java/11 : java.base/java/lang/Process.java

Process
https://openjdk.java.net/
GPLv2 + Classpath Exception
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package java.lang;

import java.io.*;
import java.lang.ProcessBuilder.Redirect;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.TimeUnit;
import java.util.stream.Stream;

Process provides control of native processes started by ProcessBuilder.start and Runtime.exec. The class provides methods for performing input from the process, performing output to the process, waiting for the process to complete, checking the exit status of the process, and destroying (killing) the process. The ProcessBuilder.start() and Runtime.exec methods create a native process and return an instance of a subclass of Process that can be used to control the process and obtain information about it. The methods that create processes may not work well for special
processes on certain native platforms, such as native windowing
processes, daemon processes, Win16/DOS processes on Microsoft
Windows, or shell scripts.
By default, the created process does not have its own terminal or console. All its standard I/O (i.e. stdin, stdout, stderr) operations will be redirected to the parent process, where they can be accessed via the streams obtained using the methods getOutputStream(), getInputStream(), and getErrorStream(). The parent process uses these streams to feed input to and get output from the process. 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 process may cause the process to block, or even deadlock. 
Where desired, 
process I/O can also be redirected using methods of the ProcessBuilder class. 
The process is not killed when there are no more references to the Process object, but rather the process continues executing asynchronously. 
There is no requirement that the process represented by a 
Process object execute asynchronously or concurrently with respect to the Java process that owns the Process object. 
As of 1.5, ProcessBuilder.start() is the preferred way to create a Process. 
Subclasses of Process should override the onExit() and toHandle() methods to provide a fully functional Process including the process id, information about the process, direct children, and direct children plus descendants of those children of the process. Delegating to the underlying Process or ProcessHandle is typically easiest and most efficient. 
Since:   1.0/**
 * {@code Process} provides control of native processes started by
 * ProcessBuilder.start and Runtime.exec.
 * The class provides methods for performing input from the process, performing
 * output to the process, waiting for the process to complete,
 * checking the exit status of the process, and destroying (killing)
 * the process.
 * The {@link ProcessBuilder#start()} and
 * {@link Runtime#exec(String[],String[],File) Runtime.exec}
 * methods create a native process and return an instance of a
 * subclass of {@code Process} that can be used to control the process
 * and obtain information about it.
 *
 * <p>The methods that create processes may not work well for special
 * processes on certain native platforms, such as native windowing
 * processes, daemon processes, Win16/DOS processes on Microsoft
 * Windows, or shell scripts.
 *
 * <p>By default, the created process does not have its own terminal
 * or console.  All its standard I/O (i.e. stdin, stdout, stderr)
 * operations will be redirected to the parent process, where they can
 * be accessed via the streams obtained using the methods
 * {@link #getOutputStream()},
 * {@link #getInputStream()}, and
 * {@link #getErrorStream()}.
 * The parent process uses these streams to feed input to and get output
 * from the process.  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 process may cause the process to block, or even deadlock.
 *
 * <p>Where desired, <a href="ProcessBuilder.html#redirect-input">
 * process I/O can also be redirected</a>
 * using methods of the {@link ProcessBuilder} class.
 *
 * <p>The process is not killed when there are no more references to
 * the {@code Process} object, but rather the process
 * continues executing asynchronously.
 *
 * <p>There is no requirement that the process represented by a {@code
 * Process} object execute asynchronously or concurrently with respect
 * to the Java process that owns the {@code Process} object.
 *
 * <p>As of 1.5, {@link ProcessBuilder#start()} is the preferred way
 * to create a {@code Process}.
 *
 * <p>Subclasses of Process should override the {@link #onExit()} and
 * {@link #toHandle()} methods to provide a fully functional Process including the
 * {@linkplain #pid() process id},
 * {@linkplain #info() information about the process},
 * {@linkplain #children() direct children}, and
 * {@linkplain #descendants() direct children plus descendants of those children} of the process.
 * Delegating to the underlying Process or ProcessHandle is typically
 * easiest and most efficient.
 *
 * @since   1.0
 */
public abstract class Process {
    Default constructor for Process.
/**
     * Default constructor for Process.
     */
    public Process() {}

