什麼是JUC?java
JUC就是java.util.concurrent包,這個包俗稱JUC,裏面都是解決併發問題的一些東西sql
該包的位置位於java下面的rt.jar包下面數據庫
4大經常使用併發工具類:安全
CountDownLatch併發
CyclicBarrierapp
Semaphore框架
ExChangerless
CountDownLatch:dom
CountDownLatch,俗稱閉鎖,做用是相似增強版的Join,是讓一組線程等待其餘的線程完成工做之後才執行ide
就好比在啓動框架服務的時候,咱們主線程須要在環境線程初始化完成以後才能啓動,這時候咱們就能夠實現使用CountDownLatch來完成
/** * Constructs a {@code CountDownLatch} initialized with the given count. * * @param count the number of times {@link #countDown} must be invoked * before threads can pass through {@link #await} * @throws IllegalArgumentException if {@code count} is negative */ public CountDownLatch(int count) { if (count < 0) throw new IllegalArgumentException("count < 0"); this.sync = new Sync(count); }
在源碼中能夠看到,建立CountDownLatch時,須要傳入一個int類型的參數,將決定在執行次扣減以後,等待的線程被喚醒
經過這個類圖就能夠知道其實CountDownLatch並無多少東西
方法介紹:
CountDownLatch:初始化方法
await:等待方法,同時帶參數的是超時重載方法
countDown:每執行一次,計數器減一,就是初始化傳入的數字,也表明着一個線程完成了任務
getCount:獲取當前值
toString:這個就不用說了
裏面的Sync是一個內部類,外面的方法其實都是操做這個內部類的,這個內部類繼承了AQS,實現的標準方法,AQS將在後面的章節寫
主線程中建立CountDownLatch(3),而後主線程await阻塞,而後線程A,B,C各自完成了任務,調用了countDown,以後,每一個線程調用一次計數器就會減一,初始是3,而後A線程調用後變成2,B線程調用後變成1,C線程調用後,變成0,這時就會喚醒正在await的主線程,而後主線程繼續執行
說一千道一萬,不如代碼寫幾行,上代碼:
休眠工具類,以後的代碼都會用到
package org.dance.tools; import java.util.concurrent.TimeUnit; /** * 類說明:線程休眠輔助工具類 */ public class SleepTools { /** * 按秒休眠 * @param seconds 秒數 */ public static final void second(int seconds) { try { TimeUnit.SECONDS.sleep(seconds); } catch (InterruptedException e) { } } /** * 按毫秒數休眠 * @param seconds 毫秒數 */ public static final void ms(int seconds) { try { TimeUnit.MILLISECONDS.sleep(seconds); } catch (InterruptedException e) { } } }
package org.dance.day2.util; import org.dance.tools.SleepTools; import java.util.concurrent.CountDownLatch; /** * CountDownLatch的使用,有五個線程,6個扣除點 * 扣除完成後主線程和業務線程,才能執行工做 * 扣除點通常都是大於等於須要初始化的線程的 * @author ZYGisComputer */ public class UseCountDownLatch { /** * 設置爲6個扣除點 */ static CountDownLatch countDownLatch = new CountDownLatch(6); /** * 初始化線程 */ private static class InitThread implements Runnable { @Override public void run() { System.out.println("thread_" + Thread.currentThread().getId() + " ready init work ....."); // 執行扣減 扣減不表明結束 countDownLatch.countDown(); for (int i = 0; i < 2; i++) { System.out.println("thread_" + Thread.currentThread().getId() + ".....continue do its work"); } } } /** * 業務線程 */ private static class BusiThread implements Runnable { @Override public void run() { // 業務線程須要在等初始化完畢後才能執行 try { countDownLatch.await(); for (int i = 0; i < 3; i++) { System.out.println("BusiThread " + Thread.currentThread().getId() + " do business-----"); } } catch (InterruptedException e) { e.printStackTrace(); } } } public static void main(String[] args) { // 建立單獨的初始化線程 new Thread(){ @Override public void run() { SleepTools.ms(1); System.out.println("thread_" + Thread.currentThread().getId() + " ready init work step 1st....."); // 扣減一次 countDownLatch.countDown(); System.out.println("begin stop 2nd....."); SleepTools.ms(1); System.out.println("thread_" + Thread.currentThread().getId() + " ready init work step 2nd....."); // 扣減一次 countDownLatch.countDown(); } }.start(); // 啓動業務線程 new Thread(new BusiThread()).start(); // 啓動初始化線程 for (int i = 0; i <= 3; i++) { new Thread(new InitThread()).start(); } // 主線程進入等待 try { countDownLatch.await(); System.out.println("Main do ites work....."); } catch (InterruptedException e) { e.printStackTrace(); } } }
返回結果:
