libgo/runtime/lfstack.c

   1 // Copyright 2012 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Lock-free stack.
   6
   7 #include "runtime.h"
   8 #include "arch.h"
   9
  10 #if __SIZEOF_POINTER__ == 8
  11 // Amd64 uses 48-bit virtual addresses, 47-th bit is used as kernel/user flag.
  12 // So we use 17msb of pointers as ABA counter.
  13 # define PTR_BITS 47
  14 #else
  15 # define PTR_BITS 32
  16 #endif
  17 #define PTR_MASK ((1ull<<PTR_BITS)-1)
  18 #define CNT_MASK (0ull-1)
  19
  20 #if __SIZEOF_POINTER__ == 8 && (defined(__sparc__) || (defined(__sun__) && defined(__amd64__)))
  21 // SPARC64 and Solaris on AMD64 uses all 64 bits of virtual addresses.
  22 // Use low-order three bits as ABA counter.
  23 // http://docs.oracle.com/cd/E19120-01/open.solaris/816-5138/6mba6ua5p/index.html
  24 #undef PTR_BITS
  25 #undef CNT_MASK
  26 #undef PTR_MASK
  27 #define PTR_BITS 0
  28 #define CNT_MASK 7
  29 #define PTR_MASK ((0ull-1)<<3)
  30 #endif
  31
  32 void
  33 runtime_lfstackpush(uint64 *head, LFNode *node)
  34 {
  35         uint64 old, new;
  36
  37         if((uintptr)node != ((uintptr)node&PTR_MASK)) {
  38                 runtime_printf("p=%p\n", node);
  39                 runtime_throw("runtime_lfstackpush: invalid pointer");
  40         }
  41
  42         node->pushcnt++;
  43         new = (uint64)(uintptr)node|(((uint64)node->pushcnt&CNT_MASK)<<PTR_BITS);
  44         for(;;) {
  45                 old = runtime_atomicload64(head);
  46                 node->next = (LFNode*)(uintptr)(old&PTR_MASK);
  47                 if(runtime_cas64(head, old, new))
  48                         break;
  49         }
  50 }
  51
  52 LFNode*
  53 runtime_lfstackpop(uint64 *head)
  54 {
  55         LFNode *node, *node2;
  56         uint64 old, new;
  57
  58         for(;;) {
  59                 old = runtime_atomicload64(head);
  60                 if(old == 0)
  61                         return nil;
  62                 node = (LFNode*)(uintptr)(old&PTR_MASK);
  63                 node2 = runtime_atomicloadp(&node->next);
  64                 new = 0;
  65                 if(node2 != nil)
  66                         new = (uint64)(uintptr)node2|(((uint64)node2->pushcnt&CNT_MASK)<<PTR_BITS);
  67                 if(runtime_cas64(head, old, new))
  68                         return node;
  69         }
  70 }
  71
  72 LFNode* runtime_lfstackpop2(uint64*)
  73   __asm__ (GOSYM_PREFIX "runtime.lfstackpop2");
  74
  75 LFNode*
  76 runtime_lfstackpop2(uint64 *head)
  77 {
  78         return runtime_lfstackpop(head);
  79 }