src/threads/threads-common.c

   1 /* src/threads/threads-common.c - machine independent thread functions
   2
   3    Copyright (C) 2007 R. Grafl, A. Krall, C. Kruegel,
   4    C. Oates, R. Obermaisser, M. Platter, M. Probst, S. Ring,
   5    E. Steiner, C. Thalinger, D. Thuernbeck, P. Tomsich, C. Ullrich,
   6    J. Wenninger, Institut f. Computersprachen - TU Wien
   7
   8    This file is part of CACAO.
   9
  10    This program is free software; you can redistribute it and/or
  11    modify it under the terms of the GNU General Public License as
  12    published by the Free Software Foundation; either version 2, or (at
  13    your option) any later version.
  14
  15    This program is distributed in the hope that it will be useful, but
  16    WITHOUT ANY WARRANTY; without even the implied warranty of
  17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  18    General Public License for more details.
  19
  20    You should have received a copy of the GNU General Public License
  21    along with this program; if not, write to the Free Software
  22    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  23    02110-1301, USA.
  24
  25    $Id: threads-common.c 8295 2007-08-11 17:57:24Z michi $
  26
  27 */
  28
  29
  30 #include "config.h"
  31
  32 #include <assert.h>
  33 #include <stdint.h>
  34 #include <unistd.h>
  35
  36 #include "vm/types.h"
  37
  38 #include "mm/memory.h"
  39
  40 #include "native/jni.h"
  41 #include "native/llni.h"
  42
  43 #include "native/include/java_lang_Object.h"
  44 #include "native/include/java_lang_String.h"
  45 #include "native/include/java_lang_Thread.h"
  46
  47 #if defined(WITH_CLASSPATH_GNU)
  48 # include "native/include/java_lang_VMThread.h"
  49 #endif
  50
  51 #include "threads/critical.h"
  52 #include "threads/lock-common.h"
  53 #include "threads/threads-common.h"
  54
  55 #include "toolbox/list.h"
  56
  57 #include "vm/builtin.h"
  58 #include "vm/stringlocal.h"
  59 #include "vm/vm.h"
  60
  61 #include "vm/jit/stacktrace.h"
  62
  63 #include "vmcore/class.h"
  64
  65 #if defined(ENABLE_STATISTICS)
  66 # include "vmcore/options.h"
  67 # include "vmcore/statistics.h"
  68 #endif
  69
  70 #include "vmcore/utf8.h"
  71
  72
  73 /* global variables ***********************************************************/
  74
  75 /* global threads list */
  76 static list_t *list_threads;
  77
  78 /* global threads free-list */
  79 static list_t *list_threads_free;
  80
  81 #if defined(__LINUX__)
  82 /* XXX Remove for exact-GC. */
  83 bool threads_pthreads_implementation_nptl;
  84 #endif
  85
  86
  87 /* threads_preinit *************************************************************
  88
  89    Do some early initialization of stuff required.
  90
  91    ATTENTION: Do NOT use any Java heap allocation here, as gc_init()
  92    is called AFTER this function!
