JDK 11 java.base.jmod - Base Module
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⏎ java/lang/Process.java
/*
* Copyright (c) 1995, 2017, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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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;
/**
* {@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.
*/
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 {@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 {@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 {@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 {@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 {@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.
*
* @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 {@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
* {@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 {@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 {@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.
*
* @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 {@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 {@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.
*
* {@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.
*
* <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 {@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 {@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.
*/
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;
}
}
}
⏎ java/lang/Process.java
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