writeLock() { return writerLock; }
/** ReentrantReadWriteLock閿?鑾峰彇璇婚攣 */
public ReentrantReadWriteLock.ReadLock readLock() { return readerLock; }
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final boolean isFair() {
return sync instanceof FairSync;
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Thread getOwner() {
return sync.getOwner();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getReadLockCount() {
return sync.getReadLockCount();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public boolean isWriteLocked() {
return sync.isWriteLocked();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public boolean isWriteLockedByCurrentThread() {
return sync.isHeldExclusively();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getWriteHoldCount() {
return sync.getWriteHoldCount();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getReadHoldCount() {
return sync.getReadHoldCount();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getQueuedWriterThreads() {
return sync.getExclusiveQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getQueuedReaderThreads() {
return sync.getSharedQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final boolean hasQueuedThreads() {
return sync.hasQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final boolean hasQueuedThread(Thread thread) {
return sync.isQueued(thread);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final int getQueueLength() {
return sync.getQueueLength();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getQueuedThreads() {
return sync.getQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public boolean hasWaiters(Condition condition) {
if (condition == null)
throw new NullPointerException();
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
throw new IllegalArgumentException("not owner");
return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getWaitingThreads(Condition condition) {
if (condition == null)
throw new NullPointerException();
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
throw new IllegalArgumentException("not owner");
return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getWaitQueueLength(Condition condition) {
if (condition == null)
throw new NullPointerException();
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
throw new IllegalArgumentException("not owner");
return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
static final long getThreadId(Thread thread) {
return UNSAFE.getLongVolatile(thread, TID_OFFSET);
}
/** ReentrantReadWriteLock閿?鍙嶅皠鏈哄埗瀹炰緥鍖朥nsafe */
static {
try {
UNSAFE = sun.misc.Unsafe.getUnsafe();
Class<?> tk = Thread.class;
TID_OFFSET = UNSAFE.objectFieldOffset
(tk.getDeclaredField("tid"));
} catch (Exception e) {
throw new Error(e);
}
}
}
- 璇诲啓閿佸悓姝ュ櫒锛氫富瑕佹彁渚涗簡2涓瀯閫犳柟娉曟潵瀹炵幇璇诲啓閿佺殑绠＄悊锛屽叾涓細
- 鏃犲弬鏁版瀯閫犳柟娉曪細榛樿闈炲叕骞虫ā寮忥紝涓昏鏄€氳繃this鍏抽敭瀛楁潵鎸囧畾鐨?/li>
- 鏈夊弬鏁版瀯閫犳柟娉曪細鍙€夊叕骞?闈炲叕骞虫ā寮忥紝渚濇嵁鎸囧畾浼犲叆鍏钩鏍囪fair鏉ュ疄渚嬪寲NonfairSync闈炲叕骞冲悓姝ュ櫒鍜孎airSync鍏钩鍚屾鍣紝鍏朵腑锛屽綋fair=true鏃讹紝鏄叕骞冲钩妯″紡锛涘惁鍒欙紝褰揻air=false鏃朵负闈炲叕骞虫ā寮忋€傚悓鏃讹紝瀹炰緥鍖朢eadLock鍜學riteLock瀵硅薄銆?/li>
