最近在学习lua的过程中发现lua居然有个东西叫协程(协同coroutine),虽然以前就听过这个概念，但没有结合实践的一些理解。

开始今天的文章前，首先需要学习下面几篇文章。

Segment Fault例子：

#include

void ping();

void pong();

void ping(){

int a = 0;

printf("ping,addr of a = %p\n",&a);

pong();

}

void pong(){

int b = 0;

printf("pong,addr of b = %p\n",&b);

ping();

}

int main(int argc, char *argv[]){

ping();

return 0;

}

将上述代码编译运行，执行结果：

ping,addr of a = 0x7ffc456b2024

pong,addr of b = 0x7ffc456b2004

ping,addr of a = 0x7ffc456b1fe4

pong,addr of b = 0x7ffc456b1fc4

ping,addr of a = 0x7ffc456b1fa4

pong,addr of b = 0x7ffc456b1f84

ping,addr of a = 0x7ffc456b1f64

pong,addr of b = 0x7ffc456b1f44

ping,addr of a = 0x7ffc456b1f24

pong,addr of b = 0x7ffc456b1f04

ping,addr of a = 0x7ffc456b1ee4

pong,addr of b = 0x7ffc456b1ec4

ping,addr of a = 0x7ffc456b1ea4

pong,addr of b = 0x7ffc456b1e84

ping,addr of a = 0x7ffc456b1e64

pong,addr of b = 0x7ffc456b1e44

ping,addr of a = 0x7ffc456b1e24

pong,addr of b = 0x7ffc456b1e04

ping,addr of a = 0x7ffc456b1de4

pong,addr of b = 0x7ffc456b1dc4

ping,addr of a = 0x7ffc456b1da4

pong,addr of b = 0x7ffc456b1d84

ping,addr of a = 0x7ffc456b1d64

pong,addr of b = 0x7ffc456b1d44

ping,addr of a = 0x7ffc456b1d24

pong,addr of b = 0x7ffc456b1d04

ping,addr of a = 0x7ffc456b1ce4

pong,addr of b = 0x7ffc456b1cc4

ping,addr of a = 0x7ffc456b1ca4

pong,addr of b = 0x7ffc456b1c84

ping,addr of a = 0x7ffc456b1c64

pong,addr of b = 0x7ffc456b1c44

ping,addr of a = 0x7ffc456b1c24

pong,addr of b = 0x7ffc456b1c04

ping,addr of a = 0x7ffc456b1be4

pong,addr of b = 0x7ffc456b1bc4

ping,addr of a = 0x7ffc456b1ba4

pong,addr of b = 0x7ffc456b1b84

Segmentation fault (core dumped)

运行10几秒左右后，程序core dumped,无限递归调用，栈耗尽。可以看到a与b的地址每次调用都不相同。

#include

#include

#define MAX_COUNT (1<<30)

static ucontext_t uc[3];

static int count = 0;

void ping();

void pong();

void ping(){

int a = 10;

while(count < MAX_COUNT){

printf("ping %d,addr of a = %p\n", ++count,&a);

// yield to pong

swapcontext(&uc[1], &uc[2]); // 保存当前context于uc[1],切换至uc[2]的context运行

}

}

void pong(){

int b = 10;

while(count < MAX_COUNT){

printf("pong %d,addr of b = %p\n", ++count,&b);

// yield to ping

swapcontext(&uc[2], &uc[1]);// 保存当前context于uc[2],切换至uc[1]的context运行

}

}

char st1[8192];

char st2[8192];

int main(int argc, char *argv[]){

// initialize context

getcontext(&uc[1]);

getcontext(&uc[2]);

uc[1].uc_link = &uc[0]; //表示uc[1]运行完成后，会跳至uc[0]指向的context继续运行

uc[1].uc_stack.ss_sp = st1; // 设置新的堆栈

uc[1].uc_stack.ss_size = sizeof st1;

makecontext (&uc[1], ping, 0);

uc[2].uc_link = &uc[0]; //表示uc[2]运行完成后，会跳至uc[0]指向的context继续运行

uc[2].uc_stack.ss_sp = st2; // 设置新的堆栈

uc[2].uc_stack.ss_size = sizeof st2;

makecontext (&uc[2], pong, 0);

// start ping-pong

swapcontext(&uc[0], &uc[1]); // 将当前context信息保存至uc[0],跳转至uc[1]保存的context去执行

//swapcontext函数会将当前点的信息保存在uc[0]中，当然我们没有设置的话，默认的堆栈一定是主堆栈啦

return 0;

}

编译运行结果：

ping 332825,addr of a = 0x561022043b14

pong 332826,addr of b = 0x561022041b14

ping 332827,addr of a = 0x561022043b14

pong 332828,addr of b = 0x561022041b14

ping 332829,addr of a = 0x561022043b14

pong 332830,addr of b = 0x561022041b14

ping 332831,addr of a = 0x561022043b14

pong 332832,addr of b = 0x561022041b14

ping 332833,addr of a = 0x561022043b14

pong 332834,addr of b = 0x561022041b14

ping 332835,addr of a = 0x561022043b14

pong 332836,addr of b = 0x561022041b14

ping 332837,addr of a = 0x561022043b14

pong 332838,addr of b = 0x561022041b14

ping 332839,addr of a = 0x561022043b14

pong 332840,addr of b = 0x561022041b14

ping 332841,addr of a = 0x561022043b14

pong 332842,addr of b = 0x561022041b14

ping 332843,addr of a = 0x561022043b14

pong 332844,addr of b = 0x561022041b14

ping 332845,addr of a = 0x561022043b14

pong 332846,addr of b = 0x561022041b14

ping 332847,addr of a = 0x561022043b14

pong 332848,addr of b = 0x561022041b14

ping 332849,addr of a = 0x561022043b14

可以看到a b的地址每次都相同，而不是每次函数调用，使用新的栈地址空间。

#include

#include

#include

int main(int argc, char *argv[])

{

ucontext_t context;

getcontext(&context);

puts("Hello world");

sleep(1);

setcontext(&context);

return 0;

}

getcontext, setcontext - get or set the user context(man setcontext)

这个函数会不断地打印Hello,world。因为上面的getcontext函数将那个点的上下文信息保存到了context中，下面调用setcontext会返回到记录的点处继续执行，因此也就出现了不断地输出。

有了上面的一些理解，我们可以学习一些开源库。(按照代码量从低到高学习)