The Signal.java Java example source code
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*
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* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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package sun.misc;
import java.util.Hashtable;
/**
* 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
* function raises an <code>IllegalArgumentException if such an attempt
* is made.
* <li>
* When <code>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 <code>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.
* </ul>
* <p>
* Signal objects are created based on their names. For example:
* <blockquote>
* new Signal("INT");
* </blockquote>
* constructs a signal object corresponding to <code>SIGINT, which is
* typically produced when the user presses <code>Ctrl-C at the command line.
* The <code>Signal constructor throws IllegalArgumentException
* when it is passed an unknown signal.
* <p>
* This is an example of how Java code handles <code>SIGINT:
* <blockquote>
* SignalHandler handler = new SignalHandler () {
* public void handle(Signal sig) {
* ... // handle SIGINT
* }
* };
* Signal.handle(new Signal("INT"), handler);
* </blockquote>
*
* @author Sheng Liang
* @author Bill Shannon
* @see sun.misc.SignalHandler
* @since 1.2
*/
public final class Signal {
private static Hashtable<Signal,SignalHandler> 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.
*
* @return the name of the signal.
* @see sun.misc.Signal#Signal(String name)
*/
public String getName() {
return name;
}
/**
* Compares the equality of two <code>Signal objects.
*
* @param other the object to compare with.
* @return whether two <code>Signal 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.
*
* @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 <code>new Signal ("INT").
*
* @return a string representation of the signal
*/
public String toString() {
return "SIG" + name;
}
/**
* Constructs a signal from its name.
*
* @param name the name of the signal.
* @exception IllegalArgumentException unknown signal
* @see sun.misc.Signal#getName()
*/
public Signal(String name) {
number = findSignal(name);
this.name = name;
if (number < 0) {
throw new IllegalArgumentException("Unknown signal: " + name);
}
}
/**
* Registers a signal handler.
*
* @param sig a signal
* @param handler the handler to be registered with the given signal.
* @result the old handler
* @exception IllegalArgumentException the signal is in use by the VM
* @see sun.misc.Signal#raise(Signal sig)
* @see sun.misc.SignalHandler
* @see sun.misc.SignalHandler#SIG_DFL
* @see sun.misc.SignalHandler#SIG_IGN
*/
public static synchronized SignalHandler handle(Signal sig,
SignalHandler handler)
throws IllegalArgumentException {
long newH = (handler instanceof NativeSignalHandler) ?
((NativeSignalHandler)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) {
SignalHandler oldHandler = handlers.get(sig);
handlers.remove(sig);
if (newH == 2) {
handlers.put(sig, handler);
}
if (oldH == 0) {
return SignalHandler.SIG_DFL;
} else if (oldH == 1) {
return SignalHandler.SIG_IGN;
} else if (oldH == 2) {
return oldHandler;
} else {
return new NativeSignalHandler(oldH);
}
}
}
/**
* Raises a signal in the current process.
*
* @param sig a signal
* @see sun.misc.Signal#handle(Signal sig, SignalHandler handler)
*/
public static void raise(Signal sig) throws IllegalArgumentException {
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 SignalHandler 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(runnable, sig + " handler").start();
}
}
/* Find the signal number, given a name. Returns -1 for unknown signals. */
private static native int findSignal(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);
}
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