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src/core/ngx_rwlock.c - nginx source code

Functions defined

Macros defined

Source code


  2. /*
  3. * Copyright (C) Ruslan Ermilov
  4. * Copyright (C) Nginx, Inc.
  5. */


  8. #include <ngx_config.h>
  9. #include <ngx_core.h>


  12. #if (NGX_HAVE_ATOMIC_OPS)


  15. ‌#define NGX_RWLOCK_SPIN   2048
  16. ‌#define NGX_RWLOCK_WLOCK  ((ngx_atomic_uint_t) -1)


  19. void
  20. ‌ngx_rwlock_wlock(ngx_atomic_t *lock)
  21. {
  22.     ngx_uint_t  i, n;

  24.     for ( ;; ) {

  26.         if (*lock == 0 && ngx_atomic_cmp_set(lock, 0, NGX_RWLOCK_WLOCK)) {
  27.             return;
  28.         }

  30.         if (ngx_ncpu > 1) {

  32.             for (n = 1; n < NGX_RWLOCK_SPIN; n <<= 1) {

  34.                 for (i = 0; i < n; i++) {
  35.                     ngx_cpu_pause();
  36.                 }

  38.                 if (*lock == 0
  39.                     && ngx_atomic_cmp_set(lock, 0, NGX_RWLOCK_WLOCK))
  40.                 {
  41.                     return;
  42.                 }
  43.             }
  44.         }

  46.         ngx_sched_yield();
  47.     }
  48. }


  51. void
  52. ‌ngx_rwlock_rlock(ngx_atomic_t *lock)
  53. {
  54.     ngx_uint_t         i, n;
  55.     ngx_atomic_uint_t  readers;

  57.     for ( ;; ) {
  58.         readers = *lock;

  60.         if (readers != NGX_RWLOCK_WLOCK
  61.             && ngx_atomic_cmp_set(lock, readers, readers + 1))
  62.         {
  63.             return;
  64.         }

  66.         if (ngx_ncpu > 1) {

  68.             for (n = 1; n < NGX_RWLOCK_SPIN; n <<= 1) {

  70.                 for (i = 0; i < n; i++) {
  71.                     ngx_cpu_pause();
  72.                 }

  74.                 readers = *lock;

  76.                 if (readers != NGX_RWLOCK_WLOCK
  77.                     && ngx_atomic_cmp_set(lock, readers, readers + 1))
  78.                 {
  79.                     return;
  80.                 }
  81.             }
  82.         }

  84.         ngx_sched_yield();
  85.     }
  86. }


  89. void
  90. ‌ngx_rwlock_unlock(ngx_atomic_t *lock)
  91. {
  92.     if (*lock == NGX_RWLOCK_WLOCK) {
  93.         (void) ngx_atomic_cmp_set(lock, NGX_RWLOCK_WLOCK, 0);
  94.     } else {
  95.         (void) ngx_atomic_fetch_add(lock, -1);
  96.     }
  97. }


  100. void
  101. ‌ngx_rwlock_downgrade(ngx_atomic_t *lock)
  102. {
  103.     if (*lock == NGX_RWLOCK_WLOCK) {
  104.         *lock = 1;
  105.     }
  106. }


  109. #else

  111. #if (NGX_HTTP_UPSTREAM_ZONE || NGX_STREAM_UPSTREAM_ZONE)

  113. #error ngx_atomic_cmp_set() is not defined!

  115. #endif

  117. #endif

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