libgcc/config/vxlib-tls.c

   1 /* Copyright (C) 2002, 2003, 2004, 2005, 2009 Free Software Foundation, Inc.
   2    Contributed by Zack Weinberg <zack@codesourcery.com>
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 Under Section 7 of GPL version 3, you are granted additional
  17 permissions described in the GCC Runtime Library Exception, version
  18 3.1, as published by the Free Software Foundation.
  19
  20 You should have received a copy of the GNU General Public License and
  21 a copy of the GCC Runtime Library Exception along with this program;
  22 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 <http://www.gnu.org/licenses/>.  */
  24
  25 /* Threads compatibility routines for libgcc2 for VxWorks.
  26    These are out-of-line routines called from gthr-vxworks.h.
  27
  28    This file provides the TLS related support routines, calling specific
  29    VxWorks kernel entry points for this purpose.  The base VxWorks 5.x kernels
  30    don't feature these entry points, and we provide gthr_supp_vxw_5x.c as an
  31    option to fill this gap.  Asking users to rebuild a kernel is not to be
  32    taken lightly, still, so we have isolated these routines from the rest of
  33    vxlib to ensure that the kernel dependencies are only dragged when really
  34    necessary.  */
  35
  36 #include "tconfig.h"
  37 #include "tsystem.h"
  38 #include "gthr.h"
  39
  40 #if defined(__GTHREADS)
  41 #include <vxWorks.h>
  42 #ifndef __RTP__
  43 #include <vxLib.h>
  44 #endif
  45 #include <taskLib.h>
  46 #ifndef __RTP__
  47 #include <taskHookLib.h>
  48 #else
  49 # include <errno.h>
  50 #endif
  51
  52 /* Thread-local storage.
  53
  54    We reserve a field in the TCB to point to a dynamically allocated
  55    array which is used to store TLS values.  A TLS key is simply an
  56    offset in this array.  The exact location of the TCB field is not
  57    known to this code nor to vxlib.c -- all access to it indirects
  58    through the routines __gthread_get_tls_data and
  59    __gthread_set_tls_data, which are provided by the VxWorks kernel.
  60
  61    There is also a global array which records which keys are valid and
  62    which have destructors.
  63
  64    A task delete hook is installed to execute key destructors.  The
  65    routines __gthread_enter_tls_dtor_context and
  66    __gthread_leave_tls_dtor_context, which are also provided by the
  67    kernel, ensure that it is safe to call free() on memory allocated
  68    by the task being deleted.  (This is a no-op on VxWorks 5, but
  69    a major undertaking on AE.)
  70
  71    The task delete hook is only installed when at least one thread
  72    has TLS data.  This is a necessary precaution, to allow this module
  73    to be unloaded - a module with a hook can not be removed.
  74
  75    Since this interface is used to allocate only a small number of
  76    keys, the table size is small and static, which simplifies the
  77    code quite a bit.  Revisit this if and when it becomes necessary.  */
  78
  79 #define MAX_KEYS 4
  80
  81 /* This is the structure pointed to by the pointer returned
  82    by __gthread_get_tls_data.  */
  83 struct tls_data
  84 {
  85   int *owner;
  86   void *values[MAX_KEYS];
  87   unsigned int generation[MAX_KEYS];
  88 };
  89
  90 /* To make sure we only delete TLS data associated with this object,
  91    include a pointer to a local variable in the TLS data object.  */
  92 static int self_owner;
  93
  94 /* Flag to check whether the delete hook is installed.  Once installed
  95    it is only removed when unloading this module.  */
  96 static volatile int delete_hook_installed;
  97
  98 /* kernel provided routines */
  99 extern void *__gthread_get_tls_data (void);
 100 extern void __gthread_set_tls_data (void *data);
 101
 102 extern void __gthread_enter_tls_dtor_context (void);
 103 extern void __gthread_leave_tls_dtor_context (void);
 104
 105
 106 /* This is a global structure which records all of the active keys.
 107
 108    A key is potentially valid (i.e. has been handed out by
 109    __gthread_key_create) iff its generation count in this structure is
 110    even.  In that case, the matching entry in the dtors array is a
 111    routine to be called when a thread terminates with a valid,
 112    non-NULL specific value for that key.
