如何在类上下文中使用std :: mutex [英] How to use a std::mutex in a class context

问题描述

我有一些麻烦使用C ++ 11 std :: mutex

i'm having some trouble using a C++11 std::mutex

在我的类我有一个变量名为信号量std :: mutex类型。

in my class I have a variable called semaphore of type std::mutex.

所以我将我的semaphore.lock（）和semaphore.unlock（）放在我的关键部分之前和之后

So I positioned my semaphore.lock() and semaphore.unlock() before and after my critical section

class Database {
public:
Database(string, string, string, string);
virtual ~Database();

struct sMyHome getMyHome(void);
struct sPhysical getPhysical(int);
struct sSystemInfo getSystemInfo(void);
void commitSystemInfo(struct sSystemInfo);
struct sTSensors getTSensors(int);
struct sWireless getWireless(int);
struct sWirelessConf getWirelessConf(int);
struct sWirelessStatus getWirelessStatus(int);

private:
void queryMyHome(void);
void queryPhysical(int);
void querySystemInfo(void);
void queryTSensors(int ID);
void queryWireless(int ID);
void queryWirelessConf(int ID);
void queryWirelessStatus(int ID);
string toString(int);

struct sMyHome MyHome;
struct sPhysical Physical[4];
struct sSystemInfo SystemInfo;
struct sTSensors TSensors[32];
struct sWireless Wireless[64];
struct sWirelessConf WirelessConf[64];
struct sWirelessStatus WirelessStatus[64];

MYSQL *connection;
mutex semaphore;
};

这是main的一部分，我在其中检索错误：

this is part of the main, where I retrieve the error:

 Database db = Database("192.168.1.10", "****", "******", "******");

但交叉编译器说

../main.cpp:8:73: error: use of deleted function 'Database::Database(const Database&)'
  Database db = Database("192.168.1.10", "root", "raspberry", "DomoHome2");
                                                                     ^
In file included from ../main.cpp:2:0:
../Database.h:79:7: note: 'Database::Database(const Database&)' is implicitly deleted      because the default definition would be ill-formed:
 class Database {
   ^
../Database.h:79:7: error: use of deleted function 'std::mutex::mutex(const std::mutex&)'
 In file included from ../Database.h:12:0,
             from ../main.cpp:2:
/Volumes/rpi-crosscompiler-toolchain/arm-none-linux-gnueabi/arm-none-linux-gnueabi/include/c++/4.8.2/mutex:128:5: error: declared here
 mutex(const mutex&) = delete;
 ^
make: *** [main.o] Error 1

这是我的构造函数：

Database::Database(string Address, string Username, string Password, string Database) {
// TODO Auto-generated constructor stub
connection = mysql_init(NULL);
mysql_real_connect(connection, Address.c_str(), Username.c_str(), Password.c_str(), Database.c_str(), 0, NULL, 0);
}

推荐答案

std :: mutex 既不可复制也不可移动。在你的类中包含一个，需要你的类变成不可复制（可移动）。如果你希望你的类是可复制的或可移动的，你必须告诉编译器你的类的对象是如何被复制或移动通过自己实现复制/移动构造/赋值。 例如：

std::mutex is neither copyable nor movable. Including one in your class necessitates that your class becomes non-copyable (-movable) as well. If you want your class to be copyable or movable, you will have to tell the compiler how objects of your class are to be copied or moved by implementing copy/move construction/assignment yourself. For example:

class synchronized_int {
  mutable std::mutex mtx;
  int value;
public:
  synchronized_int(int v = 0) : value(v) {}

  // Move initialization
  synchronized_int(synchronized_int&& other) {
    std::lock_guard<std::mutex> lock(other.mtx);
    value = std::move(other.value);
    other.value = 0;
  }

  // Copy initialization
  synchronized_int(const synchronized_int& other) {
    std::lock_guard<std::mutex> lock(other.mtx);
    value = other.value;
  }

  // Move assignment
  synchronized_int& operator = (synchronized_int&& other) {
    std::lock(mtx, other.mtx);
    std::lock_guard<std::mutex> self_lock(mtx, std::adopt_lock);
    std::lock_guard<std::mutex> other_lock(other.mtx, std::adopt_lock);
    value = std::move(other.value);
    other.value = 0;
    return *this;
  }

  // Copy assignment
  synchronized_int& operator = (const synchronized_int& other) {
    std::lock(mtx, other.mtx);
    std::lock_guard<std::mutex> self_lock(mtx, std::adopt_lock);
    std::lock_guard<std::mutex> other_lock(other.mtx, std::adopt_lock);
    value = other.value;
    return *this;
  }
};

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