async: Add preliminary time scheduler.

1 files changed, 76 insertions, 0 deletions

diff --git a/async/time_scheduler.h b/async/time_scheduler.h
new file mode 100644
index 0000000..e09de16
--- /dev/null
+++ b/async/time_scheduler.h
@@ -0,0 +1,76 @@
+#pragma once
+
+#include <chrono>
+
+#include "scheduler.h"
+
+template <typename Duration = std::chrono::milliseconds>
+struct time_scheduler_t {
+    struct wakeup_future : public schedulable {
+        time_scheduler_t& tsched;
+        Duration time;
+        wakeup_future(time_scheduler_t& tsched, Duration time) : tsched(tsched), time(time) {}
+
+        bool await_ready() {
+            return tsched.now >= time;
+        }
+
+        bool await_suspend(std::coroutine_handle<> h) {
+            if(tsched.now >= time) {
+                return false;
+            } else {
+                awaiter = h;
+                tsched.push_wakeup(this);
+                return true;
+            }
+        }
+
+        void await_resume() {}
+
+        void resume() {
+            scheduler.schedule(*this);
+        }
+    };
+
+    Duration now;
+
+    wakeup_future* wakeup_queue;
+
+    void push_wakeup(wakeup_future* fut) {
+        wakeup_future** p = &wakeup_queue;
+
+        while((*p) && (*p)->time <= fut->time) {
+            p = reinterpret_cast<wakeup_future**>(&(*p)->next);
+        }
+
+        fut->next = *p;
+        *p = fut;
+    }
+
+    async_flag tick_flag;
+
+    void tick() {
+        tick_flag.set();
+    }
+
+    task wakeup_task() {
+        while(1) {
+            co_await tick_flag;
+            now++;
+
+            while(wakeup_queue && wakeup_queue->time <= now) {
+                auto fut = wakeup_queue;
+                wakeup_queue = static_cast<wakeup_future*>(fut->next);
+                fut->resume();
+            }
+        }
+    }
+
+    wakeup_future sleep_until(Duration time) {
+        return {*this, time};
+    }
+
+    wakeup_future sleep(Duration duration) {
+        return sleep_until(now + duration);
+    }
+};