thread_13 ready init work ..... thread_13.....continue do its work thread_13.....continue do its work thread_14 ready init work ..... thread_14.....continue do its work thread_14.....continue do its work thread_15 ready init work ..... thread_15.....continue do its work thread_11 ready init work step 1st..... begin stop 2nd..... thread_16 ready init work ..... thread_16.....continue do its work thread_16.....continue do its work thread_15.....continue do its work thread_11 ready init work step 2nd..... Main do ites work..... BusiThread 12 do business----- BusiThread 12 do business----- BusiThread 12 do business-----
經過返回結果就能夠很直接的看到業務線程是在初始化線程徹底跑完以後,纔開始執行的
CyclicBarrier:
CyclicBarrier,俗稱柵欄鎖,做用是讓一組線程到達某個屏障,被阻塞,一直到組內的最後一個線程到達,而後屏障開放,接着,全部的線程繼續運行
這個感受和CountDownLatch有點類似,可是實際上是不同的,所謂的差異,將在下面詳解
CyclicBarrier的構造參數有兩個
/** * Creates a new {@code CyclicBarrier} that will trip when the * given number of parties (threads) are waiting upon it, and * does not perform a predefined action when the barrier is tripped. * * @param parties the number of threads that must invoke {@link #await} * before the barrier is tripped * @throws IllegalArgumentException if {@code parties} is less than 1 */ public CyclicBarrier(int parties) { this(parties, null); }
/** * Creates a new {@code CyclicBarrier} that will trip when the * given number of parties (threads) are waiting upon it, and which * will execute the given barrier action when the barrier is tripped, * performed by the last thread entering the barrier. * * @param parties the number of threads that must invoke {@link #await} * before the barrier is tripped * @param barrierAction the command to execute when the barrier is * tripped, or {@code null} if there is no action * @throws IllegalArgumentException if {@code parties} is less than 1 */ public CyclicBarrier(int parties, Runnable barrierAction) { if (parties <= 0) throw new IllegalArgumentException(); this.parties = parties; this.count = parties; this.barrierCommand = barrierAction; }
很明顯能感受出來,上面的構造參數調用了下面的構造參數,是一個構造方法重載
首先這個第一個參數也樹Int類型的,傳入的是執行線程的個數,這個數量和CountDownLatch不同,這個數量是須要和線程數量吻合的,CountDownLatch則不同,CountDownLatch能夠大於等於,而CyclicBarrier只能等於,而後是第二個參數,第二個參數是barrierAction,這個參數是當屏障開放後,執行的任務線程,若是當屏障開放後須要執行什麼任務,能夠寫在這個線程中
主線程建立CyclicBarrier(3,barrierAction),而後由線程開始執行,線程A,B執行完成後都調用了await,而後他們都在一個屏障前阻塞者,須要等待線程C也,執行完成,調用await以後,而後三個線程都達到屏障後,屏障開放,而後線程繼續執行,而且barrierAction在屏障開放的一瞬間也開始執行
上代碼:
package org.dance.day2.util; import org.dance.tools.SleepTools; import java.util.Map; import java.util.Random; import java.util.concurrent.BrokenBarrierException; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.CyclicBarrier; /** * CyclicBarrier的使用 * * @author ZYGisComputer */ public class UseCyclicBarrier { /** * 存放子線程工做結果的安全容器 */ private static ConcurrentHashMap<String, Long> resultMap = new ConcurrentHashMap<>(); private static CyclicBarrier cyclicBarrier = new CyclicBarrier(5,new CollectThread()); /** * 結果打印線程 * 用來演示CyclicBarrier的第二個參數,barrierAction */ private static class CollectThread implements Runnable { @Override public void run() { StringBuffer result = new StringBuffer(); for (Map.Entry<String, Long> workResult : resultMap.entrySet()) { result.append("[" + workResult.getValue() + "]"); } System.out.println("the result = " + result); System.out.println("do other business....."); } } /** * 工做子線程 * 用於CyclicBarrier的一組線程 */ private static class SubThread implements Runnable { @Override public void run() { // 獲取當前線程的ID long id = Thread.currentThread().getId(); // 放入統計容器中 resultMap.put(String.valueOf(id), id); Random random = new Random(); try { if (random.nextBoolean()) { Thread.sleep(1000 + id); System.out.println("Thread_"+id+"..... do something"); } System.out.println(id+" is await"); cyclicBarrier.await(); Thread.sleep(1000+id); System.out.println("Thread_"+id+".....do its business"); } catch (InterruptedException e) { e.printStackTrace(); } catch (BrokenBarrierException e) { e.printStackTrace(); } } } public static void main(String[] args) { for (int i = 0; i <= 4; i++) { Thread thread = new Thread(new SubThread()); thread.start(); } } }
