Asio 协程在使用右值参数时表现不佳？

我可能做了一些明显错误的事情，但为什么会在 MSVC 上打印垃圾？

#include <sdkddkver.h>

#include <boost/asio.hpp>
#include <iostream>

namespace asio = boost::asio;

template <typename Str>
asio::awaitable<void> coro_task(Str&& str) {
  std::cout << "coro_task: " << str << std::endl;
  co_await asio::this_coro::executor;
}

template <typename Str>
void sync_task(Str&& str) {
  std::cout << "sync_task: " << str << std::endl;
}

int main() {
  asio::io_context ioc;
  asio::co_spawn(ioc.get_executor(), coro_task("hello world"), asio::detached);
  asio::post(ioc.get_executor(), [] { sync_task("hello world"); });

  ioc.run();
}

例如：

coro_task: ╕÷ⁿäg
sync_task: hello world

我不明白为什么会这样。一定Str将是静态生命周期char[12] &，所以我不明白为什么它会得到垃圾数据。

如果我将任何具有暂时生命周期的东西传递给coro_task (e.g. coro_task(std::string{"hello world"})）我没有得到输出（str是空的）。我猜想它是从某个地方搬来的，但不知道在哪里。

尝试为阻塞函数创建通用异步任务/协程包装器时遇到此问题：https://stackoverflow.com/a/75228866/3554391 https://stackoverflow.com/a/75228866/3554391。这个问题代表了这个问题的一个最小例子。

