new and delete handles multithreading issues

Question

I am reading a book Efficient C++: Performance Programming Techniques Authors is saying following regarding global new and delete operators:

They manage memory in the process context, and since a process may spawn multiple threads, new() and delete() must be able to operate in a multithreaded environment. In addition, the size of memory requests may vary from one request to the next.

in Chapter 6. Single-Threaded Memory Pooling.

Is this true? I thought C++ does not have a notion of a Multi-threading environment, programmer need to handle is by using some means of mutual exclusion.

@trojanfoe Book further provides implementation of memory allocation with single and multi thread supports, but when I tried his first approach it was failing on Visual Studio compiler, so I got a doubt. — Avinash, Nov 03 '11 at 07:52

score 7 · Accepted Answer · edited Jan 08 '18 at 20:06

7

It will depend on implementation. For example, Visual C++ runtime had both a single-threaded and a multithreaded version of heap in earlier version, but starting with Visual C++ 2005 it only has a multithreaded version. This MSDN article has a nice summary table.

When a multithreaded heap is used calls to memory allocation and deallocation are thread-safe at expense of additional overhead.

edited Jan 08 '18 at 20:06

JFMR

23,265
4
52
76

answered Nov 03 '11 at 07:38

sharptooth

167,383
100
513
979

score 3 · Answer 2 · edited May 23 '17 at 12:14

3

C++ (C++03 standard) doesn't talk about multi-threading. However most of the platforms support thread-safe new/malloc. Here is a previous post discussing same kind of question.

In C++11, the threads are introduced.

edited May 23 '17 at 12:14

Community

1
1

answered Nov 03 '11 at 07:38

iammilind

68,093
33
169
336

4

+1 for the difference between the Standard and the practical applications. C and C++ have been multithreaded for a long time. – Matthieu M. Nov 03 '11 at 08:05

score 0 · Answer 3 · answered Apr 07 '15 at 14:45

As of C++11 (which has the concept of a data race) the standard guarantees that new/delete, calloc/malloc/realloc/freewill occur in a single total order.

From n3690 18.6.1.4:

For purposes of determining the existence of data races, the library versions of operator new, user replacement versions of global operator new, the C standard library functions calloc and malloc, the library versions of operator delete, user replacement versions of operator delete, the C standard library function free, and the C standard library function realloc shall not introduce a data race (17.6.5.9). 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 (1.10) the next allocation (if any) in this order.

I could not find any such guarantees in previous versions of the standard, but (like others have said) I believe most implementations provide multi-threading support for memory allocation.

new and delete handles multithreading issues

3 Answers3