Added a paper on task issues and some code changes coming out of that

dietmarkuehl · web-flow · commit cf7b478dbc59 · 2025-07-15T15:10:06.000+01:00
Issues
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -17,6 +17,7 @@ option(
     "Enable building tests and test infrastructure. Default: ON. Values: { ON, OFF }."
     ${PROJECT_IS_TOP_LEVEL}
 )
+#set(BEMAN_TASK_BUILD_TESTS FALSE)
 
 # [CMAKE.SKIP_EXAMPLES]
 option(
diff --git a/Makefile b/Makefile
@@ -1,12 +1,12 @@
 #-dk: note to self: PATH=/opt/llvm-19.1.6/bin:$PATH LDFLAGS=-fuse-ld=lld
 
-.PHONY: config test default compile clean distclean doc format tidy
+.PHONY: config test default compile clean distclean doc html pdf format tidy
 
 BUILDDIR = build
-PRESET  = gcc-debug
+PRESET  = gcc-release
 UNAME = $(shell uname -s)
 ifeq ($(UNAME),Darwin)
-    PRESET  = appleclang-debug
+    PRESET  = appleclang-release
 endif
 BUILD = $(BUILDDIR)/$(PRESET)
 
@@ -15,6 +15,9 @@ default: compile
 doc:
 	cd docs; $(MAKE)
 
+pdf html:
+	cd docs; $(MAKE) doc-$@
+
 compile:
 	CMAKE_EXPORT_COMPILE_COMMANDS=1 \
 	cmake \
diff --git a/docs/Makefile b/docs/Makefile
@@ -1,8 +1,12 @@
-.PHONY: default doc
+.PHONY: default doc doc-html doc-pdf
 
 default: doc
 
-doc: P3552-task.html
+doc: doc-html
+
+doc-html: P3552-task.html P3796-task-issues.html
+
+doc-pdf: P3552-task.pdf P3796-task-issues.pdf
 
 wg21/Makefile:
 	git clone https://github.com/mpark/wg21.git
diff --git a/docs/P3796-task-issues.md b/docs/P3796-task-issues.md
diff --git a/docs/issues-overview.md b/docs/issues-overview.md
diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
@@ -1,7 +1,8 @@
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-set(ALL_EXAMPLES co_await-task)
 set(ALL_EXAMPLES
+    customize
+    issue-symmetric-transfer
     affinity
     alloc
     c++now-affinity
@@ -23,12 +24,17 @@ set(ALL_EXAMPLES
     friendly
     hello
     into_optional
+    issue-affine_on
+    issue-frame-allocator
+    issue-start-reschedules
     loop
     query
     result_example
     stop
     task_scheduler
 )
+set(xALL_EXAMPLES issue-symmetric-transfer)
+set(xALL_EXAMPLES customize)
 
 message("Examples to be built: ${ALL_EXAMPLES}")
 
