// locks.h - Thread synchronization primitives. ARM implementation. /* Copyright (C) 2007 Free Software Foundation This file is part of libgcj. This software is copyrighted work licensed under the terms of the Libgcj License. Please consult the file "LIBGCJ_LICENSE" for details. */ #ifndef __SYSDEP_LOCKS_H__ #define __SYSDEP_LOCKS_H__ typedef size_t obj_addr_t; /* Integer type big enough for object */ /* address. */ /* Atomic compare and exchange. These sequences are not actually atomic; there is a race if *ADDR != OLD_VAL and we are preempted between the two swaps. However, they are very close to atomic, and are the best that a pre-ARMv6 implementation can do without operating system support. LinuxThreads has been using these sequences for many years. */ inline static bool compare_and_swap(volatile obj_addr_t *addr, obj_addr_t old_val, obj_addr_t new_val) { volatile obj_addr_t result, tmp; __asm__ ("\n" "0: ldr %[tmp],[%[addr]]\n" " cmp %[tmp],%[old_val]\n" " movne %[result],#0\n" " bne 1f\n" " swp %[result],%[new_val],[%[addr]]\n" " cmp %[tmp],%[result]\n" " swpne %[tmp],%[result],[%[addr]]\n" " bne 0b\n" " mov %[result],#1\n" "1:" : [result] "=&r" (result), [tmp] "=&r" (tmp) : [addr] "r" (addr), [new_val] "r" (new_val), [old_val] "r" (old_val) : "cc", "memory"); return result; } inline static void release_set(volatile obj_addr_t *addr, obj_addr_t new_val) { __asm__ __volatile__("" : : : "memory"); *(addr) = new_val; } inline static bool compare_and_swap_release(volatile obj_addr_t *addr, obj_addr_t old, obj_addr_t new_val) { return compare_and_swap(addr, old, new_val); } // Ensure that subsequent instructions do not execute on stale // data that was loaded from memory before the barrier. inline static void read_barrier() { __asm__ __volatile__("" : : : "memory"); } // Ensure that prior stores to memory are completed with respect to other // processors. inline static void write_barrier() { __asm__ __volatile__("" : : : "memory"); } #endif