add a simple coroutine scheduler that multiplexes tasks onto a single thread

examples/concurrency.cc

@@ -3,41 +3,53 @@
 
 using namespace ostd;
 
-thread_scheduler sched;
-
-void foo() {
+template<typename S>
+void foo(S &sched) {
     auto arr = ostd::iter({ 150, 38, 76, 25, 67, 18, -15, -38, 25, -10 });
 
     auto h1 = arr.slice(0, arr.size() / 2);
     auto h2 = arr.slice(arr.size() / 2, arr.size());
 
-    auto c = sched.make_channel<int>();
-    auto f = [&c](auto half) {
-        c.put(foldl(half, 0));
+    auto c = sched.template make_channel<int>();
+    auto f = [c](auto half) {
+        c->put(foldl(half, 0));
     };
     sched.spawn(f, h1);
     sched.spawn(f, h2);
 
     int a, b;
-    c.get(a);
-    c.get(b);
+    c->get(a);
+    c->get(b);
     writefln("first half: %s", a);
     writefln("second half: %s", b);
     writefln("total: %s", a + b);
 }
 
 int main() {
-    sched.start([]() {
-        writeln("starting...");
-        foo();
-        writeln("finishing...");
+    thread_scheduler tsched;
+    tsched.start([&tsched]() {
+        writeln("thread scheduler: starting...");
+        foo(tsched);
+        writeln("thread scheduler: finishing...");
+    });
+
+    simple_coroutine_scheduler scsched;
+    scsched.start([&scsched]() {
+        writeln("simple coroutine scheduler: starting...");
+        foo(scsched);
+        writeln("simple coroutine scheduler: finishing...");
     });
 }
 
 /*
-starting...
+thread scheduler: starting...
 first half: 356
 second half: -20
 total: 336
-finishing...
+thread scheduler: finishing...
+simple coroutine scheduler: starting...
+first half: 356
+second half: -20
+total: 336
+simple coroutine scheduler: finishing...
 */

ostd/channel.hh

@@ -29,7 +29,7 @@ struct channel {
      * elides copying and moving (by directly returning the type ctor call)
      */
     template<typename F>
-    channel(F func): p_cond(func()) {}
+    channel(F func): p_lock(), p_cond(func(p_lock)) {}
 
     void put(T const &val) {
         put_impl(val);
@@ -85,8 +85,8 @@ private:
     }
 
     std::list<T> p_messages;
-    C p_cond;
     mutable std::mutex p_lock;
+    C p_cond;
     bool p_closed = false;
 };
 

ostd/concurrency.hh

@@ -8,7 +8,9 @@
 
 #include <thread>
 #include <utility>
+#include <memory>
 
+#include "ostd/coroutine.hh"
 #include "ostd/channel.hh"
 
 namespace ostd {
@@ -42,8 +44,8 @@ struct thread_scheduler {
     }
 
     template<typename T>
-    channel<T> make_channel() {
-        return channel<T>{};
+    std::shared_ptr<channel<T>> make_channel() {
+        return std::shared_ptr<channel<T>>{new channel<T>{}};
     }
 
 private:
@@ -72,6 +74,122 @@ private:
     std::mutex p_lock;
 };
 
+struct simple_coroutine_scheduler {
+private:
+    /* simple one just for channels */
+    struct coro_cond {
+        coro_cond() = delete;
+        coro_cond(coro_cond const &) = delete;
+        coro_cond(coro_cond &&) = delete;
+        coro_cond &operator=(coro_cond const &) = delete;
+        coro_cond &operator=(coro_cond &&) = delete;
+
+        coro_cond(simple_coroutine_scheduler &s, std::mutex &mtx):
+            p_sched(s), p_mtx(mtx)
+        {}
+
+        template<typename L>
+        void wait(L &l) noexcept {
+            l.unlock();
+            while (!p_notified) {
+                p_sched.yield();
+            }
+            p_notified = false;
+            l.lock();
+        }
+
+        void notify_one() noexcept {
+            p_notified = true;
+            p_mtx.unlock();
+            p_sched.yield();
+            p_mtx.lock();
+        }
+
+        void notify_all() noexcept {
+            p_notified = true;
+            p_mtx.unlock();
+            p_sched.yield();
+            p_mtx.lock();
+        }
+    private:
+        simple_coroutine_scheduler &p_sched;
+        std::mutex &p_mtx;
+        bool p_notified = false;
+    };
+
+public:
+    template<typename F, typename ...A>
+    auto start(F &&func, A &&...args) -> std::result_of_t<F(A...)> {
+        using R = std::result_of_t<F(A...)>;
+        if constexpr(std::is_same_v<R, void>) {
+            spawn(std::forward<F>(func), std::forward<F>(args)...);
+            dispatch();
+        } else {
+            R ret;
+            spawn([lfunc = std::forward<F>(func), &ret](A &&...args) {
+                ret = std::move(lfunc(std::forward<A>(args)...));
+            }, std::forward<A>(args)...);
+            dispatch();
+            return ret;
+        }
+    }
+
+    template<typename F, typename ...A>
+    void spawn(F &&func, A &&...args) {
+        if constexpr(sizeof...(A) == 0) {
+            p_coros.emplace_back([lfunc = std::forward<F>(func)](auto) {
+                lfunc();
+            });
+        } else {
+            p_coros.emplace_back([lfunc = std::bind(
+                std::forward<F>(func), std::forward<A>(args)...
+            )](auto) {
+                lfunc();
+            });
+        }
+    }
+
+    void yield() {
+        auto ctx = coroutine_context::current();
+        coro *c = dynamic_cast<coro *>(ctx);
+        if (c) {
+            coro::yield_type{*c}();
+            return;
+        }
+        throw std::runtime_error{"no task to yield"};
+    }
+
+    template<typename T>
+    std::shared_ptr<channel<T, coro_cond>> make_channel() {
+        return std::shared_ptr<channel<T, coro_cond>>{
+            new channel<T, coro_cond>{[this](std::mutex &mtx) {
+                return coro_cond{*this, mtx};
+            }}
+        };
+    }
+private:
+    struct coro: coroutine<void()> {
+        using coroutine<void()>::coroutine;
+    };
+
+    void dispatch() {
+        while (!p_coros.empty()) {
+            if (p_idx == p_coros.end()) {
+                p_idx = p_coros.begin();
+            }
+            (*p_idx)();
+            if (!*p_idx) {
+                p_idx = p_coros.erase(p_idx);
+            } else {
+                ++p_idx;
+            }
+        }
+    }
+
+    std::list<coro> p_coros;
+    typename std::list<coro>::iterator p_idx = p_coros.end();
+};
+
 } /* namespace ostd */
 
 #endif