 113
 114    A key is actually valid in a thread T iff the generation count
 115    stored in this structure is equal to the generation count stored in
 116    T's specific-value structure.  */
 117
 118 typedef void (*tls_dtor) (void *);
 119
 120 struct tls_keys
 121 {
 122   tls_dtor dtor[MAX_KEYS];
 123   unsigned int generation[MAX_KEYS];
 124 };
 125
 126 #define KEY_VALID_P(key) !(tls_keys.generation[key] & 1)
 127
 128 /* Note: if MAX_KEYS is increased, this initializer must be updated
 129    to match.  All the generation counts begin at 1, which means no
 130    key is valid.  */
 131 static struct tls_keys tls_keys =
 132 {
 133   { 0, 0, 0, 0 },
 134   { 1, 1, 1, 1 }
 135 };
 136
 137 /* This lock protects the tls_keys structure.  */
 138 static __gthread_mutex_t tls_lock;
 139
 140 static __gthread_once_t tls_init_guard = __GTHREAD_ONCE_INIT;
 141
 142 /* Internal routines.  */
 143
 144 /* The task TCB has just been deleted.  Call the destructor
 145    function for each TLS key that has both a destructor and
 146    a non-NULL specific value in this thread.
 147
 148    This routine does not need to take tls_lock; the generation
 149    count protects us from calling a stale destructor.  It does
 150    need to read tls_keys.dtor[key] atomically.  */
 151
 152 static void
 153 tls_delete_hook (void *tcb ATTRIBUTE_UNUSED)
 154 {
 155   struct tls_data *data;
 156   __gthread_key_t key;
 157
 158 #ifdef __RTP__
 159   data = __gthread_get_tls_data ();
 160 #else
 161   /* In kernel mode, we can be called in the context of the thread
 162      doing the killing, so must use the TCB to determine the data of
 163      the thread being killed.  */
 164   data = __gthread_get_tsd_data (tcb);
 165 #endif
 166
 167   if (data && data->owner == &self_owner)
 168     {
 169 #ifdef __RTP__
 170       __gthread_enter_tls_dtor_context ();
 171 #else
 172       __gthread_enter_tsd_dtor_context (tcb);
 173 #endif
 174       for (key = 0; key < MAX_KEYS; key++)
 175         {
 176           if (data->generation[key] == tls_keys.generation[key])
 177             {
 178               tls_dtor dtor = tls_keys.dtor[key];
 179
 180               if (dtor)
 181                 dtor (data->values[key]);
 182             }
 183         }
 184       free (data);
 185 #ifdef __RTP__
 186       __gthread_leave_tls_dtor_context ();
 187 #else
 188       __gthread_leave_tsd_dtor_context ();
 189 #endif
 190
 191 #ifdef __RTP__
 192       __gthread_set_tls_data (0);
 193 #else
 194       __gthread_set_tsd_data (tcb, 0);
 195 #endif
 196     }
 197 }
 198
 199 /* Initialize global data used by the TLS system.  */
 200 static void
 201 tls_init (void)
 202 {
 203   __GTHREAD_MUTEX_INIT_FUNCTION (&tls_lock);
 204 }
 205
 206 static void tls_destructor (void) __attribute__ ((destructor));
 207 static void
 208 tls_destructor (void)
 209 {
 210 #ifdef __RTP__
 211   /* All threads but this one should have exited by now.  */
 212   tls_delete_hook (NULL);
 213 #endif
 214   /* Unregister the hook.  */
 215   if (delete_hook_installed)
 216     taskDeleteHookDelete ((FUNCPTR)tls_delete_hook);
 217
 218   if (tls_init_guard.done && __gthread_mutex_lock (&tls_lock) != ERROR)
 219     semDelete (tls_lock);
 220 }
 221
 222 /* External interface */
 223
 224 /* Store in KEYP a value which can be passed to __gthread_setspecific/
 225    __gthread_getspecific to store and retrieve a value which is
 226    specific to each calling thread.  If DTOR is not NULL, it will be
 227    called when a thread terminates with a non-NULL specific value for
 228    this key, with the value as its sole argument.  */
 229
 230 int
 231 __gthread_key_create (__gthread_key_t *keyp, tls_dtor dtor)
 232 {
 233   __gthread_key_t key;
