轉自：彼岸舞
鏈接：www.cnblogs.com/flower-dance/p/13714006.html
什么是JUC?
JUC就是java.util.concurrent包,這個包俗稱JUC,里面都是解決并發問題的一些東西
該包的位置位于java下面的rt.jar包下面
4大常用并發工具類:
CountDownLatch
CyclicBarrier
Semaphore
ExChanger
CountDownLatch:
CountDownLatch,俗稱閉鎖,作用是類似加強版的Join,是讓一組執行緒等待其他的執行緒完成作業以后才執行
就比如在啟動框架服務的時候,我們主執行緒需要在環境執行緒初始化完成之后才能啟動,這時候我們就可以實作使用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);
}
在原始碼中可以看到,創建CountDownLatch時,需要傳入一個int型別的引數,將決定在執行次扣減之后,等待的執行緒被喚醒
通過這個類圖就可以知道其實CountDownLatch并沒有多少東西
方法介紹:
CountDownLatch:初始化方法
await:等待方法,同時帶引數的是超時多載方法
countDown:每執行一次,計數器減一,就是初始化傳入的數字,也代表著一個執行緒完成了任務
getCount:獲取當前值
toString:這個就不用說了
里面的Sync是一個內部類,外面的方法其實都是操作這個內部類的,這個內部類繼承了AQS,實作的標準方法,AQS將在后面的章節寫
主執行緒中創建CountDownLatch(3),然后主執行緒await阻塞,然后執行緒A,B,C各自完成了任務,呼叫了countDown,之后,每個執行緒呼叫一次計數器就會減一,初始是3,然后A執行緒呼叫后變成2,B執行緒呼叫后變成1,C執行緒呼叫后,變成0,這時就會喚醒正在await的主執行緒,然后主執行緒繼續執行
說一千道一萬,不如代碼寫幾行,上代碼:
休眠工具類,之后的代碼都會用到
package org.dance.tools;
import java.util.concurrent.TimeUnit;
/**
* 類說明：執行緒休眠輔助工具類
*/
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,有五個執行緒,6個扣除點
* 扣除完成后主執行緒和業務執行緒,才能執行作業
* 扣除點一般都是大于等于需要初始化的執行緒的
* @author ZYGisComputer
*/
public class UseCountDownLatch {
/**
* 設定為6個扣除點
*/
static CountDownLatch countDownLatch = new CountDownLatch(6);
/**
* 初始化執行緒
*/
private static class InitThread implements Runnable {
@Override
public void run() {
System.out.println("thread_" + Thread.currentThread().getId() + " ready init work .....");
// 執行扣減 扣減不代表結束
countDownLatch.countDown();
for (int i = 0; i < 2; i++) {
System.out.println("thread_" + Thread.currentThread().getId() + ".....continue do its work");
}
}
}
/**
* 業務執行緒
*/
private static class BusiThread implements Runnable {
@Override
public void run() {
// 業務執行緒需要在等初始化完畢后才能執行
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) {
// 創建單獨的初始化執行緒
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();
// 啟動業務執行緒
new Thread(new BusiThread()).start();
// 啟動初始化執行緒
for (int i = 0; i <= 3; i++) {
new Thread(new InitThread()).start();
}
// 主執行緒進入等待
try {
countDownLatch.await();
System.out.println("Main do ites work.....");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
回傳結果:
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-----
通過回傳結果就可以很直接的看到業務執行緒是在初始化執行緒完全跑完之后,才開始執行的
CyclicBarrier:
CyclicBarrier,俗稱柵欄鎖,作用是讓一組執行緒到達某個屏障,被阻塞,一直到組內的最后一個執行緒到達,然后屏障開放,接著,所有的執行緒繼續運行
這個感覺和CountDownLatch有點相似,但是其實是不一樣的,所謂的差別,將在下面詳解
CyclicBarrier的構造引數有兩個
/**
* 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;
}
很明顯能感覺出來,上面的構造引數呼叫了下面的構造引數,是一個構造方法多載
首先這個第一個引數也樹Int型別的,傳入的是執行執行緒的個數,這個數量和CountDownLatch不一樣,這個數量是需要和執行緒數量吻合的,CountDownLatch則不一樣,CountDownLatch可以大于等于,而CyclicBarrier只能等于,然后是第二個引數,第二個引數是barrierAction,這個引數是當屏障開放后,執行的任務執行緒,如果當屏障開放后需要執行什么任務,可以寫在這個執行緒中
主執行緒創建CyclicBarrier(3,barrierAction),然后由執行緒開始執行,執行緒A,B執行完成后都呼叫了await,然后他們都在一個屏障前阻塞者,需要等待執行緒C也,執行完成,呼叫await之后,然后三個執行緒都達到屏障后,屏障開放,然后執行緒繼續執行,并且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 {
/**
* 存放子執行緒作業結果的安全容器
*/
private static ConcurrentHashMap<String, Long> resultMap = new ConcurrentHashMap<>();
private static CyclicBarrier cyclicBarrier = new CyclicBarrier(5,new CollectThread());
/**
* 結果列印執行緒
* 用來演示CyclicBarrier的第二個引數,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.....");
}
}
/**
* 作業子執行緒
* 用于CyclicBarrier的一組執行緒
*/
private static class SubThread implements Runnable {
@Override
public void run() {
// 獲取當前執行緒的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();
}
}
}
回傳結果:
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
通過回傳結果可以看出前面的11 14 15三個執行緒沒有進入if陳述句塊,在執行到await的時候進入了等待,而另外12 13兩個執行緒進入到了if陳述句塊當中,多休眠了1秒多,然后當5個執行緒同時到達await的時候,屏障開放,執行了barrierAction執行緒,然后執行緒組繼續執行
解釋一下CountDownLatch和CyclicBarrier的卻別吧!
