linuxthreads/ptfork.c

   1 /* Linuxthreads - a simple clone()-based implementation of Posix        */
   2 /* threads for Linux.                                                   */
   3 /* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr)              */
   4 /*                                                                      */
   5 /* This program is free software; you can redistribute it and/or        */
   6 /* modify it under the terms of the GNU Library General Public License  */
   7 /* as published by the Free Software Foundation; either version 2       */
   8 /* of the License, or (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 Library General Public License for more details.                 */
  14
  15 /* The "atfork" stuff */
  16
  17 #include <errno.h>
  18 #include <stddef.h>
  19 #include <stdlib.h>
  20 #include <unistd.h>
  21 #include "pthread.h"
  22 #include "internals.h"
  23
  24 struct handler_list {
  25   void (*handler)(void);
  26   struct handler_list * next;
  27 };
  28
  29 static pthread_mutex_t pthread_atfork_lock = PTHREAD_MUTEX_INITIALIZER;
  30 static struct handler_list * pthread_atfork_prepare = NULL;
  31 static struct handler_list * pthread_atfork_parent = NULL;
  32 static struct handler_list * pthread_atfork_child = NULL;
  33
  34 static void pthread_insert_list(struct handler_list ** list,
  35                                 void (*handler)(void),
  36                                 struct handler_list * newlist,
  37                                 int at_end)
  38 {
  39   if (handler == NULL) return;
  40   if (at_end) {
  41     while(*list != NULL) list = &((*list)->next);
  42   }
  43   newlist->handler = handler;
  44   newlist->next = *list;
  45   *list = newlist;
  46 }
  47
  48 struct handler_list_block {
  49   struct handler_list prepare, parent, child;
  50 };
  51
  52 int __pthread_atfork(void (*prepare)(void),
  53                      void (*parent)(void),
  54                      void (*child)(void))
  55 {
  56   struct handler_list_block * block =
  57     (struct handler_list_block *) malloc(sizeof(struct handler_list_block));
  58   if (block == NULL) return ENOMEM;
  59   pthread_mutex_lock(&pthread_atfork_lock);
  60   /* "prepare" handlers are called in LIFO */
  61   pthread_insert_list(&pthread_atfork_prepare, prepare, &block->prepare, 0);
  62   /* "parent" handlers are called in FIFO */
  63   pthread_insert_list(&pthread_atfork_parent, parent, &block->parent, 1);
  64   /* "child" handlers are called in FIFO */
  65   pthread_insert_list(&pthread_atfork_child, child, &block->child, 1);
  66   pthread_mutex_unlock(&pthread_atfork_lock);
  67   return 0;
  68 }
  69 weak_alias (__pthread_atfork, pthread_atfork)
  70
  71 static inline void pthread_call_handlers(struct handler_list * list)
  72 {
  73   for (/*nothing*/; list != NULL; list = list->next) (list->handler)();
  74 }
  75
  76 extern int __fork(void);
  77
  78 int fork(void)
  79 {
  80   int pid;
  81   struct handler_list * prepare, * child, * parent;
  82
  83   pthread_mutex_lock(&pthread_atfork_lock);
  84   prepare = pthread_atfork_prepare;
  85   child = pthread_atfork_child;
  86   parent = pthread_atfork_parent;
  87   pthread_mutex_unlock(&pthread_atfork_lock);
  88   pthread_call_handlers(prepare);
  89   pid = __fork();
  90   if (pid == 0) {
  91     __pthread_reset_main_thread();
  92     __fresetlockfiles();
  93     pthread_call_handlers(child);
  94   } else {
  95     pthread_call_handlers(parent);
  96   }
  97   return pid;
  98 }