Java的Runtime exe进程阻塞问题

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具体参见： https://www.javaworld.com/article/2071275/when-runtime-exec---won-t.html?page=2

原因分析

The JDK’s Javadoc documentation provides the answer to this question:

Because some native platforms only provide limited buffer size for standard input and output streams, 
failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, and even deadlock.

主进程调用 process.waitFor() 后会挂起，子进程会不多输出，如果系统提供的很小的标准输入和输出，那边子进程的输出可能会充满整个输出缓存。这样子进程也会挂起，而主进程等待子进程结束，这样两个就陷入死锁。

最佳实践

import java.util.*;
import java.io.*;
class StreamGobbler extends Thread
{
    InputStream is;
    String type;
    
    StreamGobbler(InputStream is, String type)
    {
        this.is = is;
        this.type = type;
    }
    
    public void run()
    {
        try
        {
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line=null;
            while ( (line = br.readLine()) != null)
                System.out.println(type + ">" + line);    
            } catch (IOException ioe)
              {
                ioe.printStackTrace();  
              }
    }
}
public class GoodWindowsExec
{
    public static void main(String args[])
    {
        if (args.length < 1)
        {
            System.out.println("USAGE: java GoodWindowsExec <cmd>");
            System.exit(1);
        }
        
        try
        {            
            String osName = System.getProperty("os.name" );
            String[] cmd = new String[3];
            if( osName.equals( "Windows NT" ) )
            {
                cmd[0] = "cmd.exe" ;
                cmd[1] = "/C" ;
                cmd[2] = args[0];
            }
            else if( osName.equals( "Windows 95" ) )
            {
                cmd[0] = "command.com" ;
                cmd[1] = "/C" ;
                cmd[2] = args[0];
            }
            
            Runtime rt = Runtime.getRuntime();
            System.out.println("Execing " + cmd[0] + " " + cmd[1] 
                               + " " + cmd[2]);
            Process proc = rt.exec(cmd);
            // any error message?
            StreamGobbler errorGobbler = new 
                StreamGobbler(proc.getErrorStream(), "ERROR");            
            
            // any output?
            StreamGobbler outputGobbler = new 
                StreamGobbler(proc.getInputStream(), "OUTPUT");
                
            // kick them off
            errorGobbler.start();
            outputGobbler.start();
                                    
            // any error???
            int exitVal = proc.waitFor();
            System.out.println("ExitValue: " + exitVal);        
        } catch (Throwable t)
          {
            t.printStackTrace();
          }
    }
}