import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;


public class CPUMonitor {

    private static final Logger log=LoggerFactory.getLogger(CPUMonitor.class);
    private static CPUMonitor instance = new CPUMonitor();

    private ExecutorService workpool;
    private int cpuIdleThreshold; //cpu空闲阈值
    private int cpus; //cpu核数


    private CPUMonitor() {
        cpus = Runtime.getRuntime().availableProcessors();
        workpool = Executors.newFixedThreadPool(cpus);
        cpuIdleThreshold = 35;
    }

    public static CPUMonitor getInstance() {
        return instance;
    }

    public int getProcessCpu() {
        Runtime rt = Runtime.getRuntime();
        String[] cmd = { "/bin/sh", "-c", "top -b -d 0.1 -n 2 | grep '%Cpu(s)' | sed -n '$p' | awk '{print $8}'" };
        BufferedReader in = null;
        String str = "";
        try{
            Process p = rt.exec(cmd);
            in = new BufferedReader(new InputStreamReader(p.getInputStream()));
            str = in.readLine();
        }catch(Exception e){
            log.error("Get cpu utilization error.",e);
        }
        return (int)Float.parseFloat(str);
    }

    public void work(){
        for(int i=0; i<cpus; i++){
            workpool.submit(new Runnable() {
                @Override
                public void run() {
                    long threadId = Thread.currentThread().getId();
                    while(true){
                        int idle = getProcessCpu();
                        if(idle > cpuIdleThreshold){
                            log.info(String.format("Thread-%s  cpu idle:%s", threadId, idle));
                            List<Object> addList = new ArrayList<Object>();
                            String str = "abcdefghijklmnopqrstuvwxyz";
                            double var;
                            for(int j=0; j<10000000; j++){
                                addList.add(str);
                                addList.add(str);
                                addList.add(str);
                                addList.clear();
                                var = (double)j/3.3;
                            }
                        }else{
                            try {
                                log.info(String.format("Thread-%s  sleep:100ms", threadId));
                                Thread.sleep(100);
                            }catch (Exception e){
                                log.error("Thread sleep error.",e);
                            }
                        }
                    }
                }
            });
        }

        workpool.shutdown();
        try {
            while(!workpool.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS)){
                log.info("Thread pool is not shutdown");
            }
        }catch (Exception e){
            log.error("Thread pool awaitTermination error.",e);
        }
        log.info("Thread pool is shutdown");
    }

    public static void main(String[] args){
        CPUMonitor cpuMonitor = CPUMonitor.getInstance();
        log.info("Service start...");
        cpuMonitor.work();
    }

}