diff --git a/examples/customize.cpp b/examples/customize.cpp
@@ -0,0 +1,32 @@
+// examples/customize.cpp                                             -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <beman/execution/execution.hpp>
+#include <beman/task/task.hpp>
+#include "demo-thread_pool.hpp"
+#include <iostream>
+#include <utility>
+#include <cassert>
+
+namespace ex = beman::execution;
+
+namespace {
+struct empty {};
+} // namespace
+
+int main() {
+#if 0
+    auto task = []()->ex::task<void, empty> { co_return; }();
+    static_assert(ex::sender<decltype(task)>);
+    auto env = ex::get_env(task);
+    static_assert(std::same_as<decltype(task)::env, decltype(env)>);
+    auto dom = ex::get_domain(env);
+    static_assert(std::same_as<decltype(task)::domain, decltype(dom)>);
+    auto edom = ex::detail::get_domain_early(task);
+    static_assert(std::same_as<decltype(task)::domain, decltype(edom)>);
+    std::cout << "---\n";
+    transform_sender(edom, ex::detail::make_sender(ex::affine_on, ex::inline_scheduler{}, std::move(task)));
+    std::cout << "---\n";
+    auto affine = ex::affine_on(std::move(task), ex::inline_scheduler{});
+#endif
+}
diff --git a/examples/issue-affine_on.cpp b/examples/issue-affine_on.cpp
@@ -0,0 +1,19 @@
+// examples/issue-affine_on.cpp                                       -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <beman/execution/task.hpp>
+#include <beman/execution/execution.hpp>
+#include <iostream>
+
+namespace ex = beman::execution;
+
+template <ex::sender Sender>
+ex::task<> test(Sender&& sender) {
+    co_await std::move(sender);
+}
+
+int main() {
+    ex::sync_wait(test(ex::just()));
+    ex::sync_wait(test(ex::read_env(ex::get_scheduler) |
+                       ex::let_value([](auto sched) { return ex::starts_on(sched, ex::just()); })));
+}
diff --git a/examples/issue-frame-allocator.cpp b/examples/issue-frame-allocator.cpp
@@ -0,0 +1,26 @@
+// examples/issue-frame-allocator.cpp                                 -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <beman/execution/task.hpp>
+#include <beman/execution/execution.hpp>
+#include <iostream>
+#include <functional>
+#include <memory_resource>
+
+namespace ex = beman::execution;
+
+template <typename Env>
+ex::task<int, Env> test(int i, auto&&...) {
+    co_return co_await ex::just(i);
+}
+struct default_env {};
+struct allocator_env {
+    using allocator_type = std::pmr::polymorphic_allocator<>;
+};
+
+int main() {
+    ex::sync_wait(test<default_env>(17));                                            // OK: no allocator
+    ex::sync_wait(test<default_env>(17, std::allocator_arg, std::allocator<int>())); // OK: allocator is convertible
+    // ex::sync_wait(test<default_env>(17, std::allocator_arg, std::pmr::polymorphic_allocator<>())); // error
+    ex::sync_wait(test<allocator_env>(17, std::allocator_arg, std::pmr::polymorphic_allocator<>())); // OK but unusual
+}
diff --git a/examples/issue-start-reschedules.cpp b/examples/issue-start-reschedules.cpp
@@ -0,0 +1,30 @@
+// examples/issue-start-reschedules.cpp                               -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <beman/execution/task.hpp>
+#include <beman/execution/execution.hpp>
+#include "demo-thread_pool.hpp"
+#include <iostream>
+#include <thread>
+
+namespace ex = beman::execution;
+
+ex::task<> test(auto sched) {
+    std::cout << "init =" << std::this_thread::get_id() << "\n";
+    co_await ex::starts_on(sched, ex::just());
+    std::cout << "final=" << std::this_thread::get_id() << "\n";
+}
+
+int main() {
+    demo::thread_pool pool1;
+    demo::thread_pool pool2;
+    std::cout << "main =" << std::this_thread::get_id() << "\n";
+    ex::sync_wait(ex::schedule(pool1.get_scheduler()) |
+                  ex::then([] { std::cout << "pool1=" << std::this_thread::get_id() << "\n"; }));
+    ex::sync_wait(ex::schedule(pool2.get_scheduler()) |
+                  ex::then([] { std::cout << "pool2=" << std::this_thread::get_id() << "\n"; }));
+    std::cout << "--- use 1 ---\n";
+    ex::sync_wait(test(pool2.get_scheduler()));
+    std::cout << "--- use 2 ---\n";
+    ex::sync_wait(ex::starts_on(pool1.get_scheduler(), test(pool2.get_scheduler())));
+}
diff --git a/examples/issue-symmetric-transfer.cpp b/examples/issue-symmetric-transfer.cpp
@@ -0,0 +1,30 @@
+// examples/issue-symmetric-transfer.cpp                              -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <beman/execution/task.hpp>
+#include <beman/execution/execution.hpp>
+#include <functional>
+#define NODEBUG
+#include <cassert>
+
+namespace ex = beman::execution;
+
+template <typename Env>
+ex::task<void, Env> test() {
+    for (std::size_t i{}; i < 1000000; ++i) {
+        // co_await std::invoke([]() -> ex::task<> { co_await ex::just(); });
+        co_await std::invoke([]() -> ex::task<> { co_return; });
+    }
+}
+
+int main() {
+    struct affine_env {};
+    struct inline_env {
+        using scheduler_type = ex::inline_scheduler;
+    };
+    [[maybe_unused]] auto env   = affine_env{};
+    [[maybe_unused]] auto sched = inline_env::scheduler_type{};
+
+    // ex::sync_wait(test<affine_env>()); // OK
+    // ex::sync_wait(test<inline_env>()); // error: stack overflow without symmetric transfer
+}
diff --git a/include/beman/task/detail/affine_on.hpp b/include/beman/task/detail/affine_on.hpp
@@ -25,23 +25,24 @@ struct affine_on_t {
 
 template <::beman::execution::sender Sender, ::beman::execution::scheduler Scheduler>
 struct affine_on_t::sender {
-    using sender_concept = ::beman::execution::sender_t;
-    template <typename Env>
+    using sender_concept                 = ::beman::execution::sender_t;
     static constexpr bool elide_schedule = ::std::same_as<::beman::task::detail::inline_scheduler, Scheduler>;
 
