STD :: MOVE of shared_ptr线程安全吗？
以下片段运行良好：
#include <memory>
#include <cassert>
int main()
{
auto ptr1 = std::make_shared<int>(10);
assert(ptr1.use_count() == 1);
auto ptr2 = std::move(ptr1);
assert(ptr1 == nullptr);
auto ptr3 = static_cast<std::shared_ptr<int>&&>(ptr2);
assert(ptr2 == nullptr);
assert(ptr3.use_count() == 1);
}
看起来std ::移动是否有几个操作，其中一个正在以某种方式重置移动的共享指针，那么此线程安全吗？例如，如果我有类似的东西：
void ThreadLogic()
{
if (sharedPtr != nullptr)
{
DoSomething(std::move(sharedPtr));
}
else
{
DoSomethingElse();
}
}
std :: move（sharedptr） aromic还是应该通过其他一些方式保护该支票（关键部分）？
The following snippet runs fine:
#include <memory>
#include <cassert>
int main()
{
auto ptr1 = std::make_shared<int>(10);
assert(ptr1.use_count() == 1);
auto ptr2 = std::move(ptr1);
assert(ptr1 == nullptr);
auto ptr3 = static_cast<std::shared_ptr<int>&&>(ptr2);
assert(ptr2 == nullptr);
assert(ptr3.use_count() == 1);
}
It looks std::move does several operations, one of them is reseting the moved shared pointer somehow, so is this thread safe? For instance if i have something like:
void ThreadLogic()
{
if (sharedPtr != nullptr)
{
DoSomething(std::move(sharedPtr));
}
else
{
DoSomethingElse();
}
}
Is that std::move(sharedPtr) atomic or should I protect the check (the critical section) there by some other means?
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您对什么
std :: Move有误解。实际上，std ::移动什么都不做。这只是具有含义的编译时间机制：我不再需要此名称的值。然后，这会导致编译器以不同的方式使用该值，例如调用移动构造函数/分配代替复制构造函数/分配。但是
std ::移动本身不会生成无代码，因此没有任何影响。您应该问的真正的问题是，
shared_ptr的移动构造函数是否安全，答案是：否。代码> shared_ptr ，但也要分享它的指标。请勿通过引用线程传递
shared_ptr，而是按值传递，以便每个线程获得其sharone_ptr。然后，可以随意移动而毫无问题。shared_ptr保护指出的事物的寿命。参考计数shared_ptr使用是线程安全的，但别无其他。它只以线程安全的方式管理对象的寿命，因此只要任何shared_ptr都持有对象，就不会被破坏。You have a misconception about what
std::movedoes. In factstd::movedoes nothing. It's just a compile time mechanism with the meaning: I no longer need this named value.This then causes the compiler to use the value in different ways, like call a move constructor/assignment instead of copy constructor/assignment. But the
std::moveitself generates no code so nothing to be affected by threads.The real question you should be asking is whether the move constructor of
shared_ptris thread safe and the answer is: No.But the point of the
shared_ptris not to share theshared_ptrbut to share what it points too. Do not pass ashared_ptrby reference to threads, instead pass it by value so each thread gets it ownshared_ptr. Then it is free to move that around at will without problems.The
shared_ptrprotects the lifetime of the thing it points to. The reference count theshared_ptruses is thread safe but nothing else. It only manages the lifetime of the pointed to objects in a thread safe way so it doesn't get destroyed as long as anyshared_ptrhas hold of the object.