lib/libthr/thread/thr_init.c

   1 /*
   2  * Copyright (c) 2003 Daniel M. Eischen <deischen@freebsd.org>
   3  * Copyright (c) 1995-1998 John Birrell <jb@cimlogic.com.au>
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  * 3. All advertising materials mentioning features or use of this software
  15  *    must display the following acknowledgement:
  16  *      This product includes software developed by John Birrell.
  17  * 4. Neither the name of the author nor the names of any co-contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  * $FreeBSD$
  34  */
  35
  36 #include "namespace.h"
  37 #include <sys/types.h>
  38 #include <sys/signalvar.h>
  39 #include <sys/ioctl.h>
  40 #include <sys/sysctl.h>
  41 #include <sys/ttycom.h>
  42 #include <sys/mman.h>
  43 #include <sys/rtprio.h>
  44 #include <errno.h>
  45 #include <fcntl.h>
  46 #include <paths.h>
  47 #include <pthread.h>
  48 #include <pthread_np.h>
  49 #include <signal.h>
  50 #include <stdlib.h>
  51 #include <string.h>
  52 #include <time.h>
  53 #include <unistd.h>
  54 #include "un-namespace.h"
  55
  56 #include "libc_private.h"
  57 #include "thr_private.h"
  58
  59 char            *_usrstack;
  60 struct pthread  *_thr_initial;
  61 int             _libthr_debug;
  62 int             _thread_event_mask;
  63 struct pthread  *_thread_last_event;
  64 pthreadlist     _thread_list = TAILQ_HEAD_INITIALIZER(_thread_list);
  65 pthreadlist     _thread_gc_list = TAILQ_HEAD_INITIALIZER(_thread_gc_list);
  66 int             _thread_active_threads = 1;
  67 atfork_head     _thr_atfork_list = TAILQ_HEAD_INITIALIZER(_thr_atfork_list);
  68 struct urwlock  _thr_atfork_lock = DEFAULT_URWLOCK;
  69
  70 struct pthread_prio     _thr_priorities[3] = {
  71         {RTP_PRIO_MIN,  RTP_PRIO_MAX, 0}, /* FIFO */
  72         {0, 0, 63}, /* OTHER */
  73         {RTP_PRIO_MIN, RTP_PRIO_MAX, 0}  /* RR */
  74 };
  75
  76 struct pthread_attr _pthread_attr_default = {
  77         .sched_policy = SCHED_OTHER,
  78         .sched_inherit = PTHREAD_INHERIT_SCHED,
  79         .prio = 0,
  80         .suspend = THR_CREATE_RUNNING,
  81         .flags = PTHREAD_SCOPE_SYSTEM,
  82         .stackaddr_attr = NULL,
  83         .stacksize_attr = THR_STACK_DEFAULT,
  84         .guardsize_attr = 0,
  85         .cpusetsize = 0,
  86         .cpuset = NULL
  87 };
  88
  89 struct pthread_mutex_attr _pthread_mutexattr_default = {
  90         .m_type = PTHREAD_MUTEX_DEFAULT,
  91         .m_protocol = PTHREAD_PRIO_NONE,
  92         .m_ceiling = 0
  93 };
  94
  95 struct pthread_mutex_attr _pthread_mutexattr_adaptive_default = {
  96         .m_type = PTHREAD_MUTEX_ADAPTIVE_NP,
  97         .m_protocol = PTHREAD_PRIO_NONE,
  98         .m_ceiling = 0
  99 };
 100
 101 /* Default condition variable attributes: */
 102 struct pthread_cond_attr _pthread_condattr_default = {
 103         .c_pshared = PTHREAD_PROCESS_PRIVATE,
 104         .c_clockid = CLOCK_REALTIME
 105 };
 106
 107 pid_t           _thr_pid;
 108 int             _thr_is_smp = 0;
 109 size_t          _thr_guard_default;
 110 size_t          _thr_stack_default = THR_STACK_DEFAULT;
 111 size_t          _thr_stack_initial = THR_STACK_INITIAL;
 112 int             _thr_page_size;
 113 int             _thr_spinloops;
 114 int             _thr_yieldloops;
 115 int             _gc_count;
 116 struct umutex   _mutex_static_lock = DEFAULT_UMUTEX;
 117 struct umutex   _cond_static_lock = DEFAULT_UMUTEX;
 118 struct umutex   _rwlock_static_lock = DEFAULT_UMUTEX;
 119 struct umutex   _keytable_lock = DEFAULT_UMUTEX;
 120 struct urwlock  _thr_list_lock = DEFAULT_URWLOCK;
 121 struct umutex   _thr_event_lock = DEFAULT_UMUTEX;
 122
 123 int     __pthread_cond_wait(pthread_cond_t *, pthread_mutex_t *);
 124 int     __pthread_mutex_lock(pthread_mutex_t *);
 125 int     __pthread_mutex_trylock(pthread_mutex_t *);
 126 void    _thread_init_hack(void) __attribute__ ((constructor));
 127
 128 static void init_private(void);
 129 static void init_main_thread(struct pthread *thread);
 130
 131 /*
 132  * All weak references used within libc should be in this table.
