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  1. JDK
  2. JDK-8233912

aarch64: minor improvements of atomic operations

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    • Subcomponent:
    • Resolved In Build:
      b24
    • CPU:
      aarch64
    • OS:
      generic

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        Description

        Discussion Thread: https://mail.openjdk.java.net/pipermail/aarch64-port-dev/2019-November/008164.html

        The current implementation of aarch64 atomic operations depends on the version of the GCC compiler used. The code sequence may not be expected with a certain version of GCC compiler. As a result, full memory barrier are not ensured for memory_order_conservative.

        Patch:
        diff -r dc45ed0ab083 src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.hpp
        --- a/src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.hpp Wed Nov 13 15:16:45 2019 -0800
        +++ b/src/hotspot/os_cpu/linux_aarch64/atomic_linux_aarch64.hpp Thu Nov 14 09:26:49 2019 +0800
        @@ -29,6 +29,8 @@
         #include "vm_version_aarch64.hpp"

         // Implementation of class atomic
        +// Note that memory_order_conservative requires a full barrier after atomic stores.
        +// See https://patchwork.kernel.org/patch/3575821/

         #define FULL_MEM_BARRIER __sync_synchronize()
         #define READ_MEM_BARRIER __atomic_thread_fence(__ATOMIC_ACQUIRE);
        @@ -52,7 +54,7 @@
                                                              T volatile* dest,
                                                              atomic_memory_order order) const {
           STATIC_ASSERT(byte_size == sizeof(T));
        - T res = __sync_lock_test_and_set(dest, exchange_value);
        + T res = __atomic_exchange_n(dest, exchange_value, __ATOMIC_RELEASE);
           FULL_MEM_BARRIER;
           return res;
         }
        @@ -70,7 +72,12 @@
                                       __ATOMIC_RELAXED, __ATOMIC_RELAXED);
             return value;
           } else {
        - return __sync_val_compare_and_swap(dest, compare_value, exchange_value);
        + T value = compare_value;
        + FULL_MEM_BARRIER;
        + __atomic_compare_exchange(dest, &value, &exchange_value, /*weak*/false,
        + __ATOMIC_RELAXED, __ATOMIC_RELAXED);
        + FULL_MEM_BARRIER;
        + return value;
           }
         }

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                Assignee:
                fyang Fei Yang
                Reporter:
                fyang Fei Yang
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                  Updated:
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