/*

 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

/* CopyrightVersion 1.2 */

/* This is a special library that should be loaded before libc &

 * libthread to interpose the signal handler installation functions:

 * sigaction(), signal(), sigset().

 * Used for signal-chaining. See RFE 4381843.

 */

#include <signal.h>

#include <dlfcn.h>

#include <pthread.h>

#include <stdio.h>

#include <stdlib.h>

#include <stdint.h>

#define bool int

#define true 1

#define false 0

#define MASK(sig) ((uint64_t)1 << (sig-1))  // 0 is not a signal.

// Check whether all signals fit into jvmsigs. -1 as MASK shifts by -1.

#if (64 < NSIG-1)

#error "Not all signals can be encoded in jvmsigs. Adapt its type!"

#endif

static struct sigaction sact[NSIG]; /* saved signal handlers */

static uint64_t jvmsigs = 0; /* signals used by jvm */

/* used to synchronize the installation of signal handlers */

static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

static pthread_t tid = 0;

typedef void (*sa_handler_t)(int);

typedef void (*sa_sigaction_t)(int, siginfo_t *, void *);

typedef sa_handler_t (*signal_t)(int, sa_handler_t);

typedef int (*sigaction_t)(int, const struct sigaction *, struct sigaction *);

static signal_t os_signal = 0; /* os's version of signal()/sigset() */

static sigaction_t os_sigaction = 0; /* os's version of sigaction() */

static bool jvm_signal_installing = false;

static bool jvm_signal_installed = false;

static void signal_lock() {

  pthread_mutex_lock(&mutex);

  /* When the jvm is installing its set of signal handlers, threads

   * other than the jvm thread should wait */

  if (jvm_signal_installing) {

    if (tid != pthread_self()) {

      pthread_cond_wait(&cond, &mutex);

    }

  }

}

static void signal_unlock() {

  pthread_mutex_unlock(&mutex);

}

static sa_handler_t call_os_signal(int sig, sa_handler_t disp,

                                   bool is_sigset) {

  if (os_signal == NULL) {

    if (!is_sigset) {

      os_signal = (signal_t)dlsym(RTLD_NEXT, "signal");

    } else {

      os_signal = (signal_t)dlsym(RTLD_NEXT, "sigset");

    }

    if (os_signal == NULL) {

      printf("%s\n", dlerror());

      exit(0);

    }

  }

  return (*os_signal)(sig, disp);

}

static void save_signal_handler(int sig, sa_handler_t disp) {

  sigset_t set;

  sact[sig].sa_handler = disp;

  sigemptyset(&set);

  sact[sig].sa_mask = set;

  sact[sig].sa_flags = 0;

}

static sa_handler_t set_signal(int sig, sa_handler_t disp, bool is_sigset) {

  sa_handler_t oldhandler;

  bool sigused;

  signal_lock();

  sigused = (sig < NSIG) && ((MASK(sig) & jvmsigs) != 0);

  if (jvm_signal_installed && sigused) {

    /* jvm has installed its signal handler for this signal. */

    /* Save the handler. Don't really install it. */

    oldhandler = sact[sig].sa_handler;

    save_signal_handler(sig, disp);

    signal_unlock();

    return oldhandler;

  } else if (sig < NSIG && jvm_signal_installing) {

    /* jvm is installing its signal handlers. Install the new

     * handlers and save the old ones. jvm uses sigaction().

     * Leave the piece here just in case. */

    oldhandler = call_os_signal(sig, disp, is_sigset);

    save_signal_handler(sig, oldhandler);

    /* Record the signals used by jvm */

    jvmsigs |= MASK(sig);

    signal_unlock();

    return oldhandler;

  } else {

    /* jvm has no relation with this signal (yet). Install the

     * the handler. */

    oldhandler = call_os_signal(sig, disp, is_sigset);

    signal_unlock();

    return oldhandler;

  }

}

sa_handler_t signal(int sig, sa_handler_t disp) {

  return set_signal(sig, disp, false);

}

sa_handler_t sigset(int sig, sa_handler_t disp) {

  return set_signal(sig, disp, true);

 }

static int call_os_sigaction(int sig, const struct sigaction  *act,

                             struct sigaction *oact) {

  if (os_sigaction == NULL) {

    os_sigaction = (sigaction_t)dlsym(RTLD_NEXT, "sigaction");

    if (os_sigaction == NULL) {

      printf("%s\n", dlerror());

      exit(0);

    }

  }

  return (*os_sigaction)(sig, act, oact);

}

int sigaction(int sig, const struct sigaction *act, struct sigaction *oact) {

  int res;

  bool sigused;

  struct sigaction oldAct;

  signal_lock();

  sigused = (sig < NSIG) && ((MASK(sig) & jvmsigs) != 0);

  if (jvm_signal_installed && sigused) {

    /* jvm has installed its signal handler for this signal. */

    /* Save the handler. Don't really install it. */

    if (oact != NULL) {

      *oact = sact[sig];

    }

    if (act != NULL) {

      sact[sig] = *act;

    }

    signal_unlock();

    return 0;

  } else if (sig < NSIG && jvm_signal_installing) {

    /* jvm is installing its signal handlers. Install the new

     * handlers and save the old ones. */

    res = call_os_sigaction(sig, act, &oldAct);

    sact[sig] = oldAct;

    if (oact != NULL) {

      *oact = oldAct;

    }

    /* Record the signals used by jvm */

    jvmsigs |= MASK(sig);

    signal_unlock();

    return res;

  } else {

    /* jvm has no relation with this signal (yet). Install the

     * the handler. */

    res = call_os_sigaction(sig, act, oact);

    signal_unlock();

    return res;

  }

}

/* The three functions for the jvm to call into */

void JVM_begin_signal_setting() {

  signal_lock();

  jvm_signal_installing = true;

  tid = pthread_self();

  signal_unlock();

}

void JVM_end_signal_setting() {

  signal_lock();

  jvm_signal_installed = true;

  jvm_signal_installing = false;

  pthread_cond_broadcast(&cond);

  signal_unlock();

}

struct sigaction *JVM_get_signal_action(int sig) {

  /* Does race condition make sense here? */

  if ((MASK(sig) & jvmsigs) != 0) {

    return &sact[sig];

  }

  return NULL;

}