public final class Signal {
private static final ConcurrentMap<String, Signal>
SIGNAL_BY_NAME = new ConcurrentHashMap<>(4);
private static final ConcurrentMap<Integer, Signal>
SIGNAL_BY_NUMBER = new ConcurrentHashMap<>(4);
public static Signal of(String name) {
Signal signal = SIGNAL_BY_NAME.get(name);
if (signal != null) {
return signal;
}
int number;
if (!name.startsWith("SIG") || name.length() <= 3 ||
(number = findSignal0(name.substring(3))) < 0) {
throw new UnsupportedOperationException("Unknown signal:
" + name);
}
signal = SIGNAL_BY_NUMBER.computeIfAbsent(
number,
new Function<Integer, Signal>() {
@Override
public Signal apply(Integer number) {
return new Signal(name, number);
}
}
);
SIGNAL_BY_NAME.putIfAbsent(name, signal);
return signal;
}
private final String name;
private final int number;
private volatile HandlerChain handlerChain;
private long savedNativeHandler;
private Signal(String name, int number) {
this.name = name;
this.number = number;
}
public String name() { return name; }
public int number() { return number; }
public void raise() { raise0(number); }
public void register(BiConsumer<Signal, Runnable> handler) {
synchronized (this) {
HandlerChain oldChain = handlerChain;
handlerChain = new HandlerChain(handler, oldChain);
if (oldChain == null) {
// set native to dispatch to Singnal.dispatch()
savedNativeHandler = handle1(2);
}
}
}
public boolean unregister(BiConsumer<Signal, Runnable> handler) {
synchronized (this) {
HandlerChain oldChain = handlerChain;
if (oldChain != null && oldChain.handler == handler) {
if (oldChain.next == null) {
// restore saved native handler
long oldNativeHandler = handle1(savedNativeHandler);
assert oldNativeHandler == 2L;
}
handlerChain = oldChain.next;
return true;
} else {
return false;
}
}
}
// following two should probably be hidden from public API
public void nativeIgnore() {
synchronized (this) {
if (handlerChain == null) {
handle1(1); // ignore signal
} else {
throw new IllegalStateException(
"Can't ignore signal after handlers have already
been registered.");
}
}
}
public void nativeDefault() {
synchronized (this) {
if (handlerChain == null) {
handle1(0); // default native handler
} else {
throw new IllegalStateException(
"Can't restore signal after handlers have
already been registered.");
}
}
}
private long handle1(long nativeHandler) {
long oldNativeHandler = handle0(number, nativeHandler);
if (oldNativeHandler == -1L) {
throw new UnsupportedOperationException(
"Signal already used by VM or OS: " + name);
}
return oldNativeHandler;
}
/*
* Called by the VM to execute Java signal handlers.
*/
private static void dispatch(int number) {
Signal signal = SIGNAL_BY_NUMBER.get(number);
if (signal != null) {
HandlerChain handlerChain = signal.handlerChain;
if (handlerChain != null) {
new InnocuousThread(() -> handlerChain.accept(signal))
.start();
}
}
}
/**
* Find the signal number, given a name.
*
* @param sigName the signal name
* @return the signal number or -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
* @param nativeH the index or address of the new signal handler
* @return the previous index or address
*/
private static native long handle0(int sig, long nativeH);
/*
* Raise a given signal number.
* @param sig the signal number to raise
*/
private static native void raise0(int sig);
private static class HandlerChain implements Consumer<Signal> {
final BiConsumer<Signal, Runnable> handler;
final HandlerChain next;
HandlerChain(BiConsumer<Signal, Runnable> handler,
HandlerChain next) {
this.handler = handler;
this.next = next;
}
@Override
public void accept(Signal signal) {
handler.accept(signal, () -> { >>> if (next !=
null) {
next.accept(signal);
}
});
}
}
}
Regards, Peter
On 02/01/2016 05:02 PM, Roger Riggs wrote:
Please review an API addition to handle signals such as SIGINT,
SIGHUP, and SIGTERM.
This JEP 260 motivated alternative to sun.misc.Signal supports the
use case for
interactive applications that need to handle Control-C and other
signals.
The new java.util.Signal class provides a settable primary signal
handler and a default
signal handler. The primary signal handler can be unregistered and
handling is restored
to the default signal handler. System initialization registers
default signal handlers
to terminate on SIGINT, SIGHUP, and SIGTERM. Use of the Signal API
requires
a permission if a SecurityManager is set.
The sun.misc.Signal implementation is modified to be layered on a
common
thread and dispatch mechanism. The VM handling of native signals is
not affected.
The command option to reduce signal use by the runtime with -Xrs is
unmodified.
The changes to hotspot are minimal to rename the hardcoded callback
to the Java
Signal dispatcher.
Please review and comment on the API and implementation.
javadoc:
http://cr.openjdk.java.net/~rriggs/signal-doc/
Webrev:
jdk: http://cr.openjdk.java.net/~rriggs/webrev-signal-8087286/
hotspot: http://cr.openjdk.java.net/~rriggs/webrev-hs-signal-8087286/
Issue:
https://bugs.openjdk.java.net/browse/JDK-8087286
JEP 260:
https://bugs.openjdk.java.net/browse/JDK-8132928
Thanks, Roger