- 璇婚攣涓昏鏂规硶锛氬浜庤閿佺殑鎿嶄綔锛屼竴鑸垜浠彧闇€瑕佸叧娉╮eadLock()鏂规硶鍜岀被浼糶etReadXX() 鏂规硶锛屽叾涓細
- readLock()鏂规硶锛氫富瑕佺敤浜庤幏鍙栧拰瀹炵幇璇婚攣ReadLock
- getReadHoldCount() 鏂规硶锛氫富瑕佺敤浜庣粺璁℃煇涓嚎绋嬪浜庤閿佺殑鎸佹湁鎯呭喌
- getReadLockCount() 鏂规硶锛氫富瑕佺敤浜庣粺璁℃煇涓嚎绋嬪浜庤閿佺殑鑾峰彇鐨勬鏁?/li>
- 鍐欓攣涓昏鏂规硶锛氬浜庤閿佺殑鎿嶄綔锛屼竴鑸垜浠彧闇€瑕佸叧娉╮eadLock()鏂规硶鍜岀被浼煎寘鍚玿WriteXX() 鏂规硶锛屽叾涓細
- writeLock() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栧拰瀹炵幇鍐欓攣WriteLock
- getWriteHoldCount()鏂规硶锛氫富瑕佺敤浜庣粺璁″綋鍓嶇嚎绋嬪浜庡啓閿乄riteLock鐨勬寔鏈夋儏鍐?/li>
- isWriteLocked()鏂规硶锛氫富瑕佺敤浜庡垽鏂煇涓嚎绋嬪浜庡啓閿乄riteLock鐨勬槸鍚﹀姞閿?/li>
- isWriteLockedByCurrentThread() 鏂规硶锛氫富瑕佺敤浜庡垽鏂綋鍓嶇嚎绋嬪浜庡啓閿乄riteLock鐨勬槸鍚﹀姞閿?/li>
- 鏉′欢闃熷垪鎿嶄綔鏂规硶锛氳繕鎻愪緵浜嗕竴绯诲垪鐨勫浜庢潯浠跺彉閲忛槦鍒楁搷浣滄柟娉曪紝鍏朵腑锛?
- getQueuedWriterThreads() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栧啓閿乄riteLock鐨勬儏鍐?/li>
- getQueuedReaderThreads() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栬閿丷eadLock鐨勬儏鍐?/li>
- getQueuedThreads()鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栬閿丷eadLock鍜屽啓閿乄riteLock鐨勬儏鍐?/li>
- getQueueLength() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栬閿丷eadLock鍜屽啓閿乄riteLock鐨勪釜鏁?/li>
- 绛夊緟闃熷垪鎿嶄綔鏂规硶锛?杩樻彁渚涗簡涓€绯诲垪鐨勫浜庣瓑寰呴槦鍒楁搷浣滄柟娉曪紝鍏朵腑锛?
- getWaitingThreads() 鏂规硶锛氫富瑕佷緷鎹瓹ondition鏉ョ敤浜庤幏鍙栫瓑寰呴槦鍒椾腑鎵€鏈夌殑绾跨▼鐨勫璞?/li>
- getWaitQueueLength() 鏂规硶锛氫富瑕佷緷鎹瓹ondition鏉ョ敤浜庤幏鍙栫瓑寰呴槦鍒椾腑鎵€鏈夌殑绾跨▼瀵逛簬鍐欓攣WriteLock鐨勭浉鍏崇殑涓暟
- 鍏朵粬鏂规硶锛氶櫎姝や箣澶栵紝杩樻彁渚涗簡涓€浜涢槦鍒楁搷浣滅殑甯歌鏂规硶锛屽叾涓細
- hasQueuedThread() 鏂规硶锛氫富瑕佷緷鎹崟涓猅hread瀵硅薄鐢ㄤ簬鑾峰彇绾跨▼鏄惁鏈夎幏鍙栬閿丷eadLock鍜屽啓閿乄riteLock鐨勬儏鍐?/li>
- hasQueuedThreads() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栧涓嚎绋嬫槸鍚︽湁鑾峰彇璇婚攣ReadLock鍜屽啓閿乄riteLock鐨勬儏鍐?/li>
- hasWaiters()鏂规硶锛氫富瑕佷緷鎹瓹ondition鏉ョ敤浜庡垽鏂瓑寰呴槦鍒椾腑鎵€鏈夌殑绾跨▼瀵逛簬鍐欓攣WriteLock鐨勭浉鍏虫儏鍐?/li>
- isFair() 鏂规硶锛氱敤浜庡垽鏂槸鍚﹀叕骞虫ā寮?/li>
- getThreadId()鏂规硶锛氳幏鍙栫嚎绋嬬紪鍙稩D锛屼富瑕佹槸閫氳繃鎸囧畾UNSAFE.getLongVolatile(thread, TID_OFFSET)瀹炵幇銆?/li>
/** ReentrantReadWriteLock閿?鍩轰簬Lock鎺ュ彛瀹炵幇WriteLock鍐欓攣鍐呴儴绫?/
public static class WriteLock implements Lock, java.io.Serializable {
private static final long serialVersionUID = -4992448646407690164L;
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鍚屾鍣?/
private final Sync sync;
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鍐呴儴鏋勯€犳柟娉?/
protected WriteLock(ReentrantReadWriteLock lock) {
sync = lock.sync;
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?鐙崰妯″紡)*/
public void lock() {
sync.acquire(1);
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?鍙腑鏂?*/
public void lockInterruptibly() throws InterruptedException {
sync.acquireInterruptibly(1);
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?涓€鑸ā寮?*/
public boolean tryLock( ) {
return sync.tryWriteLock();
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鑾峰彇閿佹柟娉?鏀寔瓒呮椂鏈哄埗)*/
public boolean tryLock(long timeout, TimeUnit unit)
throws InterruptedException {
return sync.tryAcquireNanos(1, unit.toNanos(timeout));
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?閲婃斁閿?/
public void unlock() {
sync.release(1);
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鏉′欢鍙橀噺*/
public Condition newCondition() {
return sync.newCondition();
}
public String toString() {
Thread o = sync.getOwner();
return super.toString() + ((o == null) ?
