[feature request] make sentinel client close resources more easier and elegant

[Anilople]

Issue Description

Type: feature request

Describe what happened (or what feature you want)

User can close sentinel client's resouces manually.

Describe what you expected to happen

User can use com.alibaba.csp.sentinel.init.InitExecutor.doInit() to init sentinel client.

Sometimes user want to close all resources in it.

Because some InitFunc will start a thread executor, and user may don't know how to close them.

For example, if user use sentinel-transport-simple-http, com.alibaba.csp.sentinel.transport.init.CommandCenterInitFunc will use com.alibaba.csp.sentinel.transport.command.SimpleHttpCommandCenter, there are 2 ExecutorService in it, user must write code to close it

		CommandCenter commandCenter = CommandCenterProvider.getCommandCenter();
		commandCenter.stop();

To make it more easier, should sentinel's client support a method to do it?

Like CloseExecutor.doClose().

Tell us your environment

OS: Centos 7.8
Jdk: 8
Sentinel Version: 1.8.0

Anything else we need to know?

When someone use Spring Cloud Alibaba Sentinel,
shutdown in actuator endpoint would be not working.

The reason is that ExecutorService in com.alibaba.csp.sentinel.transport.command.SimpleHttpCommandCenter prevents JVM to stop.

[Anilople]

It seems that infinite loops while (true) in

Sentinel/sentinel-transport/sentinel-transport-simple-http/src/main/java/com/alibaba/csp/sentinel/transport/command/SimpleHttpCommandCenter.java

Lines 184 to 209 in 2c12b07

	public void run() {
	while (true) {
	Socket socket = null;
	try {
	socket = this.serverSocket.accept();
	setSocketSoTimeout(socket);
	HttpEventTask eventTask = new HttpEventTask(socket);
	bizExecutor.submit(eventTask);
	} catch (Exception e) {
	CommandCenterLog.info("Server error", e);
	if (socket != null) {
	try {
	socket.close();
	} catch (Exception e1) {
	CommandCenterLog.info("Error when closing an opened socket", e1);
	}
	}
	try {
	// In case of infinite log.
	Thread.sleep(10);
	} catch (InterruptedException e1) {
	// Indicates the task should stop.
	break;
	}
	}
	}

prevents JVM to stop.

[Anilople]

Maybe we can change those thread to daemon thread?

Change

Sentinel/sentinel-transport/sentinel-transport-simple-http/src/main/java/com/alibaba/csp/sentinel/transport/command/SimpleHttpCommandCenter.java

Line 60 in 2c12b07

new NamedThreadFactory("sentinel-command-center-executor"));

to

new NamedThreadFactory("sentinel-command-center-executor", true)); 

Sentinel/sentinel-transport/sentinel-transport-simple-http/src/main/java/com/alibaba/csp/sentinel/transport/command/SimpleHttpCommandCenter.java

Line 78 in 2c12b07

new NamedThreadFactory("sentinel-command-center-service-executor"),

to

new NamedThreadFactory("sentinel-command-center-service-executor", true),

That will let jvm close when user thread finished.

[sczyh30]

Maybe we can change those thread to daemon thread?

Change

Sentinel/sentinel-transport/sentinel-transport-simple-http/src/main/java/com/alibaba/csp/sentinel/transport/command/SimpleHttpCommandCenter.java

Line 60 in 2c12b07

new NamedThreadFactory("sentinel-command-center-executor"));

to

new NamedThreadFactory("sentinel-command-center-executor", true)); 

Sentinel/sentinel-transport/sentinel-transport-simple-http/src/main/java/com/alibaba/csp/sentinel/transport/command/SimpleHttpCommandCenter.java

Line 78 in 2c12b07

new NamedThreadFactory("sentinel-command-center-service-executor"),

to

new NamedThreadFactory("sentinel-command-center-service-executor", true),

That will let jvm close when user thread finished.

Good idea. Fancy a PR to improve it?

[wutingjia]

please assign to me for practicing PR ~~~~(>_<)~~~~