C++ std::vector，线程安全，多线程
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std::vector, thread-safety, multi-threading
提问by 2607
I am using std::vector as shared data in a multi-threaded application. I encapsulate the thread inside a class, e.g.,
我在多线程应用程序中使用 std::vector 作为共享数据。我将线程封装在一个类中，例如，
class ABC {
public:
double a, b, c;
};
boost::mutex mutex1;
class XYZ {
public:
XYZ(vector<ABC> & pVector) {
ptrVector = &pVector;
m_thread = boost::thread(&XYZ::Start, this);
}
~XYZ() {}
void Start();
public:
vector<ABC> * ptrVector;
boost::thread m_thread;
};
void XYZ::Start() {
try {
while(1) {
boost::this_thread::interruption_point();
for (unsigned int i=0; i<ptrVector->size(); i++) {
{
boost::mutex::scoped_lock lock(mutex1);
ptrVector->at(i).a = double(rand())/10000;
ptrVector->at(i).b = double(rand())/10000;
ptrVector->at(i).c = double(rand())/10000;
}
}
}
}
catch(boost::thread_interrupted) {}
catch(std::exception) {}
}
When I close the application, sometimes, in the debug, there will be 2 error messages, sometimesthere will be no error messages. I often heard people talking about std::vector being not thread-safe, is this one of the cases? I am using Visual Studio 2008, boost thread, the size of the vector is fixed. Can anyone also offer some advice on how to use std::vector in a multi-threaded application.
当我关闭应用程序时，有时，在调试中，会出现 2 条错误消息，有时不会有任何错误消息。我经常听到人们谈论 std::vector 不是线程安全的，这是其中一种情况吗？我使用的是 Visual Studio 2008，boost 线程，向量的大小是固定的。任何人都可以就如何在多线程应用程序中使用 std::vector 提供一些建议。
- First-chance exception at 0x7688b9bc in ETP.exe: Microsoft C++ exception: std::out_of_range at memory location 0x02d8f7bc..
- First-chance exception at 0x00e916e0 in ETP.exe: 0xC0000005: Access violation reading location 0x00000008.
- Second Chance Assertion Failed: File c:\program files (x86)\microsoft visual studio 9.0\vc\include\vector, Line Second Chance Assertion Failed: File c:\program files (x86)\microsoft visual studio 9.0\vc\include\vector98
- ETP.exe 中 0x7688b9bc 处的第一次机会异常：Microsoft C++ 异常：std::out_of_range 在内存位置 0x02d8f7bc..
- ETP.exe 中 0x00e916e0 处的第一次机会异常：0xC0000005：访问冲突读取位置 0x00000008。
- Second Chance Assertion Failed: File c:\program files (x86)\microsoft visual studio 9.0\vc\include\vector, Line Second Chance Assertion Failed: File c:\program files (x86)\microsoft visual studio 9.0\vc\include \vector98
Thanks.
谢谢。
回答by Dietmar Kühl
Actually, it is absolutelypointless to state Xis or is not thread-safe! You need to qualify for what kind of uses. For example, hardly any class will be "thread-safe" when it is somehow used in one thread and destroyed in another.
实际上，声明线程安全或不是线程安全是完全没有意义的X！你需要符合什么样的用途。例如，当某个类以某种方式在一个线程中使用并在另一个线程中销毁时，几乎没有任何类是“线程安全的”。
That said, the statement that std::vector<T>is not thread- safe, independent of how often it is repeated, is wrong. However, it seems most people neither understand nor appreciate the thread-safety guarantees given. std::vector<T>is thread-safe in the following sense:
也就是说，与std::vector<T>重复频率无关的不是线程安全的语句是错误的。然而，似乎大多数人既不理解也不欣赏所提供的线程安全保证。std::vector<T>在以下意义上是线程安全的：
- You can read a vector object from multiple threads simultaneously.
- If there is one thread changing a vector object, there shall be neither concurrent readers or writers.
- Accesses to a vector object don't interfere with other vector objects.
- 您可以同时从多个线程读取向量对象。
- 如果有一个线程改变了一个向量对象，则不应有并发的读取者或写入者。
- 对矢量对象的访问不会干扰其他矢量对象。
This applies to vector structure itself. Accesses to contained object are bound to whatever rules are imposed on them. These are apparently not the thread-safety guarantees many people have in mind but anything stronger won't work with the container interface.
这适用于向量结构本身。对包含对象的访问受强加于它们的任何规则的约束。这些显然不是许多人想到的线程安全保证，但任何更强大的东西都不适用于容器接口。
回答by Clark Gaebel
You call ptrVector->size()without locking it first. This could easily be the cause of your problems. Make sure to lock your vector before any reads or writes.
您ptrVector->size()无需先锁定即可调用。这很容易成为您出现问题的原因。确保在任何读取或写入之前锁定您的向量。
回答by screig
Maybe you could use this instead?
也许你可以用这个代替？
concurrent_vector... from the Intel Threading Building Blocks
concurrent_vector... 来自英特尔线程构建模块
