granicus.if.org Git - postgresql/blob - src/include/storage/s_lock.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * s_lock.h
   4  *         This file contains the in-line portion of the implementation
   5  *         of spinlocks.
   6  *
   7  * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  *
  11  * IDENTIFICATION
  12  *        $Header: /cvsroot/pgsql/src/include/storage/s_lock.h,v 1.79 2001/01/19 02:58:59 momjian Exp $
  13  *
  14  *-------------------------------------------------------------------------
  15  */
  16
  17 /*----------
  18  * DESCRIPTION
  19  *      The public macros that must be provided are:
  20  *
  21  *      void S_INIT_LOCK(slock_t *lock)
  22  *              Initialize a spinlock (to the unlocked state).
  23  *
  24  *      void S_LOCK(slock_t *lock)
  25  *              Acquire a spinlock, waiting if necessary.
  26  *              Time out and abort() if unable to acquire the lock in a
  27  *              "reasonable" amount of time --- typically ~ 1 minute.
  28  *
  29  *      void S_UNLOCK(slock_t *lock)
  30  *              Unlock a previously acquired lock.
  31  *
  32  *      bool S_LOCK_FREE(slock_t *lock)
  33  *              Tests if the lock is free. Returns TRUE if free, FALSE if locked.
  34  *              This does *not* change the state of the lock.
  35  *
  36  *      int TAS(slock_t *lock)
  37  *              Atomic test-and-set instruction.  Attempt to acquire the lock,
  38  *              but do *not* wait.      Returns 0 if successful, nonzero if unable
  39  *              to acquire the lock.
  40  *
  41  *      TAS() is a lower-level part of the API, but is used directly in a
  42  *      few places that want to do other things while waiting for a lock.
  43  *      The S_LOCK() macro is equivalent to
  44  *
  45  *      void
  46  *      S_LOCK(slock_t *lock)
  47  *      {
  48  *              unsigned        spins = 0;
  49  *
  50  *              while (TAS(lock))
  51  *                      S_LOCK_SLEEP(lock, spins++);
  52  *      }
  53  *
  54  *      where S_LOCK_SLEEP() checks for timeout and sleeps for a short
  55  *      interval.  Callers that want to perform useful work while waiting
  56  *      can write out this entire loop and insert the "useful work" inside
  57  *      the loop.
  58  *
  59  *      CAUTION to TAS() callers: on some platforms TAS() may sometimes
  60  *      report failure to acquire a lock even when the lock is not locked.
  61  *      For example, on Alpha TAS() will "fail" if interrupted.  Therefore
  62  *      TAS() must *always* be invoked in a retry loop as depicted, even when
  63  *      you are certain the lock is free.
  64  *
  65  *      On most supported platforms, TAS() uses a tas() function written
  66  *      in assembly language to execute a hardware atomic-test-and-set
  67  *      instruction.  Equivalent OS-supplied mutex routines could be used too.
  68  *
  69  *      If no system-specific TAS() is available (ie, HAS_TEST_AND_SET is not
  70  *      defined), then we fall back on an emulation that uses SysV semaphores.
  71  *      This emulation will be MUCH MUCH MUCH slower than a proper TAS()
  72  *      implementation, because of the cost of a kernel call per lock or unlock.
  73  *      An old report is that Postgres spends around 40% of its time in semop(2)
  74  *      when using the SysV semaphore code.
  75  *
  76  *      Note to implementors: there are default implementations for all these
  77  *      macros at the bottom of the file.  Check if your platform can use
  78  *      these or needs to override them.
