java 四种线程池
Java通过Executors提供四种线程池,各有用处,下面是列子:
package executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
/**
* 线程池
Java通过Executors提供四种线程池，分别为：
newCachedThreadPool
-- 创建一个可缓存线程池，如果线程池长度超过处理需要，
-- 可灵活回收空闲线程，若无可回收，则新建线程。
newFixedThreadPool
-- 创建一个定长线程池，可控制线程最大并发数，超出的线程会在队列中等待。
newScheduledThreadPool
-- 创建一个定长线程池，支持定时及周期性任务执行。
newSingleThreadExecutor
-- 创建一个单线程化的线程池，它只会用唯一的工作线程来执行任务，
-- 保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行。
* @title - ThreadPool.java
* @author - NingZhong.Zeng
* @date - 2015年11月26日 上午11:01:32
*/
public class ThreadPool {
public static void main(String[] args) {
cachedThreadPool();
fixedThreadPool();
scheduledThreadPool();
singleThreadExecutor();
}
/**
* -- 创建一个可缓存线程池，如果线程池长度超过处理需要，
-- 可灵活回收空闲线程，若无可回收，则新建线程。
优点：长度伸缩性好
缺点：开销大，PV大容易吃内存
*/
public static void cachedThreadPool(){
ExecutorService cachedThreadPool = Executors.newCachedThreadPool();
for (int i = 0; i < 100; i++) {
final int index = i;
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
cachedThreadPool.execute(new Runnable() {
public void run() {
System.out.println(index);
}
});
}
}
/**
* -- 创建一个定长线程池，可控制线程最大并发数，超出的线程会在队列中等待。
* 优点：开销小
缺点：需要等待
*/
public static void fixedThreadPool() {
ExecutorService fixedThreadPool = Executors.newFixedThreadPool(3);
for (int i = 0; i < 100; i++) {
final int index = i;
fixedThreadPool.execute(new Runnable() {
public void run() {
try {
System.out.println(index);
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
}
}
/**
* -- 创建一个定长线程池，支持定时及周期性任务执行。
*/
public static void scheduledThreadPool() {
ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
// 定时2s执行
scheduledThreadPool.schedule(new Runnable() {
public void run() {
System.out.println("delay 2 seconds");
}
}, 2, TimeUnit.SECONDS);
// 定时1s，循环3s执行
scheduledThreadPool.scheduleAtFixedRate(new Runnable() {
public void run() {
System.out.println("delay 1 seconds, and excute every 3 seconds");
}
}, 1, 3, TimeUnit.SECONDS);
scheduledThreadPool.scheduleWithFixedDelay(new Runnable() {
public void run() {
System.out.println("delay 3 seconds, and excute every 1 seconds");
}
}, 3, 1, TimeUnit.SECONDS);
}
/**
* 创建一个单线程化的线程池，它只会用唯一的工作线程来执行任务，
*/
public static void singleThreadExecutor() {
ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();
for (int i = 0; i < 100; i++) {
final int index = i;
singleThreadExecutor.execute(new Runnable() {
public void run() {
try {
System.out.println(index);
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
}
}
}
Executors 的源码如下：
/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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/*
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* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent;
import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedExceptionAction;
import java.security.PrivilegedActionException;
import java.security.AccessControlException;
import sun.security.util.SecurityConstants;
/**
* Factory and utility methods for {@link Executor}, {@link
* ExecutorService}, {@link ScheduledExecutorService}, {@link
* ThreadFactory}, and {@link Callable} classes defined in this
* package. This class supports the following kinds of methods:
*
*
* - Methods that create and return an {@link ExecutorService}
* set up with commonly useful configuration settings.
*
- Methods that create and return a {@link ScheduledExecutorService}
* set up with commonly useful configuration settings.
*
- Methods that create and return a "wrapped" ExecutorService, that
* disables reconfiguration by making implementation-specific methods
* inaccessible.
*
- Methods that create and return a {@link ThreadFactory}
* that sets newly created threads to a known state.
*
- Methods that create and return a {@link Callable}
* out of other closure-like forms, so they can be used
* in execution methods requiring Callable.
*
*
* @since 1.5
* @author Doug Lea
*/
public class Executors {
/**
* Creates a thread pool that reuses a fixed number of threads
* operating off a shared unbounded queue. At any point, at most
* nThreads threads will be active processing tasks.
* If additional tasks are submitted when all threads are active,
* they will wait in the queue until a thread is available.
* If any thread terminates due to a failure during execution
* prior to shutdown, a new one will take its place if needed to
* execute subsequent tasks. The threads in the pool will exist
* until it is explicitly {@link ExecutorService#shutdown shutdown}.
