make channels copyable (referring to a shared state)

examples/concurrency.cc

@@ -11,15 +11,15 @@ void foo(S &sched) {
     auto h2 = arr.slice(arr.size() / 2, arr.size());
 
     auto c = sched.template make_channel<int>();
-    auto f = [c](auto half) {
-        c->put(foldl(half, 0));
+    auto f = [](auto c, auto half) {
+        c.put(foldl(half, 0));
     };
-    sched.spawn(f, h1);
-    sched.spawn(f, h2);
+    sched.spawn(f, c, h1);
+    sched.spawn(f, c, 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);

ostd/channel.hh

@@ -10,6 +10,7 @@
 #include <mutex>
 #include <condition_variable>
 #include <stdexcept>
+#include <memory>
 
 namespace ostd {
 
@@ -22,72 +23,96 @@ struct channel {
     using condition_variable_type = C;
 
     /* default ctor works for default C */
-    channel() {}
+    channel(): p_state(new impl) {}
 
     /* constructing using a function object, keep in mind that condvars are
      * not copy or move constructible, so the func has to work in a way that
      * elides copying and moving (by directly returning the type ctor call)
      */
     template<typename F>
-    channel(F func): p_lock(), p_cond(func(p_lock)) {}
+    channel(F func): p_state(new impl{func}) {}
+
+    channel(channel const &) = default;
+    channel(channel &&) = default;
+
+    channel &operator=(channel const &) = default;
+    channel &operator=(channel &&) = default;
 
     void put(T const &val) {
-        put_impl(val);
+        p_state->put(val);
     }
 
     void put(T &&val) {
-        put_impl(std::move(val));
+        p_state->put(std::move(val));
     }
 
     bool get(T &val) {
-        return get_impl(val, true);
+        return p_state->get(val, true);
     }
 
     bool try_get(T &val) {
-        return get_impl(val, false);
+        return p_state->get(val, false);
     }
 
     bool is_closed() const {
-        std::unique_lock<std::mutex> l{p_lock};
-        return p_closed;
+        return p_state->is_closed();
     }
 
     void close() {
-        std::unique_lock<std::mutex> l{p_lock};
-        p_closed = true;
-        p_cond.notify_all();
+        p_state->close();
     }
 
 private:
-    template<typename U>
-    void put_impl(U &&val) {
-        std::unique_lock<std::mutex> l{p_lock};
-        if (p_closed) {
-            throw channel_error{"put in a closed channel"};
-        }
-        p_messages.push_back(std::forward<U>(val));
-        p_cond.notify_one();
-    }
+    struct impl {
+        impl() {}
 
-    bool get_impl(T &val, bool w) {
-        std::unique_lock<std::mutex> l{p_lock};
-        if (w) {
-            while (!p_closed && p_messages.empty()) {
-                p_cond.wait(l);
+        template<typename F>
+        impl(F &func): p_lock(), p_cond(func(p_lock)) {}
+
+        template<typename U>
+        void put(U &&val) {
+            std::unique_lock<std::mutex> l{p_lock};
+            if (p_closed) {
+                throw channel_error{"put in a closed channel"};
             }
+            p_messages.push_back(std::forward<U>(val));
+            p_cond.notify_one();
         }
-        if (p_messages.empty()) {
-            return false;
-        }
-        val = p_messages.front();
-        p_messages.pop_front();
-        return true;
-    }
 
-    std::list<T> p_messages;
-    mutable std::mutex p_lock;
-    C p_cond;
-    bool p_closed = false;
+        bool get(T &val, bool w) {
+            std::unique_lock<std::mutex> l{p_lock};
+            if (w) {
+                while (!p_closed && p_messages.empty()) {
+                    p_cond.wait(l);
+                }
+            }
+            if (p_messages.empty()) {
+                return false;
+            }
+            val = p_messages.front();
+            p_messages.pop_front();
+            return true;
+        }
+
+        bool is_closed() const {
+            std::unique_lock<std::mutex> l{p_lock};
+            return p_closed;
+        }
+
+        void close() {
+            std::unique_lock<std::mutex> l{p_lock};
+            p_closed = true;
+            p_cond.notify_all();
+        }
+
+        std::list<T> p_messages;
+        mutable std::mutex p_lock;
+        C p_cond;
+        bool p_closed = false;
+    };
+
+    /* basic and inefficient, deal with it better later */
+    std::shared_ptr<impl> p_state;
 };
 
 } /* namespace ostd */

ostd/concurrency.hh

@@ -44,8 +44,8 @@ struct thread_scheduler {
     }
 
     template<typename T>
-    std::shared_ptr<channel<T>> make_channel() {
-        return std::shared_ptr<channel<T>>{new channel<T>{}};
+    channel<T> make_channel() {
+        return channel<T>{};
     }
 
 private:
@@ -143,7 +143,7 @@ public:
         } else {
             p_coros.emplace_back([lfunc = std::bind(
                 std::forward<F>(func), std::forward<A>(args)...
-            )](auto) {
+            )](auto) mutable {
                 lfunc();
             });
         }
@@ -160,12 +160,10 @@ public:
     }
 
     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};
-            }}
-        };
+    channel<T, coro_cond> make_channel() {
+        return channel<T, coro_cond>{[this](std::mutex &mtx) {
+            return coro_cond{*this, mtx};
+        }};
     }
 private:
     struct coro: coroutine<void()> {