返回結果:
11 is await 14 is await 15 is await Thread_12..... do something 12 is await Thread_13..... do something 13 is await the result = [11][12][13][14][15] do other business..... Thread_11.....do its business Thread_12.....do its business Thread_13.....do its business Thread_14.....do its business Thread_15.....do its business
經過返回結果能夠看出前面的11 14 15三個線程沒有進入if語句塊,在執行到await的時候進入了等待,而另外12 13兩個線程進入到了if語句塊當中,多休眠了1秒多,而後當5個線程同時到達await的時候,屏障開放,執行了barrierAction線程,而後線程組繼續執行
解釋一下CountDownLatch和CyclicBarrier的卻別吧!
首先就是CountDownLatch的構造參數傳入的數量通常都是大於等於線程,數量的,由於他是有第三方控制的,能夠扣減屢次,而後就是CyclicBarrier的構造參數第一個參數傳入的數量必定是等於線程的個數的,由於他是由一組線程自身控制的
區別
CountDownLatch CyclicBarrier
控制 第三方控制 自身控制
傳入數量 大於等於線程數量 等於線程數量
Semaphore:
Semaphore,俗稱信號量,做用於控制同時訪問某個特定資源的線程數量,用在流量控制
一說特定資源控制,那麼第一時間就想到了數據庫鏈接..
以前用等待超時模式寫了一個數據庫鏈接池,打算用這個Semaphone也寫一個
/** * Creates a {@code Semaphore} with the given number of * permits and nonfair fairness setting. * * @param permits the initial number of permits available. * This value may be negative, in which case releases * must occur before any acquires will be granted. */ public Semaphore(int permits) { sync = new NonfairSync(permits); }
在源碼中能夠看到在構建Semaphore信號量的時候,須要傳入許可證的數量,這個數量就是資源的最大容許的訪問的線程數
接下里用信號量實現一個數據庫鏈接池
鏈接對象
package org.dance.day2.util.pool; import org.dance.tools.SleepTools; import java.sql.*; import java.util.Map; import java.util.Properties; import java.util.concurrent.Executor; /** * 數據庫鏈接 * @author ZYGisComputer */ public class SqlConnection implements Connection { /** * 獲取數據庫鏈接 * @return */ public static final Connection fetchConnection(){ return new SqlConnection(); } @Override public void commit() throws SQLException { SleepTools.ms(70); } @Override public Statement createStatement() throws SQLException { SleepTools.ms(1); return null; } @Override public PreparedStatement prepareStatement(String sql) throws SQLException { return null; } @Override public CallableStatement prepareCall(String sql) throws SQLException { return null; } @Override public String nativeSQL(String sql) throws SQLException { return null; } @Override public void setAutoCommit(boolean autoCommit) throws SQLException { } @Override public boolean getAutoCommit() throws SQLException { return false; } @Override public void rollback() throws SQLException { } @Override public void close() throws SQLException { } @Override public boolean isClosed() throws SQLException { return false; } @Override public DatabaseMetaData getMetaData() throws SQLException { return null; } @Override public void setReadOnly(boolean readOnly) throws SQLException { } @Override public boolean isReadOnly() throws SQLException { return false; } @Override public void setCatalog(String catalog) throws SQLException { } @Override public String getCatalog() throws SQLException { return null; } @Override public void setTransactionIsolation(int level) throws SQLException { } @Override public int getTransactionIsolation() throws SQLException { return 0; } @Override public SQLWarning getWarnings() throws SQLException { return null; } @Override public void clearWarnings() throws SQLException { } @Override public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException { return null; } @Override public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException { return null; } @Override public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException { return null; } @Override public Map<String, Class<?