atomic, spinlock and mutex性能比较

我非常好奇于不同同步原理的性能，于是对atomic, spinlock和mutex做了如下实验来比较：

 1 #include <future>
 2 #include <iostream>
 3 
 4 volatile int value = 0;
 5 
 6 int loop (bool inc, int limit) {
 7   std::cout << "Started " << inc << " " << limit << std::endl;
 8   for (int i = 0; i < limit; ++i) {
 9     if (inc) { 
10       ++value;
11     } else {
12       --value;
13     }
14   }
15   return 0;
16 }
17 
18 int main () {
19   auto f = std::async (std::launch::async, std::bind(loop, true, 20000000));//开启一个线程来执行loop函数，c++11的高级特性
20   loop (false, 10000000);
21   f.wait ();
22   std::cout << value << std::endl;
23 }

View Code

通过clang编译器：

1 clang++ -std=c++11 -stdlib=libc++ -O3 -o test test.cpp && time ./test

运行：

1 SSttaarrtteedd  10  2100000000000000
2 
3 11177087
4 
5 real    0m0.070s
6 user    0m0.089s
7 sys 0m0.002s

从运行结果很显然的我们可以看出增减不是原子性操作的，变量value最后所包含的值是不确定的（垃圾）。

2. 汇编LOCK

 1 #include <future>
 2 #include <iostream>
 3 
 4 volatile int value = 0;
 5 
 6 int loop (bool inc, int limit) {
 7   std::cout << "Started " << inc << " " << limit << std::endl;
 8   for (int i = 0; i < limit; ++i) {
 9     if (inc) { 
10       asm("LOCK");
11       ++value;
12     } else {
13       asm("LOCK");
14       --value;
15     }
16   }
17   return 0;
18 }
19 
20 int main () {
21   auto f = std::async (std::launch::async, std::bind(loop, true, 20000000)); //开启一个线程来执行loop函数，c++11的高级特性
22   loop (false, 10000000);
23   f.wait ();
24   std::cout << value << std::endl;
25 } 

View Code