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祈雨的笔记

安全多方计算MPC spark原理解析 kueue执行源码分析 spark on k8s执行源码分析 spark-operator源码解析 系统压测遇到的缓存击穿问题 我的世界PC与安卓联机 蚂蚁金服流量投放平台的AIG改造 G1大对象致Old区占用率高 日志打印导致接口响应率下跌分析 Groovy加载类导致OOM分析 ERROR日志打印导致CPU满载 记OceanBase死锁超时 应用发版期间服务响应超时 Ark Serverless初探 系统优化复盘一二三 The user specified as a definer does not exist Kong网关初探 API网关选型调研 CPU火焰图常用工具 配置中心选型调研 root操作Nginx导致用户组错误 基于Proxifier使用代理 FastJSON字段智能匹配踩坑 Nacos初探 记一次Nginx服务器CPU满荷载故障 基于券系统分库分表的思考 limit不参与SQL成本计算致索引失效 Linux常用性能监控命令 golang低版本http2偶现400 hostname in certificate didn't match 常见对称加密原理以及应用 tcp_tw_recycle引起的TCP握手失败 记一次mysql执行DDL导致锁表 mysql磁盘占用查看 mysql对text字段update致磁盘增长 elasticsearch报错index read-only TIME_WAIT与Http的Keep-Alive 记一次TIME_WAIT导致连接数报警 记一次生产事故OOM问题排查 redis分布式锁RedissonLock的实现细节 webservice复杂加密签名(2)java调用 webservice复杂加密签名(1)SoapUI mysql延时关联 利用中间人拦截实现APP内H5窜改 MySQL表字符集不同导致关联查询索引失效 通过SSH隧道远程办公 数据落盘方案 BeanDefinitionRegistryPostProcessor扩展 mysql空间索引 HTTPS攻击 spring循环依赖过程解析 elasticsearch性能优化 mysql IS NULL 使用索引 mysql字符集utf8mb4失效踩坑 常用加密算法 xml与javaBean转换 初探InnoDB MVCC源码实现 mysql索引原理 redis之list源码分析 redis之key过期源码分析 redis之string源码分析 redis之hash源码分析 mysql数据页结构 Using temporary与Using filesort mysql回表致索引失效 springboot(28)HTTP连接池 定时任务之ScheduledThreadPoolExecutor elasticsearch常用script聚合 elasticsearch实现like查询 elasticsearch实现乐观锁 elasticsearch准实时原理 springboot(27)自定义缓存读写机制CachingConfigurerSupport optimizer tracing arthas常用命令 HTTP和HTTPS详解 redis集群选举机制 kafka消息重试 一点压力测试的经验 kafka架构概念 explain分析sql语句字段的解释 JVM问题分析处理手册 logstash过滤器(2)date logstash过滤器(3)dissect logstash编码器(1)json logstash编码器(2)multiline logstash表达式 logstash输入(1)通用选项 logstash输入(3)file logstash过滤器(1)通用选项 logstash输入(2)stdin logstash安装 记一次前端vConsole导致JSON序列化错误排查 解决多个异步操作嵌套问题 fastjson反序列化失败autoType is not support RTMP串流服务 POI自动调整列宽错误 Nginx+Lua实现动态黑名单 使用curl命令模拟POST和GET请求 ResponseEntity下载文件
线程池之ThreadPoolExecutor
祈雨的笔记 · 2019-06-29 · via 祈雨的笔记

线程池状态转换

java.util.concurrent.ThreadPoolExecutor为JDK的线程池对象,线程池的状态和状态转换如下图:

image

使用方式

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ThreadPoolExecutor executor = new ThreadPoolExecutor(1, 10, 1, TimeUnit.MINUTES, new ArrayBlockingQueue<>(10));
executor.execute(new Runnable() {
@Override
public void run() {
}
});

java.util.concurrent.Executors工具类下常用的快捷创建线程池的方法newCachedThreadPool()newFixedThreadPool()newSingleThreadExecutor实际上都是对ThreadPoolExecutor的封装。

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public static ExecutorService newCachedThreadPool() {

return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}
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public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());
}
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public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}

状态源码常量

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private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0)); 

private static final int RUNNING = -1 << COUNT_BITS;
private static final int SHUTDOWN = 0 << COUNT_BITS;
private static final int STOP = 1 << COUNT_BITS;
private static final int TIDYING = 2 << COUNT_BITS;
private static final int TERMINATED = 3 << COUNT_BITS;

