/*
 * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.lang;

import java.io.*;

/* java.lang.Process subclass in the UNIX environment.
 *
 * @author Mario Wolczko and Ross Knippel.
 */

final class UNIXProcess extends Process {
    private static final sun.misc.JavaIOFileDescriptorAccess fdAccess
        = sun.misc.SharedSecrets.getJavaIOFileDescriptorAccess();

    private final int pid;
    private int exitcode;
    private boolean hasExited;

    private OutputStream stdin_stream;
    private InputStream stdout_stream;
    private DeferredCloseInputStream stdout_inner_stream;
    private InputStream stderr_stream;

    /* this is for the reaping thread */
    private native int waitForProcessExit(int pid);

    /**
     * Create a process using fork(2) and exec(2).
     *
     * @param std_fds array of file descriptors.  Indexes 0, 1, and
     *        2 correspond to standard input, standard output and
     *        standard error, respectively.  On input, a value of -1
     *        means to create a pipe to connect child and parent
     *        processes.  On output, a value which is not -1 is the
     *        parent pipe fd corresponding to the pipe which has
     *        been created.  An element of this array is -1 on input
     *        if and only if it is <em>not</em> -1 on output.
     * @return the pid of the subprocess
     */
    private native int forkAndExec(byte[] prog,
                                   byte[] argBlock, int argc,
                                   byte[] envBlock, int envc,
                                   byte[] dir,
                                   int[] std_fds,
                                   boolean redirectErrorStream)
        throws IOException;

    UNIXProcess(final byte[] prog,
                final byte[] argBlock, int argc,
                final byte[] envBlock, int envc,
                final byte[] dir,
                final int[] std_fds,
                final boolean redirectErrorStream)
    throws IOException {
        pid = forkAndExec(prog,
                          argBlock, argc,
                          envBlock, envc,
                          dir,
                          std_fds,
                          redirectErrorStream);

        java.security.AccessController.doPrivileged(
        new java.security.PrivilegedAction<Void>() { public Void run() {
            if (std_fds[0] == -1)
                stdin_stream = ProcessBuilder.NullOutputStream.INSTANCE;
            else {
                FileDescriptor stdin_fd = new FileDescriptor();
                fdAccess.set(stdin_fd, std_fds[0]);
                stdin_stream = new BufferedOutputStream(
                    new FileOutputStream(stdin_fd));
            }

            if (std_fds[1] == -1)
                stdout_stream = ProcessBuilder.NullInputStream.INSTANCE;
            else {
                FileDescriptor stdout_fd = new FileDescriptor();
                fdAccess.set(stdout_fd, std_fds[1]);
                stdout_inner_stream = new DeferredCloseInputStream(stdout_fd);
                stdout_stream = new BufferedInputStream(stdout_inner_stream);
            }

            if (std_fds[2] == -1)
                stderr_stream = ProcessBuilder.NullInputStream.INSTANCE;
            else {
                FileDescriptor stderr_fd = new FileDescriptor();
                fdAccess.set(stderr_fd, std_fds[2]);
                stderr_stream = new DeferredCloseInputStream(stderr_fd);
            }

            return null; }});

        /*
         * For each subprocess forked a corresponding reaper thread
         * is started.  That thread is the only thread which waits
         * for the subprocess to terminate and it doesn't hold any
         * locks while doing so.  This design allows waitFor() and
         * exitStatus() to be safely executed in parallel (and they
         * need no native code).
         */

        java.security.AccessController.doPrivileged(
            new java.security.PrivilegedAction<Void>() { public Void run() {
                Thread t = new Thread("process reaper") {
                    public void run() {
                        int res = waitForProcessExit(pid);
                        synchronized (UNIXProcess.this) {
                            hasExited = true;
                            exitcode = res;
                            UNIXProcess.this.notifyAll();
                        }
                    }
                };
                t.setDaemon(true);
                t.start();
                return null; }});
    }

    public OutputStream getOutputStream() {
        return stdin_stream;
    }

    public InputStream getInputStream() {
        return stdout_stream;
    }

    public InputStream getErrorStream() {
        return stderr_stream;
    }

    public synchronized int waitFor() throws InterruptedException {
        while (!hasExited) {
            wait();
        }
        return exitcode;
    }

    public synchronized int exitValue() {
        if (!hasExited) {
            throw new IllegalThreadStateException("process hasn't exited");
        }
        return exitcode;
    }

    private static native void destroyProcess(int pid);
    public synchronized void destroy() {
        // There is a risk that pid will be recycled, causing us to
        // kill the wrong process!  So we only terminate processes
        // that appear to still be running.  Even with this check,
        // there is an unavoidable race condition here, but the window
        // is very small, and OSes try hard to not recycle pids too
        // soon, so this is quite safe.
        if (!hasExited)
            destroyProcess(pid);
        try {
            stdin_stream.close();
            if (stdout_inner_stream != null)
                stdout_inner_stream.closeDeferred(stdout_stream);
            if (stderr_stream instanceof DeferredCloseInputStream)
                ((DeferredCloseInputStream) stderr_stream)
                    .closeDeferred(stderr_stream);
        } catch (IOException e) {
            // ignore
        }
    }

    // A FileInputStream that supports the deferment of the actual close
    // operation until the last pending I/O operation on the stream has
    // finished.  This is required on Solaris because we must close the stdin
    // and stdout streams in the destroy method in order to reclaim the
    // underlying file descriptors.  Doing so, however, causes any thread
    // currently blocked in a read on one of those streams to receive an
    // IOException("Bad file number"), which is incompatible with historical
    // behavior.  By deferring the close we allow any pending reads to see -1
    // (EOF) as they did before.
    //
    private static class DeferredCloseInputStream
        extends FileInputStream
    {

        private DeferredCloseInputStream(FileDescriptor fd) {
            super(fd);
        }

        private Object lock = new Object();     // For the following fields
        private boolean closePending = false;
        private int useCount = 0;
        private InputStream streamToClose;

        private void raise() {
            synchronized (lock) {
                useCount++;
            }
        }

        private void lower() throws IOException {
            synchronized (lock) {
                useCount--;
                if (useCount == 0 && closePending) {
                    streamToClose.close();
                }
            }
        }

        // stc is the actual stream to be closed; it might be this object, or
        // it might be an upstream object for which this object is downstream.
        //
        private void closeDeferred(InputStream stc) throws IOException {
            synchronized (lock) {
                if (useCount == 0) {
                    stc.close();
                } else {
                    closePending = true;
                    streamToClose = stc;
                }
            }
        }

        public void close() throws IOException {
            synchronized (lock) {
                useCount = 0;
                closePending = false;
            }
            super.close();
        }

        public int read() throws IOException {
            raise();
            try {
                return super.read();
            } finally {
                lower();
            }
        }

        public int read(byte[] b) throws IOException {
            raise();
            try {
                return super.read(b);
            } finally {
                lower();
            }
        }

        public int read(byte[] b, int off, int len) throws IOException {
            raise();
            try {
                return super.read(b, off, len);
            } finally {
                lower();
            }
        }

        public long skip(long n) throws IOException {
            raise();
            try {
                return super.skip(n);
            } finally {
                lower();
            }
        }

        public int available() throws IOException {
            raise();
            try {
                return super.available();
            } finally {
                lower();
            }
        }

    }

    /* This routine initializes JNI field offsets for the class */
    private static native void initIDs();

    static {
        initIDs();
    }
}