*
* @param nThreads the number of threads in the pool
* @return the newly created thread pool
* @throws IllegalArgumentException if {@code nThreads <= 0}
*/
public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue());
}
/**
* Creates a thread pool that reuses a fixed number of threads
* operating off a shared unbounded queue, using the provided
* ThreadFactory to create new threads when needed. At any point,
* at most nThreads threads will be active processing
* tasks. If additional tasks are submitted when all threads are
* active, they will wait in the queue until a thread is
* available. If any thread terminates due to a failure during
* execution prior to shutdown, a new one will take its place if
* needed to execute subsequent tasks. The threads in the pool will
* exist until it is explicitly {@link ExecutorService#shutdown
* shutdown}.
*
* @param nThreads the number of threads in the pool
* @param threadFactory the factory to use when creating new threads
* @return the newly created thread pool
* @throws NullPointerException if threadFactory is null
* @throws IllegalArgumentException if {@code nThreads <= 0}
*/
public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue(),
threadFactory);
}
/**
* Creates an Executor that uses a single worker thread operating
* off an unbounded queue. (Note however that if this single
* thread terminates due to a failure during execution prior to
* shutdown, a new one will take its place if needed to execute
* subsequent tasks.) Tasks are guaranteed to execute
* sequentially, and no more than one task will be active at any
* given time. Unlike the otherwise equivalent
* newFixedThreadPool(1) the returned executor is
* guaranteed not to be reconfigurable to use additional threads.
*
* @return the newly created single-threaded Executor
*/
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue()));
}
/**
* Creates an Executor that uses a single worker thread operating
* off an unbounded queue, and uses the provided ThreadFactory to
* create a new thread when needed. Unlike the otherwise
* equivalent newFixedThreadPool(1, threadFactory) the
* returned executor is guaranteed not to be reconfigurable to use
* additional threads.
*
* @param threadFactory the factory to use when creating new
* threads
*
* @return the newly created single-threaded Executor
* @throws NullPointerException if threadFactory is null
*/
public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue(),
threadFactory));
}
/**
* Creates a thread pool that creates new threads as needed, but
* will reuse previously constructed threads when they are
* available. These pools will typically improve the performance
* of programs that execute many short-lived asynchronous tasks.
* Calls to execute will reuse previously constructed
* threads if available. If no existing thread is available, a new
* thread will be created and added to the pool. Threads that have
* not been used for sixty seconds are terminated and removed from
* the cache. Thus, a pool that remains idle for long enough will
* not consume any resources. Note that pools with similar
* properties but different details (for example, timeout parameters)
* may be created using {@link ThreadPoolExecutor} constructors.
*
* @return the newly created thread pool
*/
public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue());
}
/**
* Creates a thread pool that creates new threads as needed, but
* will reuse previously constructed threads when they are
* available, and uses the provided
* ThreadFactory to create new threads when needed.
* @param threadFactory the factory to use when creating new threads
* @return the newly created thread pool
* @throws NullPointerException if threadFactory is null
*/
public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue(),
threadFactory);
}
/**
* Creates a single-threaded executor that can schedule commands
* to run after a given delay, or to execute periodically.
* (Note however that if this single
* thread terminates due to a failure during execution prior to
* shutdown, a new one will take its place if needed to execute
* subsequent tasks.) Tasks are guaranteed to execute
* sequentially, and no more than one task will be active at any
* given time. Unlike the otherwise equivalent
* newScheduledThreadPool(1) the returned executor is
* guaranteed not to be reconfigurable to use additional threads.
* @return the newly created scheduled executor
*/
public static ScheduledExecutorService newSingleThreadScheduledExecutor() {
return new DelegatedScheduledExecutorService
(new ScheduledThreadPoolExecutor(1));
}
/**
* Creates a single-threaded executor that can schedule commands
* to run after a given delay, or to execute periodically. (Note
* however that if this single thread terminates due to a failure
* during execution prior to shutdown, a new one will take its
* place if needed to execute subsequent tasks.) Tasks are
* guaranteed to execute sequentially, and no more than one task
* will be active at any given time. Unlike the otherwise
* equivalent newScheduledThreadPool(1, threadFactory)
* the returned executor is guaranteed not to be reconfigurable to
* use additional threads.
* @param threadFactory the factory to use when creating new
* threads
* @return a newly created scheduled executor
* @throws NullPointerException if threadFactory is null
*/
public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) {
return new DelegatedScheduledExecutorService
(new ScheduledThreadPoolExecutor(1, threadFactory));
}
/**
* Creates a thread pool that can schedule commands to run after a
* given delay, or to execute periodically.