首先就是CountDownLatch的構造引數傳入的數量一般都是大于等于執行緒,數量的,因為他是有第三方控制的,可以扣減多次,然后就是CyclicBarrier的構造引數第一個引數傳入的數量一定是等于執行緒的個數的,因為他是由一組執行緒自身控制的
區別
CountDownLatch CyclicBarrier
控制 第三方控制 自身控制
傳入數量 大于等于執行緒數量 等于執行緒數量
Semaphore:
Semaphore,俗稱信號量,作用于控制同時訪問某個特定資源的執行緒數量,用在流量控制
一說特定資源控制,那么第一時間就想到了資料庫連接..
之前用等待超時模式寫了一個資料庫連接池,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);
}
在原始碼中可以看到在構建Semaphore信號量的時候,需要傳入許可證的數量,這個數量就是資源的最大允許的訪問的執行緒數
接下里用信號量實作一個資料庫連接池
連接物件
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;
/**
* 資料庫連接
* @author ZYGisComputer
*/
public class SqlConnection implements Connection {
/**
* 獲取資料庫連接
* @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;
}
}
連接池物件
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;
/**
* 使用信號量控制資料庫的鏈接和釋放
*
* @author ZYGisComputer
*/
public class DBPoolSemaphore {
/**
* 池容量
*/
private final static int POOL_SIZE = 10;
/**
* useful 代表可用連接
* useless 代表已用連接
* 為什么要使用兩個Semaphore呢?是因為,在連接池中不只有連接本身是資源,空位也是資源,也需要記錄
*/
private final Semaphore useful, useless;
/**
* 連接池
*/
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于池容量
useful = new Semaphore(POOL_SIZE);
// 初始不可用的許可證容量為0
useless = new Semaphore(0);
}
/**
* 獲取資料庫連接
*
* @return 連接物件
*/
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;
}
/**
* 釋放鏈接
*
* @param connection 連接物件
*/
public void returnConnection(Connection connection) throws InterruptedException {
if(null!=connection){
// 列印日志
System.out.println("當前有"+useful.getQueueLength()+"個執行緒等待獲取連接,,"
+"可用連接有"+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();
}
}
}
測驗類:
package org.dance.day2.util.pool;
import org.dance.tools.SleepTools;
import java.sql.Connection;
import java.util.Random;
/**
* 測驗Semaphore
* @author ZYGisComputer
*/
public class UseSemaphore {
/**
* 連接池
*/
public static final DBPoolSemaphore pool = new DBPoolSemaphore();
private static class BusiThread extends Thread{
@Override
public void run() {
// 亂數工具類 為了讓每個執行緒持有連接的時間不一樣
Random random = new Random();
long start = System.currentTimeMillis();
try {
Connection connection = pool.takeConnection();
System.out.println("Thread_"+Thread.currentThread().getId()+
"_獲取資料庫連接耗時["+(System.currentTimeMillis()-start)+"]ms.");
// 模擬使用連接查詢資料
SleepTools.ms(100+random.nextInt(100));
System.out.println("查詢資料完成歸還連接");
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();
}
}
}
測驗回傳結果:
Thread_11_獲取資料庫連接耗時[0]ms.
Thread_12_獲取資料庫連接耗時[0]ms.
Thread_13_獲取資料庫連接耗時[0]ms.
Thread_14_獲取資料庫連接耗時[0]ms.
Thread_15_獲取資料庫連接耗時[0]ms.
Thread_16_獲取資料庫連接耗時[0]ms.
Thread_17_獲取資料庫連接耗時[0]ms.
Thread_18_獲取資料庫連接耗時[0]ms.
Thread_19_獲取資料庫連接耗時[0]ms.
Thread_20_獲取資料庫連接耗時[0]ms.
查詢資料完成歸還連接
當前有40個執行緒等待獲取連接,,可用連接有0個
Thread_21_獲取資料庫連接耗時[112]ms.
查詢資料完成歸還連接
...................查詢資料完成歸還連接
當前有2個執行緒等待獲取連接,,可用連接有0個
Thread_59_獲取資料庫連接耗時[637]ms.
查詢資料完成歸還連接
當前有1個執行緒等待獲取連接,,可用連接有0個
Thread_60_獲取資料庫連接耗時[660]ms.
查詢資料完成歸還連接
當前有0個執行緒等待獲取連接,,可用連接有0個
查詢資料完成歸還連接...................
當前有0個執行緒等待獲取連接,,可用連接有8個
查詢資料完成歸還連接
當前有0個執行緒等待獲取連接,,可用連接有9個
通過執行結果可以很明確的看到,一上來就有10個執行緒獲取到了連接,,然后后面的40個執行緒進入阻塞,然后只有釋放鏈接之后,等待的執行緒就會有一個拿到,然后越后面的執行緒等待的時間就越長,然后一直到所有的執行緒執行完畢
最后列印的可用連接有九個不是因為少了一個是因為在釋放之前列印的,不是錯誤
從結果中可以看到,我們對連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,用于在執行緒之間交換資料,但是比較受限,因為只能兩個執行緒之間交換資料
/**
* Creates a new Exchanger.
*/
public Exchanger() {
participant = new Participant();
}
這個建構式沒有什么好說的,也沒有入參,只有在創建的時候指定一下需要交換的資料的泛型即可,下面看代碼
package org.dance.day2.util;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.Exchanger;
/**
* 執行緒之間交換資料
* @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:
bSetAbSetBbSetCaSet1aSet2aSet3
通過執行結果可以清晰的看到,兩個執行緒中的資料發生了交換,這就是Exchanger的執行緒資料交換了
以上就是JUC的4大常用并發工具類了
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標籤：Java