Is it ok to erase from stl:map in concurrent with find

Question

I wonder if is it ok to erase from stl:map in concurrent with find? concurrent means - two threads that try both at the same time one to erase and one to call find.

What do you mean by "concurrent"? One thread does `erase` while another calls `find`? That's not ok :) — jalf, Aug 19 '12 at 14:08
possible duplicate of [Do I need to protect read access to an STL container in a multithreading environment?](http://stackoverflow.com/questions/187583/do-i-need-to-protect-read-access-to-an-stl-container-in-a-multithreading-environ) — Bo Persson, Aug 19 '12 at 14:32

score 6 · Accepted Answer · edited Aug 19 '12 at 14:44

6

Of course not. stl::map is based on an auto-balancing binary tree (red-black usually). erase may eventually cause a heavy tree rearrangement.

edited Aug 19 '12 at 14:44

Johan Råde

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answered Aug 19 '12 at 14:08

valdo

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score 1 · Answer 2 · answered Aug 19 '12 at 14:30

It's not okay to call a const method and a non-const method on the same object at the same time and it's not okay to call 2 non-const methods at the same time. It is, however, okay to call 2 const methods at the same time. This applies to all* const correct code, not just the standard library.

So, in your case no, it's not safe.

_{*Unless it's internally thread-safe, which is poor design. And nothing in the standard library is.}

Is it ok to erase from stl:map in concurrent with find

2 Answers2