  93
  94 *******************************************************************************/
  95
  96 void threads_preinit(void)
  97 {
  98         threadobject *mainthread;
  99 #if defined(__LINUX__) && defined(_CS_GNU_LIBPTHREAD_VERSION)
 100         char         *pathbuf;
 101         size_t        len;
 102 #endif
 103
 104 #if defined(__LINUX__)
 105         /* XXX Remove for exact-GC. */
 106
 107         /* On Linux we need to check the pthread implementation. */
 108
 109         /* _CS_GNU_LIBPTHREAD_VERSION (GNU C library only; since glibc 2.3.2) */
 110         /* If the glibc is a pre-2.3.2 version, we fall back to
 111            linuxthreads. */
 112
 113 # if defined(_CS_GNU_LIBPTHREAD_VERSION)
 114         len = confstr(_CS_GNU_LIBPTHREAD_VERSION, NULL, (size_t) 0);
 115
 116         /* Some systems return as length 0 (maybe cross-compilation
 117            related).  In this case we also fall back to linuxthreads. */
 118
 119         if (len > 0) {
 120                 pathbuf = MNEW(char, len);
 121
 122                 (void) confstr(_CS_GNU_LIBPTHREAD_VERSION, pathbuf, len);
 123
 124                 if (strstr(pathbuf, "NPTL") != NULL)
 125                         threads_pthreads_implementation_nptl = true;
 126                 else
 127                         threads_pthreads_implementation_nptl = false;
 128         }
 129         else
 130                 threads_pthreads_implementation_nptl = false;
 131 # else
 132         threads_pthreads_implementation_nptl = false;
 133 # endif
 134 #endif
 135
 136         /* initialize the threads lists */
 137
 138         list_threads      = list_create(OFFSET(threadobject, linkage));
 139         list_threads_free = list_create(OFFSET(threadobject, linkage));
 140
 141         /* Initialize the threads implementation (sets the thinlock on the
 142            main thread). */
 143
 144         threads_impl_preinit();
 145
 146         /* create internal thread data-structure for the main thread */
 147
 148         mainthread = threads_thread_new();
 149
 150         /* thread is a Java thread and running */
 151
 152         mainthread->flags = THREAD_FLAG_JAVA;
 153         mainthread->state = THREAD_STATE_RUNNABLE;
 154
 155         /* store the internal thread data-structure in the TSD */
 156
 157         threads_set_current_threadobject(mainthread);
 158
 159         /* initialize locking subsystems */
 160
 161         lock_init();
 162
 163         /* initialize the critical section */
 164
 165         critical_init();
 166 }
 167
 168
 169 /* threads_list_first **********************************************************
 170
 171    Return the first entry in the threads list.
 172
 173    NOTE: This function does not lock the lists.
 174
 175 *******************************************************************************/
 176
 177 threadobject *threads_list_first(void)
 178 {
 179         threadobject *t;
 180
 181         t = list_first_unsynced(list_threads);
 182
 183         return t;
 184 }
 185
 186
 187 /* threads_list_next ***********************************************************
 188
 189    Return the next entry in the threads list.
 190
 191    NOTE: This function does not lock the lists.
 192
 193 *******************************************************************************/
 194
 195 threadobject *threads_list_next(threadobject *t)
 196 {
 197         threadobject *next;
 198
 199         next = list_next_unsynced(list_threads, t);
 200
 201         return next;
 202 }
 203
 204
 205 /* threads_list_get_non_daemons ************************************************
 206
 207    Return the number of non-daemon threads.
 208
 209    NOTE: This function does a linear-search over the threads list,
 210          because it's only used for joining the threads.
 211
 212 *******************************************************************************/
 213
 214 s4 threads_list_get_non_daemons(void)
 215 {
 216         threadobject *t;
 217         s4            nondaemons;
 218
 219         /* lock the threads lists */
 220
 221         threads_list_lock();
 222
 223         nondaemons = 0;
 224
 225         for (t = threads_list_first(); t != NULL; t = threads_list_next(t)) {
 226                 if (!(t->flags & THREAD_FLAG_DAEMON))
 227                         nondaemons++;
 228         }
 229
 230         /* unlock the threads lists */
 231
 232         threads_list_unlock();
 233
 234         return nondaemons;
 235 }
 236
 237
 238 /* threads_thread_new **********************************************************
 239
 240    Allocates and initializes an internal thread data-structure and
 241    adds it to the threads list.
 242
 243 *******************************************************************************/
 244
 245 threadobject *threads_thread_new(void)
 246 {
 247         threadobject *t;
 248
 249         /* lock the threads-lists */
 250
 251         threads_list_lock();
 252
 253         /* try to get a thread from the free-list */
 254
 255         t = list_first_unsynced(list_threads_free);
 256
 257         /* is a free thread available? */
 258
 259         if (t != NULL) {
 260                 /* yes, remove it from the free list */
 261
 262                 list_remove_unsynced(list_threads_free, t);
 263         }
 264         else {
 265                 /* no, allocate a new one */
 266
 267 #if defined(ENABLE_GC_BOEHM)
 268                 t = GCNEW_UNCOLLECTABLE(threadobject, 1);
 269 #else
 270                 t = NEW(threadobject);
 271 #endif
 272
 273 #if defined(ENABLE_STATISTICS)
 274                 if (opt_stat)
 275                         size_threadobject += sizeof(threadobject);
 276 #endif
 277
 278                 /* clear memory */
 279
 280                 MZERO(t, threadobject, 1);
 281
 282                 /* set the threads-index */
 283
 284                 t->index = list_threads->size + 1;
 285         }
 286
 287         /* pre-compute the thinlock-word */
 288
 289         assert(t->index != 0);
 290
 291         t->thinlock = lock_pre_compute_thinlock(t->index);
 292         t->state    = THREAD_STATE_NEW;
 293
 294         /* initialize the implementation-specific bits */
 295
 296         threads_impl_thread_new(t);
 297
 298         /* add the thread to the threads-list */
 299
 300         list_add_last_unsynced(list_threads, t);
 301
 302         /* unlock the threads-lists */
 303
 304         threads_list_unlock();
 305
 306         return t;
 307 }
 308
 309
 310 /* threads_thread_free *********************************************************
 311
 312    Frees an internal thread data-structure by removing it from the
 313    threads-list and adding it to the free-list.
