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package sun.misc;
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:
SignalHandler handler = new SignalHandler () {
public void handle(Signal sig) {
... // handle SIGINT
}
};
Signal.handle(new Signal("INT"), handler);
Author: Sheng Liang, Bill Shannon See Also: Since: 1.2
/**
* 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>
* SignalHandler handler = new SignalHandler () {
* public void handle(Signal sig) {
* ... // handle SIGINT
* }
* };
* Signal.handle(new Signal("INT"), handler);
* </pre></blockquote>
*
* @author Sheng Liang
* @author Bill Shannon
* @see sun.misc.SignalHandler
* @since 1.2
*/
public final class Signal {
// Delegate to jdk.internal.misc.Signal.
private final jdk.internal.misc.Signal iSignal;
/* Returns the signal number */
public int getNumber() {
return iSignal.getNumber();
}
Returns the signal name.
See Also: Returns: the name of the signal.
/**
* Returns the signal name.
*
* @return the name of the signal.
* @see sun.misc.Signal#Signal(String name)
*/
public String getName() {
return iSignal.getName();
}
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 iSignal.equals(other1.iSignal);
}
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 getNumber();
}
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 iSignal.toString();
}
Constructs a signal from its name.
Params: - name – the name of the signal.
Throws: - IllegalArgumentException – unknown signal
See Also:
/**
* 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) {
iSignal = new jdk.internal.misc.Signal(name);
}
Registers a signal handler.
Params: - sig – a signal
- handler – the handler to be registered with the given signal.
Throws: - IllegalArgumentException – the signal is in use by the VM
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 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 {
jdk.internal.misc.Signal.Handler oldHandler = jdk.internal.misc.Signal.handle(sig.iSignal,
InternalMiscHandler.of(sig, handler));
return SunMiscHandler.of(sig.iSignal, oldHandler);
}
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 sun.misc.Signal#handle(Signal sig, SignalHandler handler)
*/
public static void raise(Signal sig) throws IllegalArgumentException {
jdk.internal.misc.Signal.raise(sig.iSignal);
}
/*
* Wrapper class to proxy a SignalHandler to a jdk.internal.misc.Signal.Handler.
*/
static final class InternalMiscHandler implements jdk.internal.misc.Signal.Handler {
private final SignalHandler handler;
private final Signal signal;
static jdk.internal.misc.Signal.Handler of(Signal signal, SignalHandler handler) {
if (handler == SignalHandler.SIG_DFL) {
return jdk.internal.misc.Signal.Handler.SIG_DFL;
} else if (handler == SignalHandler.SIG_IGN) {
return jdk.internal.misc.Signal.Handler.SIG_IGN;
} else if (handler instanceof SunMiscHandler) {
return ((SunMiscHandler)handler).iHandler;
} else {
return new InternalMiscHandler(signal, handler);
}
}
private InternalMiscHandler(Signal signal, SignalHandler handler) {
this.handler = handler;
this.signal = signal;
}
@Override
public void handle(jdk.internal.misc.Signal ignore) {
handler.handle(signal);
}
}
/*
* Wrapper class to proxy a jdk.internal.misc.Signal.Handler to a SignalHandler.
*/
static final class SunMiscHandler implements SignalHandler {
private final jdk.internal.misc.Signal iSignal;
private final jdk.internal.misc.Signal.Handler iHandler;
static SignalHandler of(jdk.internal.misc.Signal signal, jdk.internal.misc.Signal.Handler handler) {
if (handler == jdk.internal.misc.Signal.Handler.SIG_DFL) {
return SignalHandler.SIG_DFL;
} else if (handler == jdk.internal.misc.Signal.Handler.SIG_IGN) {
return SignalHandler.SIG_IGN;
} else if (handler instanceof InternalMiscHandler) {
return ((InternalMiscHandler) handler).handler;
} else {
return new SunMiscHandler(signal, handler);
}
}
SunMiscHandler(jdk.internal.misc.Signal iSignal, jdk.internal.misc.Signal.Handler iHandler) {
this.iSignal = iSignal;
this.iHandler = iHandler;
}
@Override
public void handle(Signal sig) {
iHandler.handle(iSignal);
}
public String toString() {
return iHandler.toString();
}
}
}