C ++中的多线程内存分析

Question

I am working on profiling the memory usage of multiple threads in my application. I would like to be able to track the maximum allocation/current allocation of any given thread that is running. In order to so, I planned on interposing on mallocs/frees. During each call to malloc, I would update the allocation records for the particular thread in a static map that associated thread ids to their particular metadata record. I am currently having issues during process exit. I think the issue is that when all the destructors are called for cleanup, the static map and lock protecting it have to be destroyed. My interposed mallocs/frees, however, acquire the lock before updating the profiling metadata structures. Eventually, the lock is destroyed, but there are subsequent calls to malloc/free that result in an attempt to acquire the no longer existent lock resulting in a segfault.

Another issue that I am concerned about is that there are internal calls to malloc generated within my interposed malloc to allocate entries in the map.

Any ideas on ways of approaching the problem of profiling memory usage on a per thread basis? Any suggestions on data structures to track the usage of each thread? Does the above approach seem reasonable or are there any other ways of approaching the problem?

Answer 1

If you store your "extra" data as part of the allocation itself (before is easier, but you could do it after too - just need a size somewhere), then you shouldn't need any locks at all. Just a tad more memory. Of course, you will need to use atomics to update any lists of items.

If you look at this answer:

Setting memory on a custom heap

and imagine that HeapAlloc and HeapFree are malloc and free respectively. Then add code to store which thread is being used for the allocation.

So, instead of using a map, you simply update a linked list (using atomics to prevent multiple updates). This does of course make it a little more difficult to make the up to date measurements per thread, you'll have to scan the list of allocations.

Of course, this only works for DIRECT calls to malloc and free .

The same principle would be possible by "injecting" a replacement malloc / free function (built along the principles in the other post, but of course not using the original malloc to allocate the memory, and not using free to free the memory).

Answer 2

This is a complicated thing to do and make work for all cases. There are many issues that you'll miss and only ever find through trial and error. I should know, I've been responsible for building a tool that does what you are trying to do. We've been doing this since 1999, available commercially since 2002.

If you are using Windows, C++ Memory Validator can give you per-thread profiling statistics. http://www.softwareverify.com/cpp-memory.php .

The Objects tab and Sizes tab both have Threads sub-tabs which allow you to view data per thread. You can also run advanced queries on the Analysis tab that will allow you to view data on a per-thread basis.

Spend your time on your job, not writing tools.