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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * accompanied this code).
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package jdk.internal.misc;

import java.util.Hashtable;
import java.util.Objects;


This class provides ANSI/ISO C signal support. A Java program can register
signal handlers for the current process. There are two restrictions:

    

  • 
Java code cannot register a handler for signals that are already used
by the Java VM implementation. The Signal.handle
function raises an IllegalArgumentException if such an attempt
is made.

  • 
When Signal.handle is called, the VM internally registers a
special C signal handler. There is no way to force the Java signal handler
to run synchronously before the C signal handler returns. Instead, when the
VM receives a signal, the special C signal handler creates a new thread
(at priority Thread.MAX_PRIORITY) to
run the registered Java signal handler. The C signal handler immediately
returns. Note that because the Java signal handler runs in a newly created
thread, it may not actually be executed until some time after the C signal
handler returns.




Signal objects are created based on their names. For example:

new Signal("INT");


constructs a signal object corresponding to SIGINT, which is
typically produced when the user presses Ctrl-C at the command line.
The Signal constructor throws IllegalArgumentException
when it is passed an unknown signal.


This is an example of how Java code handles SIGINT:

Signal.Handler handler = new Signal.Handler () {
    public void handle(Signal sig) {
      ... // handle SIGINT
    }
};
Signal.handle(new Signal("INT"), handler);



Since:   9
/**
 * This class provides ANSI/ISO C signal support. A Java program can register
 * signal handlers for the current process. There are two restrictions:
 * <ul>
 * <li>
 * Java code cannot register a handler for signals that are already used
 * by the Java VM implementation. The <code>Signal.handle</code>
 * function raises an <code>IllegalArgumentException</code> if such an attempt
 * is made.
 * <li>
 * When <code>Signal.handle</code> is called, the VM internally registers a
 * special C signal handler. There is no way to force the Java signal handler
 * to run synchronously before the C signal handler returns. Instead, when the
 * VM receives a signal, the special C signal handler creates a new thread
 * (at priority <code>Thread.MAX_PRIORITY</code>) to
 * run the registered Java signal handler. The C signal handler immediately
 * returns. Note that because the Java signal handler runs in a newly created
 * thread, it may not actually be executed until some time after the C signal
 * handler returns.
 * </ul>
 * <p>
 * Signal objects are created based on their names. For example:
 * <blockquote><pre>
 * new Signal("INT");
 * </pre></blockquote>
 * constructs a signal object corresponding to <code>SIGINT</code>, which is
 * typically produced when the user presses <code>Ctrl-C</code> at the command line.
 * The <code>Signal</code> constructor throws <code>IllegalArgumentException</code>
 * when it is passed an unknown signal.
 * <p>
 * This is an example of how Java code handles <code>SIGINT</code>:
 * <blockquote><pre>
 * Signal.Handler handler = new Signal.Handler () {
 *     public void handle(Signal sig) {
 *       ... // handle SIGINT
 *     }
 * };
 * Signal.handle(new Signal("INT"), handler);
 * </pre></blockquote>
 *
 * @since    9
 */
public final class Signal {
    private static Hashtable<Signal, Signal.Handler> handlers = new Hashtable<>(4);
    private static Hashtable<Integer, Signal> signals = new Hashtable<>(4);

    private int number;
    private String name;

    /* Returns the signal number */
    public int getNumber() {
        return number;
    }

    
Returns the signal name.

See Also:
Returns:the name of the signal.
/**
     * Returns the signal name.
     *
     * @return the name of the signal.
     * @see jdk.internal.misc.Signal#Signal(String name)
     */
    public String getName() {
        return name;
    }

    
Compares the equality of two Signal objects.

Params:
  • other – the object to compare with.
Returns:whether two Signal objects are equal.
/**
     * Compares the equality of two <code>Signal</code> objects.
     *
     * @param other the object to compare with.
     * @return whether two <code>Signal</code> objects are equal.
     */
    public boolean equals(Object other) {
        if (this == other) {
            return true;
        }
        if (other == null || !(other instanceof Signal)) {
            return false;
        }
        Signal other1 = (Signal)other;
        return name.equals(other1.name) && (number == other1.number);
    }

    
Returns a hashcode for this Signal.

Returns: a hash code value for this object.
/**
     * Returns a hashcode for this Signal.
     *
     * @return  a hash code value for this object.
     */
    public int hashCode() {
        return number;
    }

    
Returns a string representation of this signal. For example, "SIGINT"
for an object constructed using new Signal ("INT").

Returns:a string representation of the signal
/**
     * Returns a string representation of this signal. For example, "SIGINT"
     * for an object constructed using <code>new Signal ("INT")</code>.
     *
     * @return a string representation of the signal
     */
    public String toString() {
        return "SIG" + name;
    }

    
Constructs a signal from its name.