 133  * This is so that static libraries will work.
 134  */
 135
 136 STATIC_LIB_REQUIRE(_fork);
 137 STATIC_LIB_REQUIRE(_pthread_getspecific);
 138 STATIC_LIB_REQUIRE(_pthread_key_create);
 139 STATIC_LIB_REQUIRE(_pthread_key_delete);
 140 STATIC_LIB_REQUIRE(_pthread_mutex_destroy);
 141 STATIC_LIB_REQUIRE(_pthread_mutex_init);
 142 STATIC_LIB_REQUIRE(_pthread_mutex_lock);
 143 STATIC_LIB_REQUIRE(_pthread_mutex_trylock);
 144 STATIC_LIB_REQUIRE(_pthread_mutex_unlock);
 145 STATIC_LIB_REQUIRE(_pthread_mutexattr_init);
 146 STATIC_LIB_REQUIRE(_pthread_mutexattr_destroy);
 147 STATIC_LIB_REQUIRE(_pthread_mutexattr_settype);
 148 STATIC_LIB_REQUIRE(_pthread_once);
 149 STATIC_LIB_REQUIRE(_pthread_setspecific);
 150 STATIC_LIB_REQUIRE(_raise);
 151 STATIC_LIB_REQUIRE(_sem_destroy);
 152 STATIC_LIB_REQUIRE(_sem_getvalue);
 153 STATIC_LIB_REQUIRE(_sem_init);
 154 STATIC_LIB_REQUIRE(_sem_post);
 155 STATIC_LIB_REQUIRE(_sem_timedwait);
 156 STATIC_LIB_REQUIRE(_sem_trywait);
 157 STATIC_LIB_REQUIRE(_sem_wait);
 158 STATIC_LIB_REQUIRE(_sigaction);
 159 STATIC_LIB_REQUIRE(_sigprocmask);
 160 STATIC_LIB_REQUIRE(_sigsuspend);
 161 STATIC_LIB_REQUIRE(_sigtimedwait);
 162 STATIC_LIB_REQUIRE(_sigwait);
 163 STATIC_LIB_REQUIRE(_sigwaitinfo);
 164 STATIC_LIB_REQUIRE(_spinlock);
 165 STATIC_LIB_REQUIRE(_spinlock_debug);
 166 STATIC_LIB_REQUIRE(_spinunlock);
 167 STATIC_LIB_REQUIRE(_thread_init_hack);
 168
 169 /*
 170  * These are needed when linking statically.  All references within
 171  * libgcc (and in the future libc) to these routines are weak, but
 172  * if they are not (strongly) referenced by the application or other
 173  * libraries, then the actual functions will not be loaded.
