function executed by resume_with() has to return a continuation

boostorg · Aug 10, 2017 · 420554f · 420554f
1 parent 8346fbf
commit 420554f
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Showing 8 changed files with 59 additions and 31 deletions.
diff --git a/doc/callcc.qbk b/doc/callcc.qbk
@@ -176,6 +176,7 @@ return `void`.
     c=c.resume_with([&data](ctx::continuation && c){
                         std::cout << "f2: entered: " << data << std::endl;
                         data=-1;
+                        return std::move( c);
                     });
     std::cout << "f1: returned third time" << std::endl;
 
@@ -221,6 +222,7 @@ an exception.
     c = c.resume_with(
            [](ctx::continuation && c){
                throw my_exception(std::move(c),"abc");
+               return std::move( c);
            });
 
     output:
@@ -527,11 +529,11 @@ e.g. ['continuation::operator bool()] returns `true`.]]
 
 [variablelist
 [[Effects:] [Captures current continuation and resumes `*this`.
-The function `resume_with`, is used to execute function `fn` in continuation
+The function `resume_with`, is used to execute function `fn` in the execution context of
 `*this` (e.g. the stack frame of `fn` is allocated on stack of `*this`).]]
 [[Returns:] [The continuation representing the continuation that has been
 suspended.]]
-[[Note:] [Function `fn` needs to return void.]]
+[[Note:] [Function `fn` needs to return `continuation`.]]
 [[Note:] [The returned continuation indicates if the suspended continuation has
 terminated (return from context-function) via `bool operator()`.]]
 ]

diff --git a/example/ontop.cpp b/example/ontop.cpp
@@ -32,6 +32,7 @@ int main() {
     c = c.resume_with( [&data](ctx::continuation && c){
                             std::cout << "f2: entered: " << data << std::endl;
                             data = -1;
+                            return std::move( c);
                         });
     std::cout << "f1: returned third time" << std::endl;
     std::cout << "main: done" << std::endl;

diff --git a/example/ontop_void.cpp b/example/ontop_void.cpp
@@ -21,8 +21,9 @@ ctx::continuation f1( ctx::continuation && c) {
     return std::move( c);
 }
 
-void f2( ctx::continuation && c) {
+ctx::continuation f2( ctx::continuation && c) {
     std::cout << "f2: entered" << std::endl;
+    return std::move( c);
 }
 
 int main() {

diff --git a/example/throw.cpp b/example/throw.cpp
@@ -38,6 +38,7 @@ int main() {
     c = c.resume_with(
            [](ctx::continuation && c){
                throw my_exception(std::move( c), "abc");
+               return std::move( c);
            });
 
     std::cout << "main: done" << std::endl;

diff --git a/include/boost/context/continuation_fcontext.hpp b/include/boost/context/continuation_fcontext.hpp
@@ -95,7 +95,7 @@ transfer_t context_ontop( transfer_t t) {
     t.data = nullptr;
     Ctx c{ t.fctx };
     // execute function, pass continuation via reference
-    fn( std::move( c) );
+    c = fn( std::move( c) );
 #if defined(BOOST_NO_CXX14_STD_EXCHANGE)
     return { exchange( c.fctx_, nullptr), nullptr };
 #else

diff --git a/include/boost/context/continuation_ucontext.hpp b/include/boost/context/continuation_ucontext.hpp
@@ -84,18 +84,18 @@ static void entry_func( void * data) noexcept {
 struct BOOST_CONTEXT_DECL activation_record {
     thread_local static activation_record   *   current_rec;
 
-    ucontext_t                                  uctx{};
-    stack_context                               sctx{};
-    bool                                        main_ctx{ true };
-	activation_record                       *	from{ nullptr };
-    std::function< void(activation_record*&) >  ontop{};
-    bool                                        terminated{ false };
-    bool                                        force_unwind{ false };
+    ucontext_t                                                  uctx{};
+    stack_context                                               sctx{};
+    bool                                                        main_ctx{ true };
+	activation_record                                       *	from{ nullptr };
+    std::function< activation_record*(activation_record*&) >    ontop{};
+    bool                                                        terminated{ false };
+    bool                                                        force_unwind{ false };
 #if defined(BOOST_USE_ASAN)
-    void                                    *   fake_stack{ nullptr };
-    void                                    *   stack_bottom{ nullptr };
-    std::size_t                                 stack_size{ 0 };
-    bool                                        started{ false };
+    void                                                    *   fake_stack{ nullptr };
+    void                                                    *   stack_bottom{ nullptr };
+    std::size_t                                                 stack_size{ 0 };
+    bool                                                        started{ false };
 #endif
 