    Returns the output stream connected to the normal input of the process. Output to the stream is piped into the standard input of the process represented by this Process object. If the standard input of the process has been redirected using 
ProcessBuilder.redirectInput then this method will return a null output stream.
Implementation note: It is a good idea for the returned
output stream to be buffered.
Returns: the output stream connected to the normal input of the
        process/**
     * Returns the output stream connected to the normal input of the
     * process.  Output to the stream is piped into the standard
     * input of the process represented by this {@code Process} object.
     *
     * <p>If the standard input of the process has been redirected using
     * {@link ProcessBuilder#redirectInput(Redirect)
     * ProcessBuilder.redirectInput}
     * then this method will return a
     * <a href="ProcessBuilder.html#redirect-input">null output stream</a>.
     *
     * <p>Implementation note: It is a good idea for the returned
     * output stream to be buffered.
     *
     * @return the output stream connected to the normal input of the
     *         process
     */
    public abstract OutputStream getOutputStream();

    Returns the input stream connected to the normal output of the process. The stream obtains data piped from the standard output of the process represented by this Process object. If the standard output of the process has been redirected using 
ProcessBuilder.redirectOutput then this method will return a null input stream.
Otherwise, if the standard error of the process has been redirected using 
ProcessBuilder.redirectErrorStream then the input stream returned by this method will receive the merged standard output and the standard error of the process. 
Implementation note: It is a good idea for the returned
input stream to be buffered.
Returns: the input stream connected to the normal output of the
        process/**
     * Returns the input stream connected to the normal output of the
     * process.  The stream obtains data piped from the standard
     * output of the process represented by this {@code Process} object.
     *
     * <p>If the standard output of the process has been redirected using
     * {@link ProcessBuilder#redirectOutput(Redirect)
     * ProcessBuilder.redirectOutput}
     * then this method will return a
     * <a href="ProcessBuilder.html#redirect-output">null input stream</a>.
     *
     * <p>Otherwise, if the standard error of the process has been
     * redirected using
     * {@link ProcessBuilder#redirectErrorStream(boolean)
     * ProcessBuilder.redirectErrorStream}
     * then the input stream returned by this method will receive the
     * merged standard output and the standard error of the process.
     *
     * <p>Implementation note: It is a good idea for the returned
     * input stream to be buffered.
     *
     * @return the input stream connected to the normal output of the
     *         process
     */
    public abstract InputStream getInputStream();

    Returns the input stream connected to the error output of the process. The stream obtains data piped from the error output of the process represented by this Process object. If the standard error of the process has been redirected using 
ProcessBuilder.redirectError or 
ProcessBuilder.redirectErrorStream then this method will return a null input stream.
Implementation note: It is a good idea for the returned
input stream to be buffered.
Returns: the input stream connected to the error output of
        the process/**
     * Returns the input stream connected to the error output of the
     * process.  The stream obtains data piped from the error output
     * of the process represented by this {@code Process} object.
     *
     * <p>If the standard error of the process has been redirected using
     * {@link ProcessBuilder#redirectError(Redirect)
     * ProcessBuilder.redirectError} or
     * {@link ProcessBuilder#redirectErrorStream(boolean)
     * ProcessBuilder.redirectErrorStream}
     * then this method will return a
     * <a href="ProcessBuilder.html#redirect-output">null input stream</a>.
     *
     * <p>Implementation note: It is a good idea for the returned
     * input stream to be buffered.
     *
     * @return the input stream connected to the error output of
     *         the process
     */
    public abstract InputStream getErrorStream();