>> getTypeMap() throws SQLException { return null; } @Override public void setTypeMap(Map<String, Class<?>> map) throws SQLException { } @Override public void setHoldability(int holdability) throws SQLException { } @Override public int getHoldability() throws SQLException { return 0; } @Override public Savepoint setSavepoint() throws SQLException { return null; } @Override public Savepoint setSavepoint(String name) throws SQLException { return null; } @Override public void rollback(Savepoint savepoint) throws SQLException { } @Override public void releaseSavepoint(Savepoint savepoint) throws SQLException { } @Override public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException { return null; } @Override public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException { return null; } @Override public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException { return null; } @Override public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException { return null; } @Override public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException { return null; } @Override public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException { return null; } @Override public Clob createClob() throws SQLException { return null; } @Override public Blob createBlob() throws SQLException { return null; } @Override public NClob createNClob() throws SQLException { return null; } @Override public SQLXML createSQLXML() throws SQLException { return null; } @Override public boolean isValid(int timeout) throws SQLException { return false; } @Override public void setClientInfo(String name, String value) throws SQLClientInfoException { } @Override public void setClientInfo(Properties properties) throws SQLClientInfoException { } @Override public String getClientInfo(String name) throws SQLException { return null; } @Override public Properties getClientInfo() throws SQLException { return null; } @Override public Array createArrayOf(String typeName, Object[] elements) throws SQLException { return null; } @Override public Struct createStruct(String typeName, Object[] attributes) throws SQLException { return null; } @Override public void setSchema(String schema) throws SQLException { } @Override public String getSchema() throws SQLException { return null; } @Override public void abort(Executor executor) throws SQLException { } @Override public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException { } @Override public int getNetworkTimeout() throws SQLException { return 0; } @Override public <T> T unwrap(Class<T> iface) throws SQLException { return null; } @Override public boolean isWrapperFor(Class<?> iface) throws SQLException { return false; } }
鏈接池對象
package org.dance.day2.util.pool; import java.sql.Connection; import java.util.ArrayList; import java.util.HashSet; import java.util.Iterator; import java.util.LinkedList; import java.util.concurrent.Semaphore; /** * 使用信號量控制數據庫的連接和釋放 * * @author ZYGisComputer */ public class DBPoolSemaphore { /** * 池容量 */ private final static int POOL_SIZE = 10; /** * useful 表明可用鏈接 * useless 表明已用鏈接 * 爲何要使用兩個Semaphore呢?是由於,在鏈接池中不僅有鏈接自己是資源,空位也是資源,也須要記錄 */ private final Semaphore useful, useless; /** * 鏈接池 */ private final static LinkedList<Connection> POOL = new LinkedList<>(); /** * 使用靜態塊初始化池 */ static { for (int i = 0; i < POOL_SIZE; i++) { POOL.addLast(SqlConnection.fetchConnection()); } } public DBPoolSemaphore() { // 初始可用的許可證等於池容量 useful = new Semaphore(POOL_SIZE); // 初始不可用的許可證容量爲0 useless = new Semaphore(0); } /** * 獲取數據庫鏈接 * * @return 鏈接對象 */ public Connection takeConnection() throws InterruptedException { // 可用許可證減一 useful.acquire(); Connection connection; synchronized (POOL) { connection = POOL.removeFirst(); } // 不可用許可證數量加一 useless.release(); return connection; } /** * 釋放連接 * * @param connection 鏈接對象 */ public void returnConnection(Connection connection) throws InterruptedException { if(null!