多线程使用(工具类)
一、Fork-Join
大规模问题,分解为n个小规模的问题,条件:(1、子问题的相互独立,2、子问题和原问题形式相同),递归的解决小问题,小问题的解合并得到N的解,RecursiveTask表示我们及计算任务有返回结果,RecursiveAction没有返回结果。
public class TestForkJoin{
private static class GetDate extends RecursiveTask<Integer> {
int k=0;
public GetDate(int k) {
this.k = k;
}
@Override
protected Integer compute() {
int i=0;
List<GetDate> subTasks = new ArrayList<>();
if(k>1){
for(int j=0;j<3;j++){
if(i<2){
i+=1;
}else{
subTasks.add(new GetDate(1));
}
}
}else{
i+=2;
}
if (!subTasks.isEmpty()) {
// 在当前的 ForkJoinPool 上调度所有的子任务。
for (GetDate subTask : invokeAll(subTasks)) {
i = i+subTask.join();
}
System.out.println("i:"+i);
}
return i;
}
}
public static void main(String[] args) {
ForkJoinPool pool =new ForkJoinPool();
GetDate task=new GetDate(2);
pool.invoke(task);
System.out.println("测试开始");
System.out.println("result:"+task.join());
System.out.println("测试结束");
}
}
二、CountDownLatch
CountDownLatch这个类能够使一个线程等待其他线程完成各自的工作后再执行。CountDownLatch是通过一个计数器来实现的,计数器的初始值为初始任务的数量。每当完成了一个任务后,计数器的值就会减1,CountDownLatch.countDown()方法。当计数器值到达0时,它表示所有的已经完成了任务,然后在闭锁上等待CountDownLatch.await()方法的线程就可以恢复执行任务。
public class UseCountDownLatch {
static CountDownLatch latch = new CountDownLatch(6);
private static class InitThread implements Runnable{
@Override
public void run() {
System.out.println("Thread_"+Thread.currentThread().getId()
+" ready init work......");
latch.countDown();
for(int i =0;i<2;i++) {
System.out.println("Thread_"+Thread.currentThread().getId()
+" ........continue do its work");
}
}
}
private static class BusiThread implements Runnable{
@Override
public void run() {
try {
latch.await();
} catch (InterruptedException e) {
}
for(int i =0;i<3;i++) {
System.out.println("BusiThread_"+Thread.currentThread().getId()
+" do business-----");
}
}
}
public static void main(String[] args) throws InterruptedException {
new Thread(new Runnable() {
@Override
public void run() {
SleepTools.ms(1);
System.out.println("Thread_"+Thread.currentThread().getId()
+" ready init work step 1st......");
latch.countDown();
System.out.println("begin step 2nd.......");
SleepTools.ms(1);
System.out.println("Thread_"+Thread.currentThread().getId()
+" ready init work step 2nd......");
latch.countDown();
}
}).start();
new Thread(new BusiThread()).start();
for(int i=0;i<=3;i++){
Thread thread = new Thread(new InitThread());
thread.start();
}
latch.await();
System.out.println("Main do ites work........");
}
}
三、 CyclicBarrier
它要做的事情是,让一组线程到达一个屏障(也可以叫同步点)时被阻塞,直到最后一个线程到达屏障时,屏障才会开门,所有被屏障拦截的线程才会继续运行。
public class UseCyclicBarrier {
private static CyclicBarrier barrier = new CyclicBarrier(5, new CollectThread());
private static ConcurrentHashMap<String,Long> resultMap
= new ConcurrentHashMap<>();//存放子线程工作结果的容器
public static void main(String[] args) {
for(int i=0;i<=4;i++){
Thread thread = new Thread(new SubThread());
thread.start();
}
}
private static class CollectThread implements Runnable{
@Override
public void run() {
StringBuilder result = new StringBuilder();
for(Map.Entry<String,Long> workResult:resultMap.entrySet()){
result.append("["+workResult.getValue()+"]");
}
System.out.println(" the result = "+ result);
System.out.println("do other business........");
}
}
private static class SubThread implements Runnable{
@Override
public void run() {
long id = Thread.currentThread().getId();
resultMap.put(Thread.currentThread().getId()+"",id);
Random r = new Random();
try {
if(r.nextBoolean()) {
Thread.sleep(1000+id);
System.out.println("Thread_"+id+" ....do something ");
}
barrier.await();
Thread.sleep(1000+id);
System.out.println("Thread_"+id+" ....do its business ");
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
四、 Exchanger
是一个用于线程间协作的工具类。Exchanger用于进行线程间的数据交换。
public class UseExchange {
private static final Exchanger<Set<String>> exchange = new Exchanger<Set<String>>();
public static void main(String[] args) {
new Thread(new Runnable() {
@Override
public void run() {
Set<String> setA = new HashSet<String>();//存放数据的容器
try {
/*添加数据
* set.add(.....)
* */
setA.add("a");
setA = exchange.exchange(setA);//交换set
System.out.println("setA:"+setA);
/*处理交换后的数据*/
} catch (InterruptedException e) {
}
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
Set<String> setB = new HashSet<String>();//存放数据的容器
try {
/*添加数据
* set.add(.....)
* set.add(.....)
