From 0da22e777dea985d42d055e42515b16b8d5d57ea Mon Sep 17 00:00:00 2001
From: q66 <daniel@octaforge.org>
Date: Fri, 17 Mar 2017 03:04:15 +0100
Subject: [PATCH] add a way to retrieve the current coroutine context

---
 ostd/internal/context.hh | 17 +++++++++++++++--
 src/context_stack.cc     |  6 ++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/ostd/internal/context.hh b/ostd/internal/context.hh
index d081cd1..398030b 100644
--- a/ostd/internal/context.hh
+++ b/ostd/internal/context.hh
@@ -15,8 +15,10 @@
 #include "ostd/context_stack.hh"
 
 namespace ostd {
-namespace detail {
 
+struct coroutine_context;
+
+namespace detail {
     /* from boost.fcontext */
     using fcontext_t = void *;
 
@@ -40,12 +42,19 @@ namespace detail {
         fcontext_t const to, void *vp, transfer_t (*fn)(transfer_t)
     );
 
+    OSTD_EXPORT extern thread_local coroutine_context *coro_current;
 } /* namespace detail */
 
 struct coroutine_context {
+    static coroutine_context *current() {
+        return detail::coro_current;
+    }
+
 protected:
     coroutine_context() {}
-    ~coroutine_context() {
+
+    /* coroutine context must be polymorphic */
+    virtual ~coroutine_context() {
         unwind();
     }
 
@@ -67,7 +76,11 @@ protected:
 
     void call() {
         p_state = state::EXEC;
+        /* switch to new coroutine */
+        coroutine_context *curr = std::exchange(detail::coro_current, this);
         coro_jump();
+        /* switch back to previous */
+        detail::coro_current = curr;
         if (p_except) {
             std::rethrow_exception(std::move(p_except));
         }
diff --git a/src/context_stack.cc b/src/context_stack.cc
index b4f4bf4..b26f41c 100644
--- a/src/context_stack.cc
+++ b/src/context_stack.cc
@@ -158,4 +158,10 @@ size_t stack_traits::default_size() noexcept {
 #endif
 }
 
+struct coroutine_context;
+
+namespace detail {
+    OSTD_EXPORT thread_local coroutine_context *coro_current = nullptr;
+}
+
 } /* namespace ostd */