我已经进行了一些谷歌搜索，并在堆栈溢出中看到了与此问题类似的问题，但是在理解导致该问题的原因/解决方案时遇到了麻烦。给定以下在ThreadPool.hpp中声明的类，我得到以下2个错误:
错误1错误C2248:'std::mutex::mutex':无法访问在类'std::mutex'中声明的私有(private)成员c:\users\jesse\documents\school\summer学期2012\并发处理\project 2\ultra_grep v2\ultra_grep\threadpool.hpp 39 1 ultra_grep2
错误2错误C2248:'std::condition_variable::condition_variable':无法访问在类'std::condition_variable'中声明的私有(private)成员c:\users\jesse\documents\school\summer 2012年学期\并发处理\项目2 v2\ultra_grep\threadpool.hpp 39 1 ultra_grep2
class ThreadPool
{
private:
std::queue<std::string> _consoleTasks;
std::queue<std::tr2::sys::path> _tasks;
std::map<std::string, std::vector<GrepMatch>> _grepMatches;
int _nThreads, _fileMatches, _totalMatches, _workingThreads;
std::vector<thread> _threads;
Arguments _args;
std::mutex _taskMutex, _wakeMutex, _consoleMutex, _threadCountMutex;
std::condition_variable _wakeCondition;
public:
ThreadPool( int threads, Arguments args );
~ThreadPool() {};
void GrepFunc();
void ConsoleFunc();
void SearchFile( std::string );
void SearchFileVerbose( std::string );
void DisplayGrepResults();
queue<std::tr2::sys::path> Tasks() { return _tasks; }
};
以及在ThreadPool.cpp内部实现的代码:
#include "ThreadPool.hpp"
using namespace std;
namespace fs = std::tr2::sys;
ThreadPool::ThreadPool( int threads, Arguments args )
: _nThreads( threads ), _args( args ), _fileMatches( 0 ), _totalMatches( 0 ), _workingThreads( 0 )
{
for( int i = 0; i < _nThreads; ++i )
{
_threads.push_back( thread( &ThreadPool::GrepFunc, this ) );
_tasks.push( args.root() );
++_workingThreads;
_wakeCondition.notify_one();
}
for( auto& t : _threads )
{
t.join();
}
DisplayGrepResults();
}
void ThreadPool::GrepFunc()
{
// implement a barrier()
while( !_workingThreads )
{
{ unique_lock<mutex> lk( _wakeMutex );
_wakeCondition.wait( lk ); }
while( !_tasks.empty() )
{
fs::path task;
bool gotTask = false;
{
lock_guard<mutex> tl( _taskMutex );
if( !_tasks.empty() )
{
{ lock_guard<mutex> tc( _threadCountMutex );
++_workingThreads; }
task = _tasks.front();
_tasks.pop();
gotTask = true;
}
}
if( gotTask )
{
if( fs::is_directory( task ) )
{
for( fs::directory_iterator dirIter( task ), endIter; dirIter != endIter; ++dirIter )
{
if( fs::is_directory( dirIter->path() ) )
{
{ lock_guard<mutex> tl( _taskMutex );
_tasks.push( dirIter->path() ); }
_wakeCondition.notify_one();
}
else
{
for( auto& e : _args.extensions() )
{
if( !dirIter->path().extension().compare( e ) )
{
{ lock_guard<mutex> tl( _taskMutex );
_tasks.push( dirIter->path() ); }
_wakeCondition.notify_one();
//SearchFile( dirIter->path() );
}
}
}
}
}
else
{
for( auto& e : _args.extensions() )
{
if( !task.extension().compare( e ) )
{
if( _args.is_verbose() )
SearchFile( task );
else
SearchFileVerbose( task );
}
}
}
{ lock_guard<mutex> tc( _threadCountMutex) ;
--_workingThreads; }
}
}
}
}
void ThreadPool::SearchFileVerbose( string path )
{
fstream file;
file.open( path );
if( !file )
{
// error handling
}
else
{
{
lock_guard<mutex> cm( _consoleMutex );
cout << "\nGrepping: " << path << endl;
int lineNumber = 1;
string line;
vector<GrepMatch> matches;
while( getline( file, line ) )
{
int lineMatches = 0;
sregex_token_iterator end;
for (sregex_token_iterator i(line.cbegin(), line.cend(), _args.regular_expression() );