 174  */
 175 STATIC_LIB_REQUIRE(_pthread_once);
 176 STATIC_LIB_REQUIRE(_pthread_key_create);
 177 STATIC_LIB_REQUIRE(_pthread_key_delete);
 178 STATIC_LIB_REQUIRE(_pthread_getspecific);
 179 STATIC_LIB_REQUIRE(_pthread_setspecific);
 180 STATIC_LIB_REQUIRE(_pthread_mutex_init);
 181 STATIC_LIB_REQUIRE(_pthread_mutex_destroy);
 182 STATIC_LIB_REQUIRE(_pthread_mutex_lock);
 183 STATIC_LIB_REQUIRE(_pthread_mutex_trylock);
 184 STATIC_LIB_REQUIRE(_pthread_mutex_unlock);
 185 STATIC_LIB_REQUIRE(_pthread_create);
 186
 187 /* Pull in all symbols required by libthread_db */
 188 STATIC_LIB_REQUIRE(_thread_state_running);
 189
 190 #define DUAL_ENTRY(entry)       \
 191         (pthread_func_t)entry, (pthread_func_t)entry
 192
 193 static pthread_func_t jmp_table[][2] = {
 194         {DUAL_ENTRY(_pthread_atfork)},  /* PJT_ATFORK */
 195         {DUAL_ENTRY(_pthread_attr_destroy)},    /* PJT_ATTR_DESTROY */
 196         {DUAL_ENTRY(_pthread_attr_getdetachstate)},     /* PJT_ATTR_GETDETACHSTATE */
 197         {DUAL_ENTRY(_pthread_attr_getguardsize)},       /* PJT_ATTR_GETGUARDSIZE */
 198         {DUAL_ENTRY(_pthread_attr_getinheritsched)},    /* PJT_ATTR_GETINHERITSCHED */
 199         {DUAL_ENTRY(_pthread_attr_getschedparam)},      /* PJT_ATTR_GETSCHEDPARAM */
 200         {DUAL_ENTRY(_pthread_attr_getschedpolicy)},     /* PJT_ATTR_GETSCHEDPOLICY */
 201         {DUAL_ENTRY(_pthread_attr_getscope)},   /* PJT_ATTR_GETSCOPE */
 202         {DUAL_ENTRY(_pthread_attr_getstackaddr)},       /* PJT_ATTR_GETSTACKADDR */
 203         {DUAL_ENTRY(_pthread_attr_getstacksize)},       /* PJT_ATTR_GETSTACKSIZE */
 204         {DUAL_ENTRY(_pthread_attr_init)},       /* PJT_ATTR_INIT */
 205         {DUAL_ENTRY(_pthread_attr_setdetachstate)},     /* PJT_ATTR_SETDETACHSTATE */
 206         {DUAL_ENTRY(_pthread_attr_setguardsize)},       /* PJT_ATTR_SETGUARDSIZE */
 207         {DUAL_ENTRY(_pthread_attr_setinheritsched)},    /* PJT_ATTR_SETINHERITSCHED */
 208         {DUAL_ENTRY(_pthread_attr_setschedparam)},      /* PJT_ATTR_SETSCHEDPARAM */
 209         {DUAL_ENTRY(_pthread_attr_setschedpolicy)},     /* PJT_ATTR_SETSCHEDPOLICY */
 210         {DUAL_ENTRY(_pthread_attr_setscope)},   /* PJT_ATTR_SETSCOPE */
 211         {DUAL_ENTRY(_pthread_attr_setstackaddr)},       /* PJT_ATTR_SETSTACKADDR */
 212         {DUAL_ENTRY(_pthread_attr_setstacksize)},       /* PJT_ATTR_SETSTACKSIZE */
 213         {DUAL_ENTRY(_pthread_cancel)},  /* PJT_CANCEL */
 214         {DUAL_ENTRY(_pthread_cleanup_pop)},     /* PJT_CLEANUP_POP */
 215         {DUAL_ENTRY(_pthread_cleanup_push)},    /* PJT_CLEANUP_PUSH */
 216         {DUAL_ENTRY(_pthread_cond_broadcast)},  /* PJT_COND_BROADCAST */
 217         {DUAL_ENTRY(_pthread_cond_destroy)},    /* PJT_COND_DESTROY */
 218         {DUAL_ENTRY(_pthread_cond_init)},       /* PJT_COND_INIT */
 219         {DUAL_ENTRY(_pthread_cond_signal)},     /* PJT_COND_SIGNAL */
 220         {DUAL_ENTRY(_pthread_cond_timedwait)},  /* PJT_COND_TIMEDWAIT */
