c++11 - c++11 std::mutex 锁定同一个线程

Question

我现在正在学习（刷新）C++。作为刷新的一部分，我尝试在std::mutex下面的代码中检查我的行为。它基本上尝试做'Manual lock/ unlock'，' std::lock_guardover mutex'和' try_lockover std::mutex'。当我提到std::mutex::try_lock时，它说如果同一个线程再次尝试锁定，这是一个死锁。但我正在检查try_lock()，根据上面的链接描述，它应该给出false. 但不知何故，std::mutex能够锁定已经锁定mutex。我尝试了谷歌搜索/stackoverflow，无法找到导致此行为的原因。你能告诉我，为什么std::mutex在锁定同一个线程后还能再次锁定？

代码：

#include <iostream>
#include <mutex>

template <typename BASICLOCKABLE>
void ManualLockUnlock(BASICLOCKABLE & mut, std::string msg)
{
    mut.lock();
    std::cout << msg << "Manually locked, unlocked\n";

    if(mut.try_lock())
    {
        std::cout << msg << "able to try_lock after manual lock\n";
        mut.unlock();
    }
    else
    {
        std::cout << msg << "UNABLE to try_lock after manual lock\n";
    }
    mut.unlock();
    std::cout << std::endl;
}

template <typename BASICLOCKABLE>
void lock_guard(BASICLOCKABLE & mut, std::string msg)
{
    std::lock_guard<BASICLOCKABLE> lc(mut);
    std::cout << msg << "lock_guard locked, unlocked\n";

    if(mut.try_lock())
    {
        std::cout << msg << "able to try_lock again inside lock_guard\n";
        mut.unlock();
    }
    else
    {
        std::cout << msg << "UNABLE to try_lock again inside lock_guard\n";
    }
    {
        std::lock_guard<BASICLOCKABLE> lc2(mut);
        std::cout << msg << "SECOND LEVEL lock_guard locked, unlocked\n";
    }
    std::cout << std::endl;
}

template <typename BASICLOCKABLE>
void try_lock(BASICLOCKABLE & mut, std::string msg)
{
    mut.try_lock();
    std::cout << msg << "try_lock locked, unlocked\n";

    if(mut.try_lock())
    {
        std::cout << msg << "able to try_lock again inside try_lock\n";
        mut.unlock();
    }
    else
    {
        std::cout << msg << "UNABLE to try_lock again inside try_lock\n";
    }

    mut.unlock();
    std::cout << std::endl;
}

int main()
{
    std::string msg;

    std::mutex mut;
    msg = "std::mutex ";
    ManualLockUnlock(mut, msg);
    lock_guard(mut, msg);
    try_lock(mut, msg);

    std::recursive_mutex    recMut;
    msg = "std::recursive_mutex ";

    ManualLockUnlock(recMut, msg);
    lock_guard(recMut, msg);
    try_lock(recMut, msg);
}

编译命令：

g++ lock_guard.cpp -std=c++11

输出：

std::mutex Manually locked, unlocked
std::mutex able to try_lock after manual lock

std::mutex lock_guard locked, unlocked
std::mutex able to try_lock again inside lock_guard
std::mutex SECOND LEVEL lock_guard locked, unlocked

std::mutex try_lock locked, unlocked
std::mutex able to try_lock again inside try_lock

std::recursive_mutex Manually locked, unlocked
std::recursive_mutex able to try_lock after manual lock

std::recursive_mutex lock_guard locked, unlocked
std::recursive_mutex able to try_lock again inside lock_guard
std::recursive_mutex SECOND LEVEL lock_guard locked, unlocked

std::recursive_mutex try_lock locked, unlocked
std::recursive_mutex able to try_lock again inside try_lock

我正在使用的编译器：

g++ (Ubuntu 5.4.0-6ubuntu1~16.04.10) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

标签： c++11stdmutex