Clock function in C ++ with threads

Question

It is really interesting to note here: http://en.cppreference.com/w/cpp/chrono/c/clock

"Only the difference between the two values ​​returned by various calls to std :: clock makes sense, since the beginning of the era std :: clock does not have to coincide with the beginning of the program. STD :: clock time may be faster or slower than a wall clock, depending from execution resources provided by the operating system by the operating system. For example, if the CPU is used by other processes, the time std :: clock may advance more slowly than the wall clock. On the other hand, if the current process is multithreaded and more than one execution core is available, in Remy std :: clock can accelerate faster than a wall clock. "

Why is the clock accelerated with multithreading? I check the performance of a C ++ program using streaming without it, and I notice that times are like streams (no better), but they feel faster (for example, they say 8 seconds in 3 seconds of execution time).

Answer 1

If more than one core is available and you are using multiple threads, then potentially multiple threads are simultaneously running on different cores. Since it clock()measures the processor’s time, it can move faster than the wall-mounted time, as several threads advance it at the same time.

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