* */
setB.add("b");
setB = exchange.exchange(setB);//交换set
System.out.println("setB:"+setB);
/*处理交换后的数据*/
} catch (InterruptedException e) {
}
}
}).start();
}
}
五、Semaphore
Semaphore(信号量)是用来控制同时访问特定资源的线程数量,它通过协调各个线程,以保证合理的使用公共资源。
SqlConnectImpl
public class SqlConnectImpl implements Connection{
/*拿一个数据库连接*/
public static final Connection fetchConnection(){
return new SqlConnectImpl();
}
@Override
public <T> T unwrap(Class<T> iface) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public boolean isWrapperFor(Class<?> iface) throws SQLException {
// TODO Auto-generated method stub
return false;
}
@Override
public Statement createStatement() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public PreparedStatement prepareStatement(String sql) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public CallableStatement prepareCall(String sql) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public String nativeSQL(String sql) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public void setAutoCommit(boolean autoCommit) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public boolean getAutoCommit() throws SQLException {
// TODO Auto-generated method stub
return false;
}
@Override
public void commit() throws SQLException {
// TODO Auto-generated method stub
}
@Override
public void rollback() throws SQLException {
// TODO Auto-generated method stub
}
@Override
public void close() throws SQLException {
// TODO Auto-generated method stub
}
@Override
public boolean isClosed() throws SQLException {
// TODO Auto-generated method stub
return false;
}
@Override
public DatabaseMetaData getMetaData() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public void setReadOnly(boolean readOnly) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public boolean isReadOnly() throws SQLException {
// TODO Auto-generated method stub
return false;
}
@Override
public void setCatalog(String catalog) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public String getCatalog() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public void setTransactionIsolation(int level) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public int getTransactionIsolation() throws SQLException {
// TODO Auto-generated method stub
return 0;
}
@Override
public SQLWarning getWarnings() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public void clearWarnings() throws SQLException {
// TODO Auto-generated method stub
}
@Override
public Statement createStatement(int resultSetType, int resultSetConcurrency) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency)
throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public Map<String, Class<?>> getTypeMap() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public void setTypeMap(Map<String, Class<?>> map) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public void setHoldability(int holdability) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public int getHoldability() throws SQLException {
// TODO Auto-generated method stub
return 0;
}
@Override
public Savepoint setSavepoint() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public Savepoint setSavepoint(String name) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public void rollback(Savepoint savepoint) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public void releaseSavepoint(Savepoint savepoint) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public Statement createStatement(int resultSetType, int resultSetConcurrency, int resultSetHoldability)
throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency,
int resultSetHoldability) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency,
int resultSetHoldability) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int autoGeneratedKeys) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, int[] columnIndexes) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public PreparedStatement prepareStatement(String sql, String[] columnNames) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public Clob createClob() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public Blob createBlob() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public NClob createNClob() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public SQLXML createSQLXML() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public boolean isValid(int timeout) throws SQLException {
// TODO Auto-generated method stub
return false;
}
@Override
public void setClientInfo(String name, String value) throws SQLClientInfoException {
// TODO Auto-generated method stub
}
@Override
public void setClientInfo(Properties properties) throws SQLClientInfoException {
// TODO Auto-generated method stub
}
@Override
public String getClientInfo(String name) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public Properties getClientInfo() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public Array createArrayOf(String typeName, Object[] elements) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public Struct createStruct(String typeName, Object[] attributes) throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public void setSchema(String schema) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public String getSchema() throws SQLException {
// TODO Auto-generated method stub
return null;
}
@Override
public void abort(Executor executor) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public void setNetworkTimeout(Executor executor, int milliseconds) throws SQLException {
// TODO Auto-generated method stub
}
@Override
public int getNetworkTimeout() throws SQLException {
// TODO Auto-generated method stub
return 0;
}
}
DBPoolSemaphore:
public class DBPoolSemaphore {
private final static int POOL_SIZE = 10;
private final Semaphore useful,useless;//两个指示器,分别表示池子还有可用连接和已用连接
//存放数据库连接的容器
private static LinkedList<Connection> pool = new LinkedList<Connection>();
//初始化池
static {
for (int i = 0; i < POOL_SIZE; i++) {
pool.addLast(SqlConnectImpl.fetchConnection());
}
}
public DBPoolSemaphore() {
this.useful = new Semaphore(10);
this.useless = new Semaphore(0);
}
/*归还连接*/
public void returnConnect(Connection connection) throws InterruptedException {
if(connection!=null) {
System.out.println("当前有"+useful.getQueueLength()+"个线程等待数据库连接!!"
+"可用连接数:"+useful.availablePermits());
useless.acquire();
synchronized (pool) {
pool.addLast(connection);
}
useful.release();
}
}
/*从池子拿连接*/
public Connection takeConnect() throws InterruptedException {
useful.acquire();
Connection connection;
synchronized (pool) {
connection = pool.removeFirst();
}
useless.release();
return connection;
}
}
AppTest:
public class AppTest {
private static DBPoolSemaphore dbPool = new DBPoolSemaphore();
private static class BusiThread extends Thread{
@Override
public void run() {
Random r = new Random();//让每个线程持有连接的时间不一样
long start = System.currentTimeMillis();
try {
Connection connect = dbPool.takeConnect();
System.out.println("Thread_"+Thread.currentThread().getId()
+"_获取数据库连接共耗时【"+(System.currentTimeMillis()-start)+"】ms.");
SleepTools.ms(100+r.nextInt(100));//模拟业务操作,线程持有连接查询数据
System.out.println("查询数据完成,归还连接!");
dbPool.returnConnect(connect);
} catch (InterruptedException e) {
}
}
}
public static void main(String[] args) {
for (int i = 0; i < 50; i++) {
Thread thread = new BusiThread();
thread.start();
}
}
}