* @param corePoolSize the number of threads to keep in the pool,
* even if they are idle.
* @return a newly created scheduled thread pool
* @throws IllegalArgumentException if {@code corePoolSize < 0}
*/
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
return new ScheduledThreadPoolExecutor(corePoolSize);
}
/**
* Creates a thread pool that can schedule commands to run after a
* given delay, or to execute periodically.
* @param corePoolSize the number of threads to keep in the pool,
* even if they are idle.
* @param threadFactory the factory to use when the executor
* creates a new thread.
* @return a newly created scheduled thread pool
* @throws IllegalArgumentException if {@code corePoolSize < 0}
* @throws NullPointerException if threadFactory is null
*/
public static ScheduledExecutorService newScheduledThreadPool(
int corePoolSize, ThreadFactory threadFactory) {
return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
}
/**
* Returns an object that delegates all defined {@link
* ExecutorService} methods to the given executor, but not any
* other methods that might otherwise be accessible using
* casts. This provides a way to safely "freeze" configuration and
* disallow tuning of a given concrete implementation.
* @param executor the underlying implementation
* @return an ExecutorService instance
* @throws NullPointerException if executor null
*/
public static ExecutorService unconfigurableExecutorService(ExecutorService executor) {
if (executor == null)
throw new NullPointerException();
return new DelegatedExecutorService(executor);
}
/**
* Returns an object that delegates all defined {@link
* ScheduledExecutorService} methods to the given executor, but
* not any other methods that might otherwise be accessible using
* casts. This provides a way to safely "freeze" configuration and
* disallow tuning of a given concrete implementation.
* @param executor the underlying implementation
* @return a ScheduledExecutorService instance
* @throws NullPointerException if executor null
*/
public static ScheduledExecutorService unconfigurableScheduledExecutorService(ScheduledExecutorService executor) {
if (executor == null)
throw new NullPointerException();
return new DelegatedScheduledExecutorService(executor);
}
/**
* Returns a default thread factory used to create new threads.
* This factory creates all new threads used by an Executor in the
* same {@link ThreadGroup}. If there is a {@link
* java.lang.SecurityManager}, it uses the group of {@link
* System#getSecurityManager}, else the group of the thread
* invoking this defaultThreadFactory method. Each new
* thread is created as a non-daemon thread with priority set to
* the smaller of Thread.NORM_PRIORITY and the maximum
* priority permitted in the thread group. New threads have names
* accessible via {@link Thread#getName} of
* pool-N-thread-M, where N is the sequence
* number of this factory, and M is the sequence number
* of the thread created by this factory.
* @return a thread factory
*/
public static ThreadFactory defaultThreadFactory() {
return new DefaultThreadFactory();
}
/**
* Returns a thread factory used to create new threads that
* have the same permissions as the current thread.
* This factory creates threads with the same settings as {@link
* Executors#defaultThreadFactory}, additionally setting the
* AccessControlContext and contextClassLoader of new threads to
* be the same as the thread invoking this
* privilegedThreadFactory method. A new
* privilegedThreadFactory can be created within an
* {@link AccessController#doPrivileged} action setting the
* current thread's access control context to create threads with
* the selected permission settings holding within that action.
*
* Note that while tasks running within such threads will have
* the same access control and class loader settings as the
* current thread, they need not have the same {@link
* java.lang.ThreadLocal} or {@link
* java.lang.InheritableThreadLocal} values. If necessary,
* particular values of thread locals can be set or reset before
* any task runs in {@link ThreadPoolExecutor} subclasses using
* {@link ThreadPoolExecutor#beforeExecute}. Also, if it is
* necessary to initialize worker threads to have the same
* InheritableThreadLocal settings as some other designated
* thread, you can create a custom ThreadFactory in which that
* thread waits for and services requests to create others that
* will inherit its values.
*
* @return a thread factory
* @throws AccessControlException if the current access control
* context does not have permission to both get and set context
* class loader.
*/
public static ThreadFactory privilegedThreadFactory() {
return new PrivilegedThreadFactory();
}
/**
* Returns a {@link Callable} object that, when
* called, runs the given task and returns the given result. This
* can be useful when applying methods requiring a
* Callable to an otherwise resultless action.
* @param task the task to run
* @param result the result to return
* @return a callable object
* @throws NullPointerException if task null
*/
public static Callable callable(Runnable task, T result) {
if (task == null)
throw new NullPointerException();
return new RunnableAdapter(task, result);
}
/**
* Returns a {@link Callable} object that, when
* called, runs the given task and returns null.
* @param task the task to run
* @return a callable object
* @throws NullPointerException if task null
*/
public static Callable