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jeremybenn |
// locks.h - Thread synchronization primitives. ARM implementation.
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/* Copyright (C) 2007 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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#if (__ARM_EABI__ && __linux)
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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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return __sync_bool_compare_and_swap(addr, old, new_val);
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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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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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__sync_synchronize();
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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 __sync_bool_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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__sync_synchronize();
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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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__sync_synchronize();
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}
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#else
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/* Atomic compare and exchange. These sequences are not actually
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atomic; there is a race if *ADDR != OLD_VAL and we are preempted
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between the two swaps. However, they are very close to atomic, and
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are the best that a pre-ARMv6 implementation can do without
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operating system support. LinuxThreads has been using these
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sequences for many years. */
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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_val,
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obj_addr_t new_val)
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{
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volatile obj_addr_t result, tmp;
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__asm__ ("\n"
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"0: ldr %[tmp],[%[addr]]\n"
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" cmp %[tmp],%[old_val]\n"
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" movne %[result],#0\n"
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" bne 1f\n"
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" swp %[result],%[new_val],[%[addr]]\n"
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" cmp %[tmp],%[result]\n"
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" swpne %[tmp],%[result],[%[addr]]\n"
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" bne 0b\n"
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" mov %[result],#1\n"
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"1:"
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: [result] "=&r" (result), [tmp] "=&r" (tmp)
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: [addr] "r" (addr), [new_val] "r" (new_val), [old_val] "r" (old_val)
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: "cc", "memory");
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return result;
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}
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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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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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inline static void
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read_barrier()
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{
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__asm__ __volatile__("" : : : "memory");
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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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__asm__ __volatile__("" : : : "memory");
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}
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#endif
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#endif
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