source3/lib/talloc_stack.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3    Implement a stack of talloc contexts
   4    Copyright (C) Volker Lendecke 2007
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program; if not, write to the Free Software
  18    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19 */
  20
  21 /*
  22  * Implement a stack of talloc frames.
  23  *
  24  * When a new talloc stackframe is allocated with talloc_stackframe(), then
  25  * the TALLOC_CTX returned with talloc_tos() is reset to that new
  26  * frame. Whenever that stack frame is TALLOC_FREE()'ed, then the reverse
  27  * happens: The previous talloc_tos() is restored.
  28  *
  29  * This API is designed to be robust in the sense that if someone forgets to
  30  * TALLOC_FREE() a stackframe, then the next outer one correctly cleans up and
  31  * resets the talloc_tos().
  32  *
  33  * This robustness feature means that we can't rely on a linked list with
  34  * talloc destructors because in a hierarchy of talloc destructors the parent
  35  * destructor is called before its children destructors. The child destructor
  36  * called after the parent would set the talloc_tos() to the wrong value.
  37  */
  38
  39 #include "includes.h"
  40
  41 static int talloc_stacksize;
  42 static TALLOC_CTX **talloc_stack;
  43
  44 static int talloc_pop(TALLOC_CTX *frame)
  45 {
  46         int i;
  47
  48         for (i=talloc_stacksize-1; i>0; i--) {
  49                 if (frame == talloc_stack[i]) {
  50                         break;
  51                 }
  52                 talloc_free(talloc_stack[i]);
  53         }
  54
  55         talloc_stacksize = i;
  56         return 0;
  57 }
  58
  59 /*
  60  * Create a new talloc stack frame.
  61  *
  62  * When free'd, it frees all stack frames that were created after this one and
  63  * not explicitly freed.
  64  */
  65
  66 TALLOC_CTX *talloc_stackframe(void)
  67 {
  68         TALLOC_CTX **tmp, *top;
  69
  70         if (!(tmp = TALLOC_REALLOC_ARRAY(NULL, talloc_stack, TALLOC_CTX *,
  71                                          talloc_stacksize + 1))) {
  72                 goto fail;
  73         }
  74
  75         talloc_stack = tmp;
  76
  77         if (!(top = talloc_new(talloc_stack))) {
  78                 goto fail;
  79         }
  80
  81         talloc_set_destructor(top, talloc_pop);
  82
  83         talloc_stack[talloc_stacksize++] = top;
  84
  85         return top;
  86
  87  fail:
  88         smb_panic("talloc_stackframe failed");
  89         return NULL;
  90 }
  91
  92 /*
  93  * Get us the current top of the talloc stack.
  94  */
  95
  96 TALLOC_CTX *talloc_tos(void)
  97 {
  98         if (talloc_stacksize == 0) {
  99                 talloc_stackframe();
 100                 DEBUG(0, ("no talloc stackframe around, leaking memory\n"));
 101         }
 102
 103         return talloc_stack[talloc_stacksize-1];
 104 }