(How) Does the compiler compile a monolithic program as a threaded one?

I wrote a monolithic designed program which is quite rough on the processors needs. And as I have a dual-core I figured that one CPU should therefore be always at 100%. But both my CPUs are on 100% all the time. Now I am guessing that my compiler somehow turned my monolithic application in a threaded one. What are the limits of those opt开发者_StackOverflow社区imization feature and when is it still needed to explicit make something threaded?

I am using the gcc on Ubuntu linux 64-Bit

It doesn't, at least not without using something like Cilk. You must be inadvertently using multiple threads (or processes) without realizing it. Perhaps you're using a third-party library that creates an extra thread or two in your process?

[EDIT]

As per the comments, use a program like top(1) to verify that is in fact your program's process that is using both CPUs at 100%. In your case, the XORG process is jumping to 100% because your program is producing a large amount of output.

Any calls to the OS, or other libraries (CRT for instance) may use other threads as well. I would hardly be surprised if the console ran in it's own thread, and if you're doing a lot of IO of any sort, that could cause the other CPU to max out.