 221         {(pthread_func_t)__pthread_cond_wait,
 222          (pthread_func_t)_pthread_cond_wait},   /* PJT_COND_WAIT */
 223         {DUAL_ENTRY(_pthread_detach)},  /* PJT_DETACH */
 224         {DUAL_ENTRY(_pthread_equal)},   /* PJT_EQUAL */
 225         {DUAL_ENTRY(_pthread_exit)},    /* PJT_EXIT */
 226         {DUAL_ENTRY(_pthread_getspecific)},     /* PJT_GETSPECIFIC */
 227         {DUAL_ENTRY(_pthread_join)},    /* PJT_JOIN */
 228         {DUAL_ENTRY(_pthread_key_create)},      /* PJT_KEY_CREATE */
 229         {DUAL_ENTRY(_pthread_key_delete)},      /* PJT_KEY_DELETE*/
 230         {DUAL_ENTRY(_pthread_kill)},    /* PJT_KILL */
 231         {DUAL_ENTRY(_pthread_main_np)},         /* PJT_MAIN_NP */
 232         {DUAL_ENTRY(_pthread_mutexattr_destroy)}, /* PJT_MUTEXATTR_DESTROY */
 233         {DUAL_ENTRY(_pthread_mutexattr_init)},  /* PJT_MUTEXATTR_INIT */
 234         {DUAL_ENTRY(_pthread_mutexattr_settype)}, /* PJT_MUTEXATTR_SETTYPE */
 235         {DUAL_ENTRY(_pthread_mutex_destroy)},   /* PJT_MUTEX_DESTROY */
 236         {DUAL_ENTRY(_pthread_mutex_init)},      /* PJT_MUTEX_INIT */
 237         {(pthread_func_t)__pthread_mutex_lock,
 238          (pthread_func_t)_pthread_mutex_lock},  /* PJT_MUTEX_LOCK */
 239         {(pthread_func_t)__pthread_mutex_trylock,
 240          (pthread_func_t)_pthread_mutex_trylock},/* PJT_MUTEX_TRYLOCK */
 241         {DUAL_ENTRY(_pthread_mutex_unlock)},    /* PJT_MUTEX_UNLOCK */
 242         {DUAL_ENTRY(_pthread_once)},            /* PJT_ONCE */
 243         {DUAL_ENTRY(_pthread_rwlock_destroy)},  /* PJT_RWLOCK_DESTROY */
 244         {DUAL_ENTRY(_pthread_rwlock_init)},     /* PJT_RWLOCK_INIT */
 245         {DUAL_ENTRY(_pthread_rwlock_rdlock)},   /* PJT_RWLOCK_RDLOCK */
 246         {DUAL_ENTRY(_pthread_rwlock_tryrdlock)},/* PJT_RWLOCK_TRYRDLOCK */
 247         {DUAL_ENTRY(_pthread_rwlock_trywrlock)},/* PJT_RWLOCK_TRYWRLOCK */
 248         {DUAL_ENTRY(_pthread_rwlock_unlock)},   /* PJT_RWLOCK_UNLOCK */
 249         {DUAL_ENTRY(_pthread_rwlock_wrlock)},   /* PJT_RWLOCK_WRLOCK */
 250         {DUAL_ENTRY(_pthread_self)},            /* PJT_SELF */
 251         {DUAL_ENTRY(_pthread_setcancelstate)},  /* PJT_SETCANCELSTATE */
 252         {DUAL_ENTRY(_pthread_setcanceltype)},   /* PJT_SETCANCELTYPE */
 253         {DUAL_ENTRY(_pthread_setspecific)},     /* PJT_SETSPECIFIC */
 254         {DUAL_ENTRY(_pthread_sigmask)},         /* PJT_SIGMASK */
 255         {DUAL_ENTRY(_pthread_testcancel)},      /* PJT_TESTCANCEL */
 256         {DUAL_ENTRY(__pthread_cleanup_pop_imp)},/* PJT_CLEANUP_POP_IMP */
 257         {DUAL_ENTRY(__pthread_cleanup_push_imp)},/* PJT_CLEANUP_PUSH_IMP */
 258         {DUAL_ENTRY(_pthread_cancel_enter)},    /* PJT_CANCEL_ENTER */
 259         {DUAL_ENTRY(_pthread_cancel_leave)}             /* PJT_CANCEL_LEAVE */
 260 };
 261
 262 static int init_once = 0;
 263
 264 /*
 265  * For the shared version of the threads library, the above is sufficient.
