Program hangs in Visual Studio debugger

Question

Some background: I am trying to track a bug which is causing me major headaches. After many dead ends (see this question) I finally ended up with this code:

#include <thread>
#include <vector>
#include <iosfwd>
#include <sstream>
#include <string>
#include <windows.h>

int main()
{
    SRWLOCK srwl;
    InitializeSRWLock(&srwl);
    for(size_t i=0;i<1000;++i)
    {
        std::vector<std::thread>threads;
        for(size_t j=0;j<100;++j)
        {
            OutputDebugString(".");
            threads.emplace_back([&](){
                AcquireSRWLockExclusive(&srwl);
                //Code below modifies the probability to see the bug.
                std::this_thread::sleep_for(std::chrono::microseconds(1));
                std::wstringstream wss;
                wss<<std::this_thread::get_id();
                wss.str();
                //Code above modifies the probability to see the bug.
                ReleaseSRWLockExclusive(&srwl);});
        }
        for(auto&t:threads){t.join();}
        OutputDebugString((std::to_string(i)+"\n").data());
    }
    return 0;
}

When I run this code inside VS 2013 debugger the program hangs with an output like this one:

....................................................................................................0
....................................................................................................1
....................................................................................................2
...........................

Strangely enough, If I pause the debugger and inspect what is going on, one of the threads is inside AcquireSRWLockExclusive (in NtWaitForAlertByThreadId) apparently there is no reason why the program is hanging. When I click resume, the program happily continues and print some more stuff until it is blocked again.

Do you have any Idea what is going on here ?

Some more info:

• As far as I can tell, this bug only exists on Windows 8.1.
• I tried VS2013.4 and VS2015 RC.
• I could reproduce it on two different computers under Windows 8.1.
• One of the machine was formatted, the RAM, CPU and Disk tested (I thought of a malfunction because at first I could only observe the bug on this particular machine)
• I could never reproduce it on Windows 7.
• It may be useful to modify the code between the comments to observe the bug. When I added the microsecond sleep, I could at last reproduce the bug on another computer.
• With VS2015 RC I could reproduce the same behavior with a simple std::mutex. On VS2013 however the SRWLOCK seems mandatory to observe the bug.

Answer 1

This issue is caused by an OS scheduler bug introduced in the spring 2014 update to Windows 8.1. A hotfix for this problem was released in May 2015 and available at https://support.microsoft.com/en-us/kb/3036169.