 314
 315    NOTE: The data-structure is NOT freed, the pointer keeps valid!
 316
 317 *******************************************************************************/
 318
 319 void threads_thread_free(threadobject *t)
 320 {
 321         int32_t  index;
 322         uint32_t state;
 323
 324         /* lock the threads-lists */
 325
 326         threads_list_lock();
 327
 328         /* cleanup the implementation-specific bits */
 329
 330         threads_impl_thread_free(t);
 331
 332         /* remove the thread from the threads-list */
 333
 334         list_remove_unsynced(list_threads, t);
 335
 336         /* Clear memory, but keep the thread-index and the
 337            thread-state. */
 338
 339         /* ATTENTION: Do this after list_remove, otherwise the linkage
 340            pointers are invalid. */
 341
 342         index = t->index;
 343         state = t->state;
 344
 345         MZERO(t, threadobject, 1);
 346
 347         t->index = index;
 348         t->state = state;
 349
 350         /* add the thread to the free list */
 351
 352         list_add_first_unsynced(list_threads_free, t);
 353
 354         /* unlock the threads-lists */
 355
 356         threads_list_unlock();
 357 }
 358
 359
 360 /* threads_thread_start_internal ***********************************************
 361
 362    Start an internal thread in the JVM.  No Java thread objects exists
 363    so far.
 364
 365    IN:
 366       name.......UTF-8 name of the thread
 367       f..........function pointer to C function to start
 368
 369 *******************************************************************************/
 370
 371 bool threads_thread_start_internal(utf *name, functionptr f)
 372 {
 373         threadobject       *t;
 374         java_lang_Thread   *object;
 375 #if defined(WITH_CLASSPATH_GNU)
 376         java_lang_VMThread *vmt;
 377 #endif
 378
 379         /* Enter the join-mutex, so if the main-thread is currently
 380            waiting to join all threads, the number of non-daemon threads
 381            is correct. */
 382
 383         threads_mutex_join_lock();
 384
 385         /* create internal thread data-structure */
 386
 387         t = threads_thread_new();
 388
 389         t->flags = THREAD_FLAG_INTERNAL | THREAD_FLAG_DAEMON;
 390
 391         /* The thread is flagged as (non-)daemon thread, we can leave the
 392            mutex. */
 393
 394         threads_mutex_join_unlock();
 395
 396         /* create the java thread object */
 397
 398         object = (java_lang_Thread *) builtin_new(class_java_lang_Thread);
 399
 400         /* XXX memory leak!!! */
 401         if (object == NULL)
 402                 return false;
 403
 404 #if defined(WITH_CLASSPATH_GNU)
 405         vmt = (java_lang_VMThread *) builtin_new(class_java_lang_VMThread);
 406
 407         /* XXX memory leak!!! */
 408         if (vmt == NULL)
 409                 return false;
 410
 411         LLNI_field_set_ref(vmt, thread, object);
 412         LLNI_field_set_val(vmt, vmdata, (java_lang_Object *) t);
 413
 414         LLNI_field_set_ref(object, vmThread, vmt);
 415 #elif defined(WITH_CLASSPATH_CLDC1_1)
 416         LLNI_field_set_val(object, vm_thread, (java_lang_Object *) t);
 417 #endif
 418
 419         t->object = object;
 420
 421         /* set java.lang.Thread fields */
 422
 423 #if defined(WITH_CLASSPATH_GNU)
 424         LLNI_field_set_ref(object, name    , (java_lang_String *) javastring_new(name));
 425 #elif defined(WITH_CLASSPATH_CLDC1_1)
 426         /* FIXME: In cldc the name is a char[] */
 427 /*      LLNI_field_set_ref(object, name    , (java_chararray *) javastring_new(name)); */
 428         LLNI_field_set_ref(object, name    , NULL);
 429 #endif
 430
 431 #if defined(ENABLE_JAVASE)
 432         LLNI_field_set_val(object, daemon  , true);
 433 #endif
 434
 435         LLNI_field_set_val(object, priority, NORM_PRIORITY);
 436
 437         /* start the thread */
 438
 439         threads_impl_thread_start(t, f);
 440
 441         /* everything's ok */
 442
 443         return true;
 444 }
 445
 446
 447 /* threads_thread_start ********************************************************
 448
 449    Start a Java thread in the JVM.  Only the java thread object exists
 450    so far.