     static activation_record *& current() noexcept;
@@ -168,20 +168,30 @@ struct BOOST_CONTEXT_DECL activation_record {
         current()->ontop = std::bind(
                 [](typename std::decay< Fn >::type & fn, activation_record *& ptr){
                     Ctx c{ ptr };
-                    fn( std::move( c) );
+                    c = fn( std::move( c) );
                     if ( ! c) {
                         ptr = nullptr;
                     }
+#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
+                    return exchange( c.ptr_, nullptr);
+#else
+                    return std::exchange( c.ptr_, nullptr);
+#endif
                 },
                 std::forward< Fn >( fn),
                 std::placeholders::_1);
 #else
         current()->ontop = [fn=std::forward<Fn>(fn)](activation_record *& ptr){
             Ctx c{ ptr };
-            fn( std::move( c) );
+            c = fn( std::move( c) );
             if ( ! c) {
                 ptr = nullptr;
             }
+#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
+            return exchange( c.ptr_, nullptr);
+#else
+            return std::exchange( c.ptr_, nullptr);
+#endif
         };
 #endif
 #if defined(BOOST_USE_SEGMENTED_STACKS)
@@ -408,7 +418,7 @@ class BOOST_CONTEXT_DECL continuation {
         if ( BOOST_UNLIKELY( detail::activation_record::current()->force_unwind) ) {
             throw detail::forced_unwind{ ptr};
         } else if ( BOOST_UNLIKELY( nullptr != detail::activation_record::current()->ontop) ) {
-            detail::activation_record::current()->ontop( ptr);
+            ptr = detail::activation_record::current()->ontop( ptr);
             detail::activation_record::current()->ontop = nullptr;
         }
         return continuation{ ptr };
@@ -426,7 +436,7 @@ class BOOST_CONTEXT_DECL continuation {
         if ( BOOST_UNLIKELY( detail::activation_record::current()->force_unwind) ) {
             throw detail::forced_unwind{ ptr};
         } else if ( BOOST_UNLIKELY( nullptr != detail::activation_record::current()->ontop) ) {
-            detail::activation_record::current()->ontop( ptr);
+            ptr = detail::activation_record::current()->ontop( ptr);
             detail::activation_record::current()->ontop = nullptr;
         }
         return continuation{ ptr };

diff --git a/include/boost/context/continuation_winfib.hpp b/include/boost/context/continuation_winfib.hpp
@@ -65,13 +65,13 @@ static VOID WINAPI entry_func( LPVOID data) noexcept {
 struct BOOST_CONTEXT_DECL activation_record {
     thread_local static activation_record   *   current_rec;
 
-    LPVOID                                      fiber{ nullptr };
-    stack_context                               sctx{};
-    bool                                        main_ctx{ true };
-    activation_record                       *   from{ nullptr };
-    std::function< void(activation_record*&) >  ontop{};
-    bool                                        terminated{ false };
-    bool                                        force_unwind{ false };
+    LPVOID                                                      fiber{ nullptr };
+    stack_context                                               sctx{};
+    bool                                                        main_ctx{ true };
+    activation_record                                       *   from{ nullptr };
+    std::function< activation_record*(activation_record*&) >    ontop{};
+    bool                                                        terminated{ false };
+    bool                                                        force_unwind{ false };
 
     static activation_record *& current() noexcept;
 
@@ -142,20 +142,30 @@ struct BOOST_CONTEXT_DECL activation_record {
         current()->ontop = std::bind(
                 [](typename std::decay< Fn >::type & fn, activation_record *& ptr){
                     Ctx c{ ptr };
-                    fn( std::move( c) );
+                    c = fn( std::move( c) );
                     if ( ! c) {
                         ptr = nullptr;
                     }
+#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
+                    return exchange( c.ptr_, nullptr);
+#else
+                    return std::exchange( c.ptr_, nullptr);
+#endif
                 },
                 std::forward< Fn >( fn),
                 std::placeholders::_1);
 #else
         current()->ontop = [fn=std::forward<Fn>(fn)](activation_record *& ptr){
             Ctx c{ ptr };
-            fn( std::move( c) );
+            c = fn( std::move( c) );
             if ( ! c) {
                 ptr = nullptr;
             }
+#if defined(BOOST_NO_CXX14_STD_EXCHANGE)
+            return exchange( c.ptr_, nullptr);
+#else
+            return std::exchange( c.ptr_, nullptr);
+#endif
         };
 #endif
         // context switch
@@ -336,7 +346,7 @@ class BOOST_CONTEXT_DECL continuation {
         if ( BOOST_UNLIKELY( detail::activation_record::current()->force_unwind) ) {
             throw detail::forced_unwind{ ptr};
         } else if ( BOOST_UNLIKELY( nullptr != detail::activation_record::current()->ontop) ) {
-            detail::activation_record::current()->ontop( ptr);
+            ptr = detail::activation_record::current()->ontop( ptr);
             detail::activation_record::current()->ontop = nullptr;
         }
         return continuation{ ptr };
@@ -354,7 +364,7 @@ class BOOST_CONTEXT_DECL continuation {
         if ( BOOST_UNLIKELY( detail::activation_record::current()->force_unwind) ) {
             throw detail::forced_unwind{ ptr};
         } else if ( BOOST_UNLIKELY( nullptr != detail::activation_record::current()->ontop) ) {
-            detail::activation_record::current()->ontop( ptr);
+            ptr = detail::activation_record::current()->ontop( ptr);
             detail::activation_record::current()->ontop = nullptr;
         }
         return continuation{ ptr };

diff --git a/test/test_callcc.cpp b/test/test_callcc.cpp
@@ -252,6 +252,7 @@ void test_ontop() {
         c = c.resume_with(
                [&i](ctx::continuation && c){
                    i -= 10;
+                   return std::move( c);
                });
         BOOST_CHECK( c);
         BOOST_CHECK_EQUAL( i, 200);
@@ -266,6 +267,7 @@ void test_ontop() {
         c = c.resume_with(
                [&c1](ctx::continuation && c){
                    c1 = std::move( c);
+                   return std::move( c);
                });
     }
 }
@@ -290,7 +292,8 @@ void test_ontop_exception() {
     const char * what = "hello world";
     c.resume_with(
        [what](ctx::continuation && c){
-           throw my_exception( std::move( c), what);
+            throw my_exception( std::move( c), what);
+            return std::move( c);
        });
     BOOST_CHECK_EQUAL( 3, value1);
     BOOST_CHECK_EQUAL( std::string( what), value2);