i != end;
++i)
{
++lineMatches;
}
if( lineMatches > 0 )
{
GrepMatch match = GrepMatch( lineNumber, lineMatches, line );
matches.push_back( match );
cout << "Matched " << lineMatches << ": " << path << " [" << lineNumber << "] " << line << endl;
}
++lineNumber;
}
if( !matches.empty() )
{
_grepMatches[ path ] = matches;
}
}
}
}
我在互斥体和condition_variable上都收到错误消息，说它们无法访问在类内部声明的私有(private)成员。据我了解，这是指复制构造函数？尽管我不明白为什么会这样做，但我却看不到我要在哪里复制，因为他们只是类的私有(private)成员。
根据最初的注释，我仅实例化ThreadPool的单个实例，并且不会将其复制到任何地方。我唯一想碰互斥的唯一机会是在我的类的.cpp实现中。
谁能帮助我更好地了解为什么会发生这种情况？
对于那些感兴趣的人是编译器输出:
1>------ Build started: Project: ultra_grep2, Configuration: Debug Win32 ------
1> ultra_grep_main.cpp
1> Unknown compiler version - please run the configure tests and report the results
1>c:\users\jesse\documents\school\summer semester 2012\concurrent processing\project 2\ultra_grep v2\ultra_grep\threadpool.hpp(39): error C2248: 'std::mutex::mutex' : cannot access private member declared in class 'std::mutex'
1> c:\program files (x86)\microsoft visual studio 11.0\vc\include\mutex(116) : see declaration of 'std::mutex::mutex'
1> c:\program files (x86)\microsoft visual studio 11.0\vc\include\mutex(107) : see declaration of 'std::mutex'
1> This diagnostic occurred in the compiler generated function 'ThreadPool::ThreadPool(const ThreadPool &)'
1> c:\program files (x86)\microsoft visual studio 11.0\vc\include\mutex(116) : see declaration of 'std::mutex::mutex'
1> c:\program files (x86)\microsoft visual studio 11.0\vc\include\mutex(107) : see declaration of 'std::mutex'
1> c:\program files (x86)\microsoft visual studio 11.0\vc\include\mutex(116) : see declaration of 'std::mutex::mutex'
1> c:\program files (x86)\microsoft visual studio 11.0\vc\include\mutex(107) : see declaration of 'std::mutex'
1> c:\program files (x86)\microsoft visual studio 11.0\vc\include\mutex(116) : see declaration of 'std::mutex::mutex'
1> c:\program files (x86)\microsoft visual studio 11.0\vc\include\mutex(107) : see declaration of 'std::mutex'
1>c:\users\jesse\documents\school\summer semester 2012\concurrent processing\project 2\ultra_grep v2\ultra_grep\threadpool.hpp(39): error C2248: 'std::condition_variable::condition_variable' : cannot access private member declared in class 'std::condition_variable'
1> c:\program files (x86)\microsoft visual studio 11.0\vc\include\condition_variable(45) : see declaration of 'std::condition_variable::condition_variable'
1> c:\program files (x86)\microsoft visual studio 11.0\vc\include\condition_variable(30) : see declaration of 'std::condition_variable'
1> This diagnostic occurred in the compiler generated function 'ThreadPool::ThreadPool(const ThreadPool &)'
1> ThreadPool.cpp
1> Generating Code...
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
最佳答案
该错误在某处:
使用ThreadPool的拷贝构造函数的位置:
实际上，令我惊讶的是，编译器没有指向隐式生成拷贝构造函数的源文件中的哪一行。
在注释中，您询问复制构造函数的外观。一个更好的问题是制作ThreadPool对象的拷贝是否有意义，答案是通常没有。为了改善错误消息，您可以将复制构造函数标记为deleted，这样(希望如此)，编译器将针对需要复制的位置生成更好的错误报告:
class ThreadPool {
ThreadPool( ThreadPool const & ) = delete;
// ...
};
如果您的编译器不支持此C++ 11功能，则替代方法是声明复制构造函数而不定义它。这将在复制构造函数的使用位置触发访问错误。
关于c++ - std::mutex和condition_variable无法访问类内的私有(private)成员，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/11996916/