     template <typename Env>
     auto get_completion_signatures(const Env& env) const& noexcept {
-        if constexpr (elide_schedule<Env>) {
-            return ::beman::execution::get_completion_signatures(this->upstream, env);
+        if constexpr (elide_schedule) {
+            return ::beman::execution::get_completion_signatures(
+                ::std::remove_cvref_t<Sender>(::std::move(this->upstream)), env);
         } else {
             return ::beman::execution::get_completion_signatures(
                 ::beman::execution::continues_on(this->upstream, this->scheduler), env);
         }
     }
     template <typename Env>
     auto get_completion_signatures(const Env& env) && noexcept {
-        if constexpr (elide_schedule<Env>) {
-            return ::beman::execution::get_completion_signatures(this->upstream, env);
+        if constexpr (elide_schedule) {
+            return ::beman::execution::get_completion_signatures(
+                ::std::remove_cvref_t<Sender>(::std::move(this->upstream)), env);
         } else {
             return ::beman::execution::get_completion_signatures(
                 ::beman::execution::continues_on(::std::move(this->upstream), ::std::move(this->scheduler)), env);
@@ -54,8 +55,7 @@ struct affine_on_t::sender {
 
     template <::beman::execution::receiver Receiver>
     auto connect(Receiver&& receiver) const& {
-        using env_t = decltype(::beman::execution::get_env(receiver));
-        if constexpr (elide_schedule<env_t>) {
+        if constexpr (elide_schedule) {
             return ::beman::execution::connect(this->upstream, ::std::forward<Receiver>(receiver));
         } else {
             return ::beman::execution::connect(::beman::execution::continues_on(this->upstream, this->scheduler),
@@ -64,8 +64,7 @@ struct affine_on_t::sender {
     }
     template <::beman::execution::receiver Receiver>
     auto connect(Receiver&& receiver) && {
-        using env_t = decltype(::beman::execution::get_env(receiver));
-        if constexpr (elide_schedule<env_t>) {
+        if constexpr (elide_schedule) {
             return ::beman::execution::connect(::std::move(this->upstream), ::std::forward<Receiver>(receiver));
         } else {
             return ::beman::execution::connect(
@@ -77,8 +76,9 @@ struct affine_on_t::sender {
 } // namespace beman::task::detail
 
 namespace beman::task {
+using affine_on_t = ::beman::task::detail::affine_on_t;
 inline constexpr ::beman::task::detail::affine_on_t affine_on{};
-}
+} // namespace beman::task
 
 // ----------------------------------------------------------------------------
 
diff --git a/include/beman/task/detail/awaiter.hpp b/include/beman/task/detail/awaiter.hpp
@@ -56,7 +56,6 @@ class awaiter : public ::beman::task::detail::state_base<Value, Env> {
         this->scheduler.emplace(
             this->template from_env<scheduler_type>(::beman::execution::get_env(parent.promise())));
         this->parent = ::std::move(parent);
-        assert(this->parent);
         return this->handle.start(this);
     }
     auto await_resume() { return this->result_resume(); }
@@ -74,7 +73,6 @@ class awaiter : public ::beman::task::detail::state_base<Value, Env> {
                 ::beman::execution::get_scheduler(::beman::execution::get_env(this->parent.promise()))) {
                 this->reschedule.emplace(this->parent.promise(), this);
                 this->reschedule->start();
-                std::cout << "awaiter rescheduled()\n";
                 return ::std::noop_coroutine();
             }
         }
diff --git a/include/beman/task/detail/promise_type.hpp b/include/beman/task/detail/promise_type.hpp
@@ -70,7 +70,7 @@ class promise_type
 
     auto get_return_object() noexcept { return Coroutine(::beman::task::detail::handle<promise_type>(this)); }
 
-    template <::beman::execution::sender Sender, typename... A>
+    template <::beman::execution::sender Sender>
     auto await_transform(Sender&& sender) noexcept {
         if constexpr (requires {
                           ::std::forward<Sender>(sender).as_awaitable(*this);
diff --git a/include/beman/task/detail/task.hpp b/include/beman/task/detail/task.hpp
diff --git a/include/beman/task/task.hpp b/include/beman/task/task.hpp
diff --git a/tests/beman/task/final_awaiter.test.cpp b/tests/beman/task/final_awaiter.test.cpp

Original file line number	Diff line number	Diff line change
`@@ -17,6 +17,7 @@ option(`
`17`	`17`	`"Enable building tests and test infrastructure. Default: ON. Values: { ON, OFF }."`
`18`	`18`	`${PROJECT_IS_TOP_LEVEL}`
`19`	`19`	`)`
	`20`	`+#set(BEMAN_TASK_BUILD_TESTS FALSE)`
`20`	`21`
`21`	`22`	`# [CMAKE.SKIP_EXAMPLES]`
`22`	`23`	`option(`