src/main/java/jnr/posix/util/ExecIt.java

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 * License Version 2.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
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 *
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 * Copyright (C) 2008 JRuby Community
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package jnr.posix.util;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import jnr.posix.POSIXHandler;

public class ExecIt {
    protected final POSIXHandler handler;

    /** Creates a new instance of ShellLauncher
     *
     * @param handler the {@link POSIXHandler} to use
     */
    public ExecIt(POSIXHandler handler) {
        this.handler = handler;
    }

    public int runAndWait(String... args) throws IOException, InterruptedException {
        return runAndWait(handler.getOutputStream(), args);
    }

    public int runAndWait(OutputStream output, String... args) throws IOException, InterruptedException {
        return runAndWait(output, handler.getErrorStream(), args);
    }

    public int runAndWait(OutputStream output, OutputStream error, String... args) throws IOException, InterruptedException {
        Process process = run(args);

        handleStreams(process, handler.getInputStream(), output, error);

        return process.waitFor();
    }

    public Process run(String... args) throws IOException {
        File cwd = handler.getCurrentWorkingDirectory();
          
        return Runtime.getRuntime().exec(args, handler.getEnv(), cwd);        
    }

    private static class StreamPumper extends Thread {
        private InputStream in;
        private OutputStream out;
        private boolean onlyIfAvailable;
        private volatile boolean quit;
        private final Object waitLock = new Object();
        StreamPumper(InputStream in, OutputStream out, boolean avail) {
            this.in = in;
            this.out = out;
            this.onlyIfAvailable = avail;
        }
        
        public void run() {
            byte[] buf = new byte[1024];
            int numRead;
            boolean hasReadSomething = false;
            try {
                while (!quit) {
                    // The problem we trying to solve below: STDIN in Java is blocked and 
                    // non-interruptible, so if we invoke read on it, we might never be able to
                    // interrupt such thread.  So, we use in.available() to see if there is any 
                    // input ready, and only then read it. But this approach can't tell whether 
                    // the end of stream reached or not, so we might end up looping right at the
                    // end of the stream.  Well, at least, we can improve the situation by checking
                    // if some input was ever available, and if so, not checking for available 
                    // anymore, and just go to read.
                    if (onlyIfAvailable && !hasReadSomething) {
                        if (in.available() == 0) {
                            synchronized (waitLock) {
                                waitLock.wait(10);                                
                            }
                            continue;
                        } else {
                            hasReadSomething = true;
                        }
                    }

                    if ((numRead = in.read(buf)) == -1) {
                        break;
                    }
                    out.write(buf, 0, numRead);
                }
            } catch (Exception e) {
            } finally {
                if (onlyIfAvailable) {
                    // We need to close the out, since some
                    // processes would just wait for the stream
                    // to be closed before they process its content,
                    // and produce the output. E.g.: "cat".
                    try { out.close(); } catch (IOException ioe) {}
                }                
            }
        }
        
        public void quit() {
            this.quit = true;
            synchronized (waitLock) {
                waitLock.notify();                
            }
        }
    }

    private void handleStreams(Process p, InputStream in, OutputStream out, OutputStream err) throws IOException {
        InputStream pOut = p.getInputStream();
        InputStream pErr = p.getErrorStream();
        OutputStream pIn = p.getOutputStream();

        StreamPumper t1 = new StreamPumper(pOut, out, false);
        StreamPumper t2 = new StreamPumper(pErr, err, false);
        StreamPumper t3 = new StreamPumper(in, pIn, true);
        t1.start();
        t2.start();
        t3.start();

        try { t1.join(); } catch (InterruptedException ie) {}
        try { t2.join(); } catch (InterruptedException ie) {}
        t3.quit();

        try { err.flush(); } catch (IOException io) {}
        try { out.flush(); } catch (IOException io) {}

        try { pIn.close(); } catch (IOException io) {}
        try { pOut.close(); } catch (IOException io) {}
        try { pErr.close(); } catch (IOException io) {}

    }
}