    Causes the current thread to wait, if necessary, until the process represented by this Process object has terminated. This method returns immediately if the process has already terminated. If the process has not yet terminated, the calling thread will be blocked until the process exits. 
Throws: InterruptedException – if the current thread is interrupted by another thread while it is waiting, then the wait is ended and an InterruptedException is thrown.
Returns: the exit value of the process represented by this Process object. By convention, the value 0 indicates normal termination./**
     * Causes the current thread to wait, if necessary, until the
     * process represented by this {@code Process} object has
     * terminated.  This method returns immediately if the process
     * has already terminated.  If the process has not yet
     * terminated, the calling thread will be blocked until the
     * process exits.
     *
     * @return the exit value of the process represented by this
     *         {@code Process} object.  By convention, the value
     *         {@code 0} indicates normal termination.
     * @throws InterruptedException if the current thread is
     *         {@linkplain Thread#interrupt() interrupted} by another
     *         thread while it is waiting, then the wait is ended and
     *         an {@link InterruptedException} is thrown.
     */
    public abstract int waitFor() throws InterruptedException;

    Causes the current thread to wait, if necessary, until the process represented by this Process object has terminated, or the specified waiting time elapses. If the process has already terminated then this method returns immediately with the value true. If the process has not terminated and the timeout value is less than, or equal to, zero, then this method returns immediately with the value false. 
The default implementation of this methods polls the exitValue to check if the process has terminated. Concrete implementations of this class are strongly encouraged to override this method with a more efficient implementation. 
Params: timeout – the maximum time to wait
unit – the time unit of the timeout argument
Throws: InterruptedException – if the current thread is interrupted
        while waiting.
NullPointerException – if unit is null
Returns: true if the process has exited and false if the waiting time elapsed before the process has exited.
Since: 1.8/**
     * Causes the current thread to wait, if necessary, until the
     * process represented by this {@code Process} object has
     * terminated, or the specified waiting time elapses.
     *
     * <p>If the process has already terminated then this method returns
     * immediately with the value {@code true}.  If the process has not
     * terminated and the timeout value is less than, or equal to, zero, then
     * this method returns immediately with the value {@code false}.
     *
     * <p>The default implementation of this methods polls the {@code exitValue}
     * to check if the process has terminated. Concrete implementations of this
     * class are strongly encouraged to override this method with a more
     * efficient implementation.
     *
     * @param timeout the maximum time to wait
     * @param unit the time unit of the {@code timeout} argument
     * @return {@code true} if the process has exited and {@code false} if
     *         the waiting time elapsed before the process has exited.
     * @throws InterruptedException if the current thread is interrupted
     *         while waiting.
     * @throws NullPointerException if unit is null
     * @since 1.8
     */
    public boolean waitFor(long timeout, TimeUnit unit)
        throws InterruptedException
    {
        long startTime = System.nanoTime();
        long rem = unit.toNanos(timeout);

        do {
            try {
                exitValue();
                return true;
            } catch(IllegalThreadStateException ex) {
                if (rem > 0)
                    Thread.sleep(
                        Math.min(TimeUnit.NANOSECONDS.toMillis(rem) + 1, 100));
            }
            rem = unit.toNanos(timeout) - (System.nanoTime() - startTime);
        } while (rem > 0);
        return false;
    }

    Returns the exit value for the process.
Throws: IllegalThreadStateException – if the process represented by this Process object has not yet terminated
Returns: the exit value of the process represented by this Process object. By convention, the value 0 indicates normal termination./**
     * Returns the exit value for the process.
     *
     * @return the exit value of the process represented by this
     *         {@code Process} object.  By convention, the value
     *         {@code 0} indicates normal termination.
     * @throws IllegalThreadStateException if the process represented
     *         by this {@code Process} object has not yet terminated
     */
    public abstract int exitValue();

    Kills the process. Whether the process represented by this Process object is normally terminated or not is implementation dependent. Forcible process destruction is defined as the immediate termination of a process, whereas normal termination allows the process to shut down cleanly. If the process is not alive, no action is taken.  The CompletableFuture from onExit is completed when the process has terminated. /**
     * Kills the process.
     * Whether the process represented by this {@code Process} object is
     * {@linkplain #supportsNormalTermination normally terminated} or not is
     * implementation dependent.
     * Forcible process destruction is defined as the immediate termination of a
     * process, whereas normal termination allows the process to shut down cleanly.
     * If the process is not alive, no action is taken.
     * <p>
     * The {@link java.util.concurrent.CompletableFuture} from {@link #onExit} is
     * {@linkplain java.util.concurrent.CompletableFuture#complete completed}
     * when the process has terminated.
     */
    public abstract void destroy();