 451
 452    IN:
 453       object.....the java thread object java.lang.Thread
 454
 455 *******************************************************************************/
 456
 457 void threads_thread_start(java_lang_Thread *object)
 458 {
 459         threadobject *thread;
 460 #if defined(WITH_CLASSPATH_GNU)
 461         java_lang_VMThread *vmt;
 462 #endif
 463
 464         /* Enter the join-mutex, so if the main-thread is currently
 465            waiting to join all threads, the number of non-daemon threads
 466            is correct. */
 467
 468         threads_mutex_join_lock();
 469
 470         /* create internal thread data-structure */
 471
 472         thread = threads_thread_new();
 473
 474         /* this is a normal Java thread */
 475
 476         thread->flags = THREAD_FLAG_JAVA;
 477
 478 #if defined(ENABLE_JAVASE)
 479         /* is this a daemon thread? */
 480
 481         if (LLNI_field_direct(object, daemon) == true)
 482                 thread->flags |= THREAD_FLAG_DAEMON;
 483 #endif
 484
 485         /* The thread is flagged and (non-)daemon thread, we can leave the
 486            mutex. */
 487
 488         threads_mutex_join_unlock();
 489
 490         /* link the two objects together */
 491
 492         thread->object = object;
 493
 494 #if defined(WITH_CLASSPATH_GNU)
 495         LLNI_field_get_ref(object, vmThread, vmt);
 496
 497         assert(vmt);
 498         assert(LLNI_field_direct(vmt, vmdata) == NULL);
 499
 500         LLNI_field_set_val(vmt, vmdata, (java_lang_Object *) thread);
 501 #elif defined(WITH_CLASSPATH_CLDC1_1)
 502         LLNI_field_set_val(object, vm_thread, (java_lang_Object *) thread);
 503 #endif
 504
 505         /* Start the thread.  Don't pass a function pointer (NULL) since
 506            we want Thread.run()V here. */
 507
 508         threads_impl_thread_start(thread, NULL);
 509 }
 510
 511
 512 /* threads_thread_print_info ***************************************************
 513
 514    Print information of the passed thread.
 515
 516 *******************************************************************************/
 517
 518 void threads_thread_print_info(threadobject *t)
 519 {
 520         java_lang_Thread *object;
 521         utf              *name;
 522
 523         assert(t->state != THREAD_STATE_NEW);
 524
 525         /* the thread may be currently in initalization, don't print it */
 526
 527         object = t->object;
 528
 529         if (object != NULL) {
 530                 /* get thread name */
 531
 532 #if defined(WITH_CLASSPATH_GNU)
 533                 name = javastring_toutf((java_handle_t *) LLNI_field_direct(object, name), false);
 534 #elif defined(WITH_CLASSPATH_SUN) || defined(WITH_CLASSPATH_CLDC1_1)
 535                 /* FIXME: In cldc the name is a char[] */
 536 /*              name = object->name; */
 537                 name = utf_null;
 538 #else
 539 # error unknown classpath configuration
 540 #endif
 541
 542                 printf("\"");
 543                 utf_display_printable_ascii(name);
 544                 printf("\"");
 545
 546                 if (t->flags & THREAD_FLAG_DAEMON)
 547                         printf(" daemon");
 548
 549                 printf(" prio=%d", LLNI_field_direct(object, priority));
 550
 551 #if SIZEOF_VOID_P == 8
 552                 printf(" t=0x%016lx tid=0x%016lx (%ld)",
 553                            (ptrint) t, (ptrint) t->tid, (ptrint) t->tid);
 554 #else
 555                 printf(" t=0x%08x tid=0x%08x (%d)",
 556                            (ptrint) t, (ptrint) t->tid, (ptrint) t->tid);
 557 #endif
 558
 559                 printf(" index=%d", t->index);
 560
 561                 /* print thread state */
 562
 563                 switch (t->state) {
 564                 case THREAD_STATE_NEW:
 565                         printf(" new");
 566                         break;
 567                 case THREAD_STATE_RUNNABLE:
 568                         printf(" runnable");
 569                         break;
 570                 case THREAD_STATE_BLOCKED:
 571                         printf(" blocked");
 572                         break;
 573                 case THREAD_STATE_WAITING:
 574                         printf(" waiting");
 575                         break;
 576                 case THREAD_STATE_TIMED_WAITING:
 577                         printf(" waiting on condition");
 578                         break;
 579                 case THREAD_STATE_TERMINATED:
 580                         printf(" terminated");
 581                         break;
 582                 default:
 583                         vm_abort("threads_thread_print_info: unknown thread state %d",
 584                                          t->state);
 585                 }
 586         }
 587 }
 588
 589
 590 /* threads_get_current_tid *****************************************************