 234
 235   __gthread_once (&tls_init_guard, tls_init);
 236
 237   if (__gthread_mutex_lock (&tls_lock) == ERROR)
 238     return errno;
 239
 240   for (key = 0; key < MAX_KEYS; key++)
 241     if (!KEY_VALID_P (key))
 242       goto found_slot;
 243
 244   /* no room */
 245   __gthread_mutex_unlock (&tls_lock);
 246   return EAGAIN;
 247
 248  found_slot:
 249   tls_keys.generation[key]++;  /* making it even */
 250   tls_keys.dtor[key] = dtor;
 251   *keyp = key;
 252   __gthread_mutex_unlock (&tls_lock);
 253   return 0;
 254 }
 255
 256 /* Invalidate KEY; it can no longer be used as an argument to
 257    setspecific/getspecific.  Note that this does NOT call destructor
 258    functions for any live values for this key.  */
 259 int
 260 __gthread_key_delete (__gthread_key_t key)
 261 {
 262   if (key >= MAX_KEYS)
 263     return EINVAL;
 264
 265   __gthread_once (&tls_init_guard, tls_init);
 266
 267   if (__gthread_mutex_lock (&tls_lock) == ERROR)
 268     return errno;
 269
 270   if (!KEY_VALID_P (key))
 271     {
 272       __gthread_mutex_unlock (&tls_lock);
 273       return EINVAL;
 274     }
 275
 276   tls_keys.generation[key]++;  /* making it odd */
 277   tls_keys.dtor[key] = 0;
 278
 279   __gthread_mutex_unlock (&tls_lock);
 280   return 0;
 281 }
 282
 283 /* Retrieve the thread-specific value for KEY.  If it has never been
 284    set in this thread, or KEY is invalid, returns NULL.
 285
 286    It does not matter if this function races with key_create or
 287    key_delete; the worst that can happen is you get a value other than
 288    the one that a serialized implementation would have provided.  */
 289
 290 void *
 291 __gthread_getspecific (__gthread_key_t key)
 292 {
 293   struct tls_data *data;
 294
 295   if (key >= MAX_KEYS)
 296     return 0;
 297
 298   data = __gthread_get_tls_data ();
 299
 300   if (!data)
 301     return 0;
 302
 303   if (data->generation[key] != tls_keys.generation[key])
 304     return 0;
 305
 306   return data->values[key];
 307 }
 308
 309 /* Set the thread-specific value for KEY.  If KEY is invalid, or
 310    memory allocation fails, returns -1, otherwise 0.
 311
 312    The generation count protects this function against races with
 313    key_create/key_delete; the worst thing that can happen is that a
 314    value is successfully stored into a dead generation (and then
 315    immediately becomes invalid).  However, we do have to make sure
 316    to read tls_keys.generation[key] atomically.  */
 317
 318 int
 319 __gthread_setspecific (__gthread_key_t key, void *value)
 320 {
 321   struct tls_data *data;
 322   unsigned int generation;
 323
 324   if (key >= MAX_KEYS)
 325     return EINVAL;
 326
 327   data = __gthread_get_tls_data ();
 328   if (!data)
 329     {
 330       if (!delete_hook_installed)
 331         {
 332           /* Install the delete hook.  */
 333           if (__gthread_mutex_lock (&tls_lock) == ERROR)
 334             return ENOMEM;
 335           if (!delete_hook_installed)
 336             {
 337               taskDeleteHookAdd ((FUNCPTR)tls_delete_hook);
 338               delete_hook_installed = 1;
 339             }
 340           __gthread_mutex_unlock (&tls_lock);
 341         }
 342
 343       data = malloc (sizeof (struct tls_data));
 344       if (!data)
 345         return ENOMEM;
 346
 347       memset (data, 0, sizeof (struct tls_data));
 348       data->owner = &self_owner;
 349       __gthread_set_tls_data (data);
 350     }
 351
 352   generation = tls_keys.generation[key];
 353
 354   if (generation & 1)
 355     return EINVAL;
 356
 357   data->generation[key] = generation;
 358   data->values[key] = value;
 359
 360   return 0;
 361 }
 362 #endif /* __GTHREADS */