"[Unlocked]" :
"[Locked by thread " + o.getName() + "]");
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?鏄惁鐙崰鍒ゆ柇*/
public boolean isHeldByCurrentThread() {
return sync.isHeldExclusively();
}
/** ReentrantReadWriteLock閿?WriteLock鍐欓攣鍐呴儴绫?缁熻鏁伴噺*/
public int getHoldCount() {
return sync.getWriteHoldCount();
}
}
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- 鏃犲弬鏁扮殑lockInterruptibly()鏂规硶锛氳幏鍙朩riteLock閿佸彲涓柇閿佺殑妯″紡锛屼富瑕佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄤ腑鐨刟cquireInterruptibly(int arg)鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄痙oAcquireInterruptibly(int arg)鏂规硶
- 鏃犲弬鏁扮殑tryLock()鏂规硶锛氬皾璇曡幏鍙朩riteLock閿侊紝涓昏鏄熀浜嶢QS鍩虹鍚屾鍣ㄤ腑鐨則ryReadLock()鏂规硶鏉ュ疄鐜帮紝鍏舵牳蹇冨鐞嗛€昏緫鏄嚜鏃?compareAndSetState()鏂规硶鐨勫姞鎸丆AS鎿嶄綔鐨勩€?/li>
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public class ReentrantReadWriteLock
implements ReadWriteLock, java.io.Serializable {
private static final long serialVersionUID = -6992448646407690164L;
/** ReentrantReadWriteLock閿?鍐呴儴ReadLock绫?*/
private final ReentrantReadWriteLock.ReadLock readerLock;
/** ReentrantReadWriteLock閿?鍐呴儴WriteLock绫?*/
private final ReentrantReadWriteLock.WriteLock writerLock;
/** ReentrantReadWriteLock閿?鍐呴儴鍚屾鍣?*/
final Sync sync;
/** ReentrantReadWriteLock閿?瀹炰緥鍖朥nsafe鏀寔 */
private static final sun.misc.Unsafe UNSAFE;
/** ReentrantReadWriteLock閿?绾跨▼鍋忕Щ閲?*/
private static final long TID_OFFSET;
/** ReentrantReadWriteLock閿?鍩轰簬AQS灏佽鍐呴儴鍚屾鍣?*/
abstract static class Sync extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 6317671515068378041L;
static final int SHARED_SHIFT = 16;
static final int SHARED_UNIT = (1 << SHARED_SHIFT);
static final int MAX_COUNT = (1 << SHARED_SHIFT) - 1;
static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;
private transient ThreadLocalHoldCounter readHolds;
private transient HoldCounter cachedHoldCounter;
private transient Thread firstReader = null;
private transient int firstReaderHoldCount;
Sync() {
readHolds = new ThreadLocalHoldCounter();
setState(getState()); // ensures visibility of readHolds
}
abstract boolean readerShouldBlock();
abstract boolean writerShouldBlock();
//... 鍏朵粬浠ｇ爜
}
/** ReentrantReadWriteLock閿?鏃犲弬鏁版瀯閫?榛樿闈炲叕骞虫ā寮? */
public ReentrantReadWriteLock() {
this(false);
}
/** ReentrantReadWriteLock閿?鏈夊弬鏁版瀯閫?鍙€夊叕骞?闈炲叕骞虫ā寮? */
public ReentrantReadWriteLock(boolean fair) {
sync = fair new FairSync() : new NonfairSync();
readerLock = new ReadLock(this);