 591
 592    Return the tid of the current thread.
 593
 594    RETURN VALUE:
 595        the current tid
 596
 597 *******************************************************************************/
 598
 599 ptrint threads_get_current_tid(void)
 600 {
 601         threadobject *thread;
 602
 603         thread = THREADOBJECT;
 604
 605         /* this may happen during bootstrap */
 606
 607         if (thread == NULL)
 608                 return 0;
 609
 610         return (ptrint) thread->tid;
 611 }
 612
 613
 614 /* threads_thread_state_runnable ***********************************************
 615
 616    Set the current state of the given thread to THREAD_STATE_RUNNABLE.
 617
 618 *******************************************************************************/
 619
 620 void threads_thread_state_runnable(threadobject *t)
 621 {
 622         /* set the state inside the lock */
 623
 624         threads_list_lock();
 625
 626         t->state = THREAD_STATE_RUNNABLE;
 627
 628         threads_list_unlock();
 629 }
 630
 631
 632 /* threads_thread_state_waiting ************************************************
 633
 634    Set the current state of the given thread to THREAD_STATE_WAITING.
 635
 636 *******************************************************************************/
 637
 638 void threads_thread_state_waiting(threadobject *t)
 639 {
 640         /* set the state in the lock */
 641
 642         threads_list_lock();
 643
 644         t->state = THREAD_STATE_WAITING;
 645
 646         threads_list_unlock();
 647 }
 648
 649
 650 /* threads_thread_state_timed_waiting ******************************************
 651
 652    Set the current state of the given thread to
 653    THREAD_STATE_TIMED_WAITING.
 654
 655 *******************************************************************************/
 656
 657 void threads_thread_state_timed_waiting(threadobject *t)
 658 {
 659         /* set the state in the lock */
 660
 661         threads_list_lock();
 662
 663         t->state = THREAD_STATE_TIMED_WAITING;
 664
 665         threads_list_unlock();
 666 }
 667
 668
 669 /* threads_thread_state_terminated *********************************************
 670
 671    Set the current state of the given thread to
 672    THREAD_STATE_TERMINATED.
 673
 674 *******************************************************************************/
 675
 676 void threads_thread_state_terminated(threadobject *t)
 677 {
 678         /* set the state in the lock */
 679
 680         threads_list_lock();
 681
 682         t->state = THREAD_STATE_TERMINATED;
 683
 684         threads_list_unlock();
 685 }
 686
 687
 688 /* threads_thread_get_state ****************************************************
 689
 690    Returns the current state of the given thread.
 691
 692 *******************************************************************************/
 693
 694 utf *threads_thread_get_state(threadobject *t)
 695 {
 696         utf *u;
 697
 698         switch (t->state) {
 699         case THREAD_STATE_NEW:
 700                 u = utf_new_char("NEW");
 701                 break;
 702         case THREAD_STATE_RUNNABLE:
 703                 u = utf_new_char("RUNNABLE");
 704                 break;
 705         case THREAD_STATE_BLOCKED:
 706                 u = utf_new_char("BLOCKED");
 707                 break;
 708         case THREAD_STATE_WAITING:
 709                 u = utf_new_char("WAITING");
 710                 break;
 711         case THREAD_STATE_TIMED_WAITING:
 712                 u = utf_new_char("TIMED_WAITING");
 713                 break;
 714         case THREAD_STATE_TERMINATED:
 715                 u = utf_new_char("TERMINATED");
 716                 break;
 717         default:
 718                 vm_abort("threads_get_state: unknown thread state %d", t->state);
 719
 720                 /* keep compiler happy */
 721
 722                 u = NULL;
 723         }
 724
 725         return u;
 726 }
 727
 728
 729 /* threads_thread_is_alive *****************************************************
 730
 731    Returns if the give thread is alive.
 732
 733 *******************************************************************************/
 734
 735 bool threads_thread_is_alive(threadobject *thread)
 736 {
 737         bool result;
 738
 739         switch (thread->state) {
 740         case THREAD_STATE_NEW:
 741         case THREAD_STATE_TERMINATED:
 742                 result = false;
 743                 break;
 744
 745         case THREAD_STATE_RUNNABLE:
 746         case THREAD_STATE_BLOCKED:
 747         case THREAD_STATE_WAITING:
 748         case THREAD_STATE_TIMED_WAITING:
 749                 result = true;
 750                 break;
 751
 752         default:
 753                 vm_abort("threads_is_alive: unknown thread state %d", thread->state);
 754
 755                 /* keep compiler happy */
 756
 757                 result = false;
 758         }
 759
 760         return result;
 761 }
 762
 763
 764 /* threads_dump ****************************************************************
 765
 766    Dumps info for all threads running in the JVM.  This function is
 767    called when SIGQUIT (<ctrl>-\) is sent to CACAO.
 768
 769 *******************************************************************************/
 770
 771 void threads_dump(void)
 772 {
 773         threadobject *t;
 774
 775         /* XXX we should stop the world here */
 776
 777         /* lock the threads lists */
 778
 779         threads_list_lock();
 780
 781         printf("Full thread dump CACAO "VERSION":\n");
 782
 783         /* iterate over all started threads */
 784
 785         for (t = threads_list_first(); t != NULL; t = threads_list_next(t)) {
 786                 /* print thread info */
 787
 788                 printf("\n");
 789                 threads_thread_print_info(t);
 790                 printf("\n");
 791
 792                 /* print trace of thread */
 793
 794                 threads_thread_print_stacktrace(t);
 795         }
 796
 797         /* unlock the threads lists */
 798
 799         threads_list_unlock();
 800 }
 801
 802
 803 /* threads_thread_print_stacktrace *********************************************
 804
 805    Print the current stacktrace of the current thread.
 806
 807 *******************************************************************************/
 808
 809 void threads_thread_print_stacktrace(threadobject *thread)
 810 {
 811         stackframeinfo   *sfi;
 812         stacktracebuffer *stb;
 813         s4                dumpsize;
 814
 815         /* mark start of dump memory area */
 816
 817         dumpsize = dump_size();
 818
 819         /* create a stacktrace for the passed thread */
 820
 821         sfi = thread->_stackframeinfo;
 822
 823         stb = stacktrace_create(sfi);
 824
 825         /* print stacktrace */
 826
 827         if (stb != NULL)
 828                 stacktrace_print_trace_from_buffer(stb);
 829         else {
 830                 puts("\t<<No stacktrace available>>");
 831                 fflush(stdout);
 832         }
 833
 834         dump_release(dumpsize);
 835 }
 836
 837
 838 /* threads_print_stacktrace ****************************************************
 839
 840    Print the current stacktrace of the current thread.
 841
 842 *******************************************************************************/
 843
 844 void threads_print_stacktrace(void)
 845 {
 846         threadobject *thread;
 847
 848         thread = THREADOBJECT;
 849
 850         threads_thread_print_stacktrace(thread);
 851 }
 852
 853
 854 /*
 855  * These are local overrides for various environment variables in Emacs.
 856  * Please do not remove this and leave it at the end of the file, where
 857  * Emacs will automagically detect them.
 858  * ---------------------------------------------------------------------
 859  * Local variables:
 860  * mode: c
 861  * indent-tabs-mode: t
 862  * c-basic-offset: 4
 863  * tab-width: 4
 864  * End:
 865  * vim:noexpandtab:sw=4:ts=4:
 866  */