    Kills the process forcibly. The process represented by this Process object is forcibly terminated. Forcible process destruction is defined as the immediate termination of a process, whereas normal termination allows the process to shut down cleanly. If the process is not alive, no action is taken.  The CompletableFuture from onExit is completed when the process has terminated. 
 Invoking this method on Process objects returned by ProcessBuilder.start and Runtime.exec forcibly terminate the process. 
Implementation Requirements:  The default implementation of this method invokes destroy and so may not forcibly terminate the process.
Implementation Note: 
Concrete implementations of this class are strongly encouraged to override
this method with a compliant implementation.
API Note:  The process may not terminate immediately. i.e. isAlive() may return true for a brief period after destroyForcibly() is called. This method may be chained to waitFor() if needed.
Returns: the Process object representing the process forcibly destroyed
Since: 1.8/**
     * Kills the process forcibly. The process represented by this
     * {@code Process} object is forcibly terminated.
     * Forcible process destruction is defined as the immediate termination of a
     * process, whereas normal termination allows the process to shut down cleanly.
     * If the process is not alive, no action is taken.
     * <p>
     * The {@link java.util.concurrent.CompletableFuture} from {@link #onExit} is
     * {@linkplain java.util.concurrent.CompletableFuture#complete completed}
     * when the process has terminated.
     * <p>
     * Invoking this method on {@code Process} objects returned by
     * {@link ProcessBuilder#start} and {@link Runtime#exec} forcibly terminate
     * the process.
     *
     * @implSpec
     * The default implementation of this method invokes {@link #destroy}
     * and so may not forcibly terminate the process.
     * @implNote
     * Concrete implementations of this class are strongly encouraged to override
     * this method with a compliant implementation.
     * @apiNote
     * The process may not terminate immediately.
     * i.e. {@code isAlive()} may return true for a brief period
     * after {@code destroyForcibly()} is called. This method
     * may be chained to {@code waitFor()} if needed.
     *
     * @return the {@code Process} object representing the
     *         process forcibly destroyed
     * @since 1.8
     */
    public Process destroyForcibly() {
        destroy();
        return this;
    }

    Returns true if the implementation of destroy is to normally terminate the process, Returns false if the implementation of destroy forcibly and immediately terminates the process.  Invoking this method on Process objects returned by ProcessBuilder.start and Runtime.exec return true or false depending on the platform implementation. 
Throws: UnsupportedOperationException – if the Process implementation
        does not support this operation
Implementation Requirements:  This implementation throws an instance of UnsupportedOperationException and performs no other action.
Returns: true if the implementation of destroy is to normally terminate the process; otherwise, destroy forcibly terminates the process
Since: 9/**
     * Returns {@code true} if the implementation of {@link #destroy} is to
     * normally terminate the process,
     * Returns {@code false} if the implementation of {@code destroy}
     * forcibly and immediately terminates the process.
     * <p>
     * Invoking this method on {@code Process} objects returned by
     * {@link ProcessBuilder#start} and {@link Runtime#exec} return
     * {@code true} or {@code false} depending on the platform implementation.
     *
     * @implSpec
     * This implementation throws an instance of
     * {@link java.lang.UnsupportedOperationException} and performs no other action.
     *
     * @return {@code true} if the implementation of {@link #destroy} is to
     *         normally terminate the process;
     *         otherwise, {@link #destroy} forcibly terminates the process
     * @throws UnsupportedOperationException if the Process implementation
     *         does not support this operation
     * @since 9
     */
    public boolean supportsNormalTermination() {
        throw new UnsupportedOperationException(this.getClass()
                + ".supportsNormalTermination() not supported" );
    }

    Tests whether the process represented by this Process is alive. 
Returns: true if the process represented by this Process object has not yet terminated.
Since: 1.8/**
     * Tests whether the process represented by this {@code Process} is
     * alive.
     *
     * @return {@code true} if the process represented by this
     *         {@code Process} object has not yet terminated.
     * @since 1.8
     */
    public boolean isAlive() {
        try {
            exitValue();
            return false;
        } catch(IllegalThreadStateException e) {
            return true;
        }
    }