源码解析

image

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public void execute(Runnable command) {
if (command == null)
throw new NullPointerException();
int c = ctl.get();

if (workerCountOf(c) < corePoolSize) {




if (addWorker(command, true))
return;
c = ctl.get();
}

if (isRunning(c) && workQueue.offer(command)) {
int recheck = ctl.get();

if (! isRunning(recheck) && remove(command))
reject(command);

else if (workerCountOf(recheck) == 0)
addWorker(null, false);
}



else if (!addWorker(command, false))
reject(command);
}
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private boolean addWorker(Runnable firstTask, boolean core) {
retry:
for (;;) {
int c = ctl.get();
int rs = runStateOf(c);










if (rs >= SHUTDOWN &&
! (rs == SHUTDOWN &&
firstTask == null &&
! workQueue.isEmpty()))
return false;

for (;;) {
int wc = workerCountOf(c);

if (wc >= CAPACITY ||
wc >= (core ? corePoolSize : maximumPoolSize))
return false;
if (compareAndIncrementWorkerCount(c))
break retry;
c = ctl.get();
if (runStateOf(c) != rs)
continue retry;
}
}

boolean workerStarted = false;
boolean workerAdded = false;
Worker w = null;
try {

w = new Worker(firstTask);
final Thread t = w.thread;
if (t != null) {
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
int rs = runStateOf(ctl.get());





if (rs < SHUTDOWN ||
(rs == SHUTDOWN && firstTask == null)) {
if (t.isAlive())
throw new IllegalThreadStateException();
workers.add(w);
int s = workers.size();
if (s > largestPoolSize)
largestPoolSize = s;
workerAdded = true;
}
} finally {
mainLock.unlock();
}
if (workerAdded) {

t.start();
workerStarted = true;
}
}
} finally {
if (! workerStarted)
addWorkerFailed(w);
}
return workerStarted;
}
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final void runWorker(Worker w) {
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
w.firstTask = null;
w.unlock();
boolean completedAbruptly = true;
try {




while (task != null || (task = getTask()) != null) {
w.lock();
if ((runStateAtLeast(ctl.get(), STOP) ||
(Thread.interrupted() &&
runStateAtLeast(ctl.get(), STOP))) &&
!wt.isInterrupted())
wt.interrupt();
try {
beforeExecute(wt, task);
Throwable thrown = null;
try {
task.run();
} catch (RuntimeException x) {
thrown = x; throw x;
} catch (Error x) {
thrown = x; throw x;
} catch (Throwable x) {
thrown = x; throw new Error(x);
} finally {
afterExecute(task, thrown);
}
} finally {
task = null;
w.completedTasks++;
w.unlock();
}
}
completedAbruptly = false;
} finally {
processWorkerExit(w, completedAbruptly);
}
}
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private Runnable getTask() {
boolean timedOut = false;

for (;;) {
int c = ctl.get();
int rs = runStateOf(c);






if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
decrementWorkerCount();
return null;
}

int wc = workerCountOf(c);



boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;

if ((wc > maximumPoolSize || (timed && timedOut))
&& (wc > 1 || workQueue.isEmpty())) {
if (compareAndDecrementWorkerCount(c))
return null;
continue;
}

try {




Runnable r = timed ?
workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
workQueue.take();
if (r != null)
return r;
timedOut = true;
} catch (InterruptedException retry) {
timedOut = false;
}
}
}

allowCoreThreadTimeOuttrue或者该Worker线程为非核心线程时,则Worker线程需要超时回收。

不需要超时回收的Worker线程从工作流程:

image

需要超时回收的Worker线程从工作流程:

image

shutdown和shutdownNow

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public void shutdown() {
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
checkShutdownAccess();
advanceRunState(SHUTDOWN);

interruptIdleWorkers();
onShutdown();
} finally {
mainLock.unlock();
}
tryTerminate();
}


public List<Runnable> shutdownNow() {
List<Runnable> tasks;
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
checkShutdownAccess();
advanceRunState(STOP);

interruptWorkers();
tasks = drainQueue();
} finally {
mainLock.unlock();
}
tryTerminate();
return tasks;
}

由于shutdown()不会中断正在执行任务的Worker线程,所有存在当任务执行一直完成不了时,线程池始终处于SHUTDOWN状态而无法关闭。

execute和submit

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public Future<?> submit(Runnable task) {
if (task == null) throw new NullPointerException();

RunnableFuture<Void> ftask = newTaskFor(task, null);
execute(ftask);
return ftask;
}

submit方法会通过newTaskFor方法创建FutureTask对象来包装任务,而FutureTaskrun方法会对任务的执行进行异常处理,保证任务执行中出现的异常不会向上抛出。代码如下:

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public void run() {
if (state != NEW ||
!UNSAFE.compareAndSwapObject(this, runnerOffset,
null, Thread.currentThread()))
return;
try {
Callable<V> c = callable;
if (c != null && state == NEW) {
V result;
boolean ran;
try {
result = c.call();
ran = true;
} catch (Throwable ex) {
result = null;
ran = false;
setException(ex);
}
if (ran)
set(result);
}
} finally {
runner = null;
int s = state;
if (s >= INTERRUPTING)
handlePossibleCancellationInterrupt(s);
}
}

由此可见,execute执行任务时,任务出现异常直接会向上抛,最终在runWorker方法中异常退出导致该Worker线程直接被回收;而submit则处理了任务中出现的异常,即使任务执行出现异常也不会导致Worker线程的回收。