如何在 c++ 中正确使用 ifstreams，带有子进程并避免泄漏?
How to correctly use ifstreams in c++, with subprocess and avoid leaks?
我正在尝试创建一个比萨店模拟来了解有关子进程和线程的更多信息。我想最大限度地避免内存泄漏。
现在，当我只创建一个厨房时，没有错误，但是当我创建 2 个或更多时，我在破坏时遇到了一些 ifstreams 和 ofstreams 的泄漏。
有主()：
int main(int argc __attribute__((unused)), char const *argv[] __attribute__((unused)))
{
Kitchen k(0, 2, 30);
Kitchen k2(0, 2, 30);
return 0;
}
厨房.hpp：
class Kitchen {
private:
bool _IsFull = false;
int _Pid = 0;
int _CookTime;
int _MaxCooks;
long _RefreshDelay;
double _MaxTime = 5;
unsigned long int _QueueSize;
std::ofstream _Opipe;
std::ifstream _Ipipe;
unsigned int _Door = 0;
std::string _FallIn = "";
std::string _FallOut = "";
void CooksAwakening (void);
void CleaningTime (void);
void OpenPipe (void);
void Quit (void);
void Run (void);
public:
explicit Kitchen (int CookingTime, int MaxCooks, long RefreshDelay);
virtual ~Kitchen ();
bool IsFull () const { return _IsFull; }
int GetPid () const { return _Pid; }
};
还有厨房.cpp：
int Knum = 0;
Kitchen::Kitchen(int CookingTime, int MaxCooks, long RefreshDelay)
: _CookTime(CookingTime), _MaxCooks(MaxCooks), _RefreshDelay(RefreshDelay), _QueueSize(_MaxCooks * 2)
{
OpenPipe();
_Pid = fork();
if (_Pid == 0) {
_Opipe.open(_FallIn.c_str(), std::ostream::out);
_Ipipe.open(_FallOut.c_str(), std::istream::in);
Run();
} else {
_Ipipe.open(_FallIn.c_str(), std::istream::in); // Valgrind point this line
_Opipe.open(_FallOut.c_str(), std::ostream::out); // Valgrind point this line too
}
}
Kitchen::~Kitchen()
{
if (_Pid == 0) {
} else {
_Opipe << "QUIT" << std::endl;
_Ipipe.close();
_Opipe.close();
unlink(_FallIn.c_str());
unlink(_FallOut.c_str());
}
}
void Kitchen::Quit(void)
{
CleaningTime();
_Ipipe.close();
_Opipe.close();
exit(0);
}
void Kitchen::CleaningTime(void)
{
while (!_Cooks.empty()) {
_Cooks.pop_back();
}
while (!_PizzaQueue.empty()) {
_PizzaQueue.pop_back();
}
_Cooks.shrink_to_fit();
_PizzaQueue.shrink_to_fit();
}
void Kitchen::OpenPipe(void)
{
std::cout << "Kit Open Pipest" << getpid() << 'n';
std::ostringstream oss1;
oss1 << "/tmp/kint" << Knum;
_FallIn = oss1.str();
std::ostringstream oss2;
oss2 << "/tmp/kout" << Knum;
_FallOut = oss2.str();
_Door = Knum;
++Knum;
if (mkfifo(_FallOut.c_str(), 0666) != 0) {
perror ("mkfifo1");
exit(84);
}
if (mkfifo(_FallIn.c_str(), 0666) != 0) {
perror("mkfifo2");
exit(84);
}
}
void Kitchen::Run(void)
{
std::string cmd;
while (_Ipipe >> cmd)
{
if (cmd == "QUIT") {
Quit();
}
}
Quit();
}
这是瓦尔格林德的结果：
total heap usage: 36 allocs, 32 frees, 109,712 bytes allocated
==20890==
==20890== 552 bytes in 1 blocks are still reachable in loss record 1 of 4
==20890== at 0x483880B: malloc (vg_replace_malloc.c:309)
==20890== by 0x4C1536E: __fopen_internal (in /usr/lib64/libc-2.28.so)
==20890== by 0x4925AA3: std::__basic_file<char>::open(char const*, std::_Ios_Openmode, int) (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x496789D: std::basic_filebuf<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode) (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x4967A73: std::basic_ifstream<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode) (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x4052F2: WorkSpace::Kitchen::Kitchen(int, int, long) (Kitchen.cpp:36)