    Returns the native process ID of the process.
The native process ID is an identification number that the operating
system assigns to the process.
Throws: UnsupportedOperationException – if the Process implementation
        does not support this operation
Implementation Requirements:  The implementation of this method returns the process id as: toHandle().pid().
Returns: the native process id of the process
Since: 9/**
     * Returns the native process ID of the process.
     * The native process ID is an identification number that the operating
     * system assigns to the process.
     *
     * @implSpec
     * The implementation of this method returns the process id as:
     * {@link #toHandle toHandle().pid()}.
     *
     * @return the native process id of the process
     * @throws UnsupportedOperationException if the Process implementation
     *         does not support this operation
     * @since 9
     */
    public long pid() {
        return toHandle().pid();
    }

    Returns a CompletableFuture<Process> for the termination of the Process. The CompletableFuture provides the ability to trigger dependent functions or actions that may be run synchronously or asynchronously upon process termination. When the process has terminated the CompletableFuture is completed regardless of the exit status of the process.  Calling onExit().get() waits for the process to terminate and returns the Process. The future can be used to check if the process is done or to wait for it to terminate. Cancelling the CompletableFuture does not affect the Process. 
 Processes returned from ProcessBuilder.start override the default implementation to provide an efficient mechanism to wait for process exit. 
API Note:  Using onExit is an alternative to waitFor that enables both additional concurrency and convenient access to the result of the Process. Lambda expressions can be used to evaluate the result of the Process execution. If there is other processing to be done before the value is used then onExit is a convenient mechanism to free the current thread and block only if and when the value is needed. 

For example, launching a process to compare two files and get a boolean if they are identical:
   Process p = new ProcessBuilder("cmp", "f1", "f2").start();
   Future<Boolean> identical = p.onExit().thenApply(p1 -> p1.exitValue() == 0);
   ...
   if (identical.get()) { ... }
Implementation Requirements:  This implementation executes waitFor() in a separate thread repeatedly until it returns successfully. If the execution of waitFor is interrupted, the thread's interrupt status is preserved.  When waitFor() returns successfully the CompletableFuture is completed regardless of the exit status of the process. This implementation may consume a lot of memory for thread stacks if a large number of processes are waited for concurrently. 

External implementations should override this method and provide
a more efficient implementation. For example, to delegate to the underlying
process, it can do the following:

   public CompletableFuture<Process> onExit() {
      return delegate.onExit().thenApply(p -> this);
   }
API Note:  The process may be observed to have terminated with isAlive before the ComputableFuture is completed and dependent actions are invoked.
Returns: a new CompletableFuture<Process> for the Process
Since: 9/**
     * Returns a {@code CompletableFuture<Process>} for the termination of the Process.
     * The {@link java.util.concurrent.CompletableFuture} provides the ability
     * to trigger dependent functions or actions that may be run synchronously
     * or asynchronously upon process termination.
     * When the process has terminated the CompletableFuture is
     * {@link java.util.concurrent.CompletableFuture#complete completed} regardless
     * of the exit status of the process.
     * <p>
     * Calling {@code onExit().get()} waits for the process to terminate and returns
     * the Process. The future can be used to check if the process is
     * {@linkplain java.util.concurrent.CompletableFuture#isDone done} or to
     * {@linkplain java.util.concurrent.CompletableFuture#get() wait} for it to terminate.
     * {@linkplain java.util.concurrent.CompletableFuture#cancel(boolean) Cancelling}
     * the CompletableFuture does not affect the Process.
     * <p>
     * Processes returned from {@link ProcessBuilder#start} override the
     * default implementation to provide an efficient mechanism to wait
     * for process exit.
     *
     * @apiNote
     * Using {@link #onExit() onExit} is an alternative to
     * {@link #waitFor() waitFor} that enables both additional concurrency
     * and convenient access to the result of the Process.
     * Lambda expressions can be used to evaluate the result of the Process
     * execution.
     * If there is other processing to be done before the value is used
     * then {@linkplain #onExit onExit} is a convenient mechanism to
     * free the current thread and block only if and when the value is needed.
     * <br>
     * For example, launching a process to compare two files and get a boolean if they are identical:
     * <pre> {@code   Process p = new ProcessBuilder("cmp", "f1", "f2").start();
     *    Future<Boolean> identical = p.onExit().thenApply(p1 -> p1.exitValue() == 0);
     *    ...
     *    if (identical.get()) { ... }
     * }</pre>
     *
     * @implSpec
     * This implementation executes {@link #waitFor()} in a separate thread
     * repeatedly until it returns successfully. If the execution of
     * {@code waitFor} is interrupted, the thread's interrupt status is preserved.
     * <p>
     * When {@link #waitFor()} returns successfully the CompletableFuture is
     * {@linkplain java.util.concurrent.CompletableFuture#complete completed} regardless
     * of the exit status of the process.
     *
     * This implementation may consume a lot of memory for thread stacks if a
     * large number of processes are waited for concurrently.
     * <p>
     * External implementations should override this method and provide
     * a more efficient implementation. For example, to delegate to the underlying
     * process, it can do the following:
     * <pre>{@code
     *    public CompletableFuture<Process> onExit() {
     *       return delegate.onExit().thenApply(p -> this);
     *    }
     * }</pre>
     * @apiNote
     * The process may be observed to have terminated with {@link #isAlive}
     * before the ComputableFuture is completed and dependent actions are invoked.
     *
     * @return a new {@code CompletableFuture<Process>} for the Process
     *
     * @since 9
     */
    public CompletableFuture<Process> onExit() {
        return CompletableFuture.supplyAsync(this::waitForInternal);
    }

    Wait for the process to exit by calling waitFor. If the thread is interrupted, remember the interrupted state to be restored before returning. Use ForkJoinPool.ManagedBlocker so that the number of workers in case ForkJoinPool is used is compensated when the thread blocks in waitFor(). 
Returns: the Process/**
     * Wait for the process to exit by calling {@code waitFor}.
     * If the thread is interrupted, remember the interrupted state to
     * be restored before returning. Use ForkJoinPool.ManagedBlocker
     * so that the number of workers in case ForkJoinPool is used is
     * compensated when the thread blocks in waitFor().
     *
     * @return the Process
     */
    private Process waitForInternal() {
        boolean interrupted = false;
        while (true) {
            try {
                ForkJoinPool.managedBlock(new ForkJoinPool.ManagedBlocker() {
                    @Override
                    public boolean block() throws InterruptedException {
                        waitFor();
                        return true;
                    }

                    @Override
                    public boolean isReleasable() {
                        return !isAlive();
                    }
                });
                break;
            } catch (InterruptedException x) {
                interrupted = true;
            }
        }
        if (interrupted) {
            Thread.currentThread().interrupt();
        }
        return this;
    }

    Returns a ProcessHandle for the Process. Process objects returned by ProcessBuilder.start and Runtime.exec implement toHandle as the equivalent of ProcessHandle.of(pid) including the check for a SecurityManager and RuntimePermission("manageProcess"). 
Throws: UnsupportedOperationException – if the Process implementation
        does not support this operation
SecurityException – if a security manager has been installed and
        it denies RuntimePermission("manageProcess")
Implementation Requirements:  This implementation throws an instance of UnsupportedOperationException and performs no other action. Subclasses should override this method to provide a ProcessHandle for the process. The methods pid, info, children, and descendants, unless overridden, operate on the ProcessHandle.
Returns: Returns a ProcessHandle for the Process
Since: 9/**
     * Returns a ProcessHandle for the Process.
     *
     * {@code Process} objects returned by {@link ProcessBuilder#start} and
     * {@link Runtime#exec} implement {@code toHandle} as the equivalent of
     * {@link ProcessHandle#of(long) ProcessHandle.of(pid)} including the
     * check for a SecurityManager and {@code RuntimePermission("manageProcess")}.
     *
     * @implSpec
     * This implementation throws an instance of
     * {@link java.lang.UnsupportedOperationException} and performs no other action.
     * Subclasses should override this method to provide a ProcessHandle for the
     * process.  The methods {@link #pid}, {@link #info}, {@link #children},
     * and {@link #descendants}, unless overridden, operate on the ProcessHandle.
     *
     * @return Returns a ProcessHandle for the Process
     * @throws UnsupportedOperationException if the Process implementation
     *         does not support this operation
     * @throws SecurityException if a security manager has been installed and
     *         it denies RuntimePermission("manageProcess")
     * @since 9
     */
    public ProcessHandle toHandle() {
        throw new UnsupportedOperationException(this.getClass()
                + ".toHandle() not supported");
    }

