C++随笔：.NET CoreCLR之corleCLR核心探索之coreconsole（2）

　　这篇文章是上篇的续集，本文将会继续介绍coreconsole.cpp里面的逻辑。也许大家会看一些CLR的书，我承认我没有看过，因为我觉得一个人，他再NB，那也是他自己的眼光，而且说句难听的，CLR也不是那个写书的人一个人完成的项目，所以他的眼光，我个人看来，也还是很有限的。 PS:谢谢@Grid Science 的建议

　　承接上篇文章的HostEnvironment，宿主环境：个人认为HOST是指的Windows内核。但是CLR有一个缺点，就是它并不是一个跨平台的，所以广义的说HOST应该是“操作系统内核”；下面我们来看看LoadCoreCLR这个方法，这个方法的核心宗旨就是从动态链接库当中得到CLR，如果出错，会记日志；

//尝试去“载入”CoreCLR,它带有一个coreCLR的路径
HMODULE TryLoadCoreCLR(const wchar_t* directoryPath) {

//coreclr 路径
wchar_t coreCLRPath[MAX_LONGPATH];
//把形参赋给实参，也就是相当于coreCLRPath= directoryPath
wcscpy_s(coreCLRPath, directoryPath);
//把coreCLRDll,append到coreCLRPathd的后面，组成一个新的字符串
wcscat_s(coreCLRPath, coreCLRDll);

//日志记录开始：尝试从路径载入CoreCLR
*m_log << W("Attempting to load: ") << coreCLRPath << Logger::endl;

//LoadLibraryEx装载指定的动态链接库。
HMODULE result = ::LoadLibraryExW(coreCLRPath, NULL, 0);

//载入失败的时候，记录日志
if (!result) {
*m_log << W("Failed to load: ") << coreCLRPath << Logger::endl;
*m_log << W("Error code: ") << GetLastError() << Logger::endl;
return nullptr;
}

// Pin the module - CoreCLR.dll does not support being unloaded.

//GetModuleHandleExW是获取一个应用程序或动态链接库的模块句柄
HMODULE dummy_coreCLRModule;

//如果是GET_MODULE_HANDLE_EX_FLAG_PIN,则模块一直映射在调用该函数的进程中，直到该进程结束
if (!::GetModuleHandleExW(GET_MODULE_HANDLE_EX_FLAG_PIN, coreCLRPath, &dummy_coreCLRModule)) {
*m_log << W("Failed to pin: ") << coreCLRPath << Logger::endl;
return nullptr;
}

wchar_t coreCLRLoadedPath[MAX_LONGPATH];
::GetModuleFileNameW(result, coreCLRLoadedPath, MAX_LONGPATH);

*m_log << W("Loaded: ") << coreCLRLoadedPath << Logger::endl;

//返回动态链接库
return result;
}

　　下面是HostEnvironment的构造函数，个人觉得主要的作用还是初始化，载入CoreCLR.

public:
// The path to the directory that CoreCLR is in
//CoreCLR的路径，注意区分“模块路径”和此路径的区别
wchar_t m_coreCLRDirectoryPath[MAX_LONGPATH];

//带有log参数的构造函数，并初始化LOG和CLR运行时
HostEnvironment(Logger *logger)
: m_log(logger), m_CLRRuntimeHost(nullptr) {

// Discover the path to this exe's module. All other files are expected to be in the same directory.
//获得目录下EXE模块的路径的长度
DWORD thisModuleLength = ::GetModuleFileNameW(::GetModuleHandleW(nullptr), m_hostPath, MAX_LONGPATH);

// Search for the last backslash in the host path.

//寻找路径当中的最后一个分隔符"\\",如果找到了，就跳出循环
int lastBackslashIndex;
for (lastBackslashIndex = thisModuleLength-1; lastBackslashIndex >= 0; lastBackslashIndex--) {
if (m_hostPath[lastBackslashIndex] == W('\\')) {
break;
}
}

// Copy the directory path

//用m_hostDirectoryPath代替之前的路径目录的地址
::wcsncpy_s(m_hostDirectoryPath, m_hostPath, lastBackslashIndex + 1);

// Save the exe name
//host 的EXE文件的名字，类似文件名，不过这里我有一个疑问：
//m_hostPath是一个字符型的指针，而lastBackslashIndex+1是数字，把它们2个加起来是什么意思？
m_hostExeName = m_hostPath + lastBackslashIndex + 1;

*m_log << W("Host directory: ")  << m_hostDirectoryPath << Logger::endl;

// Check for %CORE_ROOT% and try to load CoreCLR.dll from it if it is set
//尝试从环境变量%CORE_ROOT%载入CoreCLR

//coreRoot环境变量真实路径
wchar_t coreRoot[MAX_LONGPATH];
size_t outSize;

//如果没有使用TryLoadCoreCLR方法的话，那么采用构造函数方式去初始化CoreCLR.
m_coreCLRModule = NULL; // Initialize this here since we don't call TryLoadCoreCLR if CORE_ROOT is unset.

