使用 RAII 完成线程等待

当使用 std::thread 对象执行线程时，必须要调用 join() （或者 detach()，由于 detach() 可以立即调用，所以这里只考虑 join()）

#include <iostream>
#include <thread>
#include <chrono>

using namespace std;

void threadInvoker()
{
    cout << "thread begin
";
    this_thread::sleep_for(chrono::milliseconds(2000));
    cout << "thread end
";
}

void doSomething()
{
    cout << "doSomething begin
";
    this_thread::sleep_for(chrono::milliseconds(4000));
    cout << "doSomething end
";
}

void doOther()
{
}

void f()
{
    thread t(threadInvoker);

    doSomething();

    doOther();
    t.join();
}

int main()
{
    f();
}

编译：g++ -std=c++11 -pthread test.cpp

如果 doSomething() 会产生异常，则尝试捕获

#include <iostream>
#include <thread>
#include <chrono>

using namespace std;

void threadInvoker()
{
    cout << "thread begin
";
    this_thread::sleep_for(chrono::milliseconds(2000));
    cout << "thread end
";
}

void doSomething()
{
    cout << "doSomething begin
";
    this_thread::sleep_for(chrono::milliseconds(4000));
    throw 0;
    cout << "doSomething end
";
}

void doOther()
{
}

void f()
{
    thread t(threadInvoker);

    try {
        doSomething();
    }
    catch (...) {
        cout << "catch exception
";
        t.join();
        return;
    }

    doOther();
    t.join();
}

int main()
{
    f();
}

但是必须在 catch 块里调用 t.join()，否则会 crash。如果条件一多，很可能会在某个分支下遗忘 t.join()。

因此可以使用 RAII 来避免，在析构函数中进行 join()

#include <iostream>
#include <thread>
#include <chrono>

using namespace std;

class ThreadGuard
{
public:
    explicit ThreadGuard(thread& t):mT(t) {}
    ~ThreadGuard()
    {
        if (mT.joinable()) {
            cout << "join
";
            mT.join();
        }
    }
    ThreadGuard(ThreadGuard const&) = delete;
    ThreadGuard& operator=(ThreadGuard const&) = delete;
private:
    thread& mT;
};

void threadInvoker()
{
    cout << "thread begin
";
    this_thread::sleep_for(chrono::milliseconds(2000));
    cout << "thread end
";
}

void doSomething()
{
    cout << "doSomething begin
";
    this_thread::sleep_for(chrono::milliseconds(4000));
    throw 0;
    cout << "doSomething end
";
}

void doOther()
{
}

void f()
{
    thread t(threadInvoker);
    ThreadGuard tg(t);

    try {
        doSomething();
    }
    catch (...) {
        cout << "catch exception
";
        return;
    }

    doOther();
}

int main()
{
    f();
}

利用局部对象的析构保证 join() 的调用