  79  *----------
  80  */
  81 #ifndef S_LOCK_H
  82 #define S_LOCK_H
  83
  84 #include "storage/ipc.h"
  85
  86 /* Platform-independent out-of-line support routines */
  87 extern void s_lock(volatile slock_t *lock,
  88            const char *file, const int line);
  89 extern void s_lock_sleep(unsigned spins, int microsec,
  90                          volatile slock_t *lock,
  91                          const char *file, const int line);
  92
  93
  94 #if defined(HAS_TEST_AND_SET)
  95
  96
  97 #if defined(__GNUC__)
  98 /*************************************************************************
  99  * All the gcc inlines
 100  */
 101
 102 /*
 103  * Standard __asm__ format:
 104  *
 105  *      __asm__(
 106  *                      "command;"
 107  *                      "command;"
 108  *                      "command;"
 109  *              :       "=r"(_res)                      return value, in register
 110  *              :       "r"(lock)                       argument, 'lock pointer', in register
 111  *              :       "r0");                          inline code uses this register
 112  */
 113
 114
 115 #if defined(__i386__)
 116 #define TAS(lock) tas(lock)
 117
 118 static __inline__ int
 119 tas(volatile slock_t *lock)
 120 {
 121         register slock_t _res = 1;
 122
 123         __asm__(
 124                         "lock;"
 125                         "xchgb %0,%1;"
 126 :                       "=q"(_res), "=m"(*lock)
 127 :                       "0"(_res));
 128         return (int) _res;
 129 }
 130
 131 #endif   /* __i386__ */
 132
 133
 134 #ifdef __ia64__
 135 #define TAS(lock) tas(lock)
 136
 137 static __inline__ int
 138 tas(volatile slock_t *lock)
 139 {
 140         long int        ret;
 141
 142         __asm__         __volatile__(
 143                                                                                  "xchg4 %0=%1,%2;"
 144                                                          :                       "=r"(ret), "=m"(*lock)
 145                                                          :                       "r"(1), "1"(*lock)
 146                                                          :                       "memory");
 147
 148         return (int) ret;
 149 }
 150
 151 #endif   /* __ia64__ */
 152
 153
 154 #if defined(__arm__) || defined(__arm__)
 155 #define TAS(lock) tas(lock)
 156
 157 static __inline__ int
 158 tas(volatile slock_t *lock)
 159 {
 160         register slock_t _res = 1;
 161
 162         __asm__(
 163                         "swpb %0, %0, [%3];"
 164 :                       "=r"(_res), "=m"(*lock)
 165 :                       "0"(_res), "r"(lock));
 166         return (int) _res;
 167 }
 168
 169 #endif   /* __arm__ */
 170
 171 #if defined(__s390__)
 172 /*
 173  * S/390 Linux
 174  */
 175 #define TAS(lock)          tas(lock)
 176
 177 static inline int
 178 tas(volatile slock_t *lock)
 179 {
 180         int                     _res;
 181
 182         __asm__         __volatile(
 183                                                                            "la 1,1;"
 184                                                                            "l 2,%2;"
 185                                                                            "slr 0,0;"
 186                                                                            "cs 0,1,0(2);"
 187                                                                            "lr %1,0;"
 188                                                    :               "=m"(lock), "=d"(_res)
 189                                                    :               "m"(lock)
 190                                                    :               "0", "1", "2");
 191
 192         return (_res);
 193 }
 194
 195 #endif   /* __s390__ */
 196
 197
 198 #if defined(__sparc__)
 199 #define TAS(lock) tas(lock)
 200
 201 static __inline__ int
 202 tas(volatile slock_t *lock)
 203 {
 204         register slock_t _res = 1;
 205
 206         __asm__(
 207                         "ldstub [%2], %0;"
 208 :                       "=r"(_res), "=m"(*lock)
 209 :                       "r"(lock));
 210         return (int) _res;
 211 }
 212
 213 #endif   /* __sparc__ */
 214
 215
 216 #if defined(__mc68000__) && defined(__linux__)
 217 #define TAS(lock) tas(lock)
 218
 219 static __inline__ int
 220 tas(volatile slock_t *lock)
 221 {
 222         register int rv;
 223
 224         __asm__         __volatile__(
 225                                                                                  "tas %1;"
 226                                                                                  "sne %0;"
 227                                                          :                       "=d"(rv), "=m"(*lock)