    Returns a snapshot of information about the process.
 A Info instance has accessor methods that return information about the process if it is available. 
Throws: UnsupportedOperationException – if the Process implementation
        does not support this operation
Implementation Requirements:  This implementation returns information about the process as: toHandle().info().
Returns: a snapshot of information about the process, always non-null
Since: 9/**
     * Returns a snapshot of information about the process.
     *
     * <p> A {@link ProcessHandle.Info} instance has accessor methods
     * that return information about the process if it is available.
     *
     * @implSpec
     * This implementation returns information about the process as:
     * {@link #toHandle toHandle().info()}.
     *
     * @return a snapshot of information about the process, always non-null
     * @throws UnsupportedOperationException if the Process implementation
     *         does not support this operation
     * @since 9
     */
    public ProcessHandle.Info info() {
        return toHandle().info();
    }

    Returns a snapshot of the direct children of the process. The parent of a direct child process is the process. Typically, a process that is not alive has no children. 
Note that processes are created and terminate asynchronously. There is no guarantee that a process is alive. 
Throws: UnsupportedOperationException – if the Process implementation
        does not support this operation
SecurityException – if a security manager has been installed and
        it denies RuntimePermission("manageProcess")
Implementation Requirements:  This implementation returns the direct children as: toHandle().children().
Returns: a sequential Stream of ProcessHandles for processes that are
        direct children of the process
Since: 9/**
     * Returns a snapshot of the direct children of the process.
     * The parent of a direct child process is the process.
     * Typically, a process that is {@linkplain #isAlive not alive} has no children.
     * <p>
     * <em>Note that processes are created and terminate asynchronously.
     * There is no guarantee that a process is {@linkplain #isAlive alive}.
     * </em>
     *
     * @implSpec
     * This implementation returns the direct children as:
     * {@link #toHandle toHandle().children()}.
     *
     * @return a sequential Stream of ProcessHandles for processes that are
     *         direct children of the process
     * @throws UnsupportedOperationException if the Process implementation
     *         does not support this operation
     * @throws SecurityException if a security manager has been installed and
     *         it denies RuntimePermission("manageProcess")
     * @since 9
     */
    public Stream<ProcessHandle> children() {
        return toHandle().children();
    }

    Returns a snapshot of the descendants of the process. The descendants of a process are the children of the process plus the descendants of those children, recursively. Typically, a process that is not alive has no children. 
Note that processes are created and terminate asynchronously. There is no guarantee that a process is alive. 
Throws: UnsupportedOperationException – if the Process implementation
        does not support this operation
SecurityException – if a security manager has been installed and
        it denies RuntimePermission("manageProcess")
Implementation Requirements:  This implementation returns all children as: toHandle().descendants().
Returns: a sequential Stream of ProcessHandles for processes that
        are descendants of the process
Since: 9/**
     * Returns a snapshot of the descendants of the process.
     * The descendants of a process are the children of the process
     * plus the descendants of those children, recursively.
     * Typically, a process that is {@linkplain #isAlive not alive} has no children.
     * <p>
     * <em>Note that processes are created and terminate asynchronously.
     * There is no guarantee that a process is {@linkplain #isAlive alive}.
     * </em>
     *
     * @implSpec
     * This implementation returns all children as:
     * {@link #toHandle toHandle().descendants()}.
     *
     * @return a sequential Stream of ProcessHandles for processes that
     *         are descendants of the process
     * @throws UnsupportedOperationException if the Process implementation
     *         does not support this operation
     * @throws SecurityException if a security manager has been installed and
     *         it denies RuntimePermission("manageProcess")
     * @since 9
     */
    public Stream<ProcessHandle> descendants() {
        return toHandle().descendants();
    }

