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 /*

  * Copyright (c) 2001, 2015, 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 <stdbool.h>

 #include <string.h>

 #define MAXSIGNUM 32

 #define MASK(sig) ((unsigned int)1 << sig)

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

 static unsigned int jvmsigs = 0; /* signals used by jvm */

 static pthread_key_t reentry_flag_key;

 static pthread_once_t reentry_key_init_once = PTHREAD_ONCE_INIT;

 /* 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;

 #define check_status(cmd) \

   do { \

     int status = (cmd); \

     if (status != 0) { \

       printf("error %s (%d) in " #cmd "\n", strerror(status), status); \

       exit(1); \

     } \

   } while (0)

 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 void reentry_tls_init() {

     // value for reentry_flag_key will default to NULL (false)

     check_status(pthread_key_create(&reentry_flag_key, NULL));

 }

 static sa_handler_t call_os_signal(int sig, sa_handler_t disp,

                                    bool is_sigset) {

   sa_handler_t res;

   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);

     }

   }

   check_status(pthread_once(&reentry_key_init_once, reentry_tls_init));

   // set reentry_flag_key to non-NULL to show reentry

   check_status(pthread_setspecific(reentry_flag_key, &res));

   res = (*os_signal)(sig, disp);

   check_status(pthread_setspecific(reentry_flag_key, NULL));

   return res;

 }

 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 = (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 (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) {

   printf("sigset() is not supported by BSD");

   exit(0);

  }

 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;

   check_status(pthread_once(&reentry_key_init_once, reentry_tls_init));

   if (pthread_getspecific(reentry_flag_key) != NULL) {

     return call_os_sigaction(sig, act, oact);

   }

   signal_lock();

   sigused = (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 (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;

 }