 228                                                          :                       "1"(*lock)
 229                                                          :                       "cc");
 230
 231         return rv;
 232 }
 233
 234 #endif   /* defined(__mc68000__) && defined(__linux__) */
 235
 236
 237 #if defined(NEED_VAX_TAS_ASM)
 238 /*
 239  * VAXen -- even multiprocessor ones
 240  * (thanks to Tom Ivar Helbekkmo)
 241  */
 242 #define TAS(lock) tas(lock)
 243
 244 typedef unsigned char slock_t;
 245
 246 static __inline__ int
 247 tas(volatile slock_t *lock)
 248 {
 249         register        _res;
 250
 251         __asm__(
 252                         "movl $1, r0;"
 253                         "bbssi $0, (%1), 1f;"
 254                         "clrl r0;"
 255                         "1: movl r0, %0;"
 256 :                       "=r"(_res)
 257 :                       "r"(lock)
 258 :                       "r0");
 259         return (int) _res;
 260 }
 261
 262 #endif   /* NEED_VAX_TAS_ASM */
 263
 264
 265 #if defined(NEED_NS32K_TAS_ASM)
 266 #define TAS(lock) tas(lock)
 267
 268 static __inline__ int
 269 tas(volatile slock_t *lock)
 270 {
 271         register        _res;
 272
 273         __asm__(
 274                         "sbitb 0, %0;"
 275                         "sfsd %1;"
 276 :                       "=m"(*lock), "=r"(_res));
 277         return (int) _res;
 278 }
 279
 280 #endif   /* NEED_NS32K_TAS_ASM */
 281
 282
 283
 284 #else                                                   /* !__GNUC__ */
 285
 286 /***************************************************************************
 287  * All non-gcc inlines
 288  */
 289
 290 #if defined(NEED_I386_TAS_ASM) && defined(USE_UNIVEL_CC)
 291 #define TAS(lock)       tas(lock)
 292
 293 asm int
 294 tas(volatile slock_t *s_lock)
 295 {
 296 /* UNIVEL wants %mem in column 1, so we don't pg_indent this file */
 297         %mem s_lock
 298         pushl %ebx
 299         movl s_lock, %ebx
 300         movl $255, %eax
 301         lock
 302         xchgb %al, (%ebx)
 303         popl %ebx
 304 }
 305
 306 #endif   /* defined(NEED_I386_TAS_ASM) && defined(USE_UNIVEL_CC) */
 307
 308 #endif   /* defined(__GNUC__) */
 309
 310
 311
 312 /*************************************************************************
 313  * These are the platforms that do not use inline assembler (and hence
 314  * have common code for gcc and non-gcc compilers, if both are available).
 315  */
 316
 317
 318 #if defined(__alpha)
 319
 320 /*
 321  * Correct multi-processor locking methods are explained in section 5.5.3
 322  * of the Alpha AXP Architecture Handbook, which at this writing can be
 323  * found at ftp://ftp.netbsd.org/pub/NetBSD/misc/dec-docs/index.html.
 324  * For gcc we implement the handbook's code directly with inline assembler.
 325  */
 326 #if defined(__GNUC__)
 327
 328 #define TAS(lock)  tas(lock)
 329 #define S_UNLOCK(lock)  do { __asm__ volatile ("mb"); *(lock) = 0; } while (0)
 330
 331 static __inline__ int
 332 tas(volatile slock_t *lock)
 333 {
 334         register slock_t _res;
 335
 336         __asm__         volatile(
 337                                                                          "ldq   $0, %0;"
 338                                                                          "bne   $0, 2f;"
 339                                                                          "ldq_l %1, %0;"
 340                                                                          "bne   %1, 2f;"
 341                                                                          "mov   1, $0;"
 342                                                                          "stq_c $0, %0;"
 343                                                                          "beq   $0, 2f;"
 344                                                                          "mb;"
 345                                                                          "br 3f;"
 346                                                                          "2: mov   1, %1;"
 347                                                                          "3:"
 348                                                  :                       "=m"(*lock), "=r"(_res)
 349                                                  :
 350                                                  :                       "0");
 351
 352         return (int) _res;
 353 }
 354
 355 #else                                                   /* !defined(__GNUC__) */
 356
 357 /*
 358  * The Tru64 compiler doesn't support gcc-style inline asm, but it does
 359  * have some builtin functions that accomplish much the same results.
