monitor.c

   1 /*
   2  * inoclam - Inotify+ClamAV virus scanner
   3  * Copyright (C) 2007 Vermont Department of Taxes
   4  *
   5  * This program is free software: you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation, either version 3 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17  *
  18  * Contributor(s):
  19  *   Tom Cort <tom.cort@state.vt.us>
  20  */
  21
  22 #define _XOPEN_SOURCE 500
  23
  24 #include <pthread.h>
  25 #include <sched.h>
  26 #include <signal.h>
  27 #include <unistd.h>
  28
  29 #include "monitor.h"
  30
  31 /**
  32  * Counter for the number of running threads.
  33  */
  34 int cnt;
  35
  36 /**
  37  * A lock used to serialize access to cnt.
  38  */
  39 pthread_mutex_t mon_lock;
  40
  41 /**
  42  *  initialize monitor variables
  43  */
  44 void monitor_init()
  45 {
  46         pthread_mutex_init(&mon_lock, 0);
  47         cnt = 0;
  48 }
  49
  50 /**
  51  *  increments the thread count
  52  */
  53 void monitor_inc()
  54 {
  55         pthread_mutex_lock(&mon_lock);
  56         cnt++;
  57         pthread_mutex_unlock(&mon_lock);
  58 }
  59
  60 /**
  61  *  decrements the thread count
  62  */
  63 void monitor_dec()
  64 {
  65         pthread_mutex_lock(&mon_lock);
  66         cnt--;
  67         pthread_mutex_unlock(&mon_lock);
  68 }
  69
  70 /**
  71  *  waits until no threads are running
  72  *  blocks new threads from being created
  73  */
  74 void monitor_wait()
  75 {
  76         raise(SIGQUIT);
  77
  78         while (1) {
  79                 pthread_mutex_lock(&mon_lock);
  80
  81                 if (!cnt) {
  82                         /* Do NOT release lock; we don't want any more threads starting */
  83                         return;
  84                 } else {
  85                         pthread_mutex_unlock(&mon_lock);
  86                         sched_yield();
  87                         sleep(3);
  88                 }
  89         }
  90 }