我有一个需要在某些窗口内工作的应用程序(在这种情况下,窗口相隔30秒)。当时间不在窗口内时,计算下一个窗口中间的时间,并且线程休眠一段时间(以毫秒为单位,使用boost::this_thread::sleep_for
)。
使用Boost 1.55,我能够在极限可靠性的范围内(+/- 100ms)击中窗户。在迁移到Boost 1.58后,我无法打到这些窗口。用boost::this_thread::sleep_for
替换std::this_thread::sleep_for
可解决问题;但是,我需要boost::thread
的可中断功能以及boost::this_thread::sleep_for
提供的中断点。
以下是一些说明问题的示例代码:
#include <boost/thread.hpp>
#include <boost/chrono.hpp>
#include <chrono>
#include <iostream>
#include <thread>
void boostThreadFunction ()
{
std::cout << "Starting Boost thread" << std::endl;
for (int i = 0; i < 10; ++i)
{
auto sleep_time = boost::chrono::milliseconds {29000 + 100 * i};
auto mark = std::chrono::steady_clock::now ();
boost::this_thread::sleep_for (sleep_time);
auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(
std::chrono::steady_clock::now () - mark);
std::cout << "Boost thread:" << std::endl;
std::cout << "\tSupposed to sleep for:\t" << sleep_time.count ()
<< " ms" << std::endl;
std::cout << "\tActually slept for:\t" << duration.count ()
<< " ms" << std::endl << std::endl;
}
}
void stdThreadFunction ()
{
std::cout << "Starting Std thread" << std::endl;
for (int i = 0; i < 10; ++i)
{
auto sleep_time = std::chrono::milliseconds {29000 + 100 * i};
auto mark = std::chrono::steady_clock::now ();
std::this_thread::sleep_for (sleep_time);
auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(
std::chrono::steady_clock::now () - mark);
std::cout << "Std thread:" << std::endl;
std::cout << "\tSupposed to sleep for:\t" << sleep_time.count ()
<< " ms" << std::endl;
std::cout << "\tActually slept for:\t" << duration.count ()
<< " ms" << std::endl << std::endl;
}
}
int main ()
{
boost::thread boost_thread (&boostThreadFunction);
std::this_thread::sleep_for (std::chrono::seconds (10));
std::thread std_thread (&stdThreadFunction);
boost_thread.join ();
std_thread.join ();
return 0;
}
以下是将Boost 1.58作为包含目录引用并在我的工作站上运行时的输出(Windows 7 64位):
Starting Boost thread
Starting Std thread
Boost thread:
Supposed to sleep for: 29000 ms
Actually slept for: 29690 ms
Std thread:
Supposed to sleep for: 29000 ms
Actually slept for: 29009 ms
Boost thread:
Supposed to sleep for: 29100 ms
Actually slept for: 29999 ms
Std thread:
Supposed to sleep for: 29100 ms
Actually slept for: 29111 ms
Boost thread:
Supposed to sleep for: 29200 ms
Actually slept for: 29990 ms
Std thread:
Supposed to sleep for: 29200 ms
Actually slept for: 29172 ms
Boost thread:
Supposed to sleep for: 29300 ms
Actually slept for: 30005 ms
Std thread:
Supposed to sleep for: 29300 ms
Actually slept for: 29339 ms
Boost thread:
Supposed to sleep for: 29400 ms
Actually slept for: 30003 ms
Std thread:
Supposed to sleep for: 29400 ms
Actually slept for: 29405 ms
Boost thread:
Supposed to sleep for: 29500 ms
Actually slept for: 29999 ms
Std thread:
Supposed to sleep for: 29500 ms
Actually slept for: 29472 ms
Boost thread:
Supposed to sleep for: 29600 ms
Actually slept for: 29999 ms
Std thread:
Supposed to sleep for: 29600 ms
Actually slept for: 29645 ms
Boost thread:
Supposed to sleep for: 29700 ms
Actually slept for: 29998 ms
Std thread:
Supposed to sleep for: 29700 ms
Actually slept for: 29706 ms
Boost thread:
Supposed to sleep for: 29800 ms
Actually slept for: 29998 ms
Std thread:
Supposed to sleep for: 29800 ms
Actually slept for: 29807 ms
Boost thread:
Supposed to sleep for: 29900 ms
Actually slept for: 30014 ms
Std thread:
Supposed to sleep for: 29900 ms
Actually slept for: 29915 ms
我希望std::thread
和boost::thread
能够在相同的时间内睡觉;然而,当被要求睡了29.1 - 29.9秒时,boost::thread
似乎想要睡30秒。我是否滥用boost::thread
界面,或者这是自1.55以来引入的错误?