 360  * For simplicity, slock_t is defined as long (ie, quadword) on Alpha
 361  * regardless of the compiler in use.  LOCK_LONG and UNLOCK_LONG only
 362  * operate on an int (ie, longword), but that's OK as long as we define
 363  * S_INIT_LOCK to zero out the whole quadword.
 364  */
 365
 366 #include <alpha/builtins.h>
 367
 368 #define S_INIT_LOCK(lock)  (*(lock) = 0)
 369 #define TAS(lock)                  (__LOCK_LONG_RETRY((lock), 1) == 0)
 370 #define S_UNLOCK(lock)     __UNLOCK_LONG(lock)
 371
 372 #endif   /* defined(__GNUC__) */
 373
 374 #endif   /* __alpha */
 375
 376
 377 #if defined(__hpux)
 378 /*
 379  * HP-UX (PA-RISC)
 380  *
 381  * Note that slock_t on PA-RISC is a structure instead of char
 382  * (see include/port/hpux.h).
 383  *
 384  * a "set" slock_t has a single word cleared.  a "clear" slock_t has
 385  * all words set to non-zero. tas() is in tas.s
 386  */
 387
 388 #define S_UNLOCK(lock) \
 389 do { \
 390         volatile slock_t *lock_ = (volatile slock_t *) (lock); \
 391         lock_->sema[0] = lock_->sema[1] = lock_->sema[2] = lock_->sema[3] = -1; \
 392 } while (0)
 393
 394 #define S_LOCK_FREE(lock)       ( *(int *) (((long) (lock) + 15) & ~15) != 0)
 395
 396 #endif   /* __hpux */
 397
 398
 399 #if defined(__QNX__)
 400 /*
 401  * QNX 4
 402  *
 403  * Note that slock_t under QNX is sem_t instead of char
 404  */
 405 #define TAS(lock)               (sem_trywait((lock)) < 0)
 406 #define S_UNLOCK(lock)  sem_post((lock))
 407 #define S_INIT_LOCK(lock)               sem_init((lock), 1, 1)
 408 #define S_LOCK_FREE(lock)               ((lock)->value)
 409 #endif   /* __QNX__ */
 410
 411
 412 #if defined(__sgi)
 413 /*
 414  * SGI IRIX 5
 415  * slock_t is defined as a unsigned long. We use the standard SGI
 416  * mutex API.
 417  *
 418  * The following comment is left for historical reasons, but is probably
 419  * not a good idea since the mutex ABI is supported.
 420  *
 421  * This stuff may be supplemented in the future with Masato Kataoka's MIPS-II
 422  * assembly from his NECEWS SVR4 port, but we probably ought to retain this
 423  * for the R3000 chips out there.
 424  */
 425 #include "mutex.h"
 426 #define TAS(lock)       (test_and_set(lock,1))
 427 #define S_UNLOCK(lock)  (test_then_and(lock,0))
 428 #define S_INIT_LOCK(lock)       (test_then_and(lock,0))
 429 #define S_LOCK_FREE(lock)       (test_then_add(lock,0) == 0)
 430 #endif   /* __sgi */
 431
 432 #if defined(sinix)
 433 /*
 434  * SINIX / Reliant UNIX
 435  * slock_t is defined as a struct abilock_t, which has a single unsigned long
 436  * member. (Basically same as SGI)
 437  *
 438  */
 439 #define TAS(lock)       (!acquire_lock(lock))
 440 #define S_UNLOCK(lock)  release_lock(lock)
 441 #define S_INIT_LOCK(lock)       init_lock(lock)
 442 #define S_LOCK_FREE(lock)       (stat_lock(lock) == UNLOCKED)
 443 #endif   /* sinix */
 444
 445
 446 #if defined(_AIX)
 447 /*
 448  * AIX (POWER)
 449  *
 450  * Note that slock_t on POWER/POWER2/PowerPC is int instead of char
 451  * (see storage/ipc.h).