该问题似乎没有发生与 godbolt 上的 gcc 一起使用 https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:%271%27,fontScale:14,fontUsePx:%270%27,j:1,lang:c%2B%2B,selection:(endColumn:2,endLineNumber:23,positionColumn:2,positionLineNumber:23,selectionStartColumn:2,selectionStartLineNumber:23,startColumn:2,startLineNumber:23),source:%27%23include+%3Cboost/asio.hpp%3E%0A%23include+%3Ciostream%3E%0A%0Anamespace+asio+%3D+boost::asio%3B%0A%0Atemplate+%3Ctypename+Str%3E%0Aasio::awaitable%3Cvoid%3E+coro_task(Str%26%26+str)+%7B%0A++std::cout+%3C%3C+%22coro_task:+%22+%3C%3C+str+%3C%3C+std::endl%3B%0A++co_await+asio::this_coro::executor%3B%0A%7D%0A%0Atemplate+%3Ctypename+Str%3E%0Avoid+sync_task(Str%26%26+str)+%7B%0A++std::cout+%3C%3C+%22sync_task:+%22+%3C%3C+str+%3C%3C+std::endl%3B%0A%7D%0A%0Aint+main()+%7B%0A++asio::io_context+ioc%3B%0A++asio::co_spawn(ioc.get_executor(),+coro_task(%22hello+world%22),+asio::detached)%3B%0A++asio::post(ioc.get_executor(),+%5B%5D+%7B+sync_task(%22hello+world%22)%3B+%7D)%3B%0A%0A++ioc.run()%3B%0A%7D%27),l:%275%27,n:%270%27,o:%27C%2B%2B+source+%231%27,t:%270%27)),k:59.375,l:%274%27,n:%270%27,o:%27%27,s:0,t:%270%27),(g:!((g:!((h:compiler,i:(compiler:g131,deviceViewOpen:%271%27,filters:(b:%270%27,binary:%271%27,binaryObject:%271%27,commentOnly:%270%27,debugCalls:%271%27,demangle:%270%27,directives:%270%27,execute:%270%27,intel:%270%27,libraryCode:%270%27,trim:%271%27),flagsViewOpen:%271%27,fontScale:14,fontUsePx:%270%27,j:1,lang:c%2B%2B,libs:!((name:boost,ver:%27182%27)),options:%27-std%3Dc%2B%2B20+-Wall+-Wextra+-pedantic+-Werror+-lpthread%27,overrides:!(),selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:%275%27,n:%270%27,o:%27+x86-64+gcc+13.1+(Editor+%231)%27,t:%270%27)),header:(),l:%274%27,m:70.82658022690438,n:%270%27,o:%27%27,s:0,t:%270%27),(g:!((h:output,i:(compilerName:%27x86-64+gcc+13.1%27,editorid:1,fontScale:14,fontUsePx:%270%27,j:1,wrap:%271%27),l:%275%27,n:%270%27,o:%27Output+of+x86-64+gcc+13.1+(Compiler+%231)%27,t:%270%27)),header:(),l:%274%27,m:29.17341977309562,n:%270%27,o:%27%27,s:0,t:%270%27)),k:40.625,l:%273%27,n:%270%27,o:%27%27,t:%270%27)),l:%272%27,n:%270%27,o:%27%27,t:%270%27)),version:4 or 伴随着铿锵声 https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:%271%27,fontScale:14,fontUsePx:%270%27,j:1,lang:c%2B%2B,selection:(endColumn:2,endLineNumber:23,positionColumn:2,positionLineNumber:23,selectionStartColumn:2,selectionStartLineNumber:23,startColumn:2,startLineNumber:23),source:%27%23include+%3Cboost/asio.hpp%3E%0A%23include+%3Ciostream%3E%0A%0Anamespace+asio+%3D+boost::asio%3B%0A%0Atemplate+%3Ctypename+Str%3E%0Aasio::awaitable%3Cvoid%3E+coro_task(Str%26%26+str)+%7B%0A++std::cout+%3C%3C+%22coro_task:+%22+%3C%3C+str+%3C%3C+std::endl%3B%0A++co_await+asio::this_coro::executor%3B%0A%7D%0A%0Atemplate+%3Ctypename+Str%3E%0Avoid+sync_task(Str%26%26+str)+%7B%0A++std::cout+%3C%3C+%22sync_task:+%22+%3C%3C+str+%3C%3C+std::endl%3B%0A%7D%0A%0Aint+main()+%7B%0A++asio::io_context+ioc%3B%0A++asio::co_spawn(ioc.get_executor(),+coro_task(%22hello+world%22),+asio::detached)%3B%0A++asio::post(ioc.get_executor(),+%5B%5D+%7B+sync_task(%22hello+world%22)%3B+%7D)%3B%0A%0A++ioc.run()%3B%0A%7D%27),l:%275%27,n:%270%27,o:%27C%2B%2B+source+%231%27,t:%270%27)),k:59.375,l:%274%27,n:%270%27,o:%27%27,s:0,t:%270%27),(g:!((g:!((h:compiler,i:(compiler:clang1600,deviceViewOpen:%271%27,filters:(b:%270%27,binary:%271%27,binaryObject:%271%27,commentOnly:%270%27,debugCalls:%271%27,demangle:%270%27,directives:%270%27,execute:%270%27,intel:%270%27,libraryCode:%270%27,trim:%271%27),flagsViewOpen:%271%27,fontScale:14,fontUsePx:%270%27,j:1,lang:c%2B%2B,libs:!((name:boost,ver:%27182%27)),options:%27-std%3Dc%2B%2B20+-Wall+-Wextra+-pedantic+-Werror+-pthread%27,overrides:!(),selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:%275%27,n:%270%27,o:%27+x86-64+clang+16.0.0+(Editor+%231)%27,t:%270%27)),header:(),l:%274%27,m:70.82658022690438,n:%270%27,o:%27%27,s:0,t:%270%27),(g:!((h:output,i:(compilerName:%27x86-64+gcc+13.1%27,editorid:1,fontScale:14,fontUsePx:%270%27,j:1,wrap:%271%27),l:%275%27,n:%270%27,o:%27Output+of+x86-64+clang+16.0.0+(Compiler+%231)%27,t:%270%27)),header:(),l:%274%27,m:29.17341977309562,n:%270%27,o:%27%27,s:0,t:%270%27)),k:40.625,l:%273%27,n:%270%27,o:%27%27,t:%270%27)),l:%272%27,n:%270%27,o:%27%27,t:%270%27)),version:4.

我正在使用 Visual Studio 17.5.5 和 asio 1.25.0。

从广义上讲，协程不应该通过引用获取参数。不同于，例如，std::async，C++ 的协程系统尝试将引用参数转换为本地副本的努力为零。

这解释了当你给它类似的对象时它的行为std::string。要理解它在直接处理字符串文字时的行为......事情变得复杂。

在普通函数中，参数是由调用函数有效创建的。由于协程must它比其函数调用引用的上下文更长寿，它有一种机制可以将参数“复制”到与协程状态关联的存储中。如果参数是值参数，则它将由原始参数的 xvalue 表达式初始化（​​因此可以从中移动）。但是，如果这些参数是参考参数，则“复制”将also可以作为同类型的参考。

这就是我们遇到一些问题的地方。用于转发字符串文字引用的模板参数推导会生成对字符串数组的引用。但这是对暂时的数组，通过使用字符串文字作为模板函数的参数来体现。如果该函数采取了char const*，那么所讨论的数组将是指向静态内存的指针。但相反，您拥有的是对临时对象的引用，该引用由函数的调用者拥有。

因此将在协程暂停的那一刻到期。