线程安全的c ++映射 [英] Thread-safety of c++ maps

问题描述

这是关于线程安全 std :: map 。现在，同步读取是线程安全的，但写入不是。我的问题是，如果我每次都添加唯一的元素到地图，这将是线程安全吗？

This is about thread safety of std::map. Now, simultaneous reads are thread-safe but writes are not. My question is that if I add unique element to the map everytime, will that be thread-safe?

1. 例如，如果我有一个这样的地图 std：map< int，std :: string> myMap
   和我总是添加新的密钥，从不修改现有的键值，这将是线程安全的吗？

1. So, for an example, If I have a map like this std:map<int, std::string> myMap and I always add new keys and never modify the existing key-value, will that be thread-safe?

更重要的是，这会给我带来任何随机的运行时行为吗？

More importantly, will that give me any random run-time behavior?

添加新密钥是否也被视为修改？如果在添加时密钥总是不同，那么它应该是线程安全的，因为它修改了内存的独立部分。

Is adding new keys also considered modification? If the keys are always different while adding, shouldn't it be thread-safe as it modifies an independent part of the memory?

谢谢
Shiv

Thanks Shiv

推荐答案

1）当然不是

2）是的，我希望你在测试过程中不会遇到它。

2) Yes, I hope you'll encounter it during testing, not later

3）是的，是的。新元素添加在不同的位置，但许多指针在此期间被修改。

3) Yes, it is. The new element is added in a different location, but many pointers are modified during that.

在大多数（如果不是全部）实现中，地图是由某种树实现的。在树中插入新元素通过重置节点来修改它，通过重置指针来指向不同的节点。因此它不是线程安全的

The map is implemented by some sort of tree in most if not all implementations. Inserting a new element in a tree modifies it by rearranging nodes by means of resetting pointers to point to different nodes. So it is not thread safe

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