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Editorial Team
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Asked: 2026-05-15T07:57:14+00:00

I got a C++ program (source) that is said to work in parallel. However,

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I got a C++ program (source) that is said to work in parallel. However, if I compile it (I am using Ubuntu 10.04 and g++ 4.4.3) with g++ and run it, one of my two CPU cores gets full load while the other is doing “nothing”.

So I spoke to the one who gave me the program. I was told that I had to set specific flags for g++ in order to get the program compiled for 2 CPU cores. However, if I look at the code I’m not able to find any lines that point to parallelism.

So I have two questions:

  • Are there any C++-intrinsics for multithreaded applications, i.e. is it possible to write parallel code without any extra libraries (because I did not find any non-standard libraries included)?
  • Is it true that there are indeed flags for g++ that tell the compiler to compile the program for 2 CPU cores and to compile it so it runs in parallel (and if: what are they)?
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1 Answer

  1. Editorial Team

    AFAIK there are no compiler flags designed to make a single-threaded application exploit parallelism (it’s definitely a nontrivial operation), with the exception of parallelization of loops iterations (-ftree-parallelize-loops), that, still, must be activated carefully; still, even if there’s no explicit threads creation, there may be some OpenMP directives to parallelize several instruction sequences.

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