From where is the code for dealing with critical section originated?

Question

While learning the subject of operating systems, Critical Section is a topic which I've come across. To solve this problem, certain methods are provided like semaphores, certain software solutions, etc...etc..etc. But I've a question that from where is the code for implementing these solutions originated? As programmers never are found writing such codes for their program. Suppose I write a simple program executing printf in 'C', I never write any code for critical section problem. And the code is converted into low level instructions and is executed by OS, which behaves as our obedient servant. So, where does code dealing with critical section originate and fit in? Let resources like frame buffer be the critical section.

Answer 1

The OS kernel supplies such inter-thread comms synchronization mechanisms, mutex, semaphore, event, critical section, conditional variables etc. It has to because the kernel needs to block threads that cannot proceed. Many languages provide convenient wrappers around such calls.

Your app accesses them, directly or indirectly, via system calls, ie intrrupts that enter kernel state and ask for such services.

In some cases, a short-term user-space spinlock may get plastered on top, but such code should defer to a system call if the spinner is not quickly satisfied.

In the case of C printf, the relevant library, (stdio usually), will make the calls to lock/unlock the I/O stream, (assuming you have linked in a multithreaded version of the library).