writerLock = new WriteLock(this);
}
/** ReentrantReadWriteLock閿?鑾峰彇鍐欓攣 */
public ReentrantReadWriteLock.WriteLock writeLock() { return writerLock; }
/** ReentrantReadWriteLock閿?鑾峰彇璇婚攣 */
public ReentrantReadWriteLock.ReadLock readLock() { return readerLock; }
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final boolean isFair() {
return sync instanceof FairSync;
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Thread getOwner() {
return sync.getOwner();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getReadLockCount() {
return sync.getReadLockCount();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public boolean isWriteLocked() {
return sync.isWriteLocked();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public boolean isWriteLockedByCurrentThread() {
return sync.isHeldExclusively();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getWriteHoldCount() {
return sync.getWriteHoldCount();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getReadHoldCount() {
return sync.getReadHoldCount();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getQueuedWriterThreads() {
return sync.getExclusiveQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getQueuedReaderThreads() {
return sync.getSharedQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final boolean hasQueuedThreads() {
return sync.hasQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final boolean hasQueuedThread(Thread thread) {
return sync.isQueued(thread);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public final int getQueueLength() {
return sync.getQueueLength();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getQueuedThreads() {
return sync.getQueuedThreads();
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public boolean hasWaiters(Condition condition) {
if (condition == null)
throw new NullPointerException();
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
throw new IllegalArgumentException("not owner");
return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
protected Collection<Thread> getWaitingThreads(Condition condition) {
if (condition == null)
throw new NullPointerException();
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
throw new IllegalArgumentException("not owner");
return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
public int getWaitQueueLength(Condition condition) {
if (condition == null)
throw new NullPointerException();