 452  */
 453 #define TAS(lock)       cs((int *) (lock), 0, 1)
 454 #endif   /* _AIX */
 455
 456
 457 #if defined (nextstep)
 458 /*
 459  * NEXTSTEP (mach)
 460  * slock_t is defined as a struct mutex.
 461  */
 462
 463 #define S_LOCK(lock)    mutex_lock(lock)
 464 #define S_UNLOCK(lock)  mutex_unlock(lock)
 465 #define S_INIT_LOCK(lock)       mutex_init(lock)
 466 /* For Mach, we have to delve inside the entrails of `struct mutex'.  Ick! */
 467 #define S_LOCK_FREE(alock)      ((alock)->lock == 0)
 468 #endif   /* nextstep */
 469
 470
 471
 472 #else                                                   /* !HAS_TEST_AND_SET */
 473
 474 /*
 475  * Fake spinlock implementation using SysV semaphores --- slow and prone
 476  * to fall foul of kernel limits on number of semaphores, so don't use this
 477  * unless you must!
 478  */
 479
 480 typedef struct
 481 {
 482         /* reference to semaphore used to implement this spinlock */
 483         IpcSemaphoreId semId;
 484         int                     sem;
 485 } slock_t;
 486
 487 extern bool s_lock_free_sema(volatile slock_t *lock);
 488 extern void s_unlock_sema(volatile slock_t *lock);
 489 extern void s_init_lock_sema(volatile slock_t *lock);
 490 extern int      tas_sema(volatile slock_t *lock);
 491
 492 #define S_LOCK_FREE(lock)       s_lock_free_sema(lock)
 493 #define S_UNLOCK(lock)   s_unlock_sema(lock)
 494 #define S_INIT_LOCK(lock)       s_init_lock_sema(lock)
 495 #define TAS(lock)       tas_sema(lock)
 496
 497 #endif   /* HAS_TEST_AND_SET */
 498
 499
 500
 501 /****************************************************************************
 502  * Default Definitions - override these above as needed.
 503  */
 504
 505 #if !defined(S_LOCK)
 506 #define S_LOCK(lock) \
 507         do { \
 508                 if (TAS(lock)) \
 509                         s_lock((lock), __FILE__, __LINE__); \
 510         } while (0)
 511 #endif   /* S_LOCK */
 512
 513 #if !defined(S_LOCK_SLEEP)
 514 #define S_LOCK_SLEEP(lock,spins) \
 515         s_lock_sleep((spins), 0, (lock), __FILE__, __LINE__)
 516 #endif   /* S_LOCK_SLEEP */
 517
 518 #if !defined(S_LOCK_SLEEP_INTERVAL)
 519 #define S_LOCK_SLEEP_INTERVAL(lock,spins,microsec) \
 520         s_lock_sleep((spins), (microsec), (lock), __FILE__, __LINE__)
 521 #endif   /* S_LOCK_SLEEP_INTERVAL */
 522
 523 #if !defined(S_LOCK_FREE)
 524 #define S_LOCK_FREE(lock)       (*(lock) == 0)
 525 #endif   /* S_LOCK_FREE */
 526
 527 #if !defined(S_UNLOCK)
 528 #define S_UNLOCK(lock)          (*(lock) = 0)
 529 #endif   /* S_UNLOCK */
 530
 531 #if !defined(S_INIT_LOCK)
 532 #define S_INIT_LOCK(lock)       S_UNLOCK(lock)
 533 #endif   /* S_INIT_LOCK */
 534
 535 #if !defined(TAS)
 536 extern int      tas(volatile slock_t *lock);            /* in port/.../tas.s, or
 537                                                                                                  * s_lock.c */
 538
 539 #define TAS(lock)               tas(lock)
 540 #endif   /* TAS */
 541
 542
 543 #endif   /* S_LOCK_H */