    An input stream for a subprocess pipe that skips by reading bytes
instead of seeking, the underlying pipe does not support seek.
/**
     * An input stream for a subprocess pipe that skips by reading bytes
     * instead of seeking, the underlying pipe does not support seek.
     */
    static class PipeInputStream extends FileInputStream {

        PipeInputStream(FileDescriptor fd) {
            super(fd);
        }

        @Override
        public long skip(long n) throws IOException {
            long remaining = n;
            int nr;

            if (n <= 0) {
                return 0;
            }

            int size = (int)Math.min(2048, remaining);
            byte[] skipBuffer = new byte[size];
            while (remaining > 0) {
                nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
                if (nr < 0) {
                    break;
                }
                remaining -= nr;
            }

            return n - remaining;
        }
    }
}
Throws:	InterruptedException – if the current thread is interrupted by another thread while it is waiting, then the wait is ended and an `InterruptedException` is thrown.
Returns:	the exit value of the process represented by this `Process` object. By convention, the value `0` indicates normal termination.
Params:	timeout – the maximum time to wait unit – the time unit of the `timeout` argument
Throws:	InterruptedException – if the current thread is interrupted while waiting. NullPointerException – if unit is null
Returns:	`true` if the process has exited and `false` if the waiting time elapsed before the process has exited.
Since:	1.8
Throws:	IllegalThreadStateException – if the process represented by this `Process` object has not yet terminated
Returns:	the exit value of the process represented by this `Process` object. By convention, the value `0` indicates normal termination.
Implementation Requirements:	The default implementation of this method invokes `destroy` and so may not forcibly terminate the process.
Implementation Note:	Concrete implementations of this class are strongly encouraged to override this method with a compliant implementation.
API Note:	The process may not terminate immediately. i.e. `isAlive()` may return true for a brief period after `destroyForcibly()` is called. This method may be chained to `waitFor()` if needed.
Returns:	the `Process` object representing the process forcibly destroyed
Since:	1.8
Throws:	UnsupportedOperationException – if the Process implementation does not support this operation
Implementation Requirements:	This implementation throws an instance of `UnsupportedOperationException` and performs no other action.
Returns:	`true` if the implementation of `destroy` is to normally terminate the process; otherwise, `destroy` forcibly terminates the process
Since:	9
Returns:	`true` if the process represented by this `Process` object has not yet terminated.
Since:	1.8
API Note:	Using `onExit` is an alternative to `waitFor` that enables both additional concurrency and convenient access to the result of the Process. Lambda expressions can be used to evaluate the result of the Process execution. If there is other processing to be done before the value is used then onExit is a convenient mechanism to free the current thread and block only if and when the value is needed. For example, launching a process to compare two files and get a boolean if they are identical: `Process p = new ProcessBuilder("cmp", "f1", "f2").start(); Future<Boolean> identical = p.onExit().thenApply(p1 -> p1.exitValue() == 0); ... if (identical.get()) { ... }`
Implementation Requirements:	This implementation executes `waitFor()` in a separate thread repeatedly until it returns successfully. If the execution of `waitFor` is interrupted, the thread's interrupt status is preserved. When `waitFor()` returns successfully the CompletableFuture is completed regardless of the exit status of the process. This implementation may consume a lot of memory for thread stacks if a large number of processes are waited for concurrently. External implementations should override this method and provide a more efficient implementation. For example, to delegate to the underlying process, it can do the following: `public CompletableFuture<Process> onExit() { return delegate.onExit().thenApply(p -> this); }`
API Note:	The process may be observed to have terminated with `isAlive` before the ComputableFuture is completed and dependent actions are invoked.
Returns:	a new `CompletableFuture<Process>` for the Process
Since:	9
/

java/ 11/ java.base/java/lang/Process.java