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
throw new IllegalArgumentException("not owner");
return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
}
/** ReentrantReadWriteLock閿?鑾峰彇绾跨▼鍙橀噺 */
static final long getThreadId(Thread thread) {
return UNSAFE.getLongVolatile(thread, TID_OFFSET);
}
/** ReentrantReadWriteLock閿?鍙嶅皠鏈哄埗瀹炰緥鍖朥nsafe */
static {
try {
UNSAFE = sun.misc.Unsafe.getUnsafe();
Class<?> tk = Thread.class;
TID_OFFSET = UNSAFE.objectFieldOffset
(tk.getDeclaredField("tid"));
} catch (Exception e) {
throw new Error(e);
}
}
}
- 鏃犲弬鏁版瀯閫犳柟娉曪細榛樿闈炲叕骞虫ā寮忥紝涓昏鏄€氳繃this鍏抽敭瀛楁潵鎸囧畾鐨?/li>
- 鏈夊弬鏁版瀯閫犳柟娉曪細鍙€夊叕骞?闈炲叕骞虫ā寮忥紝渚濇嵁鎸囧畾浼犲叆鍏钩鏍囪fair鏉ュ疄渚嬪寲NonfairSync闈炲叕骞冲悓姝ュ櫒鍜孎airSync鍏钩鍚屾鍣紝鍏朵腑锛屽綋fair=true鏃讹紝鏄叕骞冲钩妯″紡锛涘惁鍒欙紝褰揻air=false鏃朵负闈炲叕骞虫ā寮忋€傚悓鏃讹紝瀹炰緥鍖朢eadLock鍜學riteLock瀵硅薄銆?/li>
- readLock()鏂规硶锛氫富瑕佺敤浜庤幏鍙栧拰瀹炵幇璇婚攣ReadLock
- getReadHoldCount() 鏂规硶锛氫富瑕佺敤浜庣粺璁℃煇涓嚎绋嬪浜庤閿佺殑鎸佹湁鎯呭喌
- getReadLockCount() 鏂规硶锛氫富瑕佺敤浜庣粺璁℃煇涓嚎绋嬪浜庤閿佺殑鑾峰彇鐨勬鏁?/li>
- writeLock() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栧拰瀹炵幇鍐欓攣WriteLock
- getWriteHoldCount()鏂规硶锛氫富瑕佺敤浜庣粺璁″綋鍓嶇嚎绋嬪浜庡啓閿乄riteLock鐨勬寔鏈夋儏鍐?/li>
- isWriteLocked()鏂规硶锛氫富瑕佺敤浜庡垽鏂煇涓嚎绋嬪浜庡啓閿乄riteLock鐨勬槸鍚﹀姞閿?/li>
- isWriteLockedByCurrentThread() 鏂规硶锛氫富瑕佺敤浜庡垽鏂綋鍓嶇嚎绋嬪浜庡啓閿乄riteLock鐨勬槸鍚﹀姞閿?/li>
- getQueuedWriterThreads() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栧啓閿乄riteLock鐨勬儏鍐?/li>
- getQueuedReaderThreads() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栬閿丷eadLock鐨勬儏鍐?/li>
- getQueuedThreads()鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栬閿丷eadLock鍜屽啓閿乄riteLock鐨勬儏鍐?/li>
- getQueueLength() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栫嚎绋嬬瓑寰呰幏鍙栬閿丷eadLock鍜屽啓閿乄riteLock鐨勪釜鏁?/li>
- getWaitingThreads() 鏂规硶锛氫富瑕佷緷鎹瓹ondition鏉ョ敤浜庤幏鍙栫瓑寰呴槦鍒椾腑鎵€鏈夌殑绾跨▼鐨勫璞?/li>
- getWaitQueueLength() 鏂规硶锛氫富瑕佷緷鎹瓹ondition鏉ョ敤浜庤幏鍙栫瓑寰呴槦鍒椾腑鎵€鏈夌殑绾跨▼瀵逛簬鍐欓攣WriteLock鐨勭浉鍏崇殑涓暟
- hasQueuedThread() 鏂规硶锛氫富瑕佷緷鎹崟涓猅hread瀵硅薄鐢ㄤ簬鑾峰彇绾跨▼鏄惁鏈夎幏鍙栬閿丷eadLock鍜屽啓閿乄riteLock鐨勬儏鍐?/li>
- hasQueuedThreads() 鏂规硶锛氫富瑕佺敤浜庤幏鍙栧涓嚎绋嬫槸鍚︽湁鑾峰彇璇婚攣ReadLock鍜屽啓閿乄riteLock鐨勬儏鍐?/li>
- hasWaiters()鏂规硶锛氫富瑕佷緷鎹瓹ondition鏉ョ敤浜庡垽鏂瓑寰呴槦鍒椾腑鎵€鏈夌殑绾跨▼瀵逛簬鍐欓攣WriteLock鐨勭浉鍏虫儏鍐?/li>
- isFair() 鏂规硶锛氱敤浜庡垽鏂槸鍚﹀叕骞虫ā寮?/li>
- getThreadId()鏂规硶锛氳幏鍙栫嚎绋嬬紪鍙稩D锛屼富瑕佹槸閫氳繃鎸囧畾UNSAFE.getLongVolatile(thread, TID_OFFSET)瀹炵幇銆?/li>
<br />缁间笂鎵€杩帮紝ReentrantReadWriteLock閿佹槸鍩轰簬AQS鍩虹鍚屾鍣ㄧ殑鍏变韩妯″紡鍜岀嫭浜ā寮忓叡鍚屽鍖栫殑浜х墿锛屾敮鎸佸叕骞?闈炲叕骞虫ā寮忥紝鍏朵腑鐨凴eadLock鍜學riteLock鏄熀浜庡悓涓€涓狝QS鍩虹鍚屾鍣ㄦ潵瀹炵幇锛岀淮鎶や簡鍏辩敤鐘舵€佸彉閲忔満鍒躲€?/p>
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