lib/util/talloc_stack.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3    Implement a stack of talloc contexts
   4    Copyright (C) Volker Lendecke 2007
   5    Copyright (C) Jeremy Allison 2009 - made thread safe.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20 */
  21
  22 /*
  23  * Implement a stack of talloc frames.
  24  *
  25  * When a new talloc stackframe is allocated with talloc_stackframe(), then
  26  * the TALLOC_CTX returned with talloc_tos() is reset to that new
  27  * frame. Whenever that stack frame is TALLOC_FREE()'ed, then the reverse
  28  * happens: The previous talloc_tos() is restored.
  29  *
  30  * This API is designed to be robust in the sense that if someone forgets to
  31  * TALLOC_FREE() a stackframe, then the next outer one correctly cleans up and
  32  * resets the talloc_tos().
  33  *
  34  * This robustness feature means that we can't rely on a linked list with
  35  * talloc destructors because in a hierarchy of talloc destructors the parent
  36  * destructor is called before its children destructors. The child destructor
  37  * called after the parent would set the talloc_tos() to the wrong value.
  38  */
  39
  40 #include "includes.h"
  41
  42 struct talloc_stackframe {
  43         int talloc_stacksize;
  44         int talloc_stack_arraysize;
  45         TALLOC_CTX **talloc_stack;
  46 };
  47
  48 /*
  49  * In the single threaded case this is a pointer
  50  * to the global talloc_stackframe. In the MT-case
  51  * this is the pointer to the thread-specific key
  52  * used to look up the per-thread talloc_stackframe
  53  * pointer.
  54  */
  55
  56 static void *global_ts;
  57
  58 /* Variable to ensure TLS value is only initialized once. */
  59 static smb_thread_once_t ts_initialized = SMB_THREAD_ONCE_INIT;
  60
  61 static void talloc_stackframe_init(void * unused)
  62 {
  63         if (SMB_THREAD_CREATE_TLS("talloc_stackframe", global_ts)) {
  64                 smb_panic("talloc_stackframe_init create_tls failed");
  65         }
  66 }
  67
  68 static struct talloc_stackframe *talloc_stackframe_create(void)
  69 {
  70 #if defined(PARANOID_MALLOC_CHECKER)
  71 #ifdef malloc
  72 #undef malloc
  73 #endif
  74 #endif
  75         struct talloc_stackframe *ts =
  76                 (struct talloc_stackframe *)malloc(sizeof(struct talloc_stackframe));
  77 #if defined(PARANOID_MALLOC_CHECKER)
  78 #define malloc(s) __ERROR_DONT_USE_MALLOC_DIRECTLY
  79 #endif
  80
  81         if (!ts) {
  82                 smb_panic("talloc_stackframe_init malloc failed");
  83         }
  84
  85         ZERO_STRUCTP(ts);
  86
  87         SMB_THREAD_ONCE(&ts_initialized, talloc_stackframe_init, NULL);
  88
  89         if (SMB_THREAD_SET_TLS(global_ts, ts)) {
  90                 smb_panic("talloc_stackframe_init set_tls failed");
  91         }
  92         return ts;
  93 }
  94
  95 static int talloc_pop(TALLOC_CTX *frame)
  96 {
  97         struct talloc_stackframe *ts =
  98                 (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
  99         int i;
 100
 101         for (i=ts->talloc_stacksize-1; i>0; i--) {
 102                 if (frame == ts->talloc_stack[i]) {
 103                         break;
 104                 }
 105                 talloc_free(ts->talloc_stack[i]);
 106                 ts->talloc_stack[i] = NULL;
 107         }
 108
 109         ts->talloc_stack[i] = NULL;
 110         ts->talloc_stacksize = i;
 111         return 0;
 112 }
 113
 114 /*
 115  * Create a new talloc stack frame.
 116  *
 117  * When free'd, it frees all stack frames that were created after this one and
 118  * not explicitly freed.
 119  */
 120
 121 static TALLOC_CTX *talloc_stackframe_internal(size_t poolsize)
 122 {
 123         TALLOC_CTX **tmp, *top, *parent;
 124         struct talloc_stackframe *ts =
 125                 (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 126
 127         if (ts == NULL) {
 128                 ts = talloc_stackframe_create();
 129         }
 130
 131         if (ts->talloc_stack_arraysize < ts->talloc_stacksize + 1) {
 132                 tmp = talloc_realloc(NULL, ts->talloc_stack, TALLOC_CTX *,
 133                                            ts->talloc_stacksize + 1);
 134                 if (tmp == NULL) {
 135                         goto fail;
 136                 }
 137                 ts->talloc_stack = tmp;
 138                 ts->talloc_stack_arraysize = ts->talloc_stacksize + 1;
 139         }
 140
 141         if (ts->talloc_stacksize == 0) {
 142                 parent = ts->talloc_stack;
 143         } else {
 144                 parent = ts->talloc_stack[ts->talloc_stacksize-1];
 145         }
 146
 147         if (poolsize) {
 148                 top = talloc_pool(parent, poolsize);
 149         } else {
 150                 top = talloc_new(parent);
 151         }
 152
 153         if (top == NULL) {
 154                 goto fail;
 155         }
 156
 157         talloc_set_destructor(top, talloc_pop);
 158
 159         ts->talloc_stack[ts->talloc_stacksize++] = top;
 160         return top;
 161
 162  fail:
 163         smb_panic("talloc_stackframe failed");
 164         return NULL;
 165 }
 166
 167 TALLOC_CTX *talloc_stackframe(void)
 168 {
 169         return talloc_stackframe_internal(0);
 170 }
 171
 172 TALLOC_CTX *talloc_stackframe_pool(size_t poolsize)
 173 {
 174         return talloc_stackframe_internal(poolsize);
 175 }
 176
 177 /*
 178  * Get us the current top of the talloc stack.
 179  */
 180
 181 TALLOC_CTX *talloc_tos(void)
 182 {
 183         struct talloc_stackframe *ts =
 184                 (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 185
 186         if (ts == NULL || ts->talloc_stacksize == 0) {
 187                 talloc_stackframe();
 188                 ts = (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 189                 DEBUG(0, ("no talloc stackframe around, leaking memory\n"));
 190         }
 191
 192         return ts->talloc_stack[ts->talloc_stacksize-1];
 193 }