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jlechner |
// locks.h - Thread synchronization primitives. X86 implementation.
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/* Copyright (C) 2002 Free Software Foundation
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This file is part of libgcj.
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This software is copyrighted work licensed under the terms of the
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Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
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details. */
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#ifndef __SYSDEP_LOCKS_H__
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#define __SYSDEP_LOCKS_H__
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typedef size_t obj_addr_t; /* Integer type big enough for object */
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/* address. */
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// Atomically replace *addr by new_val if it was initially equal to old.
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// Return true if the comparison succeeded.
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// Assumed to have acquire semantics, i.e. later memory operations
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// cannot execute before the compare_and_swap finishes.
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inline static bool
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compare_and_swap(volatile obj_addr_t *addr,
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obj_addr_t old,
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obj_addr_t new_val)
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{
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char result;
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__asm__ __volatile__("lock; cmpxchgl %2, %0; setz %1"
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: "=m"(*addr), "=q"(result)
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: "r" (new_val), "a"(old), "m"(*addr)
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: "memory");
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return (bool) result;
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}
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// Set *addr to new_val with release semantics, i.e. making sure
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// that prior loads and stores complete before this
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// assignment.
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// On X86, the hardware shouldn't reorder reads and writes,
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// so we just have to convince gcc not to do it either.
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inline static void
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release_set(volatile obj_addr_t *addr, obj_addr_t new_val)
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{
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__asm__ __volatile__(" " : : : "memory");
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*(addr) = new_val;
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}
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// Compare_and_swap with release semantics instead of acquire semantics.
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// On many architecture, the operation makes both guarantees, so the
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// implementation can be the same.
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inline static bool
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compare_and_swap_release(volatile obj_addr_t *addr,
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obj_addr_t old,
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obj_addr_t new_val)
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{
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return compare_and_swap(addr, old, new_val);
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}
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// Ensure that subsequent instructions do not execute on stale
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// data that was loaded from memory before the barrier.
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// On X86, the hardware ensures that reads are properly ordered.
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inline static void
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read_barrier()
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{
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}
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// Ensure that prior stores to memory are completed with respect to other
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// processors.
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inline static void
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write_barrier()
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{
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// X86 does not reorder writes. We just need to ensure that gcc also doesn't.
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__asm__ __volatile__(" " : : : "memory");
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}
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#endif
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