 266  * But for the archive version of the library, we need a little bit more.
 267  * Namely, we must arrange for this particular module to be pulled in from
 268  * the archive library at link time.  To accomplish that, we define and
 269  * initialize a variable, "_thread_autoinit_dummy_decl".  This variable is
 270  * referenced (as an extern) from libc/stdlib/exit.c. This will always
 271  * create a need for this module, ensuring that it is present in the
 272  * executable.
 273  */
 274 extern int _thread_autoinit_dummy_decl;
 275 int _thread_autoinit_dummy_decl = 0;
 276
 277 void
 278 _thread_init_hack(void)
 279 {
 280
 281         _libpthread_init(NULL);
 282 }
 283
 284
 285 /*
 286  * Threaded process initialization.
 287  *
 288  * This is only called under two conditions:
 289  *
 290  *   1) Some thread routines have detected that the library hasn't yet
 291  *      been initialized (_thr_initial == NULL && curthread == NULL), or
 292  *
 293  *   2) An explicit call to reinitialize after a fork (indicated
 294  *      by curthread != NULL)
 295  */
 296 void
 297 _libpthread_init(struct pthread *curthread)
 298 {
 299         int fd, first = 0;
 300
 301         /* Check if this function has already been called: */
 302         if ((_thr_initial != NULL) && (curthread == NULL))
 303                 /* Only initialize the threaded application once. */
 304                 return;
 305
 306         /*
 307          * Check the size of the jump table to make sure it is preset
 308          * with the correct number of entries.
 309          */
 310         if (sizeof(jmp_table) != (sizeof(pthread_func_t) * PJT_MAX * 2))
 311                 PANIC("Thread jump table not properly initialized");
 312         memcpy(__thr_jtable, jmp_table, sizeof(jmp_table));
 313
 314         /*
 315          * Check for the special case of this process running as
 316          * or in place of init as pid = 1:
 317          */
 318         if ((_thr_pid = getpid()) == 1) {
 319                 /*
 320                  * Setup a new session for this process which is
 321                  * assumed to be running as root.
 322                  */
 323                 if (setsid() == -1)
 324                         PANIC("Can't set session ID");
 325                 if (revoke(_PATH_CONSOLE) != 0)
 326                         PANIC("Can't revoke console");
 327                 if ((fd = __sys_open(_PATH_CONSOLE, O_RDWR)) < 0)
 328                         PANIC("Can't open console");
 329                 if (setlogin("root") == -1)
 330                         PANIC("Can't set login to root");
 331                 if (_ioctl(fd, TIOCSCTTY, (char *) NULL) == -1)
 332                         PANIC("Can't set controlling terminal");
 333         }
 334
 335         /* Initialize pthread private data. */
 336         init_private();
 337
 338         /* Set the initial thread. */
 339         if (curthread == NULL) {
 340                 first = 1;
 341                 /* Create and initialize the initial thread. */
 342                 curthread = _thr_alloc(NULL);
 343                 if (curthread == NULL)
 344                         PANIC("Can't allocate initial thread");
 345                 init_main_thread(curthread);
 346         }
 347         /*
 348          * Add the thread to the thread list queue.
 349          */
 350         THR_LIST_ADD(curthread);
 351         _thread_active_threads = 1;
 352
 353         /* Setup the thread specific data */
 354         _tcb_set(curthread->tcb);
 355
 356         if (first) {
 357                 _thr_initial = curthread;
 358                 _thr_signal_init();
 359                 if (_thread_event_mask & TD_CREATE)
 360                         _thr_report_creation(curthread, curthread);
 361         }
 362 }
 363
 364 /*
 365  * This function and pthread_create() do a lot of the same things.
 366  * It'd be nice to consolidate the common stuff in one place.
 367  */
 368 static void
 369 init_main_thread(struct pthread *thread)
 370 {
 371         struct sched_param sched_param;
 372
 373         /* Setup the thread attributes. */
 374         thr_self(&thread->tid);
 375         thread->attr = _pthread_attr_default;
 376         /*
 377          * Set up the thread stack.
