如何为动态分配的 stl 容器设置分配器？

Question

我正在使用 TBB 自定义内存分配器。

tbb::memory_pool<std::allocator<char>> shortTermPool;
typedef tbb::memory_pool_allocator<Result*> custom_allocator;
std::vector<Result*,custom_allocator>* results =(std::vector<Result*,custom_allocator>*)shortTermPool.malloc(sizeof(std::vector<Result*,custom_allocator>));

问题是在构造函数中设置分配器。 Malloc 不调用构造函数。默认用法是这样的：

tbb::memory_pool<std::allocator<char>> shortTermPool;
typedef tbb::memory_pool_allocator<Result*> custom_allocator;
std::vector<Result*,custom_allocator> results (custom_allocator(shortTermPool));

有没有办法做一个 stl 容器的 malloc，然后分配一个自定义分配器？

Answer 1

这样做之后：

std::vector<Result*,custom_allocator>* results = (std::vector<Result*,custom_allocator>*)shortTermPool.malloc(sizeof(std::vector<Result*,custom_allocator>));

您将需要使用 placement-new 来构造对象：

new(results) std::vector<Result*,custom_allocator>(custom_allocator(shortTermPool));

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不过，下面这样的操作可能更具可读性：

using MemoryPool = tbb::memory_pool<std::allocator<char>>;
using CustomAllocator = tbb::memory_pool_allocator<Result*>;
using CustomVector = std::vector<Result*, CustomAllocator>;

MemoryPool shortTermPool;
void* allocatedMemory = shortTermPool.malloc(sizeof(CustomVector);
CustomVector* results = static_cast<CustomVector*>(allocatedMemory);
new(results) CustomVector(CustomAllocator(shortTemPool));

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编辑

记住不要在指针上使用delete，因为它指向的内存不是由new分配的；并记得像这样显式破坏对象：

results->~CustomVector();

更完整：

MemoryPool shortTermPool;
void* allocatedMemory = shortTermPool.malloc(sizeof(CustomVector);
CustomVector* results = static_cast<CustomVector*>(allocatedMemory);
new(results) CustomVector(CustomAllocator(shortTemPool));

/* Knock yourself out with the objects */

/*NOTE: If an exception is thrown before the code below is executed, you'll have a leak! */

results->~CustomVector();
shorTermPool.free(results);

//Don't do
//delete results

您可能还想探索使用智能指针和自定义删除器来处理从tbb 的内存分配器获得的内存的正确销毁和释放