Java手寫線程池之向JDK線程池進發(fā)

第Java手寫線程池之向JDK線程池進發(fā)private

AtomicInteger

ct

=

new

AtomicInteger(0);

//

當前在執(zhí)行任務的線程個數(shù)

private

int

corePoolSize;

private

int

maximumPoolSize;

private

long

keepAliveTime;

private

TimeUnit

unit;

private

BlockingQueueRunnable

taskQueue;

private

RejectPolicy

policy;

private

ArrayListWorker

workers

=

new

ArrayList();

private

volatile

boolean

isStopped;

private

boolean

useTimed;

public

int

getCt()

{

return

ct.get();

public

ThreadPool(int

corePoolSize,

int

maximumPoolSize,

TimeUnit

unit,

long

keepAliveTime,

RejectPolicy

policy

,

int

maxTasks)

{

//

please

add

-ea

to

vm

options

to

make

assert

keyword

enable

assert

corePoolSize

assert

maximumPoolSize

assert

keepAliveTime

assert

maxTasks

this.corePoolSize

=

corePoolSize;

this.maximumPoolSize

=

maximumPoolSize;

this.unit

=

unit;

this.policy

=

policy;

this.keepAliveTime

=

keepAliveTime;

taskQueue

=

new

ArrayBlockingQueueRunnable(maxTasks);

useTimed

=

keepAliveTime

!=

0;

/**

*

@param

runnable

需要被執(zhí)行的任務

*

@param

max

是否使用

maximumPoolSize

*

@return

boolean

*/

public

synchronized

boolean

addWorker(Runnable

runnable,

boolean

max)

{

if

(ct.get()

=

corePoolSize

!max)

return

false;

if

(ct.get()

=

maximumPoolSize

max)

return

false;

Worker

worker

=

new

Worker(runnable);

workers.add(worker);

Thread

thread

=

new

Thread(worker,

"ThreadPool-"

+

"Thread-"

+

ct.addAndGet(1));

thread.start();

return

true;

//

下面這個方法是向線程池提交任務

public

void

execute(Runnable

runnable)

throws

InterruptedException

{

checkPoolState();

if

(addWorker(runnable,

false)

//

如果能夠加入新的線程執(zhí)行任務

加入成功就直接返回

||

!taskQueue.offer(runnable)

//

如果

taskQueue.offer(runnable)

返回

false

說明提交任務失敗

任務隊列已經(jīng)滿了

||

addWorker(runnable,

true))

//

使用能夠使用的最大的線程數(shù)

(maximumPoolSize)

看是否能夠產(chǎn)生新的線程

return;

//

如果任務隊列滿了而且不能夠加入新的線程

則拒絕這個任務

if

(!taskQueue.offer(runnable))

reject(runnable);

private

void

reject(Runnable

runnable)

throws

InterruptedException

{

switch

(policy)

{

case

ABORT:

throw

new

RuntimeException("task

queue

is

full");

case

CALLER_RUN:

runnable.run();

case

DISCARD:

return;

case

DISCARD_OLDEST:

//

放棄等待時間最長的任務

taskQueue.poll();

execute(runnable);

}

private

void

checkPoolState()

{

if

(isStopped)

{

//

如果線程池已經(jīng)停下來了，就不在向任務隊列當中提交任務了

throw

new

RuntimeException("thread

pool

has

been

stopped,

so

quit

submitting

task");

}

public

V

RunnableFutureV

submit(CallableV

task)

throws

InterruptedException

{

checkPoolState();

FutureTaskV

futureTask

=

new

FutureTask(task);

execute(futureTask);

return

futureTask;

//

強制關閉線程池

public

synchronized

void

stop()

{

isStopped

=

true;

for

(Worker

worker

:

workers)

{

worker.stopWorker();

}

public

synchronized

void

shutDown()

{

//

先表示關閉線程池

線程就不能再向線程池提交任務

isStopped

=

true;

//

先等待所有的任務執(zhí)行完成再關閉線程池

waitForAllTasks();

stop();

private

void

waitForAllTasks()

{

//

當線程池當中還有任務的時候

就不退出循環(huán)

while

(taskQueue.size()

0)

{

Thread.yield();

try

{

Thread.sleep(1000);

}

catch

(InterruptedException

e)

{

e.printStackTrace();

}

}

class

Worker

implements

Runnable

{

private

Thread

thisThread;

private

final

Runnable

firstTask;

private

volatile

boolean

isStopped;

public

Worker(Runnable

firstTask)

{

this.firstTask

=

firstTask;

}

@Override

public

void

run()

{

//

先執(zhí)行傳遞過來的第一個任務

這里是一個小的優(yōu)化

讓線程直接執(zhí)行第一個任務

不需要

//

放入任務隊列再取出來執(zhí)行了

firstTask.run();

thisThread

=

Thread.currentThread();

while

(!isStopped)

{

try

{

Runnable

task

=

useTimed

taskQueue.poll(keepAliveTime,

unit)

:

taskQueue.take();

if

(task

==

null)

{

int

i;

boolean

exit

=

true;

if

(ct.get()

corePoolSize)

{

do{

i

=

ct.get();

if

(i

=

corePoolSize)

{

exit

=

false;

break;

}

}while

(!pareAndSet(i,

i

-

1));

if

(exit)

{

return;

}

}

}else

{

task.run();

}

}

catch

(InterruptedException

e)

{

//

do

nothing

}

}

}

public

synchronized

void

stopWorker()

{

if

(isStopped)

{

throw

new

RuntimeException("thread

has

been

interrupted");

}

isStopped

=

true;

thisTerrupt();

}

線程池測試

package

cscore.concurrent.java.threadpoolv2;

import

java.util.concurrent.ExecutionException;

import

java.util.concurrent.RunnableFuture;

import

java.util.concurrent.TimeUnit;

public

class

Test

{

public

static

void

main(String[]

args)

throws

InterruptedException,

ExecutionException

{

var

pool

=

new

ThreadPool(2,

5,

TimeUnit.SECONDS,

10,

RejectPolicy.ABORT,

100000);

for

(int

i

=

0;

i

i++)

{

RunnableFutureInteger

submit

=

pool.submit(()

-

{

System.out.println(Thread.currentThread().getName()

+

"

output

a");

try

{

Thread.sleep(10);

}

catch

(InterruptedException

e)

{

e.printStackTrace();

}

return

0;

});

System.out.println(submit.get());

}

int

n

=

15;

while

(n--

0)

{

System.out.println("Number

Threads

=

"

+

pool.getCt());

Thread.sleep(1000);

}

pool.shutDown();

上面測試代碼的輸出結(jié)果如下所示：

ThreadPool-Thread-2outputa

ThreadPool-Thread-1outputa

ThreadPool-Thread-3outputa

ThreadPool-Thread-4outputa

NumberThreads=5

ThreadPool-Thread-5outputa

ThreadPool-Thread-2outputa

ThreadPool-Thread-1outputa

ThreadPool-Thread-3outputa

ThreadPool-Thread-4outputa

ThreadPool-Thread-5outputa

ThreadPool-Thread-2outputa

ThreadPool-Thread-1outputa

ThreadPool-Thread-4outputa

Thr