Thread-safety and reentrancy of new operator

分析

一、new operator最终还是会使用类似于malloc的allocator，因此它的reentrancy是由allocator决定的，一般allocator是non-reentrant的

二、thread safety，C++标准没有明确说明；并且由于C++支持overload new operator，在这种情况下就需要由programmer来决定了。

stackoverflow Thread safety of ::new in C++11

A

I believe this is implicitly guaranteed by the C++11 standard. If it were not, then usage of the operator new or new expression might cause a data race, and that would not be allowed by the standard. For reference, see §17.6.5.9 Data race avoidance and also

18.6.1.4 Data races [new.delete.dataraces]

"The library versions of operator new and operator delete, user replacement versions of global operator new and operator delete, and the C standard library functions calloc, malloc, realloc, and free shall not introduce data races (1.10) as a result of concurrent calls from different threads. Calls to these functions that allocate or deallocate a particular unit of storage shall occur in a single total order, and each such deallocation call shall happen before the next allocation (if any) in this order."

Your own overrides or your own replacements for the global operators should fulfill this requirement as well.

See also this proposal N3664 "Clarifying Memory Allocation", which puts more emphasis on that matter.

stackoverflow Thread safety for overloaded operator new