答案 0 :(得分:6)
我是将上述更改提交给Boost.Thread的人。 1.58的这一变化是在与Boost社区和微软进行了一段时间的协商之后设计的,并且导致移动设备上的电池寿命大大改善。 C ++标准不保证任何定时等待实际等待,或等待正确的时间段,或任何接近正确的时间段。因此,为了假定定时等待工作或准确而编写的任何代码都是错误的。未来的Microsoft STL可能会对Boost.Thread进行类似的更改,因此STL行为与Boost.Thread相同。我可能会在任何非实时操作系统上添加它,任何定时等待本质上都是不可预测的,任何时候都可能比请求时间大得多。因此,社区认为这种变化有助于暴露STL的错误使用。
此更改允许Windows可选地将计时器延迟一定量。它可能实际上并没有这样做,实际上只是尝试延迟常规中断,作为最新版Windows上无滴答内核设计的一部分。即使您指定了几周的容差,因为正确的截止日期始终发送到Windows,在计时器到期后发生的下一个系统中断将始终触发计时器,因此没有计时器最多会延迟超过几秒钟。
此更改修复的一个错误是系统睡眠问题。以前的实现可能会被系统睡眠混淆,因为定时等待永远不会被唤醒(好吧,他们会在29天内)。这个实现正确地处理系统休眠,并且使用由系统休眠引起的Boost.Thread的代码随机挂起现在已成为过去。
最后,我个人认为定时等待需要STL中的硬度/柔软度保证。然而,这是一个非常大的变化。即使实施,除了在硬实时操作系统上,定时等待的硬度只能是最好的努力。这就是为什么他们首先被排除在C ++标准之外,因为在移动设备功耗被认为足以修改API之前,C ++ 11已经完成。
尼尔
答案 1 :(得分:0)
从Windows上的Boost 1.58开始,sleep_for()
利用SetWaitableTimerEx()
(而非SetWaitableTimer()
)传递容差时间以利用合并计时器。
在libs / thread / src / win32 / thread.cpp中,容差是睡眠时间的5%或32 ms,以较大者为准:
// Preferentially use coalescing timers for better power consumption and timer accuracy
if(!target_time.is_sentinel())
{
detail::timeout::remaining_time const time_left=target_time.remaining_milliseconds();
timer_handle=CreateWaitableTimer(NULL,false,NULL);
if(timer_handle!=0)
{
ULONG tolerable=32; // Empirical testing shows Windows ignores this when <= 26
if(time_left.milliseconds/20>tolerable) // 5%
tolerable=time_left.milliseconds/20;
LARGE_INTEGER due_time=get_due_time(target_time);
bool const set_time_succeeded=detail_::SetWaitableTimerEx()(timer_handle,&due_time,0,0,0,&detail_::default_reason_context,tolerable)!=0;
if(set_time_succeeded)
{
timeout_index=handle_count;
handles[handle_count++]=timer_handle;
}
}
}
由于29.1秒的5%是1.455秒,这就解释了为什么使用boost::sleep_for
的睡眠时间是如此不准确。
答案 2 :(得分:0)
如果我需要sleep_for的可中断性,我会使用此代码作为解决方法:
::Sleep(20);
boost::this_thread::interruption_point();