C++ 17 shared_mutex : why read lock is even necessary for reading threads

Asked Jul 02 '17 at 08:56

Active Jul 02 '17 at 09:12

Viewed 99 times

In the example given in http://en.cppreference.com/w/cpp/thread/shared_mutex

A std::shared_lock<std::shared_mutex> is used in the get() method so

Multiple threads/readers can read the counter's value at the same time.

I wonder why the lock is even necessary for reading threads here? Is it for the consideration of variable's across thread visibility, so the reading thread is ensured to read up-to-date value of the variable (not the local copy in the cache of the CPU core where the thread is running in, which could be outdated) ?

edited Jul 02 '17 at 09:12

asked Jul 02 '17 at 08:56

Bulyume Senri

3

Because if you try to read while it's being modified by another thread you will read incoherent rubbish. You must make sure the information is safe for reading before doing so. – Havenard Jul 02 '17 at 08:59
2

`s/C++11/C++17/` – juanchopanza Jul 02 '17 at 09:00

C++ 17 shared_mutex : why read lock is even necessary for reading threads

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