是否有检查前提条件的原子增量，原子值是否小于指定值？ [英] Is there atomic increment with the check preconditions, that the atomic value was less than the specified value?

问题描述

在增加值之前，在检查前提条件中，在新的标准C ++原子增量操作中，原子值是否小于指定值？

Is in the new standard C++ atomic increment operation with the check preconditions before the incremented the value, that the atomic value was less than the specified value?

比下面的代码更容易和更快吗？

Can I do it easier and faster than the following code?

int atomic_inc(std::atomic_int& val, int less_than) {
 int new_val;
 int old_val = val.load();
 do
 {
   if (old_val > less_than) return old_val;
   new_val = old_val + 1;
 } while (!val.compare_exchange_weak(old_val, new_val));

 return new_val;
}

如果有人不知道如何工作compare_exchange_weak：
compare_exchange_weak reads val，与old_val比较，如果它们不相等，则将val保存为old_val。如果相等，则将new_val保存到val。

If somebody don't know how works compare_exchange_weak: compare_exchange_weak reads val, compares with old_val, and if they are not equal then saves val to old_val. If it is equal then save new_val to val.

推荐答案

不，没有特别支持增加小于值的值。你的代码与你能得到的一样高效。 C ++ 11中没有等待的变体

No, there is no special support for incrementing values less than a value. Your code is as efficient as you can get. There is no wait-free variant in C++11

有无限数量的可能的增量如果X模式。硬件制造商决定，增量，如果不改变是他们需要支持的唯一的东西。

There is an unlimited number of possible "increment if X" patterns. The hardware manufacturers decided that "increment if not changed" is the only thing they need to support.

理论上，你可以发明一个硬件平台与一个特殊的汇编代码，但C ++ 11不直接定向。

In theory you could invent a hardware platform with a special assembly code for it, but C++11 does not directly target that.

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