Table of Contents
1 continuation
In some senses,
Folowing code are just a demo, not suit for production usage. g++-4.7 is required.
ucontext.h is already a implementation of
continuation, which is available on most modern OS(standarded by
POSIX). In C99, we also have setjmp/longjmp to implement
continuation. But setjmp/longjmp is weaker than ucontext.h.
Folowing code are just a demo, not suit for production usage. g++-4.7 is required.
#include#include // for type erasure, or, we have to make continuation a template #define CLOG(...) // we don't have/need CLOG struct continuation { template <class Func> continuation(const Func & func, size_t stack_size=1<<18) { m_stack.resize(stack_size); m_func = func; int r = getcontext(&m_ctxs[1]); assert(r == 0); m_ctxs[1].uc_link = &m_ctxs[0]; m_ctxs[1].uc_stack.ss_sp = &m_stack[0]; m_ctxs[1].uc_stack.ss_size = m_stack.size(); // TODO: x86_64 is safe to pass pointer with glibc, but for other platform ... makecontext(&m_ctxs[1], (void (*)(void))&s_context_func, 1, this); } continuation(const continuation &r) = delete; continuation & operator=(const continuation &r) = delete; int swap() { if (m_in_done) return -1; CLOG(DEBUG, "swap from", (m_is_in ? "in" : "out")); m_is_in = !m_is_in; swapcontext(&m_ctxs[!m_is_in], &m_ctxs[m_is_in]); CLOG(DEBUG, "after swap"); if (m_in_done) return 0; return 1; } static void s_context_func(continuation *self) { return self->context_func(); } void context_func() { m_func(); m_in_done = 1; } ucontext_t m_ctxs[2]; std::function<void(void)> m_func; std::vector<char> m_stack; bool m_is_in = false; int m_in_done = 0; };
2 generator
template <class T> struct generator : continuation { template <class Func> generator(const Func &func) : continuation(func) { } void yield(const T &value) { m_value = value; swap(); } T yield() { if (swap() <= 0) throw std::runtime_error("end of iteration"); return m_value; } T volatile m_value; };
3 coroutine
struct coroutine : continuation { template <class Func> generator(const Func &func) : continuation(func) { } void yield(coroutine &other) { other.swap(); } };
4 usage and test
4.1 primes
A simple program to print primes(not all).
bool is_prime(int n) { if (n % 2 == 0) return n == 2; for (int p = 3; p * p <= n; p += 2) { if (n % p == 0) return false; } return true; } void primes(generator<int> &g) { g.yield(2); int i = 3; while (1) { if (is_prime(i)) g.yield(i); i += 2; } } int main() { generator<int> g([&]() { primes(g); }); while (1) { int p = g.yield(); std::cout << p << std::endl; } }
4.2 producer and consumer
void producer(int n, int *x, continuation & cont) { for (int i = 0; i < n; ++i) { *x = i * i; cont.swap(); } } void consumer(int volatile *x, continuation &cont) { while (cont.swap() > 0) { CLOG(INFO, "got", *x); } }
