它是确定在高频调用的std ::异步？ [英] Is it OK to call std::async at high frequency?

问题描述

我有一个小程序，我写了一个使用的std ::异步并行性，它崩溃在我身上。我是pretty确保有更好的方法可以做到这一点，但现在我只想知道这里发生了什么。我没有要发布的确切code，因为我不认为这真的有差别。基本上，它看起来是这样的：

 而（1）
{
    的std ::矢量＆lt;＆东西GT;事（256）;    汽车update_the_things = [＆放大器;（INT开始，诠释完）{//一些code};    自动=句柄1的std ::异步（的std ::推出::异步，update_the_things，0，things.size（）/ 4）;
    汽车handle2 =的std ::异步（的std ::推出::异步，update_the_things，things.size（）/ 4，things.size（）/ 4 * 2）;
    汽车handle3 =的std ::异步（的std ::推出::异步，update_the_things，things.size（）/ 4 * 2，things.size（）/ 4 * 3）;
    update_the_things（things.size（）/ 4 * 3，things.size（））;    handle1.get（）;
    handle2.get（）;
    handle3.get（）;
}
 

此循环运行每秒后一段随机量几千倍（5秒 - 1分钟），它崩溃。如果我期待在任务管理器我看到这​​个程序的线程数正在迅速波动，这让我觉得的std ::异步将推出每次调用新主题。我本来以为会用一个线程池什么工作。在任何情况下，这种崩溃，因为我做错了什么？

使用GDB我得到以下几点：

 计划接收信号SIGSEGV，分割过错。
[切换主题3560.0x107c]
0x0000000000000000在?? （）＃0 0x0000000000000000的？ （）
＃1 0x000000000041d18c在pthread_create_wrapper（）
＃2 0x0000000000000000的？ （）
 

这是按要求GCC -v输出：

 使用内置的规格。
COLLECT_GCC = GCC
COLLECT_LTO_WRAPPER = C：/ TDM-GCC-64 / bin中/../的libexec / GCC / x86_64的-W64-的mingw32 / 4.8.1 / LTO-wrapper.exe
目标：x86_64的-W64-的mingw32
../../../src/gcc-4.8.1/configure --build = x86_64的-W64-的mingw32 --enable-目标=所有--enable-语言= ADA，C，C ++，FORTRAN：与配置，LTO，objc，OBJ-C ++ --enable-libgomp --enable-LTO --enable-石墨--enable-CXX-标志= -DWINPTHREAD_STATIC --enable-libstdcxx调试--enable-线程= POSIX --enable -version-特定运行时库--enable-完全动态的串--enable-libstdcxx线程--enable-libstdcxx时间--with-GNU-LD --disable-werror --disable-NLS  - 禁用-Win32的注册表 -  preFIX = / mingw64tdm --with-局域preFIX = / mingw64tdm --with-pkgversion = tdm64-2 --with-bugurl = HTTP：// TDM-GCC。 tdragon.net/bugs
线程模型：POSIX
gcc版本4.8.1（tdm64-2）
 

解决方案

这符合标准的程序也崩溃了，平时要快得多：

 的#include＆LT;＆iostream的GT;
＃包括LT＆;＆未来GT;诠释主（）{
  尝试{
    为（;;）{
      。的std ::异步（的std ::推出::异步，[] {}）获得（）;
    }
  }赶上（...）{性病::法院LT＆;＆LT; 扔东西\\ N的; }
}
 

这是在执行中的错误。

I have a little program I wrote that uses std::async for parallelism, and it is crashing on me. I'm pretty sure that there are much better ways to do this, but for now I just want to know what is happening here. I'm not going to post the exact code since I do not think it really makes a difference. It basically looks something like this:

while(1)
{
    std::vector<Things> things(256);

    auto update_the_things = [&](int start, int end) { //some code };

    auto handle1 = std::async(std::launch::async, update_the_things, 0, things.size() / 4);
    auto handle2 = std::async(std::launch::async, update_the_things, things.size() / 4, things.size() / 4 * 2);
    auto handle3 = std::async(std::launch::async, update_the_things, things.size() / 4 * 2, things.size() / 4 * 3);
    update_the_things(things.size() / 4 * 3, things.size());

    handle1.get();
    handle2.get();
    handle3.get();
}

This loop runs several thousand times per second and after a random amount of time (5 seconds - 1 minute) it crashes. If I look in task manager I see that the thread count for this program is rapidly fluctuating, which makes me think that std::async is launching new threads with each call. I would have thought it would work with a thread pool or something. In any case, is this crashing because I am doing something wrong?

Using GDB I get the following:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 3560.0x107c]
0x0000000000000000 in ?? ()

#0 0x0000000000000000 in ?? ()
#1 0x000000000041d18c in pthread_create_wrapper ()
#2 0x0000000000000000 in ?? ()

Output from gcc -v as requested:

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=c:/tdm-gcc-64/bin/../libexec/gcc/x86_64-w64-mingw32/4.8.1/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../../../src/gcc-4.8.1/configure --build=x86_64-w64-mingw32 --enable-targets=all --enable-languages=ada,c,c++,fortran,lto,objc,obj-c++ --enable-libgomp --enable-lto --enable-graphite --enable-cxx-flags=-DWINPTHREAD_STATIC --enable-libstdcxx-debug --enable-threads=posix --enable-version-specific-runtime-libs --enable-fully-dynamic-string --enable-libstdcxx-threads --enable-libstdcxx-time --with-gnu-ld --disable-werror --disable-nls --disable-win32-registry --prefix=/mingw64tdm --with-local-prefix=/mingw64tdm --with-pkgversion=tdm64-2 --with-bugurl=http://tdm-gcc.tdragon.net/bugs
Thread model: posix
gcc version 4.8.1 (tdm64-2) 

解决方案

This standard-conforming program also crashes, and usually much faster:

#include <iostream>
#include <future>

int main() {
  try {
    for (;;) {
      std::async(std::launch::async, []{}).get();
    }
  } catch(...) { std::cout << "Something threw\n"; }
}

It's a bug in the implementation.

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