==20890== by 0x40250C: main (main.cpp:46)
==20890==
==20890== 552 bytes in 1 blocks are still reachable in loss record 2 of 4
==20890== at 0x483880B: malloc (vg_replace_malloc.c:309)
==20890== by 0x4C1536E: __fopen_internal (in /usr/lib64/libc-2.28.so)
==20890== by 0x4925AA3: std::__basic_file<char>::open(char const*, std::_Ios_Openmode, int) (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x496789D: std::basic_filebuf<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode) (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x4967AC3: std::basic_ofstream<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode) (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x40531C: WorkSpace::Kitchen::Kitchen(int, int, long) (Kitchen.cpp:37)
==20890== by 0x40250C: main (main.cpp:46)
==20890==
==20890== 8,192 bytes in 1 blocks are still reachable in loss record 3 of 4
==20890== at 0x4839593: operator new[](unsigned long) (vg_replace_malloc.c:433)
==20890== by 0x496358F: std::basic_filebuf<char, std::char_traits<char> >::_M_allocate_internal_buffer() (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x49678B5: std::basic_filebuf<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode) (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x4967A73: std::basic_ifstream<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode) (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x4052F2: WorkSpace::Kitchen::Kitchen(int, int, long) (Kitchen.cpp:36)
==20890== by 0x40250C: main (main.cpp:46)
==20890==
==20890== 8,192 bytes in 1 blocks are still reachable in loss record 4 of 4
==20890== at 0x4839593: operator new[](unsigned long) (vg_replace_malloc.c:433)
==20890== by 0x496358F: std::basic_filebuf<char, std::char_traits<char> >::_M_allocate_internal_buffer() (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x49678B5: std::basic_filebuf<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode) (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x4967AC3: std::basic_ofstream<char, std::char_traits<char> >::open(char const*, std::_Ios_Openmode) (in /usr/lib64/libstdc++.so.6.0.25)
==20890== by 0x40531C: WorkSpace::Kitchen::Kitchen(int, int, long) (Kitchen.cpp:37)
==20890== by 0x40250C: main (main.cpp:46)
==20890==
==20890== LEAK SUMMARY:
==20890== definitely lost: 0 bytes in 0 blocks
==20890== indirectly lost: 0 bytes in 0 blocks
==20890== possibly lost: 0 bytes in 0 blocks
==20890== still reachable: 17,488 bytes in 4 blocks
==20890== suppressed: 0 bytes in 0 block
我使用 gcc 和这些标志进行编译： -墙 -Wextra -Weffc++
瓦尔格林德命令如下： 瓦尔格林德 --泄漏检查=完整 --显示泄漏种类=全部 ./plazza
所示代码在子进程中执行以下内容：
void Kitchen::Quit(void)
{
CleaningTime();
_Ipipe.close();
_Opipe.close();
exit(0);
}
即使手动关闭打开的流，这些对象此时仍然存在，并且exit(0)立即终止进程。
尽管实际文件已关闭，但流对象仍然存在，并且仍然为其内部流缓冲区分配了一些内存。只有当这些对象被正确销毁时，该内存才会释放，这不会通过exit(0)发生。
exit(0)是一个标准的 C 库函数，它不知道任何C++对象。它只是从高轨道上破坏了这个过程。
valgrind检测到子进程在没有完全释放其分配的所有内存的情况下终止，并报告该情况。
为了"正确使用 ifstreams 与子进程C++并避免泄漏"，子进程必须以与主进程相同的方式终止：从main()返回。这显然会在终止子流程之前销毁子流程中自动和静态范围内的所有对象。
就程序的逻辑工作方式而言，这显然提出了几个需要解决的难题。一种常见的暴力破解方法通常是抛出异常而不是exit()ing，这会被main()捕获。当然，这仅适用于结构为在引发异常时行为正确的代码。
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