C++ cout crashes during concurrent usage with boost’s threads under embedded Linux

Last week I was testing my C++ concurrent priority queue for HTTP requests with std::cout printing on the console output for possible race conditions. I was running my unit tests for some potential problems, when I found out that there was a crash of a unit test under embedded Linux. The same code was tested under Windows 7 and I didn’t see any crash of all unit tests. I was very curious to find out the reason for this crash. Under suspicion was problem with memory allocation or something similar as usual, but I hadn’t any assertions for that. On the next morning I spent two hours experimenting with isolation of the problem code. It appears that std::cout is crashing when it’s used by threads printing on the Linux console. Test application given below is a simple example for the crash with two boost threads which are printing numbers using std::cout. Maybe it’s trivial case why this example is crashing but sometimes similar problems like this can lose more than a week in spaghetti code, when you don’t  expect crash from this kind. The used embedded Linux for testing is BusyBox and the code is executed by processor with MIPS architecture.

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int main(int argc, char* argv[] )
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{
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 boost::thread    thOne(coutOne);
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    boost::thread    thTwo(coutTwo);
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    thOne.join();
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    thTwo.join();
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    return 0;
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}
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void coutOne()
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{
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   for(int i = 0; i < 10000; i++)
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   {
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     std::cout << " coutOne  : " << i << std::endl;
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   }
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}
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void coutTwo()
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{
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   for(int i = 0; i < 10000; i++)
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   {
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       std::cout << " coutOne : " << i << std::endl;
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   }
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}