Params:
  • name – the name of the signal.
Throws:
See Also:
/**
     * Constructs a signal from its name.
     *
     * @param name the name of the signal.
     * @exception IllegalArgumentException unknown signal
     * @see jdk.internal.misc.Signal#getName()
     */
    public Signal(String name) {
        Objects.requireNonNull(name, "name");
        // Signal names are the short names;
        // the "SIG" prefix is not used for compatibility with previous JDKs
        if (name.startsWith("SIG")) {
            throw new IllegalArgumentException("Unknown signal: " + name);
        }
        this.name = name;
        number = findSignal0(name);
        if (number < 0) {
            throw new IllegalArgumentException("Unknown signal: " + name);
        }
    }

    
Registers a signal handler.

Params:
  • sig – a signal
  • handler – the handler to be registered with the given signal.
Throws:
See Also:
Returns:the old handler
/**
     * Registers a signal handler.
     *
     * @param sig a signal
     * @param handler the handler to be registered with the given signal.
     * @return the old handler
     * @exception IllegalArgumentException the signal is in use by the VM
     * @see jdk.internal.misc.Signal#raise(Signal sig)
     * @see jdk.internal.misc.Signal.Handler
     * @see jdk.internal.misc.Signal.Handler#SIG_DFL
     * @see jdk.internal.misc.Signal.Handler#SIG_IGN
     */
    public static synchronized Signal.Handler handle(Signal sig,
                                                    Signal.Handler handler)
        throws IllegalArgumentException {
        Objects.requireNonNull(sig, "sig");
        Objects.requireNonNull(handler, "handler");
        long newH = (handler instanceof NativeHandler) ?
                      ((NativeHandler)handler).getHandler() : 2;
        long oldH = handle0(sig.number, newH);
        if (oldH == -1) {
            throw new IllegalArgumentException
                ("Signal already used by VM or OS: " + sig);
        }
        signals.put(sig.number, sig);
        synchronized (handlers) {
            Signal.Handler oldHandler = handlers.get(sig);
            handlers.remove(sig);
            if (newH == 2) {
                handlers.put(sig, handler);
            }
            if (oldH == 0) {
                return Signal.Handler.SIG_DFL;
            } else if (oldH == 1) {
                return Signal.Handler.SIG_IGN;
            } else if (oldH == 2) {
                return oldHandler;
            } else {
                return new NativeHandler(oldH);
            }
        }
    }

    
Raises a signal in the current process.

Params:
  • sig – a signal
See Also:
/**
     * Raises a signal in the current process.
     *
     * @param sig a signal
     * @see jdk.internal.misc.Signal#handle(Signal sig, Signal.Handler handler)
     */
    public static void raise(Signal sig) throws IllegalArgumentException {
        Objects.requireNonNull(sig, "sig");
        if (handlers.get(sig) == null) {
            throw new IllegalArgumentException("Unhandled signal: " + sig);
        }
        raise0(sig.number);
    }

    /* Called by the VM to execute Java signal handlers. */
    private static void dispatch(final int number) {
        final Signal sig = signals.get(number);
        final Signal.Handler handler = handlers.get(sig);

        Runnable runnable = new Runnable () {
            public void run() {
              // Don't bother to reset the priority. Signal handler will
              // run at maximum priority inherited from the VM signal
              // dispatch thread.
              // Thread.currentThread().setPriority(Thread.NORM_PRIORITY);
                handler.handle(sig);
            }
        };
        if (handler != null) {
            new Thread(null, runnable, sig + " handler", 0, false).start();
        }
    }

    /* Find the signal number, given a name. Returns -1 for unknown signals. */
    private static native int findSignal0(String sigName);
    /* Registers a native signal handler, and returns the old handler.
     * Handler values:
     *   0     default handler
     *   1     ignore the signal
     *   2     call back to Signal.dispatch
     *   other arbitrary native signal handlers
     */
    private static native long handle0(int sig, long nativeH);
    /* Raise a given signal number */
    private static native void raise0(int sig);

    
This is the signal handler interface expected in Signal.handle.

/**
     * This is the signal handler interface expected in <code>Signal.handle</code>.
     */
    public interface Handler {

        
The default signal handler

/**
         * The default signal handler
         */
        public static final Signal.Handler SIG_DFL = new NativeHandler(0);
        
Ignore the signal

/**
         * Ignore the signal
         */
        public static final Signal.Handler SIG_IGN = new NativeHandler(1);

        
Handle the given signal

Params:
  • sig – a signal object
/**
         * Handle the given signal
         *
         * @param sig a signal object
         */
        public void handle(Signal sig);
    }


    /*
     * A package-private class implementing a signal handler in native code.
     */
    static final class NativeHandler implements Signal.Handler {

        private final long handler;

        long getHandler() {
            return handler;
        }

        NativeHandler(long handler) {
            this.handler = handler;
        }

        public void handle(Signal sig) {
            throw new UnsupportedOperationException("invoking native signal handle not supported");
        }

        public String toString() {
            return this == SIG_DFL ? "SIG_DFL" :
                    (this == SIG_IGN ? "SIG_IGN" : super.toString());
        }
    }

}