signalimp.c

java信号处理程序

/**
   The central clearinghouse for JavaSignals.

   Copyright 1998 Kevin Hester, [e-mail]
   
   Commerical use prohibited - non commercial distribution is OK.
   Contact the author for further information.

   I just added some fixes from [e-mail] 3/29/99 - his comments 
   below:

I am just writing an article in the German Linux-Magazin about
RMI and I thought I would use JavaSignals to make my server
behave nicely (mainly react to SIGHUP and SIGTERM), and also
to spread the news about a great Java package. But JavaSignals
breaks RMI (the method Naming.rebind(...) never returned once
SignalManager.add() was called).

The reason is simple: the rmiregistry uses signals to
communicate with the java program and JavaSignals resets all
signals to SIG_DFL, exept those I'm listening for.

I changed the code to only call sigaction for these signals, but
now sleep(...) would also return on signals I don't care about.
So some additional changes were necessary. In fact, the code is
still not clean, it would need some sort of semaphore, but it
should do for normal cases. I included the new SignalImp.c.

One additional change is necessary in SignalManagerThread.java:
you must add a "setPriority(4);" before calling start();. This
is one piece of mystery: neither green nor native threads have a
priority model implemented, but if a thread uses the console and
another thread has the same priority, the threads block each
other. Note: setting the priority below 3 will actually disable
the thread (at least on my Linux systems, NT works fine, but NT
has a native thread model with priorities).

Bernhard
*/

#include <assert.h>

#include "kh_signal_SignalManager.h"

#include <stdio.h>
#include <signal.h>


static unsigned oldMask = 0;
static int caughtSig = 0, isOurSig = 0;

static struct sigaction oldactions[_NSIG];

/**
   This is our master signal handler
*/
static void sigHandler(int signal)
{
	// printf("Caught a signal %d\n", signal);
	caughtSig = signal;
	isOurSig = 1;
}

static struct sigaction newaction = 
    {
	sigHandler,
	0,
	0,
	0
	};

static unsigned getMask(JNIEnv *env, jclass _class)
{
	jfieldID id = (*env)->GetStaticFieldID(env, _class, "interestMask", "I");
	assert(id);

	return (*env)->GetStaticIntField(env, _class, id);
}



JNIEXPORT jint JNICALL Java_kh_signal_SignalManager_waitForSignal
  (JNIEnv *env, jclass _class)
{
	while (1) {
		// Wait up to a year - we are really waiting for a signal
		int numleft = sleep(60 * 60 * 24 * 365);

		// printf("Sleep expired\n");
		if(numleft == 0)
			printf("This shouldn't happen - timer expired\n");
		else if (isOurSig) {
			isOurSig = 0;
			return caughtSig;
		}
	}
}



JNIEXPORT void JNICALL Java_kh_signal_SignalManager_setInterestMask
  (JNIEnv *env, jclass _class)
{
    unsigned newMask = getMask(env, _class);
    unsigned changed = newMask ^ oldMask;
    int bit, result, mask, installUs;

	// printf("SignalImp: setting mask to 0x%x, old mask 0x%x\n", newMask, oldMask);

	for(bit = 0; bit < 32; bit++)
		{
		mask = (1 << bit);

		if(changed & mask)
			{
			installUs = newMask & mask;

			// FIXME - we should only save the old action the FIRST time
			// we do an install
                        if (installUs) {
                           // printf("Setting signal %d\n", bit);
			   result = sigaction(bit,&newaction,(void *) NULL);
		        } 
                        if(result < 0)
				printf("Error setting signal %d\n", bit);
			}
		}

    // printf("SignalImp: mask set\n");

	oldMask = newMask;
}