=connection){ // 打印日誌 System.out.println("當前有"+useful.getQueueLength()+"個線程等待獲取鏈接,," +"可用鏈接有"+useful.availablePermits()+"個"); // 不可用許可證減一 useless.acquire(); synchronized (POOL){ POOL.addLast(connection); } // 可用許可證加一 useful.release(); } } }
測試類:
package org.dance.day2.util.pool; import org.dance.tools.SleepTools; import java.sql.Connection; import java.util.Random; /** * 測試Semaphore * @author ZYGisComputer */ public class UseSemaphore { /** * 鏈接池 */ public static final DBPoolSemaphore pool = new DBPoolSemaphore(); private static class BusiThread extends Thread{ @Override public void run() { // 隨機數工具類 爲了讓每一個線程持有鏈接的時間不同 Random random = new Random(); long start = System.currentTimeMillis(); try { Connection connection = pool.takeConnection(); System.out.println("Thread_"+Thread.currentThread().getId()+ "_獲取數據庫鏈接耗時["+(System.currentTimeMillis()-start)+"]ms."); // 模擬使用鏈接查詢數據 SleepTools.ms(100+random.nextInt(100)); System.out.println("查詢數據完成歸還鏈接"); pool.returnConnection(connection); } catch (InterruptedException e) { e.printStackTrace(); } } } public static void main(String[] args) { for (int i = 0; i < 50; i++) { BusiThread busiThread = new BusiThread(); busiThread.start(); } } }
測試返回結果:
Thread_11_獲取數據庫鏈接耗時[0]ms. Thread_12_獲取數據庫鏈接耗時[0]ms. Thread_13_獲取數據庫鏈接耗時[0]ms. Thread_14_獲取數據庫鏈接耗時[0]ms. Thread_15_獲取數據庫鏈接耗時[0]ms. Thread_16_獲取數據庫鏈接耗時[0]ms. Thread_17_獲取數據庫鏈接耗時[0]ms. Thread_18_獲取數據庫鏈接耗時[0]ms. Thread_19_獲取數據庫鏈接耗時[0]ms. Thread_20_獲取數據庫鏈接耗時[0]ms. 查詢數據完成歸還鏈接 當前有40個線程等待獲取鏈接,,可用鏈接有0個 Thread_21_獲取數據庫鏈接耗時[112]ms. 查詢數據完成歸還鏈接 ...................
查詢數據完成歸還鏈接 當前有2個線程等待獲取鏈接,,可用鏈接有0個 Thread_59_獲取數據庫鏈接耗時[637]ms. 查詢數據完成歸還鏈接 當前有1個線程等待獲取鏈接,,可用鏈接有0個 Thread_60_獲取數據庫鏈接耗時[660]ms. 查詢數據完成歸還鏈接 當前有0個線程等待獲取鏈接,,可用鏈接有0個 查詢數據完成歸還鏈接
................... 當前有0個線程等待獲取鏈接,,可用鏈接有8個 查詢數據完成歸還鏈接 當前有0個線程等待獲取鏈接,,可用鏈接有9個
經過執行結果能夠很明確的看到,一上來就有10個線程獲取到了鏈接,,而後後面的40個線程進入阻塞,而後只有釋放連接以後,等待的線程就會有一個拿到,而後越後面的線程等待的時間就越長,而後一直到全部的線程執行完畢
最後打印的可用鏈接有九個不是由於少了一個是由於在釋放以前打印的,不是錯誤
從結果中能夠看到,咱們對鏈接池中的資源的到了控制,這就是信號量的流量控制
Exchanger:
Exchanger,俗稱交換器,用於在線程之間交換數據,可是比較受限,由於只能兩個線程之間交換數據
/** * Creates a new Exchanger. */ public Exchanger() { participant = new Participant(); }
這個構造函數沒有什麼好說的,也沒有入參,只有在建立的時候指定一下須要交換的數據的泛型便可,下面看代碼
package org.dance.day2.util; import java.util.HashSet; import java.util.Set; import java.util.concurrent.Exchanger; /** * 線程之間交換數據 * @author ZYGisComputer */ public class UseExchange { private static final Exchanger<Set<String>> exchanger = new Exchanger<>(); public static void main(String[] args) { new Thread(){ @Override public void run() { Set<String> aSet = new HashSet<>(); aSet.add("A"); aSet.add("B"); aSet.add("C"); try { Set<String> exchange = exchanger.exchange(aSet); for (String s : exchange) { System.out.println("aSet"+s); } } catch (InterruptedException e) { e.printStackTrace(); } } }.start(); new Thread(){ @Override public void run() { Set<String> bSet = new HashSet<>(); bSet.add("1"); bSet.add("2"); bSet.add("3"); try { Set<String> exchange = exchanger.exchange(bSet); for (String s : exchange) { System.out.println("bSet"+s); } } catch (InterruptedException e) { e.printStackTrace(); } } }.start(); } }
執行結果:
bSetA bSetB bSetC aSet1 aSet2 aSet3
經過執行結果能夠清晰的看到,兩個線程中的數據發生了交換,這就是Exchanger的線程數據交換了
以上就是JUC的4大經常使用併發工具類了