多线程程序中boostweak_ptr实现资源池 [英] Boost weak_ptr's in a multi-threaded program to implement a resource pool

问题描述

我正在考虑使用 boost::weak_ptr 来实现一个对象池，这样当没有人使用其中一个对象时，它们就会被回收.不过，我担心的是，它是一个多线程环境，似乎在最后一个 shared_ptr 到超出范围的对象与从 weak_ptr 构造的新 shared_ptr 之间存在竞争条件.通常，您会使用锁或其他东西来保护此类操作；然而，这里的重点是您不知道 shared_ptr 何时可能超出范围.

I'm thinking of using boost::weak_ptr to implement a pool of objects such that they will get reaped when nobody is using one of the objects. My concern, though, is that it's a multi-threaded environment, and it seems there's a race condition between the last shared_ptr to an object going out of scope and a new shared_ptr being constructed from the weak_ptr. Normally, you'd protect such operations with lock or something; however, the whole point here is that you don't know when the shared_ptr might be going out of scope.

我对 boost::shared_ptr 和 boost::weak_ptr 有什么误解吗?如果没有，有人有什么好的建议吗?

Am I misunderstanding something about boost::shared_ptr and boost::weak_ptr? If not, does anybody have any good suggestions on what to do?

谢谢.

安德鲁

推荐答案

要使用 weak_ptr，您通常必须通过用它构造一个 shared_ptr 来获取强引用.最后一步是原子性的:要么得到一个强引用，要么抛出一个 bad_weak_ptr 异常.(或者，在 weak_ptr 上调用 lock()，并获得强引用或 null.)

To use a weak_ptr, you normally have to grab a strong reference by constructing a shared_ptr with it. This last step is atomic: you either get a strong reference back, or you get a bad_weak_ptr exception thrown. (Alternatively, call lock() on the weak_ptr, and either get a strong reference or null.)

示例(使用lock()；很容易适应其他风格):

Example (with lock(); easy enough to adapt to the other style):

void do_something(weak_ptr<foo> weak) {
    // Grab strong reference
    shared_ptr<foo> strong(weak.lock());
    if (strong) {
        // We now have a strong reference to use
    } else {
        // No strong references left; object already freed
    }
}

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