std::mutex （互斥量内部实现SRWLOCK）

落日映苍穹つ 2022-04-24 13:06 256阅读 0赞

**注意：mutex windows vista 以上系统用SRWLOCK 实现，winxp用的是参考 rtlocks.cpp   
critical\_section  调用InterlockedCompareExchangePointer 来实现的 **

Windows 7下  + vs2015 微软最新c++11  std::mutex 内部实现剖析
    
    一、	先说说微软c++11 里面实现的代码，废话不多说，上例子验证猜想
    Vs2015新建一个控制台程序，代码如下：
    // mutex_d.cpp : 定义应用程序的入口点。
    //此段代码是死锁程序，方便跳转到内部实现！！！！
    #include "stdafx.h"
    #include "mutex_d.h"
    #include<thread>
    #include<mutex>
    #include<iostream>
    
    std::mutex test;
    
    
    void t_fun()
    {
    	test.lock();//重入导致死锁
    	std::cout << "hello\n";
    	test.unlock();
    }
    
    int main(int argc, TCHAR* argv[])
    {
    	test.lock();
    	std::thread th(t_fun);
    	th.join();
    
    	return 0;
    }
    
    /*
    读写锁 SRWLOCK 使用方法
    
    SRWLOCK srw;
    
    InitializeSRWLock(&srw);
    //一旦初始化完成，就可以对写入线程调用AcquireSRWLockExclusive()函数和ReleaseSRWLockExclusive()函数
    AcquireSRWLockExclusive(&srw);
    //...写入数据,写入东西的时候该线程独占，其他任何线程不可进入
    ReleaseSRWLockExclusive(&srw);
    
    //对于只读线程可以调用AcquireSRWLockShared()函数和ReleaseSRWLockShared()函数, 如下
    AcquireSRWLockShared(&srw);
    //..读取数据,如果这时没有写入数据则多个读取线程可以进行
    ReleaseSRWLockShared)&srw);
    
    */
    运行程序会导致卡主不动，此时贴上堆栈：
     
    	ntdll.dll!_ZwWaitForKeyedEvent@16 ()	 
     	ntdll.dll!_RtlAcquireSRWLockExclusive@4 ()	 
     	msvcp140d.dll!__crtAcquireSRWLockExclusive(_RTL_SRWLOCK * pLock=0x00ff0388) 行 605	 
     	 	 	 	 	 	msvcp140d.dll!Concurrency::details::stl_critical_section_win7::lock() 行 166	 
     	 msvcp140d.dll!mtx_do_lock(_Mtx_internal_imp_t * mtx=0x00ff0380, const xtime * target=0x00000000) 行 100	 
     	 msvcp140d.dll!_Mtx_lock(_Mtx_internal_imp_t * mtx=0x00ff0380) 行 186	 
     	 mutex_d.exe!std::_Mtx_lockX(_Mtx_internal_imp_t * _Mtx=0x00ff0380) 行 70	 
     	 mutex_d.exe!std::_Mutex_base::lock() 行 43	 
     	 mutex_d.exe!t_fun() 行 16	 
     	 mutex_d.exe!std::_Invoker_functor::_Call<void (__cdecl*)(void)>(void(*)() && _Obj=0x00fe1235) 行 1375	 
     	 mutex_d.exe!std::invoke<void (__cdecl*)(void)>(void(*)() && _Obj=0x00fe1235) 行 1443	 
     	 mutex_d.exe!std::_LaunchPad<std::unique_ptr<std::tuple<void (__cdecl*)(void)>,std::default_delete<std::tuple<void (__cdecl*)(void)> > > >::_Execute<0>(std::tuple<void (__cdecl*)(void)> & _Tup={...}, std::integer_sequence<unsigned int,0> __formal={...}) 行 240	 
     	 mutex_d.exe!std::_LaunchPad<std::unique_ptr<std::tuple<void (__cdecl*)(void)>,std::default_delete<std::tuple<void (__cdecl*)(void)> > > >::_Run(std::_LaunchPad<std::unique_ptr<std::tuple<void (__cdecl*)(void)>,std::default_delete<std::tuple<void (__cdecl*)(void)> > > > * _Ln=0x0019f5d0) 行 247	 
     	 mutex_d.exe!std::_LaunchPad<std::unique_ptr<std::tuple<void (__cdecl*)(void)>,std::default_delete<std::tuple<void (__cdecl*)(void)> > > >::_Go() 行 232	 
     	 mutex_d.exe!std::_Pad::_Call_func(void * _Data=0x0019f5d0) 行 209	 
     	ucrtbased.dll!invoke_thread_procedure(unsigned int(__stdcall*)(void *) procedure=0x00fe11c2, void * const context=0x0019f5d0) 行 92	 
     	 ucrtbased.dll!thread_start<unsigned int (__stdcall*)(void *)>(void * const parameter=0x005fdd50) 行 115	 
     	 kernel32.dll!@BaseThreadInitThunk@12 ()	 
     	 ntdll.dll!___RtlUserThreadStart@8 ()	 
     	 ntdll.dll!__RtlUserThreadStart@8 ()	
    
    
    注意：如下三个函数其实是一样的！！！！！
    {
        Kernel32.dll !AcquireSRWLockExclusive( PSRWLOCK SRWLock
    	ntdll.dll!_RtlAcquireSRWLockExclusive@4 ()	 
     	msvcp140d.dll!__crtAcquireSRWLockExclusive(_RTL_SRWLOCK * SRWLock)
    }
    结论 windows下  std:: mutex内部使用了读写锁SRWLOCK 和 临界区相似的功能！！
    源码位置：
    Microsoft Visual Studio 14.0\VC\crt\src\stl\primitives.h
    virtual void lock() override
            {
                __crtAcquireSRWLockExclusive(&m_srw_lock);
            }