 378          *
 379          * Create a red zone below the main stack.  All other stacks
 380          * are constrained to a maximum size by the parameters
 381          * passed to mmap(), but this stack is only limited by
 382          * resource limits, so this stack needs an explicitly mapped
 383          * red zone to protect the thread stack that is just beyond.
 384          */
 385         if (mmap(_usrstack - _thr_stack_initial -
 386             _thr_guard_default, _thr_guard_default, 0, MAP_ANON,
 387             -1, 0) == MAP_FAILED)
 388                 PANIC("Cannot allocate red zone for initial thread");
 389
 390         /*
 391          * Mark the stack as an application supplied stack so that it
 392          * isn't deallocated.
 393          *
 394          * XXX - I'm not sure it would hurt anything to deallocate
 395          *       the main thread stack because deallocation doesn't
 396          *       actually free() it; it just puts it in the free
 397          *       stack queue for later reuse.
 398          */
 399         thread->attr.stackaddr_attr = _usrstack - _thr_stack_initial;
 400         thread->attr.stacksize_attr = _thr_stack_initial;
 401         thread->attr.guardsize_attr = _thr_guard_default;
 402         thread->attr.flags |= THR_STACK_USER;
 403
 404         /*
 405          * Write a magic value to the thread structure
 406          * to help identify valid ones:
 407          */
 408         thread->magic = THR_MAGIC;
 409
 410         thread->cancel_enable = 1;
 411         thread->cancel_async = 0;
 412
 413         /* Initialize the mutex queue: */
 414         TAILQ_INIT(&thread->mutexq);
 415         TAILQ_INIT(&thread->pp_mutexq);
 416
 417         thread->state = PS_RUNNING;
 418
 419         _thr_getscheduler(thread->tid, &thread->attr.sched_policy,
 420                  &sched_param);
 421         thread->attr.prio = sched_param.sched_priority;
 422
 423 #ifdef _PTHREAD_FORCED_UNWIND
 424         thread->unwind_stackend = _usrstack;
 425 #endif
 426
 427         /* Others cleared to zero by thr_alloc() */
 428 }
 429
 430 static void
 431 init_private(void)
 432 {
 433         size_t len;
 434         int mib[2];
 435         char *env;
 436
 437         _thr_umutex_init(&_mutex_static_lock);
 438         _thr_umutex_init(&_cond_static_lock);
 439         _thr_umutex_init(&_rwlock_static_lock);
 440         _thr_umutex_init(&_keytable_lock);
 441         _thr_urwlock_init(&_thr_atfork_lock);
 442         _thr_umutex_init(&_thr_event_lock);
 443         _thr_once_init();
 444         _thr_spinlock_init();
 445         _thr_list_init();
 446         _thr_wake_addr_init();
 447         _sleepq_init();
 448
 449         /*
 450          * Avoid reinitializing some things if they don't need to be,
 451          * e.g. after a fork().
 452          */
 453         if (init_once == 0) {
 454                 /* Find the stack top */
 455                 mib[0] = CTL_KERN;
 456                 mib[1] = KERN_USRSTACK;
 457                 len = sizeof (_usrstack);
 458                 if (sysctl(mib, 2, &_usrstack, &len, NULL, 0) == -1)
 459                         PANIC("Cannot get kern.usrstack from sysctl");
 460                 len = sizeof(_thr_is_smp);
 461                 sysctlbyname("kern.smp.cpus", &_thr_is_smp, &len, NULL, 0);
 462                 _thr_is_smp = (_thr_is_smp > 1);
 463                 _thr_page_size = getpagesize();
 464                 _thr_guard_default = _thr_page_size;
 465                 _pthread_attr_default.guardsize_attr = _thr_guard_default;
 466                 _pthread_attr_default.stacksize_attr = _thr_stack_default;
 467                 env = getenv("LIBPTHREAD_SPINLOOPS");
 468                 if (env)
 469                         _thr_spinloops = atoi(env);
 470                 env = getenv("LIBPTHREAD_YIELDLOOPS");
 471                 if (env)
 472                         _thr_yieldloops = atoi(env);
 473                 TAILQ_INIT(&_thr_atfork_list);
 474         }
 475         init_once = 1;
 476 }