//取环境变量的值
if (_wgetenv_s(&outSize, coreRoot, MAX_LONGPATH, W("CORE_ROOT")) == 0 && outSize > 0)
{
wcscat_s(coreRoot, MAX_LONGPATH, W("\\"));
m_coreCLRModule = TryLoadCoreCLR(coreRoot);
}
else
{
*m_log << W("CORE_ROOT not set; skipping") << Logger::endl;
*m_log << W("You can set the environment variable CORE_ROOT to point to the path") << Logger::endl;
*m_log << W("where CoreCLR.dll lives to help this executable find it.") << Logger::endl;
}

// Try to load CoreCLR from the directory that this exexutable is in
//从"目录"中尝试载入CoreCLR.
if (!m_coreCLRModule) {
m_coreCLRModule = TryLoadCoreCLR(m_hostDirectoryPath);
}

//作用同上（thisModuleLength）
if (m_coreCLRModule) {

// Save the directory that CoreCLR was found in
DWORD modulePathLength = ::GetModuleFileNameW(m_coreCLRModule, m_coreCLRDirectoryPath, MAX_LONGPATH);

// Search for the last backslash and terminate it there to keep just the directory path with trailing slash
for (lastBackslashIndex = modulePathLength-1; lastBackslashIndex >= 0; lastBackslashIndex--) {
if (m_coreCLRDirectoryPath[lastBackslashIndex] == W('\\')) {
m_coreCLRDirectoryPath[lastBackslashIndex + 1] = W('\0');
break;
}
}

} else {
*m_log << W("Unable to load ") << coreCLRDll << Logger::endl;
}
}

//析构函数，释放coreclr
~HostEnvironment() {
if(m_coreCLRModule) {
// Free the module. This is done for completeness, but in fact CoreCLR.dll
// was pinned earlier so this call won't actually free it. The pinning is
// done because CoreCLR does not support unloading.
::FreeLibrary(m_coreCLRModule);
}
}

　　下面是判断TPA列表里面的项是否有包含文件，具体作用不详。

//TPA列表的每个项是否包含文件,至少有一项是包含文件的，那么返回TRUE
//fileNameWithoutExtension:不带后缀的文件名
//rgTPAExtensions：TPA后缀,注意这里是一个指针的指针。
//countExtensions:后缀个数
bool TPAListContainsFile(wchar_t* fileNameWithoutExtension, wchar_t** rgTPAExtensions, int countExtensions)
{
if (!m_tpaList.CStr()) return false;//如果程序集路径为空，直接返回FALSE

//循环后缀。
for (int iExtension = 0; iExtension < countExtensions; iExtension++)
{
wchar_t fileName[MAX_LONGPATH];
// So that we don't match other files that end with the current file name
//不匹配其他文件结尾（和当前文件名对比）
wcscpy_s(fileName, MAX_LONGPATH, W("\\"));

//wcscat_s函数,把第三个参数添加都第一个参数的结尾
wcscat_s(fileName, MAX_LONGPATH, fileNameWithoutExtension);
wcscat_s(fileName, MAX_LONGPATH, rgTPAExtensions[iExtension] + 1);
wcscat_s(fileName, MAX_LONGPATH, W(";")); // So that we don't match other files that begin with the current file name

//类似于.NET中的Contains
if (wcsstr(m_tpaList.CStr(), fileName))
{
return true;
}
}
return false;
}

　　下面的方法是移除文件后缀的，应该是一个工具类

//移除文件后缀
void RemoveExtensionAndNi(wchar_t* fileName)
{
// Remove extension, if it exists
//如果文件存在后缀，那么久移除
wchar_t* extension = wcsrchr(fileName, W('.'));
if (extension != NULL)
{
extension[0] = W('\0');

// Check for .ni
//检测.ni文件,这种文件，我没在网上查到
size_t len = wcslen(fileName);
if (len > 3 &&
fileName[len - 1] == W('i') &&
fileName[len - 2] == W('n') &&
fileName[len - 3] == W('.') )
{
//结束字符，相当于.NET中的substring了
fileName[len - 3] = W('\0');
}
}
}

　　下面的2个方法都是加载文件到TpaList中。

// Returns the semicolon-separated list of paths to runtime dlls that are considered trusted.
// On first call, scans the coreclr directory for dlls and adds them all to the list.

//返回可信任的且分号分隔的列表给运行时
//第一次CALL的时候，搜索coreclr目录里面的所有DLL，并把它们添加到TPAList中去
const wchar_t * GetTpaList() {
if (!m_tpaList.CStr()) {

//文件后缀集合
wchar_t *rgTPAExtensions[] = {
// Probe for .ni.dll first so that it's preferred if ni and il coexist in the same dir
//如果是第一次加载 *.ni.dll文件，ni和il会有一个优先级的问题

W("*.ni.dll"),
W("*.dll"),
W("*.ni.exe"),
W("*.exe"),
};

// Add files from %CORE_LIBRARIES% if specified
//从%CORE_LIBRARIES%环境变量中加载文件，如果设定了此环境变量
wchar_t coreLibraries[MAX_LONGPATH];
size_t outSize;
if (_wgetenv_s(&outSize, coreLibraries, MAX_LONGPATH, W("CORE_LIBRARIES")) == 0 && outSize > 0)
{
wcscat_s(coreLibraries, MAX_LONGPATH, W("\\"));
AddFilesFromDirectoryToTPAList(coreLibraries, rgTPAExtensions, _countof(rgTPAExtensions));
}
else
{
*m_log << W("CORE_LIBRARIES not set; skipping") << Logger::endl;
*m_log << W("You can set the environment variable CORE_LIBRARIES to point to a") << Logger::endl;
*m_log << W("path containing additional platform assemblies,") << Logger::endl;
}

//从目录中加载文件到TpaList中
AddFilesFromDirectoryToTPAList(m_coreCLRDirectoryPath, rgTPAExtensions, _countof(rgTPAExtensions));
}

return m_tpaList.CStr(); //返回tpaList;
}

　　今天就说到这里了，下一篇跟大家预告一下，会 把GC的第三篇介绍写出来~~敬请期待哦~~~