一种在C语言中用汇编指令和System V ucontext 支撑实现的协程切换

此文在看了 python 中基于 yield 和 yield from （同步基于 yield 的子生成器/协程）机制的生成器/协程后，就想在C语言中实现类似机制。

在阅读 System V ucontext 手册后，便选择基于他来支撑协程切换；此篇文字发布后，Windoze 和 AbbyCin 为 用汇编支持协程切换 提供了信息和时间上的信心，遂用汇编指令实现了对协程切换的最小支持。

由于很喜欢 ramonza/libcoro 中对 sp 指针的运用，所以此文在汇编程序中延用了该指针相关方式，并使用纯汇编语句为协程传递参数——从而避免了全局变量的使用；同时为汇编支撑的协程添加了协程结束函数。

所实现协程机制包括：

1. yield
2. yield from
3. 基于 yield 和 yield from 机制协程的调度器 loop

这些机制皆在 ln_cs.c 中实现；支撑协程上下文和切换的代码在context目录下——经此文测试，汇编指令和ucontext在支撑协程切换时无明显的时间性能差距。experiences目录下为体验以上功能机制的例子（运行体验可参见 doc 目录下的文档）。

以下是源码目录树图（已略去工程管理文件）。

. ├── doc │   ├── A coroutine ... in C-language.md │   └── An optimization ... in C-language.md ├── experiences │   ├── loop_e │   │   ├── loop_e.c │   ├── yield_e │   │   └── yield_e.c │   └── yield_from_e │   └── yield_from_e.c ├── include │   ├── ln_co.h │   └── ln_comm.h ├── readme.md └── src ├── ln_co.c ├── context ├── ln_context.h    ├── assembly    │   ├── ln_asm.c    └── ucontext    ├── ln_uc.c 

核心逻辑代码 ln_cs.c 经过此文的一些技巧性修剪后仍不到 500 行，所以还是很想继续分享的——便补写了文档与源码一起上传到了 github 和 gitee之上。

• github地址：https://github.com/misskissC/ccoroutine
• gitee 地址：https://gitee.com/misskissC/ccoroutine

另外，此文本着更好管理工程的理念——写了一大推工程管理文件。

对CPU执行程序原理有所理解的同学应该都能胜任对该程序的阅读理解，有兴趣或与此文具相同程序理念（从源码或文档中可以看出一些吧）的同学一起出出新招继续提升下该程序吧。如

[1] 提升汇编代码以支撑协程的 return 语句

/** * ln_asm.c, * coroutine context, switching implement * by assembly instructions. * * lxr, 2020.02 */ #include "ln_context.h" #include "ln_comm.h" #include <stdlib.h> void _co_arg_medium(void); /** * because of the instructions on * stack-frame would be automatically * added by C-compiler in C-functions, * those routines can't be * inline-assembly in C-function. * * @caution: the routines on __i386 * not tested by me. */ __asm__ ( "\t.globl _co_arg_medium\n" "_co_arg_medium:\n" #if __i386 "popl %eax\n\t" // get co_fn "popl %ecx\n\t" // get arg "popl %edx\n\t" // get ci /* call convention on arguments of gcc on __i386 e.g. void fn(int a, int b); fn(1, 2); passing argument by stack in caller: push 2 --> b push 1 --> a */ "movl $0, %esi\n\t" "pushl %esi\n\t" "pushl %ecx\n\t" "pushl %esi\n\t" "pushl %edx\n\t" #elif __amd64 "popq %rax\n\t" // get co_fn "popq %rsi\n\t" // get arg "popq %rdi\n\t" // get ci /* call convention on arguments of gcc on __amd64 e.g. void fn(uint32_t a, uint32_t b, uint32_t c, uint32_t e, uint32_t f, uint32_t g, uint32_t h); passing arguments by registers and stack in caller: edi --> a, esi --> b, edx --> c, ecx --> e, r8d --> f, r9d --> g, push real h --> formal h */ "movl %esi, %edx\n\t" "movq %rsi, %rcx\n\t" "shrq $32, %rcx\n\t" "movq %rdi, %rsi\n\t" "shrq $32, %rsi\n\t" "jmpq *%rax\n\t" #endif ); __asm__( "\t.globl co_switch_asm\n" "co_switch_asm:\n" #if __i386 "pushl %ebp\n\t" "pushl %ebx\n\t" "pushl %esi\n\t" "pushl %edi\n\t" "movl %esp, (%eax)\n\t" "movl (%edx), %esp\n\t" "popl %edi\n\t" "popl %esi\n\t" "popl %ebx\n\t" "popl %ebp\n\t" "popl %ecx\n\t" "jmpl *%ecx\n\t" #elif __amd64 "pushq %rbp\n\t" "pushq %rbx\n\t" "pushq %r12\n\t" "pushq %r13\n\t" "pushq %r14\n\t" "pushq %r15\n\t" /* I want to save _CORET here by instructions just like 'pushq _CORET'(etc.)to accept coroutine return. unfortunately fail. so coroutines which use CCTX_ASM to support coroutine-switching must use co_end() to terminate itself before return. the same situation on __i386, please do a favor to accept the 'return' statement of coroutine if you owns the same faith. */ "movq %rsp, (%rdi)\n\t" "movq (%rsi), %rsp\n\t" "popq %r15\n\t" "popq %r14\n\t" "popq %r13\n\t" "popq %r12\n\t" "popq %rbx\n\t" "popq %rbp\n\t" "popq %rcx\n\t" "jmpq *%rcx\n" "_CORET:" #else #error "coroutine-context unsupported" " on current architecture" #endif ); int co_start_asm(ci_s *ci) { cctx_s *ctx = NULL; int ss = co_ssize(ci); char *stack = co_stack(ci); IF_EXPS_THEN_RETURN(!ci || !stack || !ss, CODE_BADPARAM); ctx = co_cctx(ci); ctx->sp = (void **)(stack + ss); /* ctx->sp points to (void *), so arithmetic unit of ctx->sp is sizeof(void *). initial co-stack as follow: ------+---------+------+----+----+----+ ... |co_medium| co_fn| arg| ci |NULL| ------+---------+------+----+----+----+ ^ ^ ^ | | | stack sp stack+ss */ *--ctx->sp = NULL; *--ctx->sp = ci; *--ctx->sp = co_arg(ci); *--ctx->sp = co_cofn(ci); *--ctx->sp = _co_arg_medium; /* Reserved for subroutines to backup registers: ebp, ebx, esi, edi on i386; rbp, rbx, r12, r13, r14, r15 on amd64.*/ ctx->sp -= CS_RESERVE_NR; (void)co_switch_asm(co_bcctx(ci), ctx); return CODE_NONE; } 

[2] 修整有瑕疵的工程管理文件及管理理念本身。

[3...]