1 /* locks.h - Thread synchronization primitives. X86/x86-64 implementation.
2
3 Copyright (C) 2002, 2011 Free Software Foundation
4
5 This file is part of libgcj.
6
7 This software is copyrighted work licensed under the terms of the
8 Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
9 details. */
10
11 #ifndef __SYSDEP_LOCKS_H__
12 #define __SYSDEP_LOCKS_H__
13
14 typedef size_t obj_addr_t; /* Integer type big enough for object */
15 /* address. */
16
17 // Atomically replace *addr by new_val if it was initially equal to old.
18 // Return true if the comparison succeeded.
19 // Assumed to have acquire semantics, i.e. later memory operations
20 // cannot execute before the compare_and_swap finishes.
21 inline static bool
compare_and_swap(volatile obj_addr_t * addr,obj_addr_t old,obj_addr_t new_val)22 compare_and_swap(volatile obj_addr_t *addr,
23 obj_addr_t old,
24 obj_addr_t new_val)
25 {
26 return __sync_bool_compare_and_swap (addr, old, new_val);
27 }
28
29 // Ensure that subsequent instructions do not execute on stale
30 // data that was loaded from memory before the barrier.
31 // On X86/x86-64, the hardware ensures that reads are properly ordered.
32 inline static void
read_barrier()33 read_barrier()
34 {
35 }
36
37 // Ensure that prior stores to memory are completed with respect to other
38 // processors.
39 inline static void
write_barrier()40 write_barrier()
41 {
42 /* x86-64/X86 does not reorder writes. We just need to ensure that
43 gcc also doesn't. */
44 __asm__ __volatile__(" " : : : "memory");
45 }
46
47 // Set *addr to new_val with release semantics, i.e. making sure
48 // that prior loads and stores complete before this
49 // assignment.
50 // On X86/x86-64, the hardware shouldn't reorder reads and writes,
51 // so we just have to convince gcc not to do it either.
52 inline static void
release_set(volatile obj_addr_t * addr,obj_addr_t new_val)53 release_set(volatile obj_addr_t *addr, obj_addr_t new_val)
54 {
55 write_barrier ();
56 *(addr) = new_val;
57 }
58
59 // Compare_and_swap with release semantics instead of acquire semantics.
60 // On many architecture, the operation makes both guarantees, so the
61 // implementation can be the same.
62 inline static bool
compare_and_swap_release(volatile obj_addr_t * addr,obj_addr_t old,obj_addr_t new_val)63 compare_and_swap_release(volatile obj_addr_t *addr,
64 obj_addr_t old,
65 obj_addr_t new_val)
66 {
67 return compare_